Kearns-Sayre syndrome and complex II deficiency

Area of Science:

• Biochemistry
• Genetics
• Neurology

Background:

• Kearns-Sayre syndrome (KSS) is a rare mitochondrial DNA deletion disorder.
• KSS presents with a triad of progressive external ophthalmoplegia, pigmentary retinopathy, and cardiac conduction defects.
• Mitochondrial dysfunction is central to KSS pathogenesis.

Observation:

• A 25-year-old woman with KSS exhibited external ophthalmoplegia, short stature, ataxia, and cardiac issues.
• Muscle biopsy showed ragged-red fibers and mitochondrial abnormalities on electron microscopy.
• Enzymatic analysis revealed a specific deficiency in succinic dehydrogenase (complex II).

Findings:

• This is the first reported case of complex II deficiency in a patient with KSS.
• Despite the presence of enzyme subunits, succinic dehydrogenase activity was impaired.
• Vitamin cofactor therapy did not yield short-term clinical improvement.

Implications:

• This finding expands the known molecular defects associated with KSS.
• Highlights the role of specific mitochondrial respiratory chain complex deficiencies in KSS.
• Suggests potential targets for future therapeutic strategies in KSS.