Familial idiopathic hyper-CK-emia: an underrecognized condition.

Persistent elevation of serum creatine kinase (CK) in individuals with normal neurological and laboratory examinations has been called idiopathic hyperCKemia (IH). IH has been reported in rare families and was recently ascribed to caveolin-3 gene mutations. We retrospectively found that IH was familial in 13 of 28 subjects in whom serum CK was measured in relatives. These 13 families had a total of 41 subjects with IH, including six over 60 years of age. In eight families there was male-to-male transmission and a higher prevalence of males with hyperCKemia. Muscle biopsy in one member of all families was normal or showed minimal, nonspecific changes. Morphometric examination disclosed different patterns of changes in fiber size and distribution. Caveolin-3 expression was normal and in five families molecular genetics excluded caveolin-3 gene mutations. Our findings suggest that IH is familial in 46% of cases. Familial IH is a benign genetically heterogeneous condition that is autosomal-dominant in at least 60% of cases, with a higher penetrance in men.