Motor Neuropathy in a Patient With Mitochondrial Disease and a Novel TTC19 Variant: An Underrecognized Phenotypic Feature.

TTC19 encodes a mitochondrial protein involved in the assembly of complex III of the respiratory chain. Biallelic pathogenic variants cause a rare mitochondrial disorder typically associated with cerebellar ataxia, neuropsychiatric symptoms, and characteristic brain MRI findings within the Leigh syndrome spectrum. Peripheral motor involvement has been described in a minority of cases but has rarely been documented with detailed neurophysiological data. We report a novel TTC19 variant in a patient presenting with a distinctive combination of central and peripheral motor involvement. A male patient of Malian origin presented with cerebellar ataxia and attention deficits from early childhood. During adolescence, he developed additional features including dysarthria, dysphagia, dysexecutive syndrome, and signs of peripheral motor neuropathy. Brain MRI revealed T2-FLAIR hyperintensities in the basal ganglia and brainstem. Genetic testing identified a novel homozygous nonsense variant in TTC19 (c.235G>T, p.(Gly79*)). At age 19, he experienced two acute deteriorations associated with respiratory infections, leading to severe tetraparesis and diaphragmatic weakness. Neurophysiological studies confirmed a diffuse, axonal, pure distal motor neuropathy. Follow-up imaging showed progression and cavitation of brainstem lesions. The patient died from respiratory failure at age 20. This case, featuring a novel TTC19 variant and detailed electrophysiological data, further supports the presence of pure motor neuropathy within the phenotypic spectrum of TTC19-related disease. The co-occurrence of Leigh syndrome MRI findings and motor neuropathy represents a specific diagnostic clue that may help prioritize genetic testing in patients with overlapping central and peripheral motor involvement.