Expanding the Genetic and Clinical Spectrum of Hereditary Angioedema with Normal C1 Inhibitor: Novel Variants and Treatment Insights

Abstract

Hereditary angioedema with normal C1 inhibitor (HAE-nC1-INH) is a rare and genetically heterogeneous disorder with an incomplete molecular understanding. This study aimed to identify novel genetic variants associated with HAE-nC1-INH, characterize their clinical manifestations, and evaluate real-world treatment responses. Whole-exome sequencing of 27 HAE patients, including eight with HAE-nC1-INH, identified four previously unreported MYOF variants and additional pathogenic variants in KNG1 and HS3ST6, expanding the genetic spectrum of the disease. MYOF variants were associated with recurrent edema episodes, often with prolonged duration. The HS3ST6 variant was linked to refractory angioedema with non-resolving lower extremity involvement, highlighting atypical, persistent clinical phenotypes beyond the classical self-limiting presentation of HAE. Lanadelumab effectively reduced attack frequency in most patients; however, the variability in treatment response, particularly in MYOF and HS3ST6 carriers, highlights the need for individualized therapeutic approaches. These findings provide new insights into the genetic and clinical complexity of HAE-nC1-INH and emphasize the importance of genetic testing in refining diagnosis and optimizing treatment strategies, contributing to a more precise understanding of hereditary angioedema.

Introduction

Hereditary Angioedema (HAE) is a rare, potentially life-threatening disorder characterized by recurrent episodes of localized subcutaneous and submucosal edema due to increased vascular permeability [1]. The underlying pathology is primarily driven by dysregulation of the plasma kallikrein-bradykinin pathway, resulting in excessive bradykinin production, which acts as a potent vasodilator and mediator of vascular leakage [2]. Despite its low global prevalence (1.1 to 1.6 per 100,000 individuals) [3], HAE is a clinically heterogeneous disease, and significant gaps remain in understanding its genetic diversity, clinical manifestations, and optimal therapeutic strategies. These challenges are particularly evident in HAE with normal C1 esterase inhibitor (HAE-nC1-INH), a rare subtype with an undefined molecular basis in many cases.

HAE is classically divided into Type I (HAE-1) and Type II (HAE-2), both of which are caused by mutations in the SERPING1 gene, leading to C1 esterase inhibitor (C1-INH) deficiency or dysfunction. The resulting uncontrolled activation of the kallikrein-kinin system causes bradykinin overproduction, triggering recurrent angioedema [1]. In contrast, HAE-nC1-INH represents a genetically and clinically heterogeneous subset, characterized by normal C1-INH levels and functionality. Unlike HAE-1 and HAE-2, HAE-nC1-INH is associated with mutations in alternative genes, including FXII [4], PLG [5], KNG1 [6], HS3ST6 [7], CPN1 [8], ANGPT1 [9], MYOF [10], DAB2IP [11]. These mutations contribute to HAE pathogenesis through distinct mechanisms. Mutations in FXII, PLG, KNG1, HS3ST6, and CPN1 disrupt bradykinin pathway regulation, leading to episodic angioedema [4–8]. In contrast, ANGPT1, MYOF, and DAB2IP mutations influence vascular permeability through VEGF-mediated signaling, suggesting an alternative mechanism of dysregulated endothelial function [9–11]. Despite these advances, a significant proportion of HAE-nC1-INH cases remain genetically undefined, often classified as HAE-UNK (unknown mutation status), underscoring the need for expanded genomic analysis to elucidate additional molecular contributors.

Globally, HAE-nC1-INH poses significant diagnostic and therapeutic challenges. Its genetic heterogeneity complicates the use of conventional diagnostic approaches, which primarily rely on C1-INH measurements. As a result, delays in diagnosis are common, leading to frequent misdiagnosis and inappropriate management [12, 13]. Moreover, HAE-nC1-INH symptoms often overlap with idiopathic angioedema, allergic reactions, and autoimmune disorders, further complicating differential misdiagnosis [1]. Patients with HAE-nC1-INH frequently present atypical clinical features, including delayed disease onset, persistent swelling, and higher rates of autoimmune and allergic comorbidities [1, 2]. This suggests that immune dysregulation and vascular inflammation may contribute to disease pathophysiology, extending beyond the traditional bradykinin-mediated model. Addressing these complexities requires integrating genomic analysis into routine diagnostic workflows and re-evaluating HAE subclassifications based on emerging genetic insights.

Therapeutically, lanadelumab, a monoclonal antibody targeting plasma kallikrein, has emerged as a breakthrough therapy for HAE [14, 15]. Clinical trials have demonstrated its efficacy in reducing attack frequency in HAE-1 and HAE-2 patients [16–20]. However, its effectiveness in HAE-nC1-INH remains less well defined. The variability in therapeutic response suggests that some HAE-nC1-INH subtypes may partially or entirely involve non-bradykinin-dependent mechanisms, requiring an expanded therapeutic framework. Understanding how lanadelumab modulates vascular permeability in genetically diverse HAE patients is therefore critical for optimizing precision medicine approaches for this rare condition.

In this study, we present genetic and clinical findings from one of the largest HAE cohorts to date, including eight individuals with HAE-nC1-INH. By performing whole-exome sequencing (WES), we identified four novel MYOF variants, providing the first evidence of MYOF-associated HAE in an Asian population. Additionally, we report previously uncharacterized KNG1 and HS3ST6 variants, highlighting alternative pathways of vascular permeability dysregulation beyond bradykinin overproduction.

Furthermore, we provide real-world evidence of lanadelumab’s efficacy in genetically complex HAE-nC1-INH cases, demonstrating both positive responses and cases of incomplete symptom control. These findings challenge existing paradigms of HAE pathophysiology and emphasize the need for personalized treatment approaches based on genetic profiles. By integrating genomic insights with clinical outcomes, this study contributes to the global effort to redefine HAE diagnostic criteria, expand therapeutic options, and enhance our understanding of vascular and inflammatory mechanisms underlying angioedema. These insights have broader implications for other disorders characterized by endothelial dysfunction, paving the way for precision medicine strategies in rare vascular diseases.

Patients and Methods

This retrospective study enrolled 27 patients diagnosed HAE between April 2021 and July 2024 at the Department of Allergy and Immunology and the Department of Dermatology, Huashan Hospital, affiliated with Fudan University, China. Ethical approval was obtained from the Ethics Committee of Huashan Hospital, and written informed consent was obtained from all participants in accordance with the principles outlined in the Declaration of Helsinki.

Demographic and clinical data, including age, gender, region of origin, age of symptom onset, attack frequency, anatomical locations of edema, presence of comorbidities, treatment history, and therapeutic responses, were systematically collected and recorded in a secure database. Gender was not considered as a biological variable. Particular attention was given to identifying potential attack triggers and family history of HAE to assess inheritance patterns and clinical variability.

Patients were diagnosed in accordance with the international WAO/EAACI guidelines for HAE management [21]. Clinical suspicion of HAE was based on a history of recurrent angioedema affecting the extremities, face, genitals, gastrointestinal tract (e.g., painful abdominal cramps), and/or laryngeal involvement, particularly in cases unresponsive to antihistamines, epinephrine, and glucocorticoids. And unresponsiveness was defined as persistent or worsening angioedema despite a minimum of one month of full-dose non-sedating antihistamines (e.g., cetirizine up to 40 mg/day), corticosteroids (prednisone 0.5–1.0 mg/kg/day), and, when applicable, standard doses of omalizumab. Acute-phase treatments included intramuscular epinephrine (0.5 mg) and intravenous dexamethasone (5 mg). Laboratory testing of serum or plasma levels of C1-INH function, C1-INH protein, and complement component C4 was performed to classify patients into the three major HAE subtypes. To exclude acquired angioedema, all patients underwent comprehensive history and laboratory evaluation. Genetic testing was strongly recommended, especially for patients without a known family history. HAE-1 was diagnosed in patients with both C1-INH function and C1-INH protein levels below 50% of the normal reference range. HAE-2 was defined by similarly reduced C1-INH function but normal or elevated C1-INH protein levels, along with either a positive family history or a pathogenic/likely pathogenic SERPING1 variant. HAE-nC1-INH was considered in patients with normal complement test results. These individuals underwent whole-exome sequencing (WES) to assess for pathogenic or likely pathogenic variants in known genes associated with this subtype, including FXII, ANGPT1, PLG, KNG1, MYOF, HS3ST6, DAB2IP, and CPN1. Patients with no identifiable mutation were classified as HAE-UNK (Fig. 1).

Fig. 1 Flow chart of experimental design and patient enrollment.

The chart illustrates the enrollment process of participants in this study. “↓” indicates patients with lower-than-normal levels of C1-INH, C1-INH function, and C4. “n” indicates patients with normal levels of C1-INH, C1-INH function, and C4. “↑” indicates patients with higher-than-normal levels of C1-INH, C1-INH function, and C4

Genomic DNA was extracted from whole blood using the QIAamp DNA Blood Mini Kit (Qiagen, Hilden, Germany). Exome libraries were prepared using the xGen Exome Research Panel (Integrated DNA Technologies, Skokie, USA), following DNA fragmentation and adapter ligation via a magnetic particle-based method. Sequencing was performed using the NovaSeq 6000 platform (Illumina, San Diego, USA) according to the manufacturer’s protocol. Whole-exome sequencing and genetic analysis were performed on patients with normal complement levels and function to identify potential disease-associated variants. Variants were classified based on their pathogenicity according to the American College of Medical Genetics (ACMG) guidelines. Identified mutations were further analyzed in relation to clinical phenotypes to explore potential genotype-phenotype relationships and better define the molecular landscape of HAE-nC1-INH. Raw sequencing data were converted into FASTQ format using Illumina’s BCL2FASTQ tool. Quality control was conducted using FastQC. Reads were aligned to the UCSC hg19 reference genome using BWA-MEM. Variant calling was performed using the Genome Analysis Toolkit (GATK), including local realignment (IndelRealigner) and base quality score recalibration (BaseRecalibrator). Variants were called using GATK UnifiedGenotyper and annotated using ANNOVAR. Clinical correlation was performed by filtering candidate variants against known disease genes and comparing with patient phenotypes. CNV detection was conducted using ExomeDepth and validated using in-house depth-based filtering tools.

Statistical analyses were conducted using SPSS (version 29.0, IBM). Normality of the data was assessed using the Shapiro-Wilk test. Continuous variables were reported as mean ± standard deviation (SD) for normally distributed data or as median and interquartile range (IQR) for non-normally distributed data. Categorical variables were summarized as percentages. The chi-square test was used to assess associations between categorical variables, with Fisher’s exact test applied in cases where expected frequencies in any cell were less than five. Group comparisons were conducted using independent samples t-tests for normally distributed data and the Mann-Whitney U test for non-normally distributed data. A p-value of < 0.05 was considered statistically significant.

Results

Patient Demographics and Clinical Characteristics

This study included 27 patients diagnosed with HAE, consisting of 17 patients with HAE-1 (62.96%), 2 with HAE-2 (7.41%), and 8 with HAE-nC1-INH (29.63%). The mean age of symptom onset was 25.76 ± 14.09 years, while the median diagnostic delay was 8 years (range: 1 month–36 years), underscoring significant diagnostic challenges in recognizing and classifying HAE subtypes (Table 1).

Table 1.

Clinical features of the 27 patients with hereditary angioedema (HAE)

Clinical features	HAE-1/2 (n = 19)	HAE-nC1-INH (n = 8)	p-value	Total (n = 27)
Females(%)	14 (73.68%)	4 (50%)	0.375	18 (66.67%)
At first event(years), mean ± SD	19.79 ± 8.88	39.95 ± 14.41	0.034*	25.76 ± 14.09
At diagnosis(years), mean ± SD	32.14 ± 14.01	46.08 ± 15.68	0.789	36.27 ± 15.62
Delay in diagnosis(years), median(IQR)	12 (1,22)	1.75 (0.90,1.83)	0.333	8 (1,19)
Family history of HAE(%)	14 (73.68%)	1(12.5%)	0.008*	15 (55.56%)
Genomic variant
SERPING1	12	0	/	12
FXII	0	1	/	1
KNG1	0	2	/	2
MYOF	1	4	/	5
HS3ST6	0	1	/	1
Not checked	7	0	/	7
Clinical manifestations
Skin/extremities/trunk	19	8	/	27
Gastrointestinal tract	11	3	0.420	14
Laryngeal	12	3	0.398	15
Persistent swelling	0	3	0.019*	3
Prodromal symptoms
Erythema or erythema marginatum	5	1	0.633	6
Tiredness and fatigue	2	0	1.000	2
Trigger factors
Trauma/compression	7	0	0.062	7
Stress/emotional factors	6	3	1.000	9
Infection	2	0	1.000	2
Cold weather	3	0	0.532	3
Around menstruation/Oral contraceptive	4	0	0.285	4
Exposure to specific foods or chemicals (i.e. persimmons, seafood, alcohol)	3	1	1.000	4
Comorbidities
Allergic diseases	5	6	0.033*	11
Autoimmune diseases	5	2	1.000	7
Simultaneous attacks of edema and pruritic rashes (i.e. urticaria)	1	3	0.081	4

*For the categorical variables, the p-vaule was obtained from chi-square test, with Fisher’s exact test applied when expected frequencies in any cell were less than five. For continuous variables, the p-vaule was obtained from independent samples t-tests for normally distributed data or the Mann-Whitney U test for non-normally distributed data

Recurrent cutaneous swelling was the most frequently reported symptom, occurring in all patients (100%). Gastrointestinal involvement was observed in 51.85% (n = 14), with severe abdominal pain requiring emergency care in three cases. Laryngeal edema, a life-threatening manifestation, occurred in 55.56% (n = 15), with two patients reporting a family history of asphyxiation-related deaths due to airway obstruction, highlighting the potential severity and misdiagnosis risks associated with HAE.

Genetic Findings and Novel Variants

Genetic testing was performed in 20 out of 27 patients to identify pathogenic variants contributing to HAE pathogenesis. All 10 tested patients with HAE-1 and 2 patients with HAE-2 harbored SERPING1 variants, consistent with the classical genetic etiology of HAE-1 and HAE-2. Notably, one HAE-2 patient carried both SERPING1 and a MYOF variant (NM_013451.4:c.548 C > T, p.Thr183lle), suggesting a potential dual genetic contribution to disease expression (Table 2).

Table 2.

SERPING1 variants in patients with HAE-1/2

No. of patients	cDNA numbering		Location	Effect on protein	Type of HAE	C1-INH level (g/L)	C1-INH Function (%)
1	NM_000062.2	c.1346T > C	Exon 8	p. Leu449Pro	HAE-1	0.04	0.0
2		c.1232 C > G	Exon 7	p.Ser411Ter		0.073	0.2
3		c.1291 A > C	Exon 8	p.Thr431Pro		0.04	0.0
4		Loss	Exon 2–8	16,312 bp loss		0.061	0.0
5		c.1327 C > A	Exon 7	p.His443Asn		0.063	12.6
6		c.1327 C > A	Exon 7	p.His443Asn		0.06	20.1
7		c.1427 C > T	Exon 8	p.Pro476Leu		0.07	8.6
8		c.1027 A > T	Exon 6	p.Lys343*		0.06	0.0
9		c.1048_1049del	Exon 6	p.Ser350Profs*18		0.06	1.7
10	NC_000011.9	g.57363946_57372945del	Intron	/		0.08	0.0
11	NM_000062.2	c.1396 C > T	Exon 8	p.Arg466Cys	HAE-2	0.82	0.4
12		c.1114 C > T	Exon 7	p.Gln372*		0.28	0.0

*The normal range for C1-INH levels is 0.21–0.39 g/L, and normal C1-INH function is defined as equal to or greater than 68%

* Patient 12 was detected to harbor both SERPING1 and MYOF (NM_013451.4:c.548 C > T, p.Thr183lle) gene variants

Among the 8 HAE-nC1-INH patients, pathogenic variants were identified in FXII, KNG1, MYOF, and HS3ST6, contributing to the growing understanding of genetic heterogeneity in this subset (Table 3).

Table 3.

Gene variants in patients with HAE-nC1-INH

Patient #	Laboratory testing						Clinical manifestation
	Gene	Chromosome	cDNA numbering	Effect on protein	C1-INH level (g/L)	C1-INH Function (%)	Gender	Age at onset	Family history	Skin	Laryngeal	Gastrointestinal tract	Allergic diseases	Autoimmune diseases	Simultaneous attacks of edema and pruritic rashes
1	MYOF	10	NM_013451.4 c.5923G > A	p.Glu1975Lys	0.31	> 93	F	43.5	No	Yes	Yes	Yes	Yes	No	Yes
2	MYOF	10	NM_013451.4 c.6001 C > G	p.Arg2001Gly	0.28	100.7	F	49.2	Yes	Yes	Yes	Yes	Yes	Yes	Yes
3	MYOF	10	NM_013451.4 c.3965 C > G; c.2542_2543delinsAA	p.Ala1322Gly; p.Lys848=	0.21	106.3	F	30	No	Yes	No	Yes	Yes	No	Yes
4	MYOF	10	NM_ 013451.4 c.1097G > T	p.Arg366Leu	0.28	88.2	M	30	No	Yes	No	No	No	No	No
5	HS3ST6	16	NM_001009606.4 c.497G > A	p.Arg166His	0.45	60.4	M	31	No	Yes	No	No	Yes	No	No
6	FXII	5	NM_000505.3 c.303_304del	p.His101Glnfs*36	0.22	37.94	F	20	No	Yes	No	No	Yes	Yes	No
7	KNG1	3	NM_001102416.3 c.1690 C > T	p.Gln564Ter	0.29	> 93	M	53.9	No	Yes	No	No	No	No	No
8	KNG1	3	NM_001102416.3 c.1143G > C	p.Arg381Ser	0.25	2.6	M	62	No	Yes	Yes	No	Yes	No	No

*The normal range for C1-INH levels is 0.21–0.39 g/L, and normal C1-INH function is defined as equal to or greater than 68%

1. Four novel MYOF variants (c.5923G > A, c.6001 C > G, c.3965 C > G, c.1097G > T) were associated with recurrent abdominal pain, edema, and immune comorbidities, expanding the known genetic spectrum of HAE-nC1-INH.

2. A variant in HS3ST6 (c.497G > A) was identified in one patient with persistent lower extremity edema that was resistant to conventional therapies.

3. Variants in FXII (c.303_304del) and KNG1 (c.1690 C > T, c.1143G > C) add to the limited existing data on non-SERPING1 genetic drivers of HAE, providing insights into alternative pathogenic pathways contributing to angioedema.

Variants were annotated against HGMD and ClinVar databases, and cross-checked with published HAE mutation updates. Among the SERPING1 variants identified, seven were novel: Loss1 (Exon 2–8), c.1327 C > A (p.His443Asn), c.1232 C > G (p.Ser411Ter), c.1291 A > C (p.Thr431Pro), c.1027 A > T (p.Lys343*), c.1048_1049del (p.Ser350Profs*18), and g.57363946_57372945del. All others, including p.Gln372*, have been previously reported.

Clinical Presentation of HAE-nC1-INH Patients

Patient 1 (MYOF, c.5923G > A)

A 43-year-old woman developed unilateral lower extremity swelling after a dog bite and vaccination. The edema subsequently progressed to involve both lower extremities, trunk, upper extremities, and facial region, including transient perioral swelling. The swelling remained incompletely resolved but demonstrated intermittent exacerbations, particularly under stress. The patient also reported two episodes of severe abdominal pain and transient voice changes, raising suspicion of laryngeal involvement. Treatment with antihistamines, corticosteroids, herbal medicines, and omalizumab yielded no improvement. Whole-exome sequencing identified a rare MYOF variant. While the chronic baseline edema complicates diagnosis, the episodic flares and multi-site involvement suggest a paroxysmal angioedema component. We thus provisionally classified this case as HAE-nC1-INH, though we acknowledge it does not meet all conventional diagnostic criteria. Future functional validation and family-based analysis will be required to confirm the pathogenicity of the variant.

Patient 2 (MYOF, c.6001 C > G)

A 49-year-old female patient presented with recurrent severe abdominal pain, vomiting, diarrhea, and episodic swelling affecting the wrists and bilateral lower extremities. Symptoms persisted for 2–7 days per episode and were occasionally accompanied by pruritic rashes. Notably, the patient experienced two episodes of life-threatening dyspnea requiring emergency resuscitation. Her mother had a similar symptom onset at age 40, raising suspicion of familial inheritance. Despite more than a year of oral glucocorticoid treatment, no improvement was observed. Complement testing was normal, and WES identified a MYOF sequence variant. A diagnosis of HAE-MYOF was established. The patient also had allergic rhinitis and Type 1 diabetes mellitus, consistent with immune dysfunction. After diagnosis, the patient received Icatibant during three distinct episodes of acute abdominal pain. In each case, a single injection reduced symptom severity and shortened episode duration. The patient then began regular injections of lanadelumab for prophylaxis, and the frequency and severity of attacks gradually decreased. She reported that she had not experienced any spontaneous abdominal pain since initiating lanadelumab treatment, indicating a significant therapeutic effect and effective symptom control.

Patient 3 (MYOF, c.3965 C > G)

A female patient presented with recurrent swelling of the hands and eyelids along with severe abdominal pain since age 30. Symptoms were exacerbated by stress, emotional factors, and pollen exposure. Conventional oral antihistamines failed to provide relief. Complement levels were normal, and genetic testing revealed a MYOF variant. Her mother harbored the same variant but was asymptomatic, suggesting variable penetrance. Following IgG4 testing and targeted dietary avoidance, the patient’s symptoms improved significantly. She also had allergic rhinitis and allergic conjunctivitis, further implicating MYOF variants in vascular permeability dysregulation and allergic predisposition.

Patient 4 (MYOF, c.1097G > T)

A 59-year-old male patient reported recurrent skin swelling over a 30-year period, primarily involving the extremities, vulva, and tongue. The swelling episodes were more frequent following emotional stress and poor sleep, though he denied associated itching, rashes, dyspnea, or recurrent abdominal pain. Each episode lasted a few hours to one day. He denied any family history of HAE. Laboratory testing showed normal C4 and C1-INH levels and function, but WES revealed a MYOF variant. Due to occasional tongue swelling, Icatibant was prescribed as a backup treatment, though its specific efficacy remains under evaluation.

Patient 5 (HS3ST6, c.497G > A)

A 31-year-old man developed unilateral lower extremity erysipelas, which resolved following antibiotic therapy. However, persistent, non-pitting edema developed in the same limb and subsequently progressed to the contralateral side. Extensive investigations—including imaging, skin biopsy, autoimmunity work-up, and infectious screening—did not reveal an alternative etiology. Complement testing showed normal C1-INH levels and borderline-low C1-INH function. Whole-exome sequencing identified a rare missense variant in HS3ST6, a gene implicated in endothelial regulation via heparan sulfate biosynthesis. The patient’s mother carried the same variant but was asymptomatic. Notably, the patient did not report episodic or recurrent attacks of angioedema. Despite administration of Icatibant and six biweekly injections of lanadelumab, symptoms persisted without improvement. Given the absence of classical HAE features, this case was provisionally considered under the broader HAE-nC1-INH spectrum, based on exclusion of alternative causes, variant rarity, and biological plausibility. However, we emphasize that this patient does not meet formal diagnostic criteria for HAE, and ongoing studies are required to clarify the pathogenicity and clinical relevance of this variant.

Patient 6 (FXII, c.303_304del)

A 20-year-old woman presented with recurrent swelling of the face, trunk, and extremities for over four months, with no identifiable trigger. The edema worsened over time, occasionally accompanied by itching and wheals. Several months of oral antihistamines and diuretics provided no relief. Complement testing revealed C1-INH levels and function were lower than normal but not below 50%, leading to a suspected diagnosis of HAE-FXII. Whole-exome sequencing confirmed a FXII variant, and her father, who carries the same variant, remained asymptomatic. The patient also had ankylosing spondylitis and cephalosporin allergy, further suggesting immune dysregulation in HAE-FXII carriers. Initial lanadelumab therapy did not immediately control her symptoms, but after ten consecutive injections, her edema was fully resolved. The patient continues lanadelumab treatment with no recurrence of symptoms, indicating potential efficacy in FXII-driven HAE despite a delayed response.

Patient 7 (KNG1, c.1690 C > T)

A 53-year-old man presented with recurrent episodes of swelling affecting the cheeks and lips, with no itching, rash, or identifiable trigger. Each episode persisted for 2–3 days and resolved spontaneously. Months of antihistamine and traditional Chinese medicine therapy failed to prevent further attacks. Laboratory tests confirmed normal C1-INH levels and function, but WES identified a KNG1 variant, leading to a diagnosis of HAE-KNG1. The patient denied any family history of similar symptoms. During a one-year follow-up period, no further edema episodes occurred, and the patient declined further genetic screening or prophylactic treatment.

Patient 8 (KNG1, c.1143G > C)

A 70-year-old man presented with recurrent swelling with blisters for over seven years, along with irregular episodes of pharyngeal edema and two emergency room visits for dyspnea within the past three years. Complement testing showed decreased C4 levels and low C1-INH function, though C1-INH concentration remained normal. WES revealed a variant in KNG1, expanding the genetic spectrum of KNG1-associated HAE. Notably, the patient also had elevated rheumatoid factor and specific IgE positivity for wheat, shrimp, and crab allergens, suggesting a potential link between KNG1 variants, autoimmunity, and allergic reactivity. Due to financial constraints, the patient did not initiate Icatibant or lanadelumab treatment. However, after three months of strict avoidance of wheat, shrimp, and crab, he reported a significant reduction in the frequency of edema episodes, highlighting a possible allergen-triggered component in KNG1-driven HAE.

To further contextualize the molecular findings, we performed preliminary variant classification according to the 2015 ACMG/AMP guidelines and analyzed available family data to assess potential co-segregation. Among the eight HAE-nC1-INH cases, four patients had genetic testing data from first-degree relatives. In several instances, variants were identified in asymptomatic carriers, suggesting incomplete penetrance. A summary of variant classification, familial observations, and preliminary interpretation is provided in Table 4.

Table 4.

Genetic variant classification, co-segregation analysis, and clinical interpretation in HAE-nC1-INH patients

Patient #	Gene	cDNA change	Protein change	ACMG classification	Family data summary	Co-segregation observation	Final interpretation
1	MYOF	c.5923G > A	p.Glu1975Lys	VUS (PM2)	No family tested	Not available	Variant of uncertain significance
2	MYOF	c.6001 C > G	p.Arg2001Gly	VUS (PM2)	Daughters negative; mother deceased (symptomatic)	Incomplete	Variant of uncertain significance
3	MYOF	c.3965 C > G	p.Ala1322Gly	VUS (PM2)	Mother carrier, asymptomatic	Yes	Variant of uncertain significance
4	MYOF	c.1097G > T	p.Arg366Leu	VUS (PM2)	Not tested	Not available	Variant of uncertain significance
5	HS3ST6	c.497G > A	p.Arg166His	VUS (PM2)	Mother carrier, asymptomatic	Yes	Variant of uncertain significance
6	FXII	c.303_304del	p.His101Glnfs*36	Likely pathogenic (PVS1 + PM2)	Father carrier (asymptomatic); mother and sister negative	Partial (carrier asymptomatic)	Likely pathogenic
7	KNG1	c.1690 C > T	p.Gln564Ter	Likely pathogenic (PVS1 + PM2)	No family data	Not available	Likely pathogenic
8	KNG1	c.1143G > C	p.Arg381Ser	VUS (PM2)	No family data	Not available	Variant of uncertain significance

ACMG classification was determined based on 2015 ACMG/AMP criteria. “VUS” denotes “variant of uncertain significance.” “Partial” co-segregation indicates that the variant was found in a relative without symptoms (suggesting incomplete penetrance)

Clinical interpretation incorporates genotype, phenotype, family history, and treatment response

Patient numbers correspond to those listed in Table 3 for HAE-nC1-INH

Although Patients 1 (MYOF), 5 (HS3ST6), and 6 (FXII) presented with persistent, non-cyclic swelling rather than classical episodic attacks, all three met the diagnostic criteria for HAE-nC1-INH based on a combination of clinical morphology, absence of histaminergic response, exclusion of alternative diagnoses, and the presence of rare variants in genes previously associated with HAE. In Patient 6, symptoms fully resolved following lanadelumab, consistent with bradykinin-pathway modulation. These observations support the inclusion of persistent angioedema within the phenotypic range of HAE-nC1-INH and reflect emerging consensus that this subtype may involve broader and more heterogeneous clinical patterns than classical HAE.

Comorbidities and Attack Triggers

Concurrent allergic diseases (e.g., rhinitis, urticaria, food allergies) were identified in 40.74% (n = 11) of patients, with 3 of 8 HAE-nC1-INH patients exhibiting simultaneous pruritic rashes and angioedema, suggesting a mixed mediator pathway. Autoimmune disorders, including systemic lupus erythematosus and ankylosing spondylitis, were diagnosed in 25.93% (n = 7) of patients, further supporting a potential association between HAE and immune dysregulation.

Common attack triggers included trauma (25.93%), emotional stress (33.33%), and cold exposure (11.11%). Additionally, hormonal fluctuations (e.g., menstruation or oral contraceptive use) were reported by four female patients, reinforcing estrogen’s potential role in exacerbating angioedema episodes in specific HAE subtypes.

Treatment Responses and Long-Term Outcomes

Among the nine patients who received Icatibant for acute HAE attacks, seven (77.78%) reported complete resolution of edema progression following administration. These cases involved severe cutaneous swelling and abdominal pain, which are hallmark symptoms of bradykinin-mediated HAE episodes. The remaining two patients experienced a noticeable reduction in the rate of edema progression, though they required additional symptomatic interventions to achieve full resolution. Two individual patients in our cohort—one with HAE-FXII and one with HAE-HS3ST6—exhibited persistent edema that did not improve with Icatibant treatment. Although anecdotal, these findings illustrate potential therapeutic variability across genetic subtypes and underscore the need to further explore non-bradykinin-dependent mechanisms in select HAE-nC1-INH cases (Table 5).

Table 5.

Treatment and outcomes for patients with HAE-nC1-INH

Patient #	Gene	cDNA change	Clinical symptoms	Treatment	Outcomes	Follow-up treatment plans
1	MYOF	c.5923G > A	Persistent swelling	No treatment (refused by the patient)	Persistent swelling	Icatibant and lanadelumab
2	MYOF	c.6001 C > G	Recurrent edema with spontaneous resolution	Icatibant	Shorten duration of edema	Lanadelumab 300 mg q2w
				Lanadelumab	Decreased frequency and shorten duration of edema
3	MYOF	c.3965 C > G	Recurrent edema with spontaneous resolution	Allergen avoidance	Decreased frequency of edema	Follow-up
4	MYOF	c.1097G > T	Recurrent edema with spontaneous resolution	No treatment (refused by the patient)	Frequent attack of edema	Icatibant and lanadelumab
5	HS3ST6	c.497G > A	Persistent swelling	Icatibant and lanadelumab for 6 injections	No improvement in symptoms	Follow-up
6	FXII	c.303_304del	Persistent swelling	Icatibant	No improvement in symptoms	Lanadelumab 300 mg q4w
				Lanadelumab for 10 injections	Fully remission
7	KNG1	c.1690 C > T	Recurrent edema with spontaneous resolution	No treatment (refused by the patient)	No episodes within 1 year of follow-up	Follow-up
8	KNG1	c.1143G > C	Recurrent edema and bullae with spontaneous resolution	Allergen avoidance	Decreased frequency of edema	Icatibant and lanadelumab

Lanadelumab, a monoclonal antibody that inhibits plasma kallikrein, was administered for long-term prophylaxis in nine patients, including six with HAE-1, one with HAE-2, and two with HAE-nC1-INH. After three months of biweekly treatment, all patients exhibited a significant reduction in attack frequency, with marked improvement in disease control. AECT (Angioedema Control Test) scores significantly increased, with a mean improvement of 12.86 ± 0.69 (p < 0.001) among patients with HAE-1/2, reflecting enhanced quality of life and sustained symptom relief (Table 6).

Table 6.

Comparison of edema attacks and AECT scores before and after lanadelumab treatment

No. of patients	HAE type	Attacks in 3 months		AECT scores
		Base-line	Post-treatment	Base-line	Post-treatment
1	HAE-1	9	0	2	12
2		2	0	4	13
3		12	1	1	12
4		4	0	3	13
5		3	0	3	13
6		2	0	2	13
7	HAE-2	2	0	1	14
8	HAE-nC1-INH	5	3	2	8
Mean ± SD/Median (IQR)		3.5 (2,8)	0 (0,0.75)	2.25 ± 1.04	13 (12,13)
p		< 0.001		< 0.001

*AECT refers to the Angioedema Control Test, with a score of 10 or higher indicating good control. Normality of the sample distribution was assessed using the Shapiro-Wilk test. The p-value for comparison of edema attacks was obtained using the Mann-Whitney U test, while the p-value for comparing AECT scores was derived from an independent samples t-test

*The patient with “HAE-FXII” was also treated with lanadelumab but is not listed in this table because her swelling was persistent and cannot made a before-and-after comparison on the number of episodes and the AECT score

One patient with HAE-MYOF received lanadelumab for long-term prophylaxis. While she reported substantial improvement in daily functioning and symptom control, the frequency and severity of abdominal pain episodes remained higher than in HAE-1/2 patients, indicating that MYOF-associated HAE may not be fully responsive to kallikrein inhibition alone. These findings reinforce the hypothesis that MYOF variants may contribute to vascular permeability through alternative pathways, such as dysregulated VEGF signaling, rather than solely through the kallikrein-kinin cascade.

A patient with an FXII variant (c.303_304del) experienced persistent swelling of the face and lower limbs for over four months prior to diagnosis. After ten biweekly injections of lanadelumab, complete and sustained remission was achieved, with no subsequent attacks reported during the 12-month follow-up period. This case underscores lanadelumab’s potential to provide long-term disease control in genetically complex cases of HAE-nC1-INH, although some patients may require extended treatment durations before achieving full therapeutic efficacy.

No significant changes in C4 or C1-INH levels were observed before and after lanadelumab therapy, reinforcing that its mechanism of action is independent of C1-INH status. This further supports its effectiveness across various HAE subtypes, including HAE-nC1-INH with undefined molecular drivers. Importantly, no serious adverse events were reported, and patient adherence was high, with no treatment discontinuations due to side effects. These findings provide strong real-world evidence for the safety and efficacy of lanadelumab as a long-term prophylactic option for HAE, even in patients with genetically complex disease manifestations.

Discussion

Our study represents a significant advancement in the genetic characterization of HAE-nC1-INH, particularly in underrepresented populations. The identification of four novel MYOF variants provides the first evidence that MYOF-associated vascular permeability dysfunction may play a distinct role in HAE pathogenesis. While previous reports have suggested that MYOF variants may contribute to endothelial dysfunction, our findings establish a direct clinical correlation with persistent swelling, late-onset disease, and allergic comorbidities, further expanding the genetic heterogeneity of HAE-nC1-INH [10]. These findings suggest that disease mechanisms may extend beyond the bradykinin pathway to involve VEGF-mediated endothelial regulation, which has not been widely recognized in HAE pathophysiology [11].

Importantly, our study is the first to systematically analyze MYOF variants in an Asian cohort, revealing a higher frequency of MYOF variants compared to previous European reports [10]. This suggests potential ethnic and population-specific genetic predispositions, warranting further investigation into genetic-environmental interactions in HAE pathogenesis. Expanding genetic screening efforts across different populations will be essential to defining the true genetic landscape of HAE-nC1-INH and determining whether specific variants contribute to distinct phenotypic variations observed across geographic regions [12]. Given the growing evidence that MYOF plays a role in vascular permeability, further studies using functional validation approaches will be necessary to understand the pathogenic mechanisms of these variants and their implications for targeted therapies.

The discovery of HS3ST6 variants in HAE-nC1-INH further highlights alternative mechanisms of vascular permeability dysregulation, reinforcing the complex genetic architecture of this condition. HS3ST6, involved in heparan sulfate biosynthesis, has been linked to vascular integrity and inflammatory signaling, suggesting that mutations in this gene may promote non-bradykinin-dependent pathways of angioedema [7]. Our study found that patients with HS3ST6 variants displayed persistent swelling resistant to icatibant, reinforcing the need for further research into alternative therapeutic targets in HAE-nC1-INH cases that do not fully respond to traditional bradykinin-targeted therapies.

Our real-world evaluation of lanadelumab in a genetically diverse HAE cohort provides compelling evidence for the importance of personalized treatment approaches in HAE-nC1-INH. While lanadelumab effectively reduced attack frequency in most patients, its efficacy varied significantly across different genetic backgrounds, particularly in carriers of MYOF, KNG1, and HS3ST6 mutations. This variability in response underscores the necessity of tailoring HAE treatment strategies based on individual genetic profiles, as kallikrein inhibition alone may not be universally effective across all HAE-nC1-INH subtypes. Patients with HAE-FXII, one of the more extensively studied forms of HAE-nC1-INH, often exhibit bradykinin-mediated angioedema, and account for approximately 30% of cases in European cohorts [4]. The most frequently reported FXII mutations include c.983 C > A (p.Thr328Lys) and c.983 C > G (p.Thr328Arg) [21], a large deletion mutation spanning 72 base pairs (c.971_1018 + 24del72) [22], and a duplication mutation (c.892_909dup) [23]. HAE-FXII predominantly affects women, with attacks often triggered by estrogen fluctuations, and typically involves the skin, gastrointestinal tract, and occasionally the upper airway.

However, our HAE-FXII case presented with a distinct clinical phenotype, diverging from the classical hormonally influenced exacerbations commonly described in the literature. Unlike previous reports, our patient exhibited persistent, non-cyclical swelling, with no clear exacerbations linked to menstruation, pregnancy, or oral contraceptive use. Furthermore, despite initial resistance to therapy, her symptoms resolved abruptly following multiple lanadelumab administrations, suggesting a possible delayed therapeutic response in certain HAE-FXII carriers. This atypical disease progression and treatment response raises important questions regarding pathophysiological heterogeneity within FXII mutation carriers and suggest that additional molecular mechanisms beyond bradykinin dysregulation may contribute to persistent angioedema. Further research is warranted to elucidate whether FXII-driven HAE subtypes may involve alternative pathways or additional genetic modifiers influencing disease severity and treatment outcomes.

Another notable observation in our study was the patient harboring an HS3ST6 variant, who exhibited persistent edema resistant to conventional therapies. This clinical presentation contrasts with previous reports of HS3ST6-associated HAE, particularly the case of a c.430 A > T (p.Thr144Ser) mutation, where affected individuals displayed episodic swelling primarily involving the skin, throat, and gastrointestinal mucosa [6]. Our patient, however, presented with chronic, non-resolving edema rather than the acute, recurrent attacks typically seen in HAE, raising the possibility that different HS3ST6 variants may contribute to distinct angioedema phenotypes.

The biological function of HS3ST6 in heparan sulfate biosynthesis has been well-documented, with established roles in regulating endothelial function and inflammatory responses [7]. Disruption of heparan sulfate biosynthesis could impair the normal endocytosis of kininogen, leading to increased bradykinin production and subsequent excessive vascular permeability. However, the failure of icatibant to alleviate symptoms in our HS3ST6 patient, despite its well-established efficacy in bradykinin-mediated angioedema, suggests that this variant may also contribute to non-bradykinin-driven angioedema pathways. We hypothesize that HS3ST6 variants could alter endothelial barrier function via mechanisms beyond direct kallikrein-kinin system activation, warranting further functional studies to confirm its role and identify potential therapeutic targets.

MYOF mutations are an uncommon but emerging genetic cause of HAE, with a limited number of cases documented in the literature. One previous study described three affected female relatives in an Italian family harboring a c.651G > T (p.Arg217Ser) mutation, with episodic swelling of the face, lips, and oral mucosa [24]. However, our study significantly expands upon prior findings by identifying four distinct MYOF variants across multiple unrelated patients, including both male and female carriers, each displaying heterogeneous clinical phenotypes. This genetic and clinical diversity suggests that MYOF variants may not represent a single disease entity but rather a broader category of vascular permeability disorders with variable expressions.

Although HAE is traditionally classified as a bradykinin-mediated disorder, the presence of MYOF variants in our cohort suggests that other regulatory pathways, such as VEGF signaling, may also play a role in disease pathophysiology [10]. MYOF (myoferlin) is a critical regulator of VEGFR2, and its dysfunction could lead to excessive vascular permeability and abnormal endothelial barrier function. The co-occurrence of pruritic rashes and angioedema in certain MYOF carriers further suggests that histamine and other inflammatory mediators may also contribute to edema formation, distinguishing MYOF-associated HAE from classical bradykinin-mediated angioedema. The potential involvement of multiple mediators underscores the need for further in vitro and in vivo studies to determine whether MYOF-driven HAE could benefit from alternative therapeutic approaches beyond bradykinin-targeted treatments.

MYOF mutation-associated HAE has rarely been reported worldwide, making our cohort particularly valuable in understanding the genetic and clinical diversity of this HAE subtype. Among our patients with MYOF variants, one individual also harbored a SERPING1 variant and was diagnosed with HAE-2, demonstrating that MYOF mutations may coexist with other pathogenic variants and contribute to complex disease presentations. Interestingly, we observed a notably high prevalence of MYOF variants in our Chinese cohort, raising questions about whether genetic predisposition, environmental factors, or population-specific variations contribute to this increased frequency.

In addition to its potential role in bradykinin-independent vascular permeability regulation, MYOF mutations may also lower the threshold for endothelial dysfunction, leading to exaggerated edema responses even under normal concentrations of vasoactive substances. The partial but incomplete response to lanadelumab in one of our HAE-MYOF patients suggests that MYOF-associated angioedema may not be fully dependent on kallikrein activation and may require alternative treatment strategies targeting VEGF or endothelial barrier function. Although lanadelumab significantly reduced attack frequency, our findings emphasize the importance of considering genetic background when selecting long-term prophylactic therapies. Future research should explore whether combining kallikrein inhibitors with VEGF-targeted agents could provide a more effective therapeutic approach for MYOF-driven HAE.

Diagnosing HAE-nC1-INH remains challenging, as current diagnostic approaches rely heavily on clinical manifestations, including recurrent, unexplained angioedema episodes affecting the skin, airway, and gastrointestinal tract, in the setting of normal C1-INH levels and function. However, HAE-nC1-INH is a genetically and phenotypically heterogeneous disorder, and reliance on phenotypic assessment alone often leads to diagnostic uncertainty and delays in appropriate treatment [25]. In our study, we observed substantial clinical heterogeneity among patients, including unusual presentations such as persistent swelling in HAE-FXII, MYOF, and HS3ST6 variant carriers, further underscoring the limitations of a purely phenotype-driven approach. In these cases, standard biochemical testing was insufficient to establish a definitive diagnosis, highlighting the need for integrating genetic testing into clinical workflows.

Genetic testing, while valuable, does not always provide clear-cut answers, as the relationship between genotype and phenotype in HAE-nC1-INH is complex and not fully understood. Different mutations within the same gene can lead to highly variable clinical presentations, complicating efforts to establish definitive diagnostic criteria. Some patients with known pathogenic variants remain asymptomatic, while others experience severe, refractory disease, indicating that additional genetic, epigenetic, or environmental factors may contribute to disease expression. Given this variability, our findings support the integration of genetic testing into existing diagnostic algorithms, not as a standalone tool, but as a complementary approach alongside clinical and laboratory assessments to refine the classification of HAE-nC1-INH and improve individualized patient management. We hope that our insights will contribute to updates in international diagnostic guidelines, ensuring that genetic findings are appropriately incorporated into standardized HAE evaluation protocols.

Since 2021, lanadelumab—a monoclonal antibody targeting plasma kallikrein—has been available in mainland China for the long-term prophylaxis of HAE. This availability provided us with a unique opportunity to evaluate its real-world efficacy among patients with genetically diverse forms of HAE, including HAE-1, HAE-2, and HAE-nC1-INH. To our knowledge, this is the first study to systematically assess lanadelumab’s performance in Eastern Asian HAE patients, with particular attention to its efficacy across different genetic backgrounds.

Among our HAE-1 and HAE-2 patients, all seven individuals achieved complete remission of edema episodes during biweekly lanadelumab therapy, supporting its high efficacy in conventional bradykinin-mediated HAE. However, its effects in HAE-nC1-INH were more variable, reinforcing the notion that some genetic subtypes may not be entirely driven by kallikrein overactivation. One patient with an HAE-FXII variant experienced an atypical response, requiring ten consecutive injections before achieving complete symptom resolution, suggesting that certain genetic backgrounds may influence the timeline and effectiveness of treatment.

Recognizing the high cost and limited accessibility of lanadelumab in China, we also explored the possibility of extending dosing intervals. After six months of stable disease control, one patient successfully extended the dosing interval to 16 weeks, while others maintained remission with a less-than-four-week interval. Although preliminary and limited by sample size, these findings suggest that personalized dose-interval adjustments may help optimize treatment efficiency while reducing financial burden, particularly in regions where high-cost biologics remain a significant barrier to care. Future larger-scale studies are warranted to determine whether individualized dosing schedules can maintain efficacy without compromising disease control, and whether biomarkers such as residual C1-INH activity or attack frequency could guide patient-specific treatment protocols.

The patient with the FXII gene variant in our cohort presented an intriguing clinical scenario, as her symptoms persisted for nearly five months despite ongoing lanadelumab therapy. Initially, she showed minimal improvement, but after ten consecutive injections, she achieved complete remission, with no further attacks reported over the next 12 months. This delayed but eventual full response suggests that certain HAE-FXII cases may require prolonged kallikrein inhibition before reaching maximum therapeutic benefit.

The variable responsiveness of HAE-FXII to lanadelumab reflects the complexity of HAE-nC1-INH and raises several critical questions regarding treatment mechanisms and patient selection. While kallikrein inhibition is highly effective for bradykinin-mediated angioedema, it is possible that other pathways—such as alternative contact system activation or endothelial barrier dysfunction—contribute to symptom persistence in certain genetic backgrounds. Although several reports have confirmed lanadelumab’s efficacy in HAE-FXII [14], treatment options for other HAE-nC1-INH subtypes remain limited, particularly for HS3ST6 and MYOF-driven disease. Our findings highlight the urgent need for further research into the molecular underpinnings of HAE-nC1-INH, as well as the development of precision medicine approaches tailored to specific genetic drivers.

Our study also provides an updated epidemiologic assessment of HAE in China, offering new insights into the distribution of HAE subtypes in Eastern Asian populations. In Western cohorts, HAE-2 accounts for approximately 15% of all HAE cases [26]. However, in our study of 27 Chinese HAE patients, only two were diagnosed with HAE-2, suggesting a notably lower prevalence compared to Western populations. These findings align with two prior large-scale Chinese studies, which reported HAE-2 prevalences of 2.26% (3/133) ²⁶ and 1.27% (2/158) [27], respectively. Such discrepancies in subtype distribution across populations emphasize the importance of local epidemiologic surveillance, as regional genetic backgrounds, environmental influences, and referral biases may contribute to these variations.

Further supporting this geographic variability, data from South Korea indicate that 9.2% (6/65) of HAE patients have HAE-2 [28], while Danish reports suggest a prevalence of approximately 6.1% (5/82) [29]. These comparative analyses reinforce the need for country-specific epidemiological studies to ensure that HAE diagnostic and treatment guidelines are appropriately adapted to regional patient populations. The lower observed prevalence of HAE-2 in China raises the possibility that genetic variations unique to East Asian populations may influence disease susceptibility and subtype distribution, warranting further genomic studies to identify potential population-specific risk factors.

In addition to subtype distribution, our findings highlight important differences in disease onset and progression between Eastern and Western HAE cohorts. The mean age at first symptom onset in our Chinese cohort was approximately 26 years, which closely mirrors prior Chinese, Taiwanese, and South Korean reports. However, European and North American studies frequently report earlier disease onset, often in childhood or adolescence [26, 27, 29]. Earlier onset has been associated with more severe disease progression, potentially explaining why HAE appears to have a lower incidence and seemingly milder presentation in East Asian populations. These ethnic and regional differences further emphasize the importance of genetic and environmental modifiers in shaping disease expression, reinforcing the need for population-specific studies to refine clinical management strategies.

Despite advances in diagnostic awareness, diagnostic delay remains a critical challenge. Historical reports from mainland China indicate average delays of 13–16 years [26–29], whereas our study observed an average diagnostic delay of 8 years. While this suggests gradual improvement in early recognition, nearly a decade-long delay in diagnosis remains far from optimal for a potentially life-threatening condition. Enhanced education for healthcare professionals, increased availability of genetic and biochemical testing, and the development of standardized diagnostic workflows are urgently needed to further shorten diagnostic delays and ensure timely intervention for HAE patients.

Abdominal involvement is a common and often debilitating feature of HAE, frequently leading to severe pain that can mimic surgical emergencies, sometimes resulting in unnecessary medical procedures such as exploratory laparotomies or appendectomies [1, 12, 18]. In our cohort, 14 of 27 patients (51.85%) experienced abdominal attacks, underscoring the importance of recognizing gastrointestinal manifestations as part of the HAE disease spectrum. Notably, three patients with HAE-nC1-INH and MYOF variants presented with particularly severe abdominal symptoms, raising important questions about potential genotype-phenotype correlations in gastrointestinal involvement.

While it remains uncertain whether MYOF mutations have a direct mechanistic role in triggering abdominal symptoms, there is a growing body of evidence suggesting that MYOF dysfunction may contribute to increased vascular permeability, not only in cutaneous tissues but also in the intestinal vasculature [10]. MYOF is known to interact with VEGFR2 signaling, which regulates endothelial barrier integrity, and its dysfunction could increase susceptibility to intestinal edema and bowel wall thickening, similar to what is observed in bradykinin-driven abdominal HAE attacks. Awareness that certain genetic variants, particularly MYOF mutations, may predispose patients to gastrointestinal involvement could aid in earlier recognition and more targeted treatment strategies for these cases. Future studies investigating the role of MYOF in intestinal permeability could provide valuable insights into alternative disease pathways and potential therapeutic targets beyond kallikrein inhibition.

The association between HAE and autoimmune diseases has been well documented, with estimates suggesting that 11–12% of HAE patients also have concurrent autoimmune conditions, most commonly systemic lupus erythematosus (SLE) [30–35]. Our findings are consistent with this epidemiologic trend, as 7 of our 27 patients (26%) had coexisting autoimmune disorders, including both HAE-1 and HAE-nC1-INH cases. Although we did not identify a clear relationship between autoimmune disease activity and the frequency or severity of HAE attacks, it is possible that dysregulation of the complement system, heightened B-cell activity, or inflammatory mediators contribute to both conditions simultaneously [31, 32].

The pathophysiology linking HAE to autoimmunity remains poorly understood, but previous studies suggest that defective complement regulation, abnormal cytokine profiles, and chronic immune activation may be shared mechanisms between HAE and certain autoimmune conditions [34, 35]. Interestingly, a recent case report described a patient with multiple sclerosis (MS) who experienced significant improvement in HAE symptoms following MS-directed immunotherapy, suggesting that modulating immune dysregulation may influence angioedema severity and frequency. These observations highlight the need for further research into the immunological mechanisms underlying HAE, particularly in patients with coexisting autoimmune conditions, as such insights could facilitate the development of novel therapies targeting both immune dysregulation and vascular permeability [35, 36].

Another noteworthy finding in our study was that 11 out of 27 HAE patients (40.74%) also had allergic diseases, and 4 patients experienced angioedema episodes accompanied by pruritic rashes, which is uncommon in traditionally bradykinin-mediated HAE. This raises important questions about the role of mast cells, histamine release, and allergic pathways in specific HAE subtypes, particularly in HAE-nC1-INH. Among these cases, a patient with a MYOF variant reported significant improvement in symptoms following the avoidance of specific food allergens, which were identified through IgG4 testing.

Furthermore, an off-study case involving a patient with low C1-INH function and recurrent angioedema demonstrated a marked reduction in attack frequency and severity following treatment with omalizumab, an anti-IgE monoclonal antibody. These findings suggest that certain HAE subtypes—especially those with MYOF mutations—may involve additional inflammatory or mast cell-mediated pathways, rather than being exclusively bradykinin-driven [10]. While more rigorous investigation is needed, these preliminary observations point toward a possible overlap between HAE and allergic pathophysiology, expanding the potential therapeutic landscape to include anti-IgE therapies or allergen avoidance strategies in select cases. This new perspective on HAE pathogenesis could provide clinicians with additional treatment options, particularly for patients who exhibit partial responsiveness to bradykinin-targeted therapies.

This study contributes significantly to the understanding of HAE in an Asian context, particularly given the rarity and under-recognition of HAE-nC1-INH worldwide. As the first study to characterize both the genetic landscape and real-world treatment outcomes of HAE-nC1-INH in an Asian population, our findings highlight both the genetic diversity and therapeutic potential within this patient group. The identification of novel MYOF, KNG1, and HS3ST6 variants, along with the differential responses to lanadelumab, underscores the heterogeneity of HAE-nC1-INH and the necessity for a more individualized approach to diagnosis and treatment.

The classification of certain HAE-nC1-INH cases with persistent edema highlights a clinically relevant, genetically defined phenotype that diverges from classical recurrence-based definitions but remains consistent with the known pathophysiology and treatment profile of bradykinin-mediated angioedema. Recognizing this spectrum is essential for improving diagnosis and guiding appropriate therapeutic strategies, especially in populations with rare or novel variants.

Despite the significant contributions of this study, we acknowledge several limitations. The low incidence of HAE, combined with the limited sample size and single-center design, constrains the generalizability of our findings. Additionally, longitudinal follow-up is needed to further assess long-term treatment outcomes, particularly with adjusted lanadelumab dosing intervals. Nonetheless, these initial observations serve as a foundation for future multicenter collaborations, which will be critical for accurately delineating epidemiology, genotype-phenotype relationships, and treatment responses in diverse HAE populations.

Ultimately, advancing these research efforts will improve diagnostic precision, enhance therapeutic decision-making, and contribute to the development of more personalized management strategies. These efforts will not only optimize patient care within Asia but also provide broader insights into HAE pathogenesis worldwide, reinforcing the need for standardized diagnostic and treatment protocols tailored to regional and genetic variations. By leveraging multinational collaborations and cutting-edge genomic analysis, the field can move toward precision medicine approaches, ultimately enhancing patient outcomes and improving quality of life for individuals living with HAE.

Conclusions

This study significantly expands the global understanding of HAE, particularly HAE-nC1-INH, by identifying previously unreported MYOF, KNG1, and HS3ST6 variants in patients from mainland China, a population largely underrepresented in the literature. Our findings confirm the genetic diversity and clinical complexity of HAE-nC1-INH, extending beyond European cohorts and challenging existing diagnostic and therapeutic paradigms. The identification of novel genetic drivers reinforces the necessity for genetic testing in HAE-nC1-INH cases, particularly when conventional biochemical markers are inconclusive. These insights provide a foundation for refining genotype-phenotype correlations, which will be essential in improving diagnostic precision and tailoring personalized treatment approaches.

Moreover, our real-world evaluation of lanadelumab in genetically diverse HAE patients suggests that personalized prophylactic strategies can be effective across multiple genetic backgrounds, though variable responses in HAE-nC1-INH highlight the need for alternative or adjunctive therapies. The partial but incomplete response in MYOF carriers and delayed therapeutic effect in an HAE-FXII case suggest that certain genetic subtypes may involve alternative pathways beyond plasma kallikrein activation, necessitating broader therapeutic considerations.

Author Contributions

H.G., L.M., Y.Z., A.Z., Z.C., L.W., Z.Z., S.C., F.Y., J.Y., S.H., C.T., S.Z., L.T., C.G., Y.X., M.M., D.L., and X.L. conceived and designed the analysis, collected the data, and performed the analysis. X.L. supervised the project. H.G., L.M., Y.Z., A.Z., Z.C., L.W., Z.Z., S.C., F.Y., J.Y., S.H., C.T., S.Z., C.G., Y.X., M.M., D.L., and X.L. wrote the manuscript. H.G., L.M., Y.Z., A.Z., and X.L. had access to and verified the underlying data in the study. All authors read and approved the final manuscript.

Funding

The study was supported by the grant from the National Natural Science Foundation of China (81872525), Construction Program of the National Key Clinical Specialties of China (Departmentof Allergy & Immunology, Huashan Hospital) and Multidisciplinary Full-course Management of Allergic Diseases andthe Construction of a Metaverse-Based Intelligent Diagnosis and Treatment Platform.

Data Availability

No datasets were generated or analysed during the current study.

Declarations

Competing interests

The authors declare no competing interests.