Multiple mitochondrial dysfunction syndrome type 3 (MMDS3) is a rare mitochondrial leukoencephalopathy caused by biallelic pathogenic variants in IBA57. Here, we describe a homozygous variant in IBA57, (NM_001010867.2): c.310G>T (p.Gly104Cys), in a 2-month-old infant of Cuban descent who presented with a one-month history of progressive hypotonia, weakness, and episodes of upgaze deviation. This is the first report of a patient homozygous for this variant and the first report of MMDS3 in a patient of Hispanic descent described to our knowledge. Using in silico tools, we found that the variant resides in a putative mutational hotspot located in the neighborhood of a key active ligand required for iron-sulfur cluster coordination. In addition, while previous case reports/series have reported the variable phenotypic features of the disease, the incidence of these features across the literature has not been well described. In order to construct a clearer global picture of the typical presentation of MMDS3, we reviewed 52 cases across the literature with respect to their clinical, biochemical, genotypic, and neuroradiographic features.

Multiple mitochondrial dysfunction syndrome (MMDS) refers to a class of mitochondrial diseases caused by nuclear gene mutations, which usually begins in early infancy and is classically characterized by markedly impaired neurological development, generalized muscle weakness, lactic acidosis, and hyperglycinemia, cavitating leukoencephalopathy, respiratory failure, as well as early fatality resulted from dysfunction of energy metabolism in multiple systems. So far, six types of MMDS have been identified based on different genotypes, which are caused by mutations in NFU1, BOLA3, IBA57, ISCA2, ISCA1 and PMPCB, respectively. IBA57 encodes a protein involved in the mitochondrial Fe/S cluster assembly process, which plays a vital role in the activity of multiple mitochondrial enzymes. Herein, detailed clinical investigation of 2 Chinese patients from two unrelated families were described, both of them showed mildly delay in developmental milestone before disease onset, the initial symptoms were all presented with acute motor and mental retrogression, and brain MRI showed diffused leukoencephalopathy with cavities, dysplasia of corpus callosum and cerebral atrophy. Exome sequencing revealed three IBA57 variants, one shared variant (c.286T>C) has been previously reported, the remaining two (c.189delC and c.580 A>G) are novel. To enhance the understanding of this rare disease, we further made a literature review about the current progress in clinical, genetic and treatment of the disorder. Due to the rapid progress of MMDS, early awareness is crucial to prompt and proper administration, as well as genetic counseling.

Mitochondrial proteins carrying iron-sulfur (Fe-S) clusters are involved in essential cellular pathways such as oxidative phosphorylation, lipoic acid synthesis, and iron metabolism. NFU1, BOLA3, IBA57, ISCA2, and ISCA1 are involved in the last steps of the maturation of mitochondrial [4Fe-4S]-containing proteins. Since 2011, mutations in their genes leading to five multiple mitochondrial dysfunction syndromes (MMDS types 1 to 5) were reported. The aim of this systematic review is to describe all reported MMDS-patients. Their clinical, biological, and radiological data and associated genotype will be compared to each other. Despite certain specific clinical elements such as pulmonary hypertension or dilated cardiomyopathy in MMDS type 1 or 2, respectively, nearly all of the patients with MMDS presented with severe and early onset leukoencephalopathy. Diagnosis could be suggested by high lactate, pyruvate, and glycine levels in body fluids. Genetic analysis including large gene panels (Next Generation Sequencing) or whole exome sequencing is needed to confirm diagnosis.