Abnormal adenine metabolism of erythrocytes in Duchenne and myotonic muscular dystrophy

Abstract

DUCHENNE muscular dystrophy (DUD) and myotonic muscular dystrophy (MYD) are inherited as sex-linked recessive and autosomal dominant traits, respectively. Although the primary manifestation is progressive muscle weakness, multiple organ systems seem to be affected. Cardiac abnormalities and mental retardation are described in both conditions, and defects in immunoglobulins and endocrine functions have been reported in MYD¹. The primary inherited metabolic defect is unknown, but there is evidence to suggest an abnormal sarcolemmal membrane¹. The possibility that muscle disease, especially involving membrane dysfunction, is reflected in the erythrocytes is supported by the demonstration of defective phosphorylation in the erythrocytes of patients with DUD² and MYD³. In DUD the erythrocytes appear abnormal in the scanning electron microscope⁴ and in MYD electron spin resonance reveals abnormal membrane fluidity. There are other reasons to study erythrocytes, for the direct study of muscle is hampered by the need for repeated biopsies and by atrophy and fibrous tissue, which can cause secondary biochemical changes. Furthermore, the yield of isolated sarcolemmal membranes is often small and impure. In DUD, there is a 30% reduction in muscle ATP⁶ and an abnormal ATP : ADP ratio of 1.57. Whether this is a significant defect or is a result of secondary changes in the muscle has yet to be clarified. We report here that the intracellular phosphorylation of adenine nucleotides derived from adenine incorporated by the erythrocytes is abnormal in both DUD and MYD.