Central core disease: clinical and pathological evidence of progression within a family.

A family is described whose members showed different clinical presentations of central core disease. In 4 members the myopathy was congenital and nonprogressive, but in 2, muscle weakness first developed in adult life. Two further members had raised CPK levels without muscle weakness. Muscle weakness in one of the late-onset cases increased over eighteen months. This was associated with evidence of loss of type 2 fibres and the appearance of type 3 fibres on muscle biopsy. It is suggested that central core disease involves reinnervation of type 2 fibres by type 1 axons, and that the clinical manifestation of the disease depends on the age of onset and rate of progression of this process.