C19orf12 gene variants causing mitochondrial membrane protein-associated neurodegeneration (MPAN)

Mitochondrial membrane protein-associated neurodegeneration (MPAN) is a rare neurodegenerative disorder characterized by spastic paraplegia, parkinsonism and psychiatric and/or behavioral symptoms caused by variants in gene encoding chromosome-19 open reading frame-12 (C19orf12). We present here seven patients from six unrelated families with detailed clinical, radiological, and genetic investigations. Childhood-onset patients predominantly had a spastic ataxic phenotype with optic atrophy, while adult-onset patients were presented with cognitive, behavioral, and parkinsonian symptoms. Levodopa induced choreiform dyskinesia was observed in one patient who showed a response to levodopa. Brain magnetic resonance imaging showed mineralization in all patients and cerebellar atrophy in one patient. The "pallidal splitting sign" was found in two patients and additional caudate and putamen mineralization was noted in two patients. Exome sequencing identified six variants in the C19orf12 gene, including two novel splice-site variants, four previously reported missense variants. Transcript analysis using RT-PCR followed by Sanger sequencing was performed on a splice site variant (c.194-2delA) to understand the splice defect and its consequences. This analysis confirmed the splice defect and use of an alternate cryptic splice site in the downstream exonic region. The variants identified in this study expand the spectrum of clinical and genetic knowledge on MPAN patients, highlighting the importance of genetic testing in the diagnosis and management of this disorder.