MYOPATHY AND HYPERTROPHIC CARDIOMYOPATHY WITH SELECTIVE LYSIS OF THICK FILAMENTS

We present a undescribed condition in a girl who died at 8 years of hy pertrophic cardiomyopathy. Muscle and endomyocardial biopsies disclose d a selective loss of thick filaments ultrastructurally. In muscle bio psy histochemical abnormalities of myofibrillar ATPase were confined t o type 1 fibres. Gel electrophoresis of muscle homogenate showed no qu alitative abnormalities of slow and fast myosin heavy chains (MHC) and light chains, and the amount of the different myosin isozymes was in agreement with histochemical myofibrillar ATPase findings. The pathoge netic mechanisms have not been elucidated in this case but we suspect an abnormality of the beta-cardiac MHC gene, the only gene expressed i n the heart and in type 1 skeletal muscle fibres.