A novel C19orf12 frameshift mutation in a MPAN pedigree impairs mitochondrial function and connectivity leading to neurodegeneration.

BACKGROUND: Mitochondrial membrane protein‒associated neurodegeneration (MPAN) is a rare genetic disease characterized by progressive neurodegeneration with brain iron accumulations combined with neuronal α-synuclein and tau aggregations. Mutations in C19orf12 have been associated with both autosomal recessive and autosomal dominant inheritance patterns of MPAN.

METHODS: We present clinical features and functional evidence from a Taiwanese family with autosomal dominant MPAN caused by a novel heterozygous frameshift and nonsense mutation in C19orf12, c273_274 insA (p.P92Tfs*9). To verify the pathogenicity of the identified variant, we examined the mitochondrial function, morphology, protein aggregation, neuronal apoptosis, and RNA interactome in p.P92Tfs*9 mutant knock-in SH-SY5Y cells created with CRISPR-Cas9 technology.

RESULTS: Clinically, the patients with the C19orf12 p.P92Tfs*9 mutation presented with generalized dystonia, retrocollis, cerebellar ataxia, and cognitive decline, starting in their mid-20s. The identified novel frameshift mutation is located in the evolutionarily conserved region of the last exon of C19orf12. In vitro studies revealed that the p.P92Tfs*9 variant is associated with impaired mitochondrial function, reduced ATP production, aberrant mitochondria interconnectivity and ultrastructure. Increased neuronal α-synuclein and tau aggregations, and apoptosis were observed under conditions of mitochondrial stress. Transcriptomic analysis revealed that the expression of genes in clusters related to mitochondrial fission, lipid metabolism, and iron homeostasis pathways was altered in the C19orf12 p.P92Tfs*9 mutant cells compared to control cells.

CONCLUSION: Our findings provide clinical, genetic, and mechanistic insight revealing a novel heterozygous C19orf12 frameshift mutation to be a cause of autosomal dominant MPAN, further strengthening the importance of mitochondrial dysfunction in the pathogenesis of MPAN.