Pathogenic variants of IBA57 (OMIM ID: 615330) are usually associated with multiple mitochondrial dysfunction syndrome (MMDS) and hereditary spastic paraplegia type 74 (SPG74). Here, we present a novel compound heterozygous IBA57 mutation in a boy with severe global developmental delay, optic atrophy, spastic paraplegia, and focal epileptic seizures. The clinical data of a child diagnosed with MMDS were retrospectively collected. Video electroencephalogram (VEEG), cranial magnetic resonance imaging (MRI), and family whole-exome sequencing (WES) were performed. Suspected mutation sites were further confirmed using Sanger sequencing. The activities of mitochondrial respiratory chain complexes I-IV were determined in peripheral blood mononuclear cells. The phylogenetic conservation of the affected residues was assessed by multiple sequence alignment of IBA57 gene orthologs. Furthermore, we conducted a review of the relevant literature. Whole-exome sequencing identified compound heterozygous variants in the IBA57 gene: c.395_400dup (p.V132_Q133dup) and c.832delC (p.R278Afs*23), inherited from his phenotypically normal father and mother, respectively. Biochemical assays demonstrated selective reduction of complexes I and II activities, with normal complexes III and IV, consistent with impaired 4Fe-4S cluster maturation. Phylogenetic alignment revealed strict conservation of residues V132-Q133 and R278 across vertebrates. These variants had not been previously reported in domestic or international databases. According to the American College of Medical Genetics and Genomics (ACMG) guidelines, the former was classified as a variant of uncertain significance (PM4 + PM2), while the latter was classified as likely pathogenic (PVS1 + PM2). Diseases associated with IBA57 gene variants are autosomal recessive disorders with a broad clinical phenotypic spectrum. Early genetic testing and family screening are beneficial for the diagnosis, treatment, and prognosis of the disease.

To investigate the clinical features and genetic variants associated with Multiple mitochondrial dysfunction syndrome (MMDS) type 3 in two children. Two children diagnosed with MMDS type 3 at Zhuhai Maternal and Child Health Care Hospital in January 2021 were selected for this study. A retrospective analysis of their clinical data was carried out. Whole exome sequencing was conducted on the two children and their parents, followed by Sanger sequencing for candidate variants and bioinformatic analysis. Both children received comprehensive rehabilitative therapy and were followed up for 3 years. This study was approved by the Ethics Committee of Zhuhai Maternal and Child Health Hospital (Ethics No. 202380). The two MMDS type 3 children were monozygotic twin girls, aged 9 months, presenting with developmental regression, pyramidal signs, and other clinical manifestations. Cranial MRI revealed widespread abnormal signals and vacuolar changes in the white matter. Whole exome sequencing revealed that both children had harbored compound heterozygous variants of the IBA57 gene, namely c.286T>C (p.Tyr96His) and c.307C>T (p.Gln103Ter). Sanger sequencing confirmed that these variants were inherited from their father and mother, respectively. According to the American College of Medical Genetics and Genomics (ACMG) guidelines, both variants were classified as pathogenic (PM2_Supporting+PM3_Very Strong+PP3_Moderate; PVS1+PM2_Supporting+PM3). After treatment with vitamins, levocarnitine, ATP, coenzyme Q10, and other drugs, both children showed partial recovery of neurodevelopmental regression, with improvement in feeding and sleep. Over the 3-year follow-up, there was slow but progressive improvement in motor, language, and cognitive development. The compound heterozygous variants c.286T>C (p.Tyr96His) and c.307C>T (p.Gln103Ter) of the IBA57 gene probably underlay the MMDS type 3 in the twin pair. Clinicians should be vigilant about the possibility of MMDS type 3 in children with neurodevelopmental regression and early cranial MRI findings indicating widespread white matter abnormalities with vacuolar changes, as these may be indicative of IBA57 gene variants.

To further comprehend the phenotype of multiple mitochondrial dysfunction syndrome type 3 (MMDS3:OMIM#615330) caused by IBA57 mutation. We present a case involving a patient who experienced acute neurological regression, and the literature was reviewed. Clinical data and laboratory test results were collected; early language and development progress were tested; and genetic testing was performed. Bioinformatics analysis was performed using Mutation Taster and PolyPhen-2, and the literature in databases such as PubMed and CNKI was searched using MMDS3 and IBA57 as keywords. The child, aged 1 year and 2 months, had motor decline, unable to sit alone, limited right arm movement, hypotonia, hyperreflexia of both knees, and Babinski sign positivity on the right side, accompanied by nystagmus. Blood lactate levels were elevated at 2.50 mmol/L. Brain MR indicated slight swelling in the bilateral frontoparietal and occipital white matter areas and the corpus callosum, with extensive abnormal signals on T1 and T2 images, along with the semioval center and occipital lobes bilaterally. The multiple abnormal signals in the brain suggested metabolic leukoencephalopathy. Whole-exome sequencing analysis revealed that the child had two heterozygous mutations in the IBA57 gene, c.286T>C (p.Y96H) (likely pathogenic, LP) and c.992T>A (p.L331Q) (variant of uncertain significance, VUS). As of March 2023, a literature search showed that 56 cases of MMDS3 caused by IBA57 mutation had been reported worldwide, with 35 cases reported in China. Among the 35 IBA57 mutations listed in the HGMD database, there were 28 missense or nonsense mutations, 2 splicing mutations, 2 small deletions, and 3 small insertions. MMDS3 predominantly manifests in infancy, with primary symptoms including feeding difficulties, neurological functional regression, muscle weakness, with severe cases potentially leading to mortality. Diagnosis is supported by elevated lactate levels, multisystem impairment (including auditory and visual systems), and distinctive MRI findings. Whole-exome sequencing is crucial for diagnosis. Currently, cocktail therapy offers symptomatic relief.

Multiple mitochondrial dysfunctions syndrome (MMDS) is a rare neurodegenerative disorder associated with mutations in genes with a vital role in the biogenesis of mitochondrial [4Fe-4S] proteins. Mutations in one of these genes encoding for BOLA3 protein lead to MMDS type 2 (MMDS2). Recently, a novel phenotype for MMDS2 with complete clinical recovery was observed in a patient containing a novel variant (c.176G > A, p.Cys59Tyr) in compound heterozygosity. In this work, we aimed to rationalize this unique phenotype observed in MMDS2. To do so, we first investigated the structural impact of the Cys59Tyr mutation on BOLA3 by NMR, and then we analyzed how the mutation affects both the formation of a hetero-complex between BOLA3 and its protein partner GLRX5 and the iron-sulfur cluster-binding properties of the hetero-complex by various spectroscopic techniques and by experimentally driven molecular docking. We show that (1) the mutation structurally perturbed the iron-sulfur cluster-binding region of BOLA3, but without abolishing [2Fe-2S]2+ cluster-binding on the hetero-complex; (2) tyrosine 59 did not replace cysteine 59 as iron-sulfur cluster ligand; and (3) the mutation promoted the formation of an aberrant apo C59Y BOLA3-GLRX5 complex. All these aspects allowed us to rationalize the unique phenotype observed in MMDS2 caused by Cys59Tyr mutation.

Iron-Sulfur Cluster (ISC) biogenesis is a vital cellular process required to produce various ISC-containing proteins. These ISC proteins are responsible for essential functions such as glycine cleavage and the formation of lipoic acid, an essential cofactor of respiratory chain complexes. Defects in ISC biogenesis lead to multiple mitochondrial dysfunction syndromes including: ISCA2 with infantile onset leukodystrophy. Recently, a founder mutation, c.229G > A, p.Gly77Ser in ISCA2 was reported to cause Multiple Mitochondrial Dysfunction Syndrome type 4. In a retrospective review of children diagnosed with the ISCA2 defect, we were able to identify ten new patients who were not reported previously with the identical founder mutation. High CSF glycine levels and elevated glycine peaks on MR spectroscopy were demonstrated in all tested probands. All patients were between 3 and 7 months of age with a triad of neurodevelopmental regression, nystagmus and optic atrophy and leukodystrophy. MRI findings were typical in the patients with diffuse, abnormal white matter signal in the cerebrum, cerebellum, brain stem and spinal cord. The patients ended up in a vegetative state, and often premature death due to respiratory infections. We alert clinicians to consider the ISCA2 defect as a differential diagnosis of infantile onset leukodystrophies affecting the brain as well as the spinal cord, especially in the presence of elevated CSF glycine or elevated glycine peaks in MR spectroscopy.