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. 2025 Sep 30;45(1):137. doi: 10.1007/s10875-025-01937-4

A Child with Chronic Mucocutaneous Candidiasis Harbors a Novel Gain-of-Function Mutation in STAT1

Yang Xiang 1,#, Shuo Sun 2,#, Hong Wang 2,#, Chia‑Chi Lo 3, Jie Wu 2, Wei‑Te Lei 3,4,5, Fengming Li 2, Xiaodong Liu 2, Ningning Dang 2, Cheng-Lung Ku 3,5,6,✉, Jing Guo 2,✉
PMCID: PMC12484367  PMID: 41026300

Abstract

Objective

Germline heterozygous gain-of-function (GOF) mutations in STAT1 impair IL-17-mediated immunity, resulting in carriers’ susceptibility to chronic mucocutaneous candidiasis (CMC). JAK inhibitors have shown therapeutic effectiveness in patients with STAT1-GOF mutations.

Methods

The mutation was detected using whole-exome sequencing (WES) and confirmed by Sanger sequencing. The functional impact of the mutation was verified by luciferase reporter assay. The phosphorylation level of STAT1 in patient cells, the phenotyping of leukocyte subtypes, and serum cytokine levels were determined by flow cytometry.

Results

The patient with CMC harbors a heterozygous missense mutation in STAT1 (c.1078G > C, p.V360L). This mutation was functionally validated as a GOF mutation based on functional analysis of the variant and enhanced phosphorylation upon IFN-γ stimulation in the patient’s cells. Additionally, the patient demonstrated a decreased proportion of CD4 + T cells, NK cells, and Th17 cells. Flow cytometry analysis revealed a significant decrease in the expression of IL-17 A in CD4 + T cells from the patient. Serological test results showed that the patient’s IgM level was decreased, while the levels of IL-2, IL-5, IL-6 and TNF-α were elevated. Topical application of ruxolitinib demonstrated therapeutic efficacy.

Conclusions

The present study reports a pediatric patient with CMC who carries a novel GOF mutation in STAT1. This mutation may impair IL-17 immunity, which could potentially increase the patient’s susceptibility to CMC. However, further research is needed to elucidate the underlying mechanism. Although ruxolitinib shows potential as a therapeutic option for CMC, its clinical efficacy requires further validation through experimental studies and long-term patient follow-up.

Keywords: Chronic mucocutaneous candidiasis, STAT1-GOF mutation, Fungal susceptibility, IL-17 immunity, JAK inhibitors

Introduction

Germline heterozygous signal transducer and activator of transcription 1 (STAT1) GOF mutation in patients with autosomal dominant chronic mucocutaneous candidiasis disease (AD-CMC) is a rare and severe primary immunodeficiency [1]. The clinical symptoms of impaired immunity against fungi involve various parts of the body and are characterized by persistent or recurrent fungal infections of the skin, oral cavity, nails, or genital mucosal membranes. These infections are predominantly caused by Candida species, especially Candida albicans (C. albicans) [2]. This condition poses significant challenges for treatment and causes considerable distress and anguish for both patients and caregivers. In addition to the CMC, patients may subsequently develop severe autoimmune diseases, aneurysms, or malignant tumors, which can lead to a decline in life expectancy [3].

STAT1 is a central component of the JAK-STAT signaling pathway and plays a critical role in anti-infective immunity. It is activated by cytokines such as IFN-α/β, IFN-γ, and IL-27 through JAK-mediated phosphorylation [4]. Upon phosphorylation, STAT1 forms dimers, translocates into the nucleus, and modulates the expression of genes (e.g., IRF1 and CXCL10) involved in antifungal immunity [5, 6]. STAT1-GOF mutations are responsible for more than 50% of inherited CMC cases [7]. To date, over 120 pathogenic STAT1-GOF mutations have been identified, with the majority (87.6%) located in the coiled-coil domain (CCD) or the DNA-binding domain (DBD) [8, 9]. The elevated phosphorylation levels of STAT1 caused by GOF mutations are considered a potential pathogenic mechanism underlying CMC.

The continuous activation of STAT1 caused by STAT1-GOF mutations can inhibit the differentiation of Th17 cells induced by cytokines such as IL-6 and IL-23. Th17 cells secrete cytokines such as IL-17 and IL-22, which are key mediators of antifungal immunity [10]. Defects in IL-17 immunity have been extensively documented to contribute to the occurrence of CMC [11–13]. STAT1-GOF mutations can interfere with both innate and adaptive immune cells, such as naïve and effector memory CD4 + T cells, memory B cells, monocytes, and NK cells, thereby further weakening the host’s antifungal immune response [14–16]. The overactivation of STAT1 can also enhance the IFN-γ-mediated signaling pathway, thereby affecting local inflammatory responses and the efficiency of fungal clearance [17, 18].

A recent multicenter retrospective study, which included a total of 45 CMC patients (with over 78% being children) with STAT1-GOF mutations, assessed the clinical utility of JAK inhibitor therapy [19]. Among these patients, 81% received ruxolitinib, with approximately 82% achieving disease remission. A further 7% were treated with baricitinib, of whom approximately one-third experienced remission. Another 7% were administered tofacitinib, and all demonstrated clinical improvement. The remaining patients were treated with a combination of ruxolitinib and baricitinib, and their conditions also showed improvement. This study suggests that JAK inhibitors may offer promising therapeutic benefits for CMC patients with STAT1-GOF mutations. JAK inhibitor therapy restores damaged cellular and humoral immune functions, potentially explaining its efficacy in treating CMC in patients with STAT1-GOF mutations [16, 17, 20, 21]. It is worth noting that hematopoietic stem cell transplantation (HSCT) has been used to treat CMC patients with STAT1-GOF mutations and has demonstrated promising results [19, 21, 22]. This approach could potentially serve as a valuable new treatment option.

In this report, we present the case of a pediatric AD-CMC patient with a novel heterozygous GOF mutation in the STAT1 gene. This finding provides new insights into the clinical and genetic characteristics of AD-CMC. Additionally, we observed that topical application of ruxolitinib showed promising therapeutic effects for the patient.

Materials and Methods

Study Subjects

The study enrolled a 5-year-old male patient who had been diagnosed with AD-CMC, along with his legal guardians. He was admitted to the Department of Dermatology at Shandong Provincial Hospital, affiliated to Shandong First Medical University (Jinan, China).

Ethics

This study was approved by the Medical Ethics Committee of Shandong Provincial Hospital, affiliated to Shandong First Medical University (Jinan, China) and was conducted in accordance with the Declaration of Helsinki. Written informed consent was obtained from all human subjects.

DNA Sequencing

Peripheral blood samples were collected from the enrolled subjects. Genomic DNA was extracted from peripheral blood leukocytes using a commercial DNA extraction kit (Simgen, Hangzhou). The DNA samples were subsequently subjected to whole-genome sequencing (WGS) in collaboration with Beijing KANGSO Medical Inspection. The DNA samples were first used to construct a DNA library. The amplified DNA library was subjected to hybridization and capture by probes, followed by amplification with the SureSelect target enrichment system (Agilent, USA). Paired-end sequencing was performed on a NextSeq500 (Illumina, USA), and all sequenced DNA reads were mapped to the hg19 human genome. SNP analysis and DIP analysis were conducted to obtain information on mutation sites in the targeted regions. The identified variant was validated using Sanger sequencing.

Luciferase Reporter Assay

The luciferase reporter assay was conducted as previously described [4]. Briefly, U3C cells were seeded into 96-well plates (1 × 104/well) and transfected with a reporter plasmid (Cignal GAS Reporter Assay kit; SABiosciences, USA). The plasmid DNA carrying either the wild-type or variant alleles of STAT1, or a mock vector, was transfected using Lipofectamine LTX (Invitrogen, USA). After 6 h of transfection, the cells were reintroduced into medium supplemented with 10% FBS and incubated for an additional 24 h. The transfectants were then stimulated with IFN-γ (103 IU/mL, Sigma, Germany) for 12 h and subjected to luciferase assays using the Dual-Glo Luciferase Assay System (Promega, USA). The firefly luciferase activity was normalized relative to the Renilla luciferase activity, and the results were presented as fold induction compared to non-stimulated cells.

Flow Cytometry

The peripheral blood mononuclear cells (PBMCs) from the patient and healthy controls were isolated using density gradient centrifugation with Ficoll/Hypaque at a density of 1.077 g/mL (Solarbio, Beijing). PBMCs (5 × 10⁶ cells per tube) were first stained with mouse anti-human monoclonal FITC-conjugated anti-CD14 antibody (BD, USA) for 5 min at 37 °C. Subsequently, the cells were washed with PBS and then stimulated with IFN-γ (1 × 10² IU/mL, Sigma, Germany) for 15 min at 37 °C. Following permeabilization and fixation, the cells were incubated with mouse anti-human monoclonal PE-conjugated anti-Phospho-STAT1-Tyr701 antibody (Invitrogen, USA) for 45 min at 37 °C. The cells were then washed and analyzed using a BD LSRFortessa™ X-20 system.

The PBMCs (1 × 10⁶ cells/tube) were stained with a mixture of mouse anti-human monoclonal PE-conjugated anti-CD4 (BD, USA) and mouse anti-human monoclonal FITC-conjugated anti-IL-17 A (BD, USA) for 15 min at 4 °C in the dark. The cells were then washed and analyzed using a BD LSRFortessa™ X-20 system.

Peripheral blood serum samples were obtained from the patient and healthy controls. Lymphocyte subset analysis was performed in the clinical laboratory using a commercially available BD Multitest 6-Color TBNK Reagent kit (BD, USA). This product is used to identify and determine the percentages and absolute counts of T lymphocytes, B lymphocytes, and NK cells, as well as CD4 + and CD8 + subsets of T cells, in peripheral blood. The product is a 6-color direct immunofluorescence reagent used in conjunction with BD Trucount™ absolute counting tubes and the BDFACSCanto™ flow cytometer. Peripheral blood serum cytokine levels were measured in the clinical laboratory using a commercially available 12-item (IL-1β, IL-2, IL-4, IL-5, IL-6, IL-8, IL-10, IL-12p70, IL-17, IFN-γ, IFN-α, and TNF-α) cytokine detection kit (RAISECARE, Qingdao), and analyzed using the BDFACSCanto™ flow cytometer.

Statistical Analysis

The continuous variables were reported as mean ± SD or median (inter-quartile range). Statistical comparisons between the continuous variables were conducted using either the student’s t-test or the Mann-Whitney U test. The statistical analysis was conducted using SPSS software version 17.0 (USA) and GraphPad Prism 8.0 (USA). A p value < 0.05 (two-tailed) was considered statistically significant.

Results

Case Description

This study reported a case of a 5-year-old male patient who came to our hospital due to recurrent erythema and crusting on the scalp and facial area that had persisted for over two years. His parents were not consanguineous, and he was the only family member to exhibit susceptibility to fungal infections. The patient initially presented with recurrent high fever that showed no significant response to conventional antibiotic therapy, accompanied by a recurrent thrush. The condition was controlled with oral nystatin tablets at local hospitals.

In June 2021, the patient developed a severe erythematous rash of unknown etiology on the right cheek (Fig. 1A). Subsequently, the rash gradually spread to the nasal and labial regions and evolved into induration (Fig. 1B). The facial erythema further spread to the forehead, neck, and scalp thereafter (Fig. 1C). Pruritus persisted throughout the course of the disease. Initially, the patient was admitted to a local hospital for medical treatment. Skin lesion samples were collected from the affected area using sterile swabs and were subsequently sent for microbiological culture. In the pathogenic microorganism laboratory, the strain obtained through culture was identified as C. albicans. Based on the positive fungal test result, the patient was treated with topical bifonazole cream. Antifungal treatment controlled the further progression of the patient’s symptoms, with some erythema subsiding, but complete remission was not achieved. After the medication was discontinued, the symptoms recurred. In January 2022, the patient was admitted to our hospital (Fig. 1D). During hospitalization, the patient was treated with oral itraconazole, topical bifonazole cream, fusidic acid cream, and a 1:5 benzalkonium chloride solution for cleaning the skin lesions. The patient’s condition significantly improved following the treatment. After the patient’s first discharge, we prescribed oral itraconazole along with topical bifonazole treatment. However, the patient did not adhere to the prescribed regimen and failed to take the medication regularly. Without consulting his physician, he discontinued the treatment on his own. Upon recurrence of symptoms, he resumed the medication without medical guidance. Eventually, this led to a deterioration of his condition.

Fig. 1.

Fig. 1

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Clinical images (A) In June 2021, the patient developed an erythematous rash on the right cheek of unknown etiology. (B) Erythematous rash subsequently extended to involve the nasal and labial regions. (C) Erythema on the face spread to the forehead, neck, and scalp and was associated with pruritus. (D) In January 2022, the patient was admitted to our hospital. (E) Skin lesions of the patient during the readmission visit. The child presented with extensive erythema and papules, accompanied by yellow crusts, on the bilateral cheeks, nose, lips, forehead, and scalp. (F) After eight months since the second discharge, the patient underwent a follow-up examination. The image indicated that the extensive erythema and papules on both cheeks, the nose, the lips, the forehead, and the sides of the scalp had largely disappeared. (G) The patient was readmitted to our hospital eleven months after the second discharge due to progressively worsening symptoms. The imaging revealed prominent erythema and crusting on the nose and the right side of the cheek

In February 2023, the patient was readmitted due to worsening symptoms. Skin examination revealed extensive erythema, papules, and yellow crusts on the patient’s bilateral cheeks, nose, lips, forehead, and scalp (Fig. 1E). Physical examination showed a congested throat and markedly enlarged bilateral tonsils. Chest CT examination revealed bronchitis in both lungs, inflammatory changes in the left lower lobe, and a small amount of effusion in the left pleural cavity. The patient was diagnosed with influenza A virus infection and received antiviral therapy. The laboratory test results revealed impaired liver function in the patient. Additionally, the patient exhibited anemia, which may be associated with the dysfunction of STAT1 resulting from the GOF mutation [22–24]. Through fungal and bacterial culture, C. albicans and Staphylococcus (methicillin-sensitive Staphylococcus aureus, MSSA) were found in exudates, and C. albicans, Aspergillus, and MSSA were identified in tissues (Fig. 2A, B). The histopathological results showed chronic inflammatory granulation tissue (Fig. 2C). During hospitalization, antifungal therapy was administered using oral itraconazole capsules (100 mg once daily) and topical miconazole cream [19]. Antibacterial therapy was given by external use of topical fusidic acid, erythromycin ointment, mupirocin, and wet application of Huangbai liquid. Considering the potential hepatotoxicity associated with prolonged use of oral antifungal agents and the fact that the patient already exhibited impaired liver function, compound glycyrrhizin tablets (25 mg, twice daily) were administered and bicyclol tablets (25 mg, three times daily) were used as hepatoprotective measures. The patient was discharged after the symptoms improved and continued taking oral itraconazole capsules (100 mg once a day) and bicyclol tablets (25 mg three times a day). Eight months after discharge, the patient underwent a follow-up examination, which revealed a significant reduction in erythema and papules (Fig. 1F).

Fig. 2.

Fig. 2

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Clinical laboratory and pathological examination results (A) C. albicans was isolated from the skin lesion exudate culture. (B) Aspergillus was isolated from the tissue culture. (C) The pathological findings were characterized by hyperkeratosis with focal areas of parakeratosis. There was a mild inflammatory exudate, and the epidermal cells showed irregular hyperplasia. The intercellular substance showed slight edema. In addition, scattered atypical keratinocytes were present. Fibroblastic and capillary hyperplasia were observed in the upper and middle parts of the dermis, accompanied by diffuse lymphocytic infiltration. Histiocytes and multinucleated giant cells were not observed

Two months after the follow-up, the patient’s parents arbitrarily discontinued the medication. Erythema and papules reappeared on the child’s nasal ala. In response to the recurrence of clinical symptoms, the patient’s parents self-administered mupirocin, erythromycin ointment, and bifonazole cream for local treatment. However, after the treatment, the skin lesions did not improve and instead progressively worsened. Eleven months after the second discharge, the patient was readmitted to our hospital due to the progressively worsening symptoms (Fig. 1G).

The Treatment of JAK Inhibitor

After traditional antifungal treatment, the patient continued to experience recurrent fungal infections and developed drug-induced liver injury. Recent studies have indicated that JAK inhibitors have demonstrated beneficial therapeutic effects in patients with STAT1-GOF, including pediatric cases. Following the patient’s third hospital discharge, we recommended the topical application of ruxolitinib for treatment. The medication was applied topically twice daily during the first month, after which the frequency was adjusted to once every other day. The prescribed dosage was 15 mg/m² per day [19]. During follow-up, the patient has not experienced any recurrence of fungal infections or other adverse effects.

The Patient Harbored a Novel Heterozygous Mutation (c.1078G > C), in DBD Region of STAT1

Through comprehensive whole-exome sequencing (WES) and validation via Sanger sequencing, a novel heterozygous missense mutation in the STAT1 gene was identified at nucleotide position 1078 (c.1078G > C, hg19), leading to a valine-to-leucine substitution at amino acid 360 (p.V360L). This mutation was located in the DBD of the STAT1 gene. As illustrated in Fig. 3, the mutation was a de novo mutation within this family. Additionally, it has never been reported in public databases (e.g., gnomAD v4.1.0) or in the literature [2].

Fig. 3.

Fig. 3

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Pedigree of STAT1 mutation and genetic sequencing (A) The patient was the proband in the family. (B) The patient harbored a mutation at position 1078 (1078 G > C) of the STAT1 gene, where guanine was substituted with cytosine, resulting in an amino acid substitution from valine to leucine at position 360 (p.V360L). (C, D) The parents did not carry this mutation

V360L was a Gain-of-Function Mutation

Lipotransfection was employed to introduce reporter plasmids and plasmid DNA encoding the wild-type (WT) and mutants (V360L, Y701C, and P725L) of STAT1 into U3C cells. P725L was a documented GOF mutation observed in patients with CMC [14], whereas Y701C represented a LOF mutation frequently associated with Mendelian susceptibility to mycobacterial disease (MSMD) [7]. Twenty-four hours post-transfection, the cells were stimulated with IFN-γ for another sixteen hours, and subsequent luciferase activity assays were conducted. Upon stimulation, cells transfected with the V360L and P725L alleles responded two to three times more strongly than those transfected with the wild-type allele, as shown by the induction of γ-activated sequence (GAS)-dependent reporter gene transcription activity. In contrast, cells transfected with the Y701C allele exhibited no response (Fig. 4A). Flow cytometry was utilized to assess the phosphorylation levels of STAT1 in CD14 + monocytes derived from the patient and healthy controls following stimulation with IFN-γ. In accordance with the results from the reporter assay, the patient exhibited a higher phosphorylation level of STAT1 at Tyr701 (Fig. 4B-D). Accordingly, the V360L variant identified in the patient is likely a GOF mutation.

Fig. 4.

Fig. 4

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V360L was a gain-of-function mutation (A) Upon IFN-γ stimulation, U3C cells transfected with the V360L and P725L alleles exhibited a two- to threefold stronger response compared to those transfected with the wild-type allele, as evidenced by the measurement of γ-activated sequence (GAS)-dependent reporter gene transcription activity (n = 2). (B, C) The patient exhibited a higher phosphorylation level of STAT1 at Tyr701 compared to that of the healthy control (MFI: case vs. control = 314.3 ± 16.3 vs. 181.7 ± 8.4, n = 3, p = 0.0002). (D) Following IFN-γ stimulation, the patient exhibited a more pronounced increase in the phosphorylation level of STAT1 at Tyr701 (MFI fold change: case vs. control = 1.44 ± 0.13 vs. 1.03 ± 0.06, n = 3, p = 0.0066). (**p < 0.01, ***p < 0.001, ****p < 0.0001. MFI, Mean fluorescence intensity)

The Patient Exhibited Reduced CD4+ T cells, CD16+ CD56+ NK Cells and Th17 Cells

We used flow cytometry to assess the proportions of peripheral blood T cells, B cells, and NK cells in the patient. The patient exhibited a decrease in the proportion of CD4 + T cells and in both the proportions and absolute counts of CD16 + CD56 + NK cells (Table 1). In addition, the serum levels of IL-2, IL-5, IL-6, and TNF-α were all found to be elevated in the patient, whereas the serum level of IgM was reduced (Table 1). Additionally, the proportion of Th17 cells and the expression level of IL-17 A were lower in the patient compared to those in the healthy control (Fig. 5).

Table 1.

Immunological characteristics of the patient. Based on the results, the patient exhibited a decrease in both the percentage of CD4+ T cells and the percentage and absolute count of CD16+CD56+ NK cells. In addition, the serum levels of IL-2, IL-5, IL-6 and TNF-α were all found to be elevated in the patient, whereas the serum level of IgM was reduced

Laboratory assays of immunity Measured value Reference range
Cellular immunity
total T cells (%) 78.85 56–86
CD4 T cells (%) 30.69 ↓ 33–58
CD8 T cells (%) 30.08 13–39
B cells (%) 17.02 5–22
NK cells (%) 3.71 ↓ 5–26
Number of T (cells/µl) 1667.83 603–2990
Number of CD4 T (cells/µl) 486.26 441–2156
Number of CD8 T (cells/µl) 636.29 125–1312
Number of B (cells/µl) 360.07 107–698
Number of NK (cells/µl) 78.58 ↓ 95–640
Humoral immunity
IgA (g/L) 1.18 0.38–2.22
IgM (g/L) 0.37 ↓ 0.45–2.08
IgE (IU/ml) < 17.50 0–60
IgG (g/L) 7.03 5.9–14.3
IgG4 mg/L < 63 13-1446
C3 (g/L) 1.06 0.7–1.4
C4 (g/L) 0.27 0.1–0.4
Cytokines
IL-5 (pg/ml) 3.5 ↑ 0-3.1
IFN-α (pg/ml) < 0.53 0-8.5
IL-2 (pg/ml) 15.44 ↑ 0-7.5
IL-6 (pg/ml) 12.54 ↑ 0-5.4
IL-1β (pg/ml) 4.47 0-12.4
IL-10 (pg/ml) 1.64 0-12.9
IFN-γ (pg/ml) 7.52 0-23.1
IL-8 (pg/ml) 10.34 0-20.6
IL-17 (pg/ml) 2.82 0-21.4
IL-4 (pg/ml) 0.47 0-8.56
IL-12P70 (pg/ml) < 0.93 0-3.4
TNF-α (pg/ml) 17.02 ↑ 0-16.5
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Fig. 5.

Fig. 5

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The patient exhibited a reduced proportion of Th17 cells and a decreased level of IL-17 A. (A) Flow cytometry was used to detect the proportion of TH17 cells and the expression level of IL-17 A. (B) The proportion of Th17 cells was decreased in the patient compared to the healthy controls (Percentage: case vs. HC1 = 0.05 ± 0.03 vs. 0.52 ± 0.21, n = 3, p = 0.0182; case vs. HC2 = 0.05 ± 0.03 vs. 0.48 ± 0.20, n = 3, p = 0.0203). (C) The expression level of IL-17 A was lower in the patient compared to the healthy controls (MFI: case vs. HC1 = 1335 ± 158 vs. 8850 ± 1373, n = 3, p = 0.0007; case vs. HC2 = 1335 ± 158 vs. 9826 ± 1937, n = 3, p = 0.0016). (*p < 0.05, **p < 0.01, ***p < 0.001)

Discussion

The present study provided a case analysis of a child with a heterozygous STAT1-GOF mutation underlying AD-CMC. The patient in this study presented with recurrent and persistent C. albicans infections of the skin and mucosa, accompanied by Staphylococcus aureus and Aspergillus infections. WES sequencing of genomic DNA revealed a novel heterozygous missense mutation in exon 12 of the STAT1 gene (c.1078 G > C, p.V360L) in the patient. The detection of luciferase activity following IFN-γ induction demonstrated that V360L exhibited GOF activity.

In humans, the IL-17 immunity has been demonstrated to play an essential role in protecting mucosal surfaces against C. albicans infection. Defects in IL-17 immunity have been shown to correlate with the onset of CMC [15, 25]. In 2011, Frank et al. first revealed that CMC patients with heterozygous STAT1 gene mutations exhibit impaired IL-17 production in response to Candida stimulation, representing a new category of inborn errors of immunity underlying CMC [26]. At the same time, Liu et al., through an original study of 12 STAT1 variants in 47 patients presenting with CMC, indicated that the GOF mutation in STAT1 causes AD-CMC by impairing IL-17 immunity [4]. The GOF was demonstrated by an increase in STAT1 Tyr701 residue phosphorylation, as detected by western blot, in U3C cells transfected with the patients’ variants compared to those transfected with the wild-type allele following stimulation with IFN-γ, IFN-α, and IL-27 [4]. In subsequent studies, the enhanced STAT1 phosphorylation in response to IFN-α, IFN-γ, and IL-27 was repeatedly confirmed in hematopoietic cells such as NK cells, B cells, and T cells [27–30]. The underlying mechanism for their GOF dominance was considered to be the disruption of dimerization required for the formation of antiparallel STAT1 dimers, leading to impaired nuclear dephosphorylation of activated STAT1, which was thought to represent the main molecular mechanism [2, 7, 31–33]. Up to now, over 120 STAT1-GOF mutations have been discovered, and over 85% of these mutations were found in the CCD or DBD regions of STAT1 [2, 8]. In the STAT1-GOF cellular model, mutations in the DBD have been shown to enhance the nuclear accumulation of STAT1, reduce its nuclear mobility, and slow down the dephosphorylation process of STAT1 [34]. In this study, we identified V360L as a novel mutation located in the DBD region of the STAT1 gene in the patient. Following the induction with IFN-γ, U3C cells transfected with the V360L allele exhibited a stronger GAF DNA-binding activity than the wild-type allele. In addition, the phosphorylation level of STAT1 at Tyr701 was higher in the patient than in healthy controls. Therefore, the hyperphosphorylation of STAT1 observed in the patient’s monocytes may be attributed to the V360L-GOF mutation.

Previous study has revealed that patients with DBD mutations exhibit a higher prevalence of invasive and opportunistic infections, an increased frequency of NK cell depletion, and may present with additional disease manifestations such as pulmonary infection, inflammatory bowel disease, lymphoproliferative manifestations, and recurrent fever [35]. This is consistent with our findings, wherein the initial illness was characterized by recurrent high fevers unresponsive to conventional antibiotic therapy. Throughout the entire clinical course, the patient experienced repeated infections, not only with severe superficial fungal infections caused by C. albicans, but also simultaneous bacterial and invasive fungal infections, including Staphylococcus aureus and Aspergillus. Moreover, the patient also developed bronchitis in both lungs as a complication of an influenza A virus infection. The clinical course of bronchitis was mild and non-toxic, leading to complete recovery. No evidence of bronchiectasis was found on chest CT. Although previous reports described severe non-CF bronchiectasis as the initial manifestation of autosomal dominant STAT1-GOF and associated it with a reduction in class-switched memory B cells prone to purulent lung disease, this phenotype was not present in our case [36]. Ongoing surveillance for recurrent lower respiratory infections, hypogammaglobulinemia (particularly low IgG levels), and abnormalities in B-cell subsets will be important to guide future clinical follow-up and management strategies.

CMC patients with STAT1-GOF mutations may exhibit specific cellular phenotypes that are associated with their clinically immunocompromised features, including a reduced total number of T cells, CD4 + T cells, CD8 + T cells, B cells, and NK cells, as well as defects in the production of IL-17 and IFN-γ [28]. In the present study, we found that the patient exhibited decreased proportions of CD4 + T cells and NK cells, as well as low levels of IgM. The patient also demonstrated impaired IL-17 immunity, as indicated by a decreased proportion of Th17 cells and lower expression of IL-17 A compared to healthy controls. We speculated that the novel STAT1-V360L-GOF mutation may have impaired IL-17 immunity, which probably led to the patient’s recurrent and persistent susceptibility to C. albicans.

The majority of STAT1-GOF patients required long-term antifungal therapy for CMC, with azoles commonly used as the treatment. The most frequently used oral antifungal agent is fluconazole, followed by itraconazole and posaconazole [37]. During hospitalization, we used itraconazole and fusidic acid for the treatment of fungal and bacterial infections. Liver-protective agents were co-administered to mitigate the hepatotoxic burden associated with antifungal therapy. After standardized treatment, the patient’s symptoms showed significant improvement. Unfortunately, the fungal infection recurred shortly after the patient was discharged. The following reasons may explain the recurrence. First of all, the patient has a deficiency in antifungal immunity. Without the intervention of drugs, the patient’s immune system is insufficient to combat fungal infection. Second, the patient did not strictly adhere to the prescribed medication regimen after discharge. Finally, it is imperative to acknowledge that approximately 39% of STAT1-GOF patients demonstrate resistance toward antifungal agents, necessitating the administration of multiple antifungal drugs for effective antifungal therapy [8]. Fortunately, recent immunotherapy using JAK inhibitors, histone deacetylase inhibitors, and G-CSF has demonstrated a beneficial effect in enhancing the antifungal capacity of the immune system in STAT1-GOF patients [6, 14, 37, 38]. In this study, after the patient’s third discharge from the hospital, we recommended the topical application of ruxolitinib for treatment. The patient received ruxolitinib at a dose of 15 mg/m²/day, which was determined based on the dosing regimen for cases of the same age reported in previous studies [19]. Through follow-up, the patient has not experienced any recurrent fungal infections or other side effects. However, since the patient self-administered the medication at home, subsequent monitoring of drug concentration becomes challenging, which is a limitation of this study. Given the current limited clinical experience with this drug in children with AD-CMC, it is imperative to focus on critical issues such as the route of administration, indications, dosage, and monitoring.

It is worth noting that, in addition to the topical treatment approach of JAK inhibitors, HSCT has been reported in existing studies as a systemic treatment option for STAT1-GOF patients. A recent retrospective study indicates that 11 patients eventually underwent HSCT after receiving prior JAK inhibitor therapy as bridging treatment, with an overall survival rate of 91% [19]. Although this study demonstrates that HSCT has a favorable therapeutic effect, its application in patients with STAT1-GOF remains relatively limited on a global scale, and long-term follow-up data are still insufficient. To date, only one successful case has been reported in China [22]. Due to limited clinical experience, low patient acceptance of high-risk treatments, and the good clinical efficacy demonstrated by JAK inhibitor therapy, a more conservative topical treatment plan was selected based on these factors. For our team and the patient, HSCT remains a potential treatment option. Should the procedure become more established in the future or if opportunities arise for collaboration with more specialized centers, we will consider exploring this therapeutic strategy.

However, it is important to acknowledge that this study has several limitations. Firstly, the underlying mechanisms by which the STAT1-GOF mutation affects cellular and humoral immune functions related to antifungal immunity have not been thoroughly investigated, limiting the understanding of its functional significance. Secondly, although patients received treatment with conventional antifungal agents and JAK inhibitors, continuous monitoring of cellular and humoral immune function following therapy was not conducted, potentially missing insights into how these treatment strategies modulate antifungal immunity. Finally, despite the administration of ruxolitinib, drug concentrations and clinical responses were not systematically monitored, which to some extent limits its reference value for the treatment of similar cases in the future. Moreover, its underlying treatment mechanism requires further investigation.

In summary, this study identified a novel GOF mutation in the STAT1 gene in a pediatric patient with CMC. This mutation may lead to alterations in the functions of various immune cells and cytokines, including CD4 + T cells, NK cells, Th17 cells, and IL-17 A. These changes might explain the patient’s recurrent and persistent susceptibility to C. albicans infections. Ruxolitinib could potentially serve as an effective treatment option for CMC patients with a STAT1-GOF mutation. Nevertheless, more clinical and experimental research is necessary to confirm these findings.

Acknowledgements

We thank the patient and his parents for their participation in this study.

Author Contributions

YX and SS: designing and drafting the study, analyzing the data, and writing manuscript. HW and WTL: revising the manuscript. CCL, JW and FML: laboratory testing and data analysis. XDL: collecting data. NND, CLK and JG: designing the study, revising and finalizing the manuscript. All authors contributed to the article and approved the submitted version.

Funding

This work was supported by the China Postdoctoral Science Foundation (2022M710852), National Natural Science Foundation of China (82102420), the Natural Science Foundation of Shandong Province (ZR2024QH034), and the Taishan Scholars Foundation of Shandong Province (tsqnz20221173).

Data Availability

No datasets were generated or analysed during the current study.

Declarations

Ethics Statement

The studies involving human participants were reviewed and approved by the ethics committee of Shandong Provincial Hospital, affiliated to Shandong First Medical University. The patients provided written informed consent for participation in the study and publication of potentially identifiable images or data included in this article.

Competing Interests

The authors declare no competing interests.

Footnotes

Publisher’s Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Yang Xiang, Shuo Sun and Hong Wang contributed equally.

Contributor Information

Cheng-Lung Ku, Email: clku@cgu.edu.tw.

Jing Guo, guojing@email.sdfmu.edu.cn.

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Data Availability Statement

No datasets were generated or analysed during the current study.

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