A 9-year-old girl is brought to her physician for an assessment of potential causes for her increased vision problems. Examination demonstrates that her eye movement is impaired and she has pigmentary retinopathy. Her physician suspects the child has Kearns-Sayre syndrome which is caused by a defect in complex II of the electron transport chain. If this diagnosis is correct, oxidation of which of the following substrates would be associated with impaired electron transfer?

Question

Quizplus · Accepted Answer

Kearns-Sayre syndrome is associated with defects in mitochondrial DNA, often affecting complexes I, III, or IV, but not complex II. However, if complex II were affected, succinate oxidation would be impaired, as succinate dehydrogenase is part of complex II. Electrons from the oxidation of succinate, via succinate dehydrogenase, enter the electron transport chain (ETC) from FADH₂ at complex II. Therefore, an impairment of complex II function as in this patient would impair electron flow. Oxidation of each of the other substrates generates NADH which feeds its electrons to the ETC at complex I.

A 9-Year-Old Girl Is Brought to Her Physician for an Assessment