A novel mutation of the fumarase gene in a family with autosomal recessive fumarase deficiency

Case report: response to immunotherapy and association with the fh gene in hereditary leiomyomatosis and renal cell cancer-associated renal cell cancer

Hereditary leiomyomatosis and renal cell cancer (HLRCC) is a rare autosomal dominant syndrome caused by a germline mutation in the fumarate hydratase (FH) gene that manifests with cutaneous leiomyomas, uterine fibroids, and renal cell cancer (RCC). Patients with HLRCC-associated RCC (HLRCC-RCC) have aggressive clinical courses, but there is no standardized therapy for advanced HLRCC-RCC. In this study, we described a case of aggressive HLRCC in a 33-year-old female who exhibited a novel heterozygous germline insertion mutation in exon 8 of the FH gene (c.1126 C > T; p.Q376*). The patient underwent laparoscopic resection of the right kidney, but metastases appeared within 3 months after surgery. Histological staining of the resected tumor revealed high expression levels of programmed cell death-ligand 1 (PD-L1). Therefore, the patient was treated with immunotherapy. The patient achieved a partial response to immunotherapy, and the treatment of metastatic lesions has continued to improve. A thorough literature review pinpointed 76 historical cases of HLRCC-RCC that had undergone immunotherapy. From this pool, 46 patients were selected for this study to scrutinize the association between mutations in the FH gene and the effectiveness of immunotherapy. Our results indicate that immunotherapy could significantly improve the overall survival (OS) of patients with HLRCC-RCC. However, no influence of different mutations in the FH germline gene on the therapeutic efficacy of immunotherapy was observed. Therefore, our study suggested that immunotherapy was an effective therapeutic option for patients with HLRCC regardless of the type of FH germline mutation.

Fumarate and its downstream signalling pathways in the cardiorenal system: Recent insights and novel expositions in the etiology of hypertension

Hypertension, a risk factor for cardiorenal disease has a huge global health impact. Hence, there is a continuous search for new therapeutic targets and putative antihypertensive ligands. This search has transcended into the realm of mitochondrial metabolism which has been reported to underline the etiology of certain diseases, including hypertension. Recently, genetic alterations in the tricarboxylic acid (TCA) cycle enzyme, fumarase, which converts fumarate to malate, reportedly worsened salt-sensitive hypertension. These novel expositions shifted focus into the activity of TCA in the pathogenesis of hypertension. There is now evidence to show that a mechanistic link exists between blood pressure regulation and intermediaries in the TCA cycle involving fumarate metabolism. Fumarate has been reported to mediate the actions of endogenous ligands such as nitric oxide (NO), and hypoxia inducible factor (HIF)-1α. Similarly, there has been upregulation of protective genes such as nuclear erythroid factor 2 (Nrf2) and reduction in the expression of certain markers like kidney injury molecule 1 (KIM-1). There are reports of interactions with endogenous enzymes such as catalase (CAT) and renin via the activation of GPR91. Fumarate has also been shown to modulate the actions of renal ion channels and by extension, natriuresis. These actions of fumarate have conferred a reno- and cardio-protective effect in hypertension. This review evaluates the role of the TCA cycle, its mechanistic links, and significant contribution to blood pressure regulation with a view to understanding the possibility of a new pathological axis which may be involved in the pathogenesis of hypertension.

A Missense Mutation c.1132G > A in Fumarate Hydratase (FH) Leads to Hereditary Leiomyomatosis and Renal Cell Cancer (HLRCC) Syndrome and Insights into Clinical Management in Uterine Leiomyomata

BACKGROUND

HLRCC syndrome is a hereditary cancer predisposition syndrome caused by heterozygous germline pathogenic variant of the fumarate hydratase (FH) gene and characterized by cutaneous leiomyomas (CL), uterine leiomyomas (UL), and renal cell carcinoma (RCC). Loss of function variant of FH gene inactivates the Kreb's cycle enzyme activity and predisposes individuals with such variant to the development of HLRCC.

METHODS

Next-generation sequencing (NGS) and Sanger confirmation were given to family members accessible. Following that, a functional study in vitro was performed to further confirm the pathogenicity of the variant. FH-Wild type (FH-WT) and FH-mutant (FH-MUT) (E378K) plasmid were constructed and transfected into 293T and uterine leiomyoma cell lines, respectively. Proliferation assessment was executed to show how this mutation affects the growth of uterine leiomyoma. qPCR and Western blotting were performed to investigate the change of transcription and translation of FH with mutation (E378K), and FH enzyme assay activity were tested in 293T cells with mutation and wild-type plasmids.

RESULTS

Here, we presented two families with the same missense variant (c.1132G > A) that has not been reported as a germline mutation in hereditary uterine leiomyomas before and classified as VUS in gene databases. Our in vitro experiments supported the pathogenicity of this missense variant, especially in uterine leiomyomata.

CONCLUSIONS

According to the American College of Medical Genetics (ACMG) guideline, the E378K variant was classified as likely pathogenic (with evidence PS4_support, PS3_support, PM2_support, PP1, PP3 and PP4 evidence). Further insights into clinical management in uterine leiomyomata were discussed and should be practiced in gynecological clinical settings.

Effects of fumarate on renal vascular reactivity and the modulation of blood pressure in normotensive rats: Possible contribution of the nitric oxide synthase-nitric oxide system

Introduction: Fumarate, the tricarboxylic acid (TCA) cycle intermediary, has been linked to nitric oxide (NO) production. NO plays a prominent role in the physiological regulation of blood pressure and renal hemodynamics. This study is aimed to investigate any contribution of fumarate to blood pressure and renal hemodynamics in normotensive rats with a possible link to the nitrergic system.

Materials and methods: Fumarate (1, 3 and 10 µmol) was injected into isolated perfused kidneys, pre-constricted with epinephrine (30 µM). The fumarase inhibitor, pyromellitic acid (PMA) (1, 3 and 10 µM), was used to perfuse the isolated kidney and perfusate was collected for nitric oxide and fumarate assays. An acute blood pressure study involved the injection of bolus doses of fumarate (0.1, 0.3 and 1 µg/kg, iv) or PMA (1, 3 and 10 µg/kg, iv) to normotensive rats in the presence of N(ω)-nitro-L-arginine methyl ester (L-NAME) (10 mg/kg, iv) or PMA (1, 3 and 10 µg/kg).

Results and discussion: Fumarate reduced perfusion pressure and elicited a peak reduction at the highest dose. Perfusing the kidney with PMA caused a paradoxical increase in perfusion pressure (70%, p<0.05), compared to baseline. Bolus doses of fumarate reduced blood pressure (-29.3±6.2 mmHg, p<0.05), cortical blood flow (CBF) and increased medullary blood flow (MBF). L-NAME did not abolish the vasodilatory effect of fumarate, but reduced the magnitude of response (50%, p<0.05). PMA did not significantly affect the vasodilatory effect of fumarate (p>0.05).

Conclusion: These data suggest that fumarate exerts a vasodilatory effect on renal and systemic hemodynamics that may partly involve the nitric oxide signaling.

Graphical abstract:

Fumarase Deficiency: A Case With a New Pathogenic Mutation and a Review of the Literature

Fumarase deficiency (FD) is a rare and severe autosomal disorder, caused by inactivity of the enzyme fumarase, due to biallelic mutations of the fumarase hydratase (FH) gene. Several pathogenic mutations have been published. The article describes an infant with failure to thrive, microcephaly, axial hypotonia, and developmental retardation with increased excretion of fumarate, no activity of fumarase and a homozygous mutation of the FH gene, which was until recently only known as a variant of unknown significance. Carriers of pathogenic mutations in the FH gene are at risk for developing renal cell carcinoma and should therefore be screened. Both parents were healthy carriers of the mutation and had decreased levels of enzyme activity. In addition, the article presents an overview and analysis of all cases of FD reported thus far in the literature.

Clinical report and biochemical analysis of a patient with fumarate hydratase deficiency

Fumarate hydratase deficiency (FHD) is a rare metabolic disease caused by two defective copies of the FH gene, which encodes the Krebs cycle enzyme fumarase. FHD is associated with brain and developmental abnormalities, seizures, and high childhood mortality. We describe the symptoms and treatment of a patient with FHD. While infantile spasms are common in FHD, the patient presented with epileptic spasms later in childhood. Also unexpectedly, the patient responded excellently to lacosamide for her non-convulsive status epilepticus and epileptic spasms after three first-line medication trials failed. We biochemically analyzed the patient's two fumarase variants (E432Kfs*17 and D65G). While E432Kfs*17 was extremely enzymatically defective, D65G exhibited only a mild defect, possibly playing a role in the patient's longer survival.

Human Metabolic Enzymes Deficiency: A Genetic Mutation Based Approach

One of the extreme challenges in biology is to ameliorate the understanding of the mechanisms which emphasize metabolic enzyme deficiency (MED) and how these pretend to have influence on human health. However, it has been manifested that MED could be either inherited as inborn error of metabolism (IEM) or acquired, which carries a high risk of interrupted biochemical reactions. Enzyme deficiency results in accumulation of toxic compounds that may disrupt normal organ functions and cause failure in producing crucial biological compounds and other intermediates. The MED related disorders cover widespread clinical presentations and can involve almost any organ system. To sum up the causal factors of almost all the MED-associated disorders, we decided to embark on a less traveled but nonetheless relevant direction, by focusing our attention on associated gene family products, regulation of their expression, genetic mutation, and mutation types. In addition, the review also outlines the clinical presentations as well as diagnostic and therapeutic approaches.

Clinical and biochemical heterogeneity associated with fumarase deficiency

Fumarase deficiency (FD), caused by biallelic alteration of the Fumarase Hydratase gene (FH), and a rare metabolic disorder that affects the Krebs cycle, causes severe neurological impairment and fumaric aciduria. Less than 30 unrelated cases are known to date. In addition, heterozygous mutations of the FH gene are responsible for hereditary leiomyomatosis and renal cell cancer (HLRCC). We report three additional patients with dramatically different clinical presentations of FD and novel missense mutations in the FH gene. One patient had severe neonatal encephalopathy, polymicrogyria, <1% enzyme activity, and mildly increased levels of urinary fumarate. The second patient had microcephaly, mental retardation, 20% of fumarase activity, and intermediate levels of urinary fumarate. The third patient had mild mental retardation, polymicrogyria, 42-61% enzyme activity in different cell types and massive amounts of urinary fumarate. In silico analysis predicted minor yet significant structural changes in the encoded proteins. The nuclear translocation of hypoxia-inducible factor (HIF)-1alpha (HIF1A) in cultured fibroblasts was similar to controls. These results extend the range of clinical and biochemical variation associated with FD, supporting the notion that patients with moderate increases in fumarate excretion should be investigated for this disease. The tumoral risk in the patients and their relatives requires adequate screening protocols.

Structural basis of fumarate hydratase deficiency

Fumarate hydratase catalyzes the stereospecific hydration across the olefinic double bond in fumarate leading to L-malate. The enzyme is expressed in mitochondrial and cytosolic compartments, and participates in the Krebs cycle in mitochondria, as well as in regulation of cytosolic fumarate levels. Fumarate hydratase deficiency is an autosomal recessive trait presenting as metabolic disorder with severe encephalopathy, seizures and poor neurological outcome. Heterozygous mutations are associated with a predisposition to cutaneous and uterine leiomyomas and to renal cancer. The crystal structure of human fumarate hydratase shows that mutations can be grouped into two distinct classes either affecting structural integrity of the core enzyme architecture, or are localized around the enzyme active site. An interactive version of this manuscript (which may contain additional mutations appended after acceptance of this manuscript) may be found on the SSIEM website at: http://www.ssiem.org/resources/structures/FH .

Fumaric aciduria: an overview and the first Brazilian case report

Fumaric aciduria is a rare metabolic disease, with 40 cases reported so far. Fumarase deficiency leads mainly to brain abnormalities, developmental delay, and great accumulation of fumaric acid in urine. This work presents the first case of fumaric aciduria described in Brazil, which presented with some interesting clinical and biochemical findings such as colpocephaly, hepatic alterations, and marked metabolic acidosis since birth. Common findings were ventriculomegaly, hypotonia, and microcephaly. Biochemically, besides the high urinary fumaric acid excretion, atypical elevation of plasma citrulline, tyrosine and methionine levels were also observed. In order to show all features and variants of fumaric aciduria, literature data of 40 patients was reviewed and compared with the case reported here. Findings in all these patients demonstrate that this disorder does not yet have its phenotype completely defined; it is important that more patients be described.

Downregulation of SRF-FOS-JUNB pathway in fumarate hydratase deficiency and in uterine leiomyomas

Defects of metabolic enzymes result in a variety of manifestations not logically explained by the primary metabolic function. Dominant defects of fumarate hydratase (FH) result in predisposition to cutaneous and uterine leiomyomas, and renal cell cancer. FH is a metabolic enzyme of the tricarboxylic acid cycle, and its tumor-suppressor mechanism is not fully understood. We compared the consequences of FH deficiency and respiratory chain (RC) deficiency using global expression pattern of diploid primary fibroblasts. This approach utilized the information that RC defects do not seem to predispose to tumorigenesis, and the aim was to identify FH-specific signaling effects that might have relevance to tumor formation. These results were then compared to global expression patterns of FH-deficient and sporadic uterine leiomyoma data sets. We show here that FH-deficient fibroblasts share a common transcriptional fingerprint with FH-deficient and sporadic leiomyomas, highlighting the downregulation of serum response factor (SRF)-regulated transcripts, particularly the FOS-JUNB pathway. We confirmed the downregulation of this pathway at transcriptional and protein level. SRF has a fundamental function in the differentiation of smooth muscle progenitor cells, and its downregulation both in diploid FH-deficient primary fibroblasts and in leiomyomas suggests an early function in the mechanism of uterine leiomyoma formation in FH deficiency. Concordantly, the phosphorylated form of SRF, known to activate transcription, is undetectable in leiomyomas whereas clearly detected in several nuclei in the differentiated myometrium. A similar transcriptional SRF-pathway fingerprint in FH-deficient and sporadic leiomyomas emphasizes the potential importance of this pathway in primary events leading to leiomyomatosis.

Inhibition of hypoxia-inducible factor (HIF) hydroxylases by citric acid cycle intermediates: possible links between cell metabolism and stabilization of HIF

The stability and transcriptional activity of the hypoxia-inducible factors (HIFs) are regulated by two oxygen-dependent events that are catalyzed by three HIF prolyl 4-hydroxylases (HIF-P4Hs) and one HIF asparaginyl hydroxylase (FIH). We have studied possible links between metabolic pathways and HIF hydroxylases by analyzing the abilities of citric acid cycle intermediates to inhibit purified human HIF-P4Hs and FIH. Fumarate and succinate were identified as in vitro inhibitors of all three HIF-P4Hs, fumarate having K(i) values of 50-80 microM and succinate 350-460 microM, whereas neither inhibited FIH. Oxaloacetate was an additional inhibitor of all three HIF-P4Hs with K(i) values of 400-1000 microM and citrate of HIF-P4H-3, citrate being the most effective inhibitor of FIH with a K(i) of 110 microM. Culturing of cells with fumarate diethyl or dimethyl ester, or a high concentration of monoethyl ester, stabilized HIF-1alpha and increased production of vascular endothelial growth factor and erythropoietin. Similar, although much smaller, changes were found in cultured fibroblasts from a patient with fumarate hydratase (FH) deficiency and upon silencing FH using small interfering RNA. No such effects were seen upon culturing of cells with succinate diethyl or dimethyl ester. As FIH was not inhibited by fumarate, our data indicate that the transcriptional activity of HIF is quite high even when binding of the coactivator p300 is prevented. Our data also support recent suggestions that the increased fumarate and succinate levels present in the FH and succinate dehydrogenase-deficient tumors, respectively, can inhibit the HIF-P4Hs with consequent stabilization of HIF-alphas and effects on tumor pathology.

Tricarboxylic acid cycle dysfunction as a cause of human diseases and tumor formation

A renewed interest in tricarboxylic acid cycle enzymopathies has resulted from the report that, in addition to devastating encephalopathies, these can result in various types of tumors in human. We first review the major features of the cycle that may underlie this surprising variety of clinical features. After discussing the rare cases of encephalopathies associated with specific deficiencies of some of the tricarboxylic acid cycle enzyme, we finally examine the mechanism possibly causing tumor/cancer formation in the cases of mutations affecting fumarase or succinate dehydrogenase genes.

Molecular and biochemical investigations in fumarase deficiency

Fumarase (FH) deficiency is a rare autosomal recessive disease of the Krebs cycle causing severe neurological impairment in early childhood, characterized by encephalopathy with seizures and muscular hypotonia. Only a handful of patients with various recessive mutations in the FH gene have been described so far. Interestingly, autosomal dominant mutations in the same gene are associated with hereditary leiomyomatosis and renal cell cancer (HLRCC). We investigated a boy with developmental and growth delay, microcephaly, and muscular hypotonia recognized at the age of 3 months. No leiomyomatosis or renal cancer is known in the parents. Investigation of the patient's urine revealed massive fumarate excretion. FH activity was severely reduced in muscle and fibroblasts. Respirometric investigation of fibroblasts showed only modest changes indicating that fumarate mediated inhibition of enzymatic pathways other than oxidative phosphorylation might be more relevant in pathophysiology of FH deficiency. Molecular analysis revealed a known 435insK mutation on the paternal allele and a novel H275L mutation due to an A to T transversion of nucleotide 824 on the maternal allele. This mutation affects the same codon as a C to T transition of nucleotide 823, resulting in a H275Y mutation that was found in two families with HLRCC.

Increased risk of cancer in patients with fumarate hydratase germline mutation

Hereditary leiomyomatosis and renal cell cancer (HLRCC) is a tumour predisposition syndrome caused by heterozygous germline mutations in the fumarate hydratase (FH) gene. The condition is characterised by predisposition to benign leiomyomas of the skin and the uterus, renal cell carcinoma (RCC), and uterine leiomyosarcoma (ULMS). To comprehensively examine the cancer risk and tumour spectrum in Finnish FH mutation positive families, genealogical and cancer data were obtained from 868 individuals. The cohort analysis of the standardised incidence ratios (SIR) was analysed from 256 individuals. FH mutation status was analysed from all available individuals (n = 98). To study tumour spectrum in FH mutation carriers, loss of the wild type allele was analysed from all available tumours (n = 22). The SIR was 6.5 for RCC and 71 for ULMS. The overall cancer risk was statistically significantly increased in the age group of 15-29 years, consistent with features of cancer predisposition families in general. FH germline mutation was found in 55% of studied individuals. Most RCC and ULMS tumours displayed biallelic inactivation of FH, as did breast and bladder cancers. In addition, several benign tumours including atypical uterine leiomyomas, kidney cysts, and adrenal gland adenomas were observed. The present study confirms with calculated risk ratios the association of early onset RCC and ULMS with FH germline mutations in Finns. Some evidence for association of breast and bladder carcinoma with HLRCC was obtained. The data enlighten the organ specific malignant potential of HLRCC.

Fumarase deficiency caused by homozygous P131R mutation and paternal partial isodisomy of chromosome 1

We report on the first case of fumarase deficiency (FD) caused by uniparental isodisomy. An affected patient was found to be homozygous for the P131R mutation in the FH gene. In this nonconsanguineous family, the unaffected father was found to be heterozygous for the same mutation, and the mother was found to be homozygous wild-type. Analysis of chromosome 1 markers showed that the patient inherited both paternal alleles with complete absence of the maternal homolog. The two copies of the paternal chromosome 1 are heterodisomic for most of the chromosome except the distal 1q region which is isodisomic for the mutant alleles of the FH gene. The genotypes of other chromosome markers are consistent with the patient inheriting alleles from both parents. Although FD is an autosomal recessive disorder, the effects of uniparental disomy (UPD) should be considered in genetic counseling since the recurrence risk of an affected child is significantly reduced when the disorder is due to UPD.