Multiple Mitochondrial Dysfunctions Syndrome 4 Due to ISCA2 Gene Defects: A Review

Multiple mitochondrial dysfunctions syndrome 4, caused by ISCA2 gene defects (OMIM #616370), was first described by Al-Hassnan et al in 2015. To date, 20 cases have been reported: 13 females and 7 males from 18 different families. All cases are from Saudi Arabia except those from one Italian family. Typically, the patients have normal antenatal and birth history and attain normal development initially. Rapid deterioration occurs between 2 and 7 months of age, with the triad of neurodevelopmental regression, optic atrophy with nystagmus, and diffuse white matter disease. Magnetic resonance imaging findings include 75% of patients have cerebellar white matter abnormalities, and the spinal cord was affected in 55%. Magnetic resonance spectroscopy showed elevated glycine peaks in 2 (10%) cases and elevated lactate peaks in 5 (25%) cases. Biochemical abnormalities include high cerebrospinal fluid glycine and lactate and high plasma glycine and lactate, but these findings were not consistent. Diagnosis is based on the detection of biallelic mutations in the ISCA2 gene. To date, no curative treatment has been discovered, and disease management is exclusively supportive. In this report, the authors review the published cases of ISCA2 gene defects and retrospectively characterize disease phenotypes, the affected biochemical pathways, neuroradiological abnormalities, diagnosis, genetics, and treatment.