Expanding the phenotype of mitochondrial disease: Novel pathogenic variant in ISCA1 leading to instability of the iron-sulfur cluster in the protein.

We report a patient carrying a novel pathogenic variant p.(Tyr101Cys) in ISCA1 leading to MMDS type 5. He initially presented a psychomotor regression with loss of gait and language skills and a tetrapyramidal spastic syndrome. Biochemical analysis of patient fibroblasts revealed impaired lipoic acid synthesis and decreased activities of complex I and II of respiratory chain. While ISCA1 is involved in the mitochondrial machinery for iron-sulfur cluster biogenesis, these dysfunctions are secondary to impaired maturation of mitochondrial proteins containing the [4Fe-4S] clusters. Expression and purification of the human ISCA1 showed a decreased stability of the [2Fe-2S] cluster in the mutated protein.