Progressive encephalopathy and complex I deficiency associated with mutations in MTND1

Area of Science:

• Biochemistry
• Genetics
• Neuroscience

Background:

• The oxidative phosphorylation system's Complex I is crucial for cellular energy production.
• Complex I is assembled from nuclear and mitochondrial DNA (mtDNA)-encoded subunits.
• Defects in Complex I lead to various mitochondrial diseases.

Observation:

• Two pediatric patients with muscle mitochondrial Complex I deficiency were studied.
• Patient 1 exhibited Leigh syndrome (LS) with cerebellar ataxia, while Patient 2 presented with neonatal lactic acidosis and psychomotor retardation.
• Both patients harbored de novo mutations in the MTND1 gene, encoding a Complex I subunit.

Findings:

• Patient 1 had a novel heteroplasmic G3890A mutation (R195Q) in MTND1, associated with LS and Complex I deficiency.
• Patient 2 carried a heteroplasmic G3481A mutation (E59K) in MTND1, leading to hypertrophic cardiomyopathy and cardiac insufficiency.
• These findings identify new clinical manifestations of MTND1 mutations and highlight their pathogenicity even at low mutation percentages.

Implications:

• The study expands the known clinical spectrum of MTND1 mutations, linking them to Leigh syndrome and other severe phenotypes.
• It underscores the importance of investigating mitochondrial gene mutations in unexplained neurological and metabolic disorders.
• The results suggest that even low levels of pathogenic mtDNA mutations can cause significant disease, impacting diagnostic approaches.