Spastic paraplegia type 7 is associated with multiple mitochondrial DNA deletions

Area of Science:

• Genetics
• Neuroscience
• Mitochondrial Biology

Background:

• Spastic paraplegia 7 (SPG7) is an autosomal recessive disorder linked to mutations in the paraplegin gene (SPG7).
• The precise mechanism by which paraplegin dysfunction leads to SPG7 remains unclear.
• Paraplegin is an inner mitochondrial membrane protein involved in processing other mitochondrial proteins.

Observation:

• Two Norwegian families with spastic paraplegia and progressive external ophthalmoplegia (PEO) were studied.
• Genetic sequencing identified novel and known pathogenic mutations in the SPG7 gene in affected individuals.
• Muscle biopsies revealed deficiencies in mitochondrial respiratory complexes I, III, and IV, alongside multiple mitochondrial DNA deletions in affected fibers.

Findings:

• SPG7 mutations directly cause the accumulation of mitochondrial DNA damage.
• Paraplegin dysfunction leads to multiple mitochondrial respiratory chain deficiencies.
• This study establishes a link between paraplegin, mitochondrial genome stability, and neurodegenerative disease.

Implications:

• SPG7 mutations contribute to PEO and spasticity through mitochondrial dysfunction.
• Understanding paraplegin's role in mitochondrial homeostasis is crucial for SPG7 pathogenesis.
• SPG7 gene testing is recommended for diagnosing autosomal recessive PEO, particularly when spasticity is present.