First identification of the rare FH-Q185R germline mutation in a Chinese HLRCC patient: A case report and literature review

Abstract

Hereditary Leiomyomatosis and Renal Cell Cancer (HLRCC) is a rare autosomal dominant disorder caused by the fumarate hydratase (FH) gene mutations. Here, we report the first identification of the rare FH-Q185R mutation in a Chinese patient with HLRCC. This case report not only examines the distribution of the FH gene using the Cancer Genome Atlas database but also provides a series of evidence to assess the pathogenicity of the Q185R mutation. This missense mutation, encoded by mitochondrial DNA, corresponds to the cytoplasmic amino acid residue 142 in human cells. These findings could pave the way for more effective management and treatment approaches for patients suffering from HLRCC.

Introduction

Hereditary Leiomyomatosis and Renal Cell Cancer (HLRCC) syndrome is a rare autosomal dominant disorder, which is clinically characterized by an increased risk of skin smooth muscle tumors, uterine leiomyomas, and renal cell carcinomas. ¹ The occurrence of HLRCC is closely linked to pathogenic mechanisms involving disruptions in the tricarboxylic acid (TCA) cycle, increased oxidative stress, and metabolic alterations. ² More than 200 families with HLRCC have been previously reported in the literature.^3–5 In affected individuals, multiple large uterine leiomyomas are common, with a high recurrence rate after myomectomy. These tumors may differ pathologically from sporadic leiomyomas, showing enhanced proliferative potential and an increased risk of malignancy. ⁶ Unlike common familial renal cell carcinoma, HLRCC is classified as a nonclear cell carcinoma with diverse subtypes that are relatively infrequent and difficult to diagnose. Therefore, early detection, accurate diagnosis, and timely intervention are crucial for preventing its occurrence.

The fumarate hydratase (FH) gene acts as a tumor suppressor, encoding fumarate hydratase, which is crucial for the TCA cycle and DNA repair. ⁷ FH mutations, often missense, can lead to fumarate accumulation, inhibiting Hypoxia-inducible factor (HIF) prolyl hydroxylases and activating the HIF pathway, promoting tumorigenesis. FH loss (FH-) and 2SC positivity (2SC+) suggest FH germline mutations, but immunohistochemical detection is not always reliable, necessitating genetic sequencing for HLRCC diagnosis. Both monoallelic and biallelic pathogenic FH variants can cause HLRCC, with definitive diagnosis requiring genetic confirmation per Schmidt et al.’s criteria.^8–10

Next-generation sequencing (NGS) technology is a high-throughput gene sequencing technique that enables rapid and efficient sequencing of entire genomes or specific gene sequences. NGS technology is widely used for whole-exome sequencing, genome sequencing, and transcriptome sequencing, and it can be used to identify unknown gene variations or unknown gene sequences.^11,12 In the process of germline genetic testing, we rely on the guidelines published by the American College of Medical Genetics and Genomics (ACMG) for the classification and interpretation of gene variants to determine the pathogenicity of genetic mutations ¹³ . However, due to the inclusion of a series of criteria in assessing the pathogenicity grade of gene variants, there are sometimes complex situations where it is difficult to determine the pathogenicity of certain mutations.

In this case report, we identified a young Chinese patient with multiple uterine leiomyomas. Through testing and DNA sequencing analysis, we further elucidated the genetic characteristics of the gene FH, which was a rare mutation site. This research would provide a theoretical basis for clearer evidence in future clinical germline determination of the FH gene related to hereditary diseases.

Case presentation

This 31-year-old patient presented with symptomatic multiple uterine leiomyomas, including progressively worsening dysmenorrhea, increased menstrual volume, and intermittent pelvic pressure. Imaging revealed multiple masses measuring 0.4–7 cm in diameter. Pelvic ultrasound confirmed the enlargement and heterogeneous echotexture of the uterus. Post-surgical examination revealed fibroid tumors appearing as gray powdery nodules with exfoliated surfaces. Furthermore, the sections were pale brown, solid, braided, and slightly tough. Pathological diagnosis confirmed multiple uterine smooth muscle tumors with focal areas of high cellularity. Some cells exhibited mildly moderately heterogeneous, with alveolar-like edema, collagen blobs, and perinuclear hollow halos visible (Figure 1(a), (b)).

Figure 1.

Immunohistochemical analysis of the uterine leiomyoma tissues.

(a) Hematoxylin and eosin (H&E) stained pathological images (scale: 30 μm) showed tumor cell morphology. Yellow arrows: heterogeneous nuclei, prominent nucleoli with perinuclear halos; Green arrows: eosinophilic spherules. (b) H&E stained pathological images (scale: 50 μm) showed areas of alveolar-like edema; Blue arrow: antler-like vessels. (c) Immunohistochemical staining of FH showed negative in the tumor cells. The positive vascular endothelium cells could serve as an internal control. (d) Immunohistochemical staining of 2SC showed the tumor cells were positive in cytoplasm and nuclei.

FH: Fumarate hydratase.

Following the identification of the FH mutation, the patient underwent structured HLRCC surveillance, including annual renal MRI, abdominal CT every 1–2 years, and urinalysis with urine cytology. Cystoscopy was recommended every 2–3 years or earlier if symptomatic; the most recent exam was unremarkable. The patient has a family history of breast cancer on the paternal side—her aunt was diagnosed at the age of 52. Both parents are currently healthy and over the age of 60.

Immunohistochemical analysis was performed to assess key markers commonly expressed in uterine smooth muscle tumors, including P53, Ki-67 (MIB1), CD10, Caldesmon, FH, and 2SC. As shown in Figure 1(c) and (d), the results revealed wild-type P53 expression, Ki-67 positivity of <10%, CD10 (±), diffuse Caldesmon positivity, FH loss, 2SC positivity. These phenotypes were basically consistent with the pathological features of FH-deficient smooth muscle tumors. Since deficiency in FH activity, the relevant genetic testings were carried out to confirm whether the patient had HLRCC syndrome.

We conducted DNA-seq analysis containing 85 hereditary genes on the patient’s blood sample. In Table 1, we found a potential variant that was absent in the population databases of Exome Sequencing Project (ESP), 1000 Genomes, and Exome Aggregation Consortium (ExAC). Predictions by various software (Sorting Intolerant From Tolerant [SIFT]/Polyphen/MutationTaster) suggested that the variant would be disease-causing based on conservativeness prediction, evolutionary prediction, and splice site effects. The patient harbored a missense mutation, c.554A > G (p.Gln185Arg, Het), in the FH gene, resulting in an amino acid substitution from Glutamine (Q) to Arginine (R) at position 185. According to the results of the Cancer Genome Atlas database, ninety-five mutations for the FH gene were found in the tumor samples. However, the Q185R(Gln185Arg) missense change was detected in the gnomAD database(v4.1.0). Notably, the ClinVar and gnomAD databases classified it as “Pathogenic/Likely pathogenic.” From the citations for germline classification of this variant, one study (PMID:28300276) mentioned the Q185R missense change, detecting it in French individuals with FH germline mutation with HLRCC syndrome. Collectively, these findings indicated that the missense mutation of Q185R was infrequent and may cause fumarate hydratase loss of function.

Table 1.

Population frequency and in silico predictive algorithms.

#	Amino acid change	Nucleotide change	Databases	score	Prediction
1	c.554A > G	p. Q185R	Exome Sequencing Project database	NA	NA
2	c.554A > G	p. Q185R	1000 genomes	NA	NA
3	c.554A > G	p. Q185R	Exome Aggregation Consortium	NA	NA
4	c.554A > G	p. Q185R	Sorting Intolerant From Tolerant model	0	Damaging
5	c.554A > G	p. Q185R	Polyphen-2 model	1	Probably damaging
6	c.554A > G	p. Q185R	MutationTaster model	1	Disease causing

In contrast to yeast lacking the mitochondrial targeting sequence, the human FH gene could encode two gene products: cytosolic and mitochondrial fumarate hydratase. According to the sequence alignment (Figure 2), the missense mutation of Q185R from mitochondria in human cells is exactly the cytoplasmic amino acid residue 142. A PubMed search identified five relevant publications (Table 2). The nuclear-encoded fumarate hydratase acted as the tumor suppressor. The missense mutation of Q185R led to reduced FH enzymatic activity, resulting in intracellular accumulation of fumaric acid. Individuals carrying this mutant FH gene are predisposed to leiomyomas, renal cancer, and paragangliomas. Related cases have been reported in the French and North American populations.

Figure 2.

Amino acid sequence alignment shows that the missense mutation of Q185R is the same as cytoplasmic amino acid residue 142.

Table 2.

The literature clearly documenting the missense mutation of Q185R (Gln185Arg).

#	Mutation site	Mutated residue	Protein change	DNA change	Exon	Mutation type	Localization	Pubmed ID	Year
1	Gln142	Arg	Q142R	—	3	Missense	Active site	11865300	2002
2	Gln142	Arg	Q142R	—	3	Missense	Active site	12761039	2003
3	Gln142	Arg	Q142R	—	3	Missense	Active site	16237213	2005
4	Gln185	Arg	Q185R	c.554A > G	4	Missense	Active site	21445611	2011
5	Gln185	Arg	Q185R	c.554A > G	4	Missense	Active site	28300276	2017

DNA: Deoxyribonucleic acid.

The interpretation of genetic variations refers to the “Standards and Guidelines for the Interpretation of Sequence Variants” published by the ACMG, categorizing genetic variations into five levels: pathogenic, likely pathogenic, variant of uncertain significance, likely benign, and benign. Concerning the Q185R locus, our findings are as follows: (1) Evidence PM2: No variations were found in the normal control population in the ESP database, 1000 Genomes, or the ExAC database; (2) Evidence PP3: Several statistical software methods predict that this mutation could be detrimental to the gene or gene product, including conservation prediction, evolutionary prediction, and splice site impact; (3) Evidence PS3_Moderate: Alam et al. ¹⁴ mapped 68 different missense mutations onto the crystal structure of Escherichia coli. This research conducted functional testing of fumarate hydratase using lymphoblastoid cell lines from 23 probands with Multiple Cutaneous and Uterine Leiomyomatosis (MCUL) syndrome in the UK. The study suggested that all tested MCUL missense mutations would lead to reduced FH activity, including FH Q142R (equivalent to p.Gln185Arg)^14–17; (4) Evidence PP5: In a study reassessing the clinical spectrum associated with HLRCC syndrome in FH mutation carriers in France, FH c.554A > G was detected among 182 FH germline mutation carriers. ³ According to ACMG criteria and accumulated evidence, the c.554A > G (p.Gln185Arg, Het) missense mutation is classified as likely pathogenic (Table 3). Comprehensive genetic counseling was provided before and after testing. Counseling included discussion of autosomal dominant inheritance, 50% transmission risk to offspring, options for family cascade testing, reproductive counseling (including in vitro fertilization (IVF) with PGT-M), and psychosocial considerations.

Table 3.

ACMG guidelines applied to FH c.554A > G (p.Gln185Arg, Het) variant reclassification.

Criteria	Comments
PM2	Criterion: Variants absent in normal control populations from the ESP, 1000 Genomes, or ExAC databases. Description: This variant was not detected in the normal control populations of the ESP, 1000 Genomes, or ExAC databases. However, the Q185R(Gln185Arg) missense change was detected in the gnomAD database(v4.1.0). Notably, the ClinVar and gnomAD database classified it as “Pathogenic/Likely pathogenic.”
PP3	Criterion: Multiple statistical methods predict that this variant is likely deleterious to the gene or its product, including conservation analysis, evolutionary prediction, and splice site impact assessment. Description: Predictions by various software (SIFT/Polyphen/MutationTaster) suggested that the variant would be disease-causing. According to the results of the TCGA database, ninety-five mutations for FH gene were found in the tumor samples.
PS3_Moderate	Criterion: In vivo and in vitro functional studies have confirmed that this variant causes gene function impairment. Description: Alam NA et al. mapped 68 different missense mutations onto the crystal structure of Escherichia coli and conducted functional testing of FH using lymphoblastoid cell lines from 23 UK probands with MCUL syndrome. The study suggested that all tested MCUL missense mutations would lead to reduced FH activity, including FH Q142R (equivalent to p.Gln185Arg).
PP5	Criterion: Reliable sources report this variant as pathogenic, but evidence remains insufficient for independent validation. Description: In a French study reassessing the clinical spectrum associated with HLRCC syndrome among FH mutation carriers, FH c.554A > G was detected in individuals with germline FH mutations.

ACMG: American College of Medical Genetics and Genomics; TCGA: The Cancer Genome Atlas; FH: fumarate hydratase; HLRCC: Hereditary Leiomyomatosis and Renal Cell Cancer; MCUL: Multiple Cutaneous and Uterine Leiomyomatosis; ESP: Exome Sequencing Project database; EXAC: Exome Aggregation Consortium; SIFT: Sorting Intolerant From Tolerant.

Discussion

This case report marks the first reported case of the FH c.554A > G (p.Gln185Arg, Het) mutation in a Chinese HLRCC patient. Within the FH gene, oncogenic missense mutations are most commonly observed in exons 4, 5, 7, and 8. The Q185R mutation studied in our research is located at the end of exon 4. Glutamine (Q) is a polar amino acid, whereas arginine (R) is a positively charged basic amino acid. This substitution may alter the conformation of the FH protein, affecting its catalytic activity. The cells with FH defects lose the ability to metabolize fumarate, leading to its accumulation in the cytoplasm and triggering a series of metabolic abnormalities, along with other oncogenic changes. Affected patients exhibit elevated levels of fumarate in their urine, with abnormal serum levels of other TCA cycle metabolites. These individuals may present with various physiological and developmental defects during the neonatal period, with very few reports of survival beyond childhood in the literature.

Currently, most reports on FH gene mutations have focused on Western populations, with limited studies in the Chinese population. Wang et al. identified a novel FH missense mutation (c.1240A > G; p.Lys414Glu) in exon 9 in a Chinese patient with HLRCC. Using Sanger sequencing, family history analysis, and FH/2SC immunohistochemistry, the study provided evidence supporting its pathogenicity. ⁶ The fumarate accumulation results in the overexpression of 2-SC, making immunohistochemical detection of 2-SC a useful complementary evidence for FH deficiency. Their findings underscore the diagnostic value of FH-deficient morphology and 2SC staining, enhancing the understanding of FH mutations and classification. In this report, we also used FH/2SC immunohistochemistry but employed a targeted NGS approach. Besides, A Chinese study reported an HLRCC-affected family identified through a patient with FH-deficient uterine leiomyoma (FHDUL). Genetic analysis detected three germline FH mutations within the family. Both our findings and this research further validated the potential for using uterine leiomyoma pathology for initial FHDUL screening, followed by genetic testing to identify HLRCC syndrome. Another Chinese study analyzed three HLRCC patients with germline FH mutations, including a novel missense variant (FH c.454A > G, p.N152D) predicted to be pathogenic. ¹⁸ Immunohistochemistry and Whole-exome sequencing provided valuable diagnostic insights. All female RCC patients had uterine fibroids, emphasizing the importance of germline screening and clinicopathological data for early diagnosis of HLRCC-related RCC.

Alam et al. ¹⁶ reported that 27 distinct missense mutations account for 68% of FH mutations in MCUL, predominantly affecting conserved residues in the A-site, B-site, or subunit-interacting region. Among 24 missense variants, 54% were located in the substrate-binding A-site, including Q142R. Functional assays of lymphoblastoid cell lines from 23 individuals with heterozygous FH missense mutations demonstrated significantly lower residual activity in A-site mutants, consistent with Escherichia coli data indicating the A-site as the primary catalytic site. Their study provides direct evidence that the Q142R (Q185R) mutation may lead to FH functional loss and highlights the critical role of A-site mutations in FH enzymatic activity reduction and the pathogenesis of MCUL/HLRCC.

In the determination of hereditary tumors, the ACMG evidence grading system is extensive and follows strict criteria. In the investigation of evidence for this pathogenic locus, it was found that Q185R is an extremely rare mutation. Moreover, earlier literature (PMID: 11865300; PMID: 16237213) referred to this mutation as Q142R of exon 3, which is actually the same locus as Q185R of exon 4 in the mitochondria of human cells.^14,15 This discrepancy posed significant challenges in the determination of the tumor pathogenicity grade. Ultimately, through sequence alignment analysis, it was discovered that these mutations represent the same alteration in different transcript sequences. This finding highlights a new challenge in accurately determining relevant literature for future hereditary pathogenicity assessments.

Although the patient’s relatives did not undergo FH gene sequencing, limiting further cosegregation analysis, and neither the patient nor her family members showed any signs of renal tumors, the identification of the FH c.554A > G (p.Gln185Arg, heterozygous) variant in the Chinese population holds notable research value. This finding highlights the importance of comprehensive individual assessment as a systematic diagnostic approach and underscores the need for heightened vigilance in managing HLRCC-related conditions associated with FH mutations. In addition to renal cell carcinoma and uterine leiomyomas, germline FH mutations have also been reported to be associated with other tumor types, including bladder carcinoma and Leydig cell tumors of the testis. Although these manifestations are relatively uncommon, they expand the clinical spectrum of hereditary leiomyomatosis and renal cell carcinoma syndrome and emphasize the importance of comprehensive, long-term surveillance. Therefore, regular urological monitoring, including periodic cystoscopy and urine cytology, should be considered as part of the follow-up strategy for individuals carrying FH germline mutations, particularly during long-term surveillance or when urinary symptoms are present. In particular, uterine leiomyomas should be recognized as potential sentinel tumors. Given the high prevalence of uterine leiomyomas in the general population, any screening strategy based on their presence must achieve high specificity to effectively distinguish HLRCC-associated cases from common sporadic leiomyomas.

Genetic counseling is an integral component of the management of individuals with FH germline mutations. In the present case, comprehensive pre- and post-test counseling helped the patient understand the autosomal dominant inheritance pattern, the 50% transmission risk to offspring, and the implications for first-degree relatives. Through genetic counseling, cascade testing can be offered to at-risk family members, enabling early identification of carriers and implementation of tailored surveillance protocols. In addition, reproductive counseling, including discussion of options such as in vitro fertilization with preimplantation genetic testing for monogenic disorders (IVF with PGT-M), provides affected individuals with informed choices regarding family planning and risk reduction.

Beyond diagnosis and surveillance, growing attention has been directed toward therapeutic strategies specifically targeting FH-deficient tumors. FH loss leads to accumulation of the oncometabolite fumarate, epigenetic reprogramming, and pseudohypoxia, which together create potential vulnerabilities that may be exploited therapeutically. Recent work has evaluated hypomethylating agents and other epigenetic modulators in this context. In particular, a Phase II clinical trial of guadecitabine in patients with SDH-deficient Gastrointestinal stromal tumor, pheochromocytoma, paraganglioma, and HLRCC-associated renal cell carcinoma suggested that epigenetic therapy may offer clinical benefit in this molecular subset, although further validation is required. These findings indicate that patients with FH mutations could be candidates for participation in biomarker-driven clinical trials exploring novel targeted or combination therapies. ¹⁸

The identification of the FH-Q185R mutation in a young patient with uterine leiomyomas, therefore, has important clinical and therapeutic implications. On one hand, it supports the use of uterine leiomyomas with FH-deficient morphology as a trigger for genetic referral and HLRCC screening; on the other hand, it underscores the necessity of integrating molecular diagnosis, genetic counseling, structured surveillance, and emerging precision therapeutic approaches into a comprehensive care model. As additional cases and functional data on FH-Q185R accumulate, this variant may further refine risk stratification and help guide individualized surveillance and treatment strategies for patients with HLRCC.

Conclusion

The rare FH-Q185R mutation was first identified in a Chinese patient with HLRCC. Although HLRCC represents only 3% of malignant renal tumors, its early-onset uterine leiomyomas and highly aggressive renal cancers highlight the need to elucidate the biology and genetic mechanisms of FH gene alterations. Through further clarification of the evidence base for the pathogenic site Q185R, this provides a crucial theoretical foundation for early intervention and screening of HLRCC.