Duchenne carriers: Lactate dehydrogenase isoenzyme 5 in serum and muscle

Only two (5.5%) of 36 possible or known carriers of the gene in Duchenne dystrophy showed increased lactate dehydrogenase isoenzyme 5 (LDH-5) (U/L) in serum, while creatine kinase (CK) was increased in ten (27.8%). LDH-5 and CK did not increase simultaneously; in all five known carriers CK activity was abnormal but LDH-5 was normal. In muscle biopsy, LDH-5 was reduced in patients with Duchenne dystrophy (25.6 ± 11.5% of total, mean ± SD; controls 59.9 ± 10.3%; p < 0.01) and in two of nine possible carriers, but as a group the carriers did not differ from controls: (49.9 ± 12.1%; p > 0.05).