Mammalian mitochondrial DNA (mtDNA) is considered to be inherited in a strictly maternal manner as sperm mitochondria disappear in early embryogenesis by a process of selective destruction or inactivation. But, in August 22 New England Journal of Medicine, Marianne Schwartz and John Vissing at University Hospital Rigshospitalet, Copenhagen, Denmark present evidence that mitochondrial DNA can be paternally inherited (NEJM 2002, 347:576-580).

Schwartz & Vissing examined a 28-year-old patient with severe exercise intolerance and analyzed DNA from his blood, muscle, hair roots and fibroblasts. DNA was also analyzed from the blood of the patient's parents and paternal uncle and from the blood and the quadriceps muscle of the patient's sister. They identified a 2-bp deletion in the mitochondrial ND2 gene and observed that this mutation occurred only in other paternal lineage mtDNA samples.

"Because the patient had an isolated myopathy due to a mutation found only in...

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