Concurrent AFG3L2 and SPG7 mutations associated with syndromic parkinsonism and optic atrophy with aberrant OPA1...

Area of Science:

• Neuroscience
• Genetics
• Mitochondrial Biology

Background:

• Mitochondrial dynamics and quality control are vital for neuronal health; their disruption contributes to neurodegeneration.
• The mitochondrial AAA+ (m-AAA) protease complex, located in the inner mitochondrial membrane, is essential for protein quality control.
• Mutations in m-AAA subunits AFG3L2 and SPG7 cause spinocerebellar ataxia (SCA28) and hereditary spastic paraplegia (SPG7), respectively.

Observation:

• A novel phenotype of early-onset optic atrophy, spastic ataxia, and parkinsonism was observed in a patient with compound heterozygous mutations in AFG3L2 and SPG7.
• The patient presented with a de novo AFG3L2 mutation (p.R468C) and a maternally inherited SPG7 deletion.
• Functional studies in yeast confirmed the pathogenicity of the AFG3L2 p.R468C mutation.

Findings:

• Patient fibroblasts displayed aberrant OPA1 processing, a key protein for mitochondrial fusion.
• Mitochondrial morphology analysis revealed significant fragmentation of the mitochondrial network, unlike in typical SCA28 or SPG7 cases.
• The combined effect of mutations in both m-AAA protease components leads to a distinct and severe neurodegenerative phenotype.

Implications:

• This case highlights that concurrent mutations in m-AAA protease subunits can result in complex neurological disorders.
• It underscores the critical role of OPA1 processing in the pathogenesis of neurodegenerative diseases linked to m-AAA complex dysfunction.
• Understanding these complex genetic interactions provides new insights into mitochondrial disease mechanisms and potential therapeutic targets.