RMND1 Mutation Case Report and Literature Review

The required for meiotic nuclear division 1 homolog (RMND1) protein localizes to the inner mitochondrial membrane and is encoded by the nuclear genome. Although the functional properties of the protein are not fully known, it is thought to promote the translation of mtDNA-encoded polypeptides that represent essential structural components of oxidative phosphorylation complexes [1, 2]. Mitochondrial disorders are clinically heterogeneous and typically affect multiple organ systems. These disorders tend to be severely debilitating, progressive, and often fatal [3]. The estimated prevalence of mitochondrial respiratory chain defects is 1 in 5,000 live births, and they are among the most common inborn errors in the metabolism [4]. Combined oxidative phosphorylation deficiency (COXPD) is an autosomal recessive, multisystem, and fatal disorder that occurs early in life and involves the central nervous, renal, cardiac, and hepatic systems with developmental delay. COXPD has subtypes. Pathogenic variants in the RMND1 gene cause COXPD11 (MIM #614922) [5]. COXPD11 patients usually present with clinical signs in the neonatal period and mortality in the first decade has been reported to be approximately 55% [6].

Here we describe a pediatric patient affected by a homozygous mutation in the RMND1 gene with severe renal phenotype and heterogeneity in nonrenal manifestations, sensorineural deafness, failure to thrive, heart failure, and developmental delay. Online supplementary Table 1 (for all online suppl. material, see https://doi.org/10.1159/000538930) summarizes all previously published cases and our new patient.

The proband is the fourth daughter of healthy consanguineous Turkish parents. The mother had an uneventful full-term pregnancy. She was born at 38 weeks gestation by normal spontaneous vaginal delivery. Birth weight, height, and head circumference were 2,910 g (−0.9 SD), 49 cm (−0.2 SD), and 34 cm (−0.3 SD), respectively. She had pes equinovarus deformity at birth. In the pulse oximetry screening performed at the 24th hour of birth, there was an oxygen saturation difference of more than 2% between the extremities. Echocardiography (ECHO) was performed in the patient who failed the pulse oximetry scan performed at 24 h of birth. ECHO was consistent with hypertrophic cardiomyopathy and patent foramen ovale. On the sixth day of her life, she was admitted to the intensive care unit because of failure to feed, vomiting, hypotonia, and associated respiratory failure. Hypertension was detected during intensive care unit follow-up. Laboratory findings included hyponatremia, hyperkalemia, hyperphosphatemia, hyperlactatemia, and metabolic acidosis. Renal function values including creatinine, urea nitrogen, and uric acid were elevated. Cranial magnetic resonance imaging was normal. Renal ultrasonography revealed bilateral renal parenchymal echogenicity. Mitochondrial disease was considered in the patient with hearing loss and cardiac and renal involvement. Thiamine, biotin, and carnitine supplements were started. WES and mitochondrial genome analysis were planned for definitive diagnosis. Proband WES analysis revealed a homozygous variant (c.713A>G) in the RMND1 gene (NM_017909.3). The patient was considered compatible with COXPD11. Supportive treatments were administered to the patient for this disease, which did not have a specific treatment option and had a generally poor prognosis.

WES analysis was performed for the index case, followed by confirmation of a priority variant in a candidate gene by Sanger sequencing. Genomic DNA was isolated from circulating lymphocytes using the QIAamp DNA blood kit according to the manufacturer’s instructions (Qiagen, USA). DNA concentration and purity were assessed using a NanoDrop ND-1000 UV-VIS spectrophotometer. For the whole exome-enriched library from the affected band, 100 ng/μL genomic DNA was used. Hexonic regions of protein-encoded genes registered in CCDS and RefSeq databases were captured using the Agilent Sure Select capture kit (Agilent Technologies, USA). The HiSeq 2000 Illumina platform was used to generate large-scale short-read sequencing. Selected probably causative variants were confirmed using direct Sanger sequencing and reported based on the RMND1 NM_017909.4 and NP_060379.2 reference sequences. Patients previously described in the literature were recruited from databases. A literature review was conducted to determine the effect of variants on mortality and phenotype. Variant identification was performed using several algorithms: HaplotypeCaller from GATK (Genome Analysis Toolkit) [7], FreeBayes [8], DeepVariant [9], and Mutect2 [10]. Previously identified variants were annotated using Ensembl VEP [11] and several databases including gnomAD [12], ClinVar [13], and HGMD [14].

A systematic literature search on RMND1 was conducted using the search terms “combined oxidative phosphorylation deficiency 11,” “infantile encephaloneuromyopathy due to mitochondrial translation defect,” and “COXPD11” in the PubMed, Cochrane, and CINAHL databases for data up to December 2023. No language or data filters were used. The reference list of Ng et al. [31] large case series was searched for additional references. Due to the limited number of publications on COXPD11, conference abstracts from posters or symposia were included for literature review. Clinical and laboratory data were collated using a standardized data collection form.

Data analyses were performed using SPSS for Windows, version 22.0 (SPSS Inc., Chicago, IL, USA). Categorical data were described as a number of cases (%). Categorical variables were compared using Pearson’s χ² test or Fisher’s exact test was accepted p value <0.05 as a significant level on all statistical analysis.

Clinical characteristics of 49 cases (male:female = 15:31, three patients sex unknown) from 36 pedigrees are summarized in online supplementary Table 1. Seventeen cases (61%) were full-term (≥37 weeks) and 11 cases (39%) were preterm (<37 weeks); the earliest delivery (P28) was at the 24th gestational week. Forty-nine cases were divided into three groups as the age of onset of clinical findings in the first month, between 1st and 12th months, and after 1 year of age. Nineteen cases (38.8%) had clinical findings in the neonatal period, 21 cases (42.9%) had between 1st and 12th months, and 9 cases (18.4%) had after 1 year of age (Table 1). The most common clinical features associated with RMND1 mutations were sensorineural hearing loss (n = 39/42, 93%) and global developmental delay (n = 37/41, 90%), followed by failure to thrive (n = 29/33, 88%). Ear and kidney were the most frequently involved organs in the COXPD11 patients. Kidney findings were more common than neurological and cardiac findings. Additionally, kidney imaging findings (n = 16/20, 80%) were more common than neuroimaging findings (n = 24/31, 77%) and ECHO findings (n = 18/34, 53%). Death was reported in 23 cases (46%). WES was the most widely used genetic analysis for the diagnosis of the disease (n = 36/44, 81%). Only 1 patient was diagnosed by Sanger analysis of the RMND1 gene (P30). Homozygous mutations were detected in 55% of the patients. Consanguinity was reported in twenty-one cases (n = 21/43, 48.8%). Kidney involvement was observed in 81.3% (39/48) of cases. It was the most common organ involvement following hearing loss. Twenty-five cases developed end-stage kidney disease. Renal tubular acidosis was reported in 22 cases. Eight cases have been treated by transplant. The manifestations of kidney disease included different stages of chronic kidney disease (CKD, n = 31), dysplastic or hypoplastic kidneys (n = 12), normocytic anemia (n = 11), and proteinuria (n = 4). Hypertrophic cardiomyopathy/left ventricular hypertrophy was identified in 6 cases (P2, P3, P7, P8, P19, and P36) and 2 cases had dilated cardiomyopathy (P12, P30). ECHO was reported as normal in 7 cases (P1, P8, P11.2, P18.1, P18.2, P26.1, and P27). The most common laboratory feature associated with RMND1 mutations was lactate elevation (n = 36/43, 84%). Hormonal deficiencies have been reported in recent studies. Parathyroid hormone elevation was reported in 7 cases. Growth retardation was reported in 5 cases, and primary ovarian insufficiency was reported in 3 cases. Other rare findings are listed in Table 2.

We examined the association between kidney, heart, and hearing loss involvement, which are common in RMND1 mutation, and other findings. Hypertension was more common in both kidney and heart involvement (p = 0.015 and 0.015, respectively). Similarly, seizures were significantly reduced in both kidney and heart involvement (p = 0.005, 0.010, respectively). Microcephaly was reported less frequently in patients with renal involvement (p = 0.046). There was no statistically significant correlation with plasma lactate elevation in patients with renal and cardiac involvement. A statistically significant correlation was found between kidney involvement and cardiac involvement in cases with RMND1 mutation. Mortality was less frequent in patients with renal involvement (p = 0.007). However, it was more frequent in patients with cardiac involvement (p = 0.034). No separate assessment was conducted for patients with both kidney and cardiac involvement. Furthermore, mortality was statistically significantly lower in patients with deafness (p = 0.049). The 98 allele variant types were analyzed. The most common variant type was missense mutation (55.6%). Stop-codon loss mutation was the second most common variant type (22.4%). This was followed by donor splice site (13.6%), frameshift deletion (6.3%), and nonsense (2.1%). 49 cases (98 alleles) were analyzed, and the most common variant in RMND1 cases was c.713A>G (p.Asn238Ser). This sequence change replaces asparagine, which is neutral and polar, with serine, which is neutral and polar, at codon 238 of the RMND1 protein (p.Asn238Ser). This variant was reported in 25 cases (51%). Homozygous mutations were reported in 6 cases, and compound heterozygous mutations were reported in 19 cases. It was shown that cases with c.713A>G (p.Asn238Ser) allele mutation would have more frequent kidney involvement (p = 0.009). No mortality was observed in any of the 6 cases with a homozygous c.713A>G (p.Asn238Ser) mutation (p = 0.024). Mortality was statistically significantly lower in cases with homozygous and compound heterozygous c.713A>G (p.Asn238Ser) mutations (p < 0.001). The second most common mutation was c.1349G>C (p.*450Serext*31) and was reported in 11 cases (22.4%). This mutation has been reported as a homozygous in all cases. Cardiac involvement and mortality were more common in cases with homozygous c.1349G>C (p.*450Serext*32) mutation (p = 0.008 and 0.008, respectively). Current findings show that renal involvement is more frequent and mortality is lower in patients with c.713A>G (p.Asn238Ser) mutation, while cardiac involvement is more frequent and mortality is higher in patients with c.1349G>C (p.*450Serext*32) mutation (Table 3).

Mutations in the RMND1 gene that cause defects in the mitochondrial respiratory chain result in a very heterogeneous phenotype. Janer et al. [1] and Garcia-Diaz et al. [2] first described the biallelic pathogenic variants in the nuclear-encoded RMND1 gene in 2012. Mutations in RMND1 have been associated with a neonatal encephaloneuromyopathy termed COXPD11 (#614922). COXPD11 is an autosomal recessive disease characterized by multiple organ involvement with deficiencies of multiple respiratory chain complexes, leading to neonatal hypotonia and lactic acidosis [15]. Patients mainly have sensorineural hearing loss, cardiac involvement, kidney involvement, neurological findings, and lactate elevation. However, a phenotype resembling Perrault syndrome (PRLTS) has recently been reported to be due to the RMND1 mutation [16]. The coexistence of sensorineural hearing loss and primary ovarian insufficiency is known as PRLTS. Thus, 3 patients (P22, P35.1, P35.2) showed with RMND1 mutations were reported as PRLTS. These studies have been reported in 2018 and 2020 [17, 18]. We think that PRLTS will be reported more frequently as the age of patients with reported RMND1 mutations gets older.

Kidney involvement is the most common finding along with deafness. Kidney involvement begins in the neonatal period. Patients develop progressive renal failure. CKD is a rare phenotype in mitochondrial gene mutations. CKD with COQ2, SARS2, and RMND1 mutations have been reported [19]. In RMND1 mutation, the most common kidney finding is CKD. Renal involvement was also observed in our patient in the first week of labor. In our study, microcephaly, seizures, and hypertension were observed more frequently in patients with renal involvement. This is the first article reporting these associations. We think that more RMND1 patients should be included to confirm these correlations. Cardiac involvement has been reported in many metabolic disorders such as lysosomal storage disorders, primary carnitine deficiency, and mitochondrial disorders [20]. Cardiac involvement is one of the other typical organ involvement seen in patients with RMND1 mutations. The main finding of cardiac involvement is hypertrophic cardiomyopathy. Pulse oximetry scanning is a useful, practical, and cost-effective method for screening for congenital heart diseases [21]. Pulse oximetry screening was performed in our patient at the 24th hour of delivery. When she failed the screening test, ECHO was performed and hypertrophic cardiomyopathy was detected. It is the first reported case of RMND1 mutation after pulse oximetry screening. Our study highlights the importance of pulse oximetry screening in mitochondrial diseases such as RMND1 mutations. Central nervous system involvement is observed in patients with RMND1 mutation. Ulrick et al. [22] reported white matter abnormalities, temporal lobe involvement, thinning of the corpus callosum, and T2 hyperinsensitivity on cranial MR images. Our patient had no central nervous system findings or cranial MR uptake. Neurologic examination was normal except for motor developmental stages and language. Retardation in language development due to hearing loss has been reported. Elevated lactate was the most common laboratory finding. Vinu et al. [23] reported FGF-21 elevation caused by RMND1 mutation. FGF-21 has higher sensitivity and specificity compared to lactate [23, 24]. RMND1 belongs to the evolutionarily conserved sif2 gene family, which shares the DUF155 domain [25]. In our study, 38.7% (38/98) of the mutations in RMND1 gene were reported in this region. The mutation frequency increases toward the N-terminal region (Fig. 1). Taylor et al. [26] reported the importance of the role of next-generation techniques in the early stages of the diagnostic algorithm for mutations in the RMND1 gene. WES is the most frequently used molecular analysis method in the diagnosis of RMND1 mutation. WES analysis provides rapid and comprehensive information on known or novel mutations in candidate genes, enabling rapid molecular diagnosis of clinically challenging cases and family members [27]. Sanger sequencing of the RMND1 gene has been performed in only 1 patient so far (P30) [19]. Almost all patients are diagnosed by WES analysis. This suggests how difficult the diagnosis of RMND1 mutation. Rapid molecular genetic methods are important in the early diagnosis for difficult-to-diagnose diseases such as RMND1 mutations that present clinical signs in the neonatal period [28]. In these patients, kidney transplantation has been tried as a supportive treatment. Kidney failure is a cause of mortality and prolongs survival in patients who have undergone kidney transplantation [29, 30]. The most common mutation in our study was c.713A>G (p.Asn238Ser). Similar results were obtained in the study by Ng et al. [31]. It has been previously reported that mortality is lower in patients with kidney involvement. Ng et al. [31] showed that patients with kidney involvement had an average lifespan 6 years longer. In our study, mortality was also lower in patients with kidney involvement (14/39, 35.9%). However, it was more common in patients with cardiac involvement (11/18, 61.1%). These results are consistent with the study by Ng et al. [31]. However, Ng et al. [31] did not specify the reason for the increased mortality. In our study, we found that cardiac involvement increased mortality. The reason for the increased mortality in cardiac involvement may be associated with the c.1349G>C (p.450Serext32) mutation. Cardiac involvement and mortality were more frequent in patients with homozygous c.1349G>C (p.450Serext32) mutation. However, kidney involvement was more frequent and mortality was lower in patients with c.713A>G (p.Asn238Ser) mutation. This suggests that the mutation in the RMND1 gene may be associated with organ involvement.

We think that cardiac involvement, unlike kidney involvement, increased mortality. In this study, the effect of cardiac involvement on mortality in RMND1 mutation has been shown for the first time. We also examined the association of RMND1 mutations and mortality. We reported that mortality was lower in the c.713A>G (p.Asn238Ser) mutation. Additionally, mortality was more common in the c.1349G>C (p.*450Serext*32) mutation (Fig. 2). These findings have not been previously reported in the literature. We think that our findings will be important for genotype-phenotype correlation in RMND1 mutation.

We thank the patient and her family for their helpful participation in this work.

Ethical approval was not required for this study in accordance with local/national guidelines. Written informed consent was obtained from the patient and family for the publication of this case report and accompanying images.

The authors have no conflicts of interest to declare.

There was no funding for this study.

Harun Bayrak, Abdullah Sezer, and Mustafa Kılıç designed and conducted this study. Harun Bayrak and Mustafa Kılıç undertook the statistical analyses. Harun Bayrak wrote the first draft of the manuscript. All authors have participated in drafting the manuscript; Harun Bayrak and Mustafa Kılıç revised it critically. All authors read and approved the final version of the manuscript.

All the data have been included.