A 3-year-old boy is brought to the physician for a follow-up examination. He has generalized hypotonia. Conduction audiometry shows mild impairment. Serum lactic acid is elevated. He has a 6 year-old brother with hypotonia and an 8-year-old sister with poor eyesight and hearing. Which of the following is the most likely explanation for this patient’s findings?
Allelic heterogeneity
Heteroplasmy
Imprinting
Incomplete penetrance
Variable expressivity
