Hearing impairment and renal failure associated with RMND1 mutations

New insights into Perrault syndrome, a clinically and genetically heterogeneous disorder

Hearing loss and impaired fertility are common human disorders each with multiple genetic causes. Sometimes deafness and impaired fertility, which are the hallmarks of Perrault syndrome, co-occur in a person. Perrault syndrome is inherited as an autosomal recessive disorder characterized by bilateral mild to severe childhood sensorineural hearing loss with variable age of onset in both sexes and ovarian dysfunction in females who have a 46, XX karyotype. Since the initial clinical description of Perrault syndrome 70 years ago, the phenotype of some subjects may additionally involve developmental delay, intellectual deficit and other neurological disabilities, which can vary in severity in part dependent upon the genetic variants and the gene involved. Here, we review the molecular genetics and clinical phenotype of Perrault syndrome and focus on supporting evidence for the eight genes (CLPP, ERAL1, GGPS1, HARS2, HSD17B4, LARS2, RMND1, TWNK) associated with Perrault syndrome. Variants of these eight genes only account for approximately half of the individuals with clinical features of Perrault syndrome where the molecular genetic base remains under investigation. Additional environmental etiologies and novel Perrault disease-associated genes remain to be identified to account for unresolved cases. We also report a new genetic variant of CLPP, computational structural insight about CLPP and single cell RNAseq data for eight reported Perrault syndrome genes suggesting a common cellular pathophysiology for this disorder. Some unanswered questions are raised to kindle future research about Perrault syndrome.

Two Novel Pathogenic Variants Confirm RMND1 Causative Role in Perrault Syndrome with Renal Involvement

RMND1 (required for meiotic nuclear division 1 homolog) pathogenic variants are known to cause combined oxidative phosphorylation deficiency (COXPD11), a severe multisystem disorder. In one patient, a homozygous RMND1 pathogenic variant, with an established role in COXPD11, was associated with a Perrault-like syndrome. We performed a thorough clinical investigation and applied a targeted multigene hearing loss panel to reveal the cause of hearing loss, ovarian dysfunction (two cardinal features of Perrault syndrome) and chronic kidney disease in two adult female siblings. Two compound heterozygous missense variants, c.583G>A (p.Gly195Arg) and c.818A>C (p.Tyr273Ser), not previously associated with disease, were identified in RMND1 in both patients, and their segregation with disease was confirmed in family members. The patients have no neurological or intellectual impairment, and nephrological evaluation predicts a benign course of kidney disease. Our study presents the mildest, so far reported, RMND1-related phenotype and delivers the first independent confirmation that RMND1 is causally involved in the development of Perrault syndrome with renal involvement. This highlights the importance of including RMND1 to the list of Perrault syndrome causative factors and provides new insight into the clinical manifestation of RMND1 deficiency.

Characterization of the renal phenotype in RMND1-related mitochondrial disease

BACKGROUND

The nuclear encoded gene RMND1 (Required for Meiotic Nuclear Division 1 homolog) has recently been linked to RMND1-related mitochondrial disease (RRMD). This autosomal recessive condition characteristically presents with an infantile-onset multisystem disease characterized by severe hypotonia, global developmental delay, failure to thrive, sensorineural hearing loss, and lactic acidosis. Renal disease, however, appears to be one of the more prominent features of RRMD, affecting patients at significantly higher numbers compared to other mitochondrial diseases. We report the clinical, histological, and molecular findings of four RRMD patients across three academic institutions with a focus on the renal manifestations.

METHODS

Four patients were identified for the purpose of this study, all of whom had molecular confirmation at the time of inclusion, which included the common pathogenic variant c.713A>G (p.N238S) as well as the three rare variants: c.485delC (p.P162fs), c.533C>T (p.T178M), and c.1317 + 1G>C splice donor variant. Medical history and laboratory findings were collected from the medical records and medical providers.

RESULTS

In this study, all four patients developed renal disease characterized as tubulopathy (3/4), renal tubular acidosis (2/4), interstitial nephritis (1/4), and/or end-stage renal disease (4/4) necessitating renal transplantation (2/4). Histological evaluation of renal biopsy specimens revealed generalized tubular atrophy and on electron microscopy, abundant mitochondria with pleomorphism and abnormal cristae.

CONCLUSION

Our experience with RRMD demonstrates a specific pattern of renal disease manifestations and clinical course. Patients are unlikely to respond to traditional chronic kidney disease (CKD) treatments, making early diagnosis and consideration of renal transplantation paramount to the management of RRMD.

Evidence that 6q25.1 variant rs6931104 confers susceptibility to chronic myeloid leukemia through RMND1 regulation

Chronic myeloid leukemia (CML) is a clonal myeloproliferative disorder. Our previous study reported novel loci as genetic markers associated with increased susceptibility to CML. The present study conducted an expression quantitative trait loci (eQTL) analysis to confirm that the single nucleotide polymorphisms (SNPs) at these loci affect the expression of candidate CML-susceptible genes. We identified that three SNPs (rs963193, rs6931104, and rs9371517) were related to the gene expression pattern of RMND1 (Required For Meiotic Nuclear Division 1 Homolog) in both granulocytes and mononuclear cells from 83 healthy donors. Furthermore, reduced expression of RMND1 expression was noted in CML patients compared with that in healthy individuals. We used the eQTL browsing tool to assess the regulatory information on the three associated significant SNPs, out of which rs6931104 showed strong evidence of regulatory effects. Chromatin immunoprecipitation (ChIP) assays demonstrated that A alleles of rs6931104 could significantly change the binding affinity of transcription factor (TF) RFX3 compared to the G alleles. Then, we performed in vitro experiments on BCR-ABL1-positive (BCR-ABL1+) cell lines. We found that expression of the CML-susceptible gene RMND1 is affected by the binding affinity of TF RFX3, suggesting that RFX3 plays a role in RMND1 expression. Our findings suggest potential target genes for associations of genetic susceptibility risk loci and provide further insights into the pathogenesis and mechanism of CML.

Hearing loss and renal syndromes

The association between ear and kidney abnormalities has long been recognized; however, the connection between these two disparate organs is not always straightforward. Although Alport syndrome is the most well-known, there are over 20 disorders that need to be considered in the differential diagnosis of patients with both ear and kidney abnormalities. Commonalities are present between the kidney and ear in a number of structural proteins, developmentally important transcription factors, ciliary proteins, and channel proteins, and mutations in these pathways can lead to disease in both organ systems. This manuscript reviews the congenital disorders with both hearing and kidney manifestations.

Mitochondrial DNA transcription and translation: clinical syndromes

Diagnosing primary mitochondrial diseases is challenging in clinical practice. Although, defective oxidative phosphorylation (OXPHOS) is the common final pathway, it is unknown why different mtDNA or nuclear mutations result in largely heterogeneous and often tissue -specific clinical presentations. Mitochondrial tRNA (mt-tRNA) mutations are frequent causes of mitochondrial diseases both in children and adults. However numerous nuclear mutations involved in mitochondrial protein synthesis affecting ubiquitously expressed genes have been reported in association with very tissue specific clinical manifestations suggesting that there are so far unknown factors determining the tissue specificity in mitochondrial translation. Most of these gene defects result in histological abnormalities and multiple respiratory chain defects in the affected organs. The clinical phenotypes are usually early-onset, severe, and often fatal, implying the importance of mitochondrial translation from birth. However, some rare, reversible infantile mitochondrial diseases are caused by very specific defects of mitochondrial translation. An unbiased genetic approach (whole exome sequencing, RNA sequencing) combined with proteomics and functional studies revealed novel factors involved in mitochondrial translation which contribute to the clinical manifestation and recovery in these rare reversible mitochondrial conditions.

Expanding the Phenotype of the Founder South Asian Mutation in the Nuclear Encoding Mitochondrial RMND1 Gene

BACKGROUND

Mitochondrial disorders have a wide variability in the phenotype. A 10-mo-old girl presented with a severe phenotype of multisystem involvement due to an uncommon mitochondrial disease. Mutations in the RMND1 gene of nuclear DNA were identified on next generation sequencing. This mutation results in combined oxidative phosphorylation deficiency -11 (OMIM #614922) of the respiratory chain complex. So far in South Asia, patients of this disorder have been reported only from Pakistan and Bangladesh.

RESULTS

In addition to the features reported in other patients of South Asia with the same mutation at c.1349G>C, index patient from India had hyperaldosteronism, long QT interval but no deafness.

CONCLUSIONS

Thus, to conclude, this report emphasizes the diagnostic value of FGF21 assay in this disorder. It extends the phenotype associated with the founder mutation in RMND1 gene in patients from South Asia.

The clinical, biochemical and genetic features associated with RMND1-related mitochondrial disease

Background

Mutations in the RMND1 (Required for Meiotic Nuclear Division protein 1) gene have recently been linked to infantile onset mitochondrial disease characterised by multiple mitochondrial respiratory chain defects.

Methods

We summarised the clinical, biochemical and molecular genetic investigation of an international cohort of affected individuals with RMND1 mutations. In addition, we reviewed all the previously published cases to determine the genotype–phenotype correlates and performed survival analysis to identify prognostic factors.

Results

We identified 14 new cases from 11 pedigrees that harbour recessive RMND1 mutations, including 6 novel variants: c.533C>A, p.(Thr178Lys); c.565C>T, p.(Gln189*); c.631G>A, p.(Val211Met); c.1303C>T, p.(Leu435Phe); c.830+1G>A and c.1317+1G>T. Together with all previously published cases (n=32), we show that congenital sensorineural deafness, hypotonia, developmental delay and lactic acidaemia are common clinical manifestations with disease onset under 2 years. Renal involvement is more prevalent than seizures (66% vs 44%). In addition, median survival time was longer in patients with renal involvement compared with those without renal disease (6 years vs 8 months, p=0.009). The neurological phenotype also appears milder in patients with renal involvement.

Conclusions

The clinical phenotypes and prognosis associated with RMND1 mutations are more heterogeneous than that were initially described. Regular monitoring of kidney function is imperative in the clinical practice in light of nephropathy being present in over 60% of cases. Furthermore, renal replacement therapy should be considered particularly in those patients with mild neurological manifestation as shown in our study that four recipients of kidney transplant demonstrate good clinical outcome to date.

Compound heterozygous RMND1 gene variants associated with chronic kidney disease, dilated cardiomyopathy and neurological involvement: a case report

Background

Nuclear gene mutations are being increasingly recognised as causes of mitochondrial disease. The nuclear gene RMND1 has recently been implicated in mitochondrial disease, but the spectrum of pathogenic variants and associated phenotype for this gene, has not been fully elucidated.

Case presentation

An 11-month-old boy presented with renal impairment associated with a truncal ataxia, bilateral sensorineural hearing loss, hypotonia, delayed visual maturation and global developmental delay. Over a 9-year period, he progressed to chronic kidney disease stage V and developed a dilated cardiomyopathy. Abnormalities in renal and muscle biopsy as well as cytochrome c oxidase activity prompted genetic testing. After exclusion of mitochondrial DNA defects, nuclear genetic studies identified compound heterozygous RMND1 (c.713A>G, p. Asn238Ser and c.565C>T, p.Gln189*) variants.

Conclusion

We report RMND1 gene variants associated with end stage renal failure, dilated cardiomyopathy, deafness and neurological involvement due to mitochondrial disease. This case expands current knowledge of mitochondrial disease secondary to mutation of the RMND1 gene by further delineating renal manifestations including histopathology. To our knowledge dilated cardiomyopathy has not been reported with renal failure in mitochondrial disease due to mutations of RMND1. The presence of this complication was important in this case as it precluded renal transplantation.