Mitochondrial complex III deficiency nuclear type 2: a case report and analysis of clinical onset age-related phenotypic features.

case presentationMitochondrial complex III deficiency nuclear type 2 (MC3DN2) is a rare inherited neurometabolic disease. A 34-year-old male had neuropsychiatric episodes, progressive cerebellar degeneration, myopathy, polyneuropathy, and brain stem and basal ganglion lesions since childhood. Muscle biopsy revealed mitochondrial abnormalities. Two novel TTC19 pathogenic variants were detected. LITERATURE REVIEW: To analyze phenotypic characteristics of MC3DN2 related to clinical onset age, neurological presentation and brain MRI regarding infantile and childhood-onset (ICO) and adolescent and adult-onset (AAO) disease in a cohort composed of our patient and the cases reported in the literature were compared. It revealed that, clinically, cerebellar ataxia was common in both groups, nystagmus was more frequently noted in AAO patients, and psychiatric disturbances were more common in ICO patients. Regarding MRI findings, basal ganglion lesions were more prevalent in ICO patients, and inferior olive lesions were more frequent in AAO patients. DISCUSSION: These conspicuous phenotypic features of MC3DN2 may suggest diagnosis of this distinctive disease. The differences in clinical features and brain lesions associated with clinical onset age could provide crucial insights into the phenotypic landscape of MC3DN2.