EXPRESSION OF LAMININ SUBUNITS IN CONGENITAL MUSCULAR-DYSTROPHY

The expression of laminin subunits M, A, B1 and B2 was studied immunoc ytochemically in 25 cases of classical congenital muscular dystrophy ( CMD), 11 hypotonic infants, 20 cases of a variety of inherited and acq uired neuromuscular disorders, and 11 controls. Merosin, as indicated by labelling for the M chain, was deficient in 12 (48%) of the cases o f classical CMD. Seven cases had no detectable labelling for the M cha in whereas five showed traces, including three cousins from the same f amily. This suggests that very low expression may relate to a possible difference in the molecular defect, compared with cases completely de void of the M chain. The A chain was abundant in regenerating fibres a nd in immature fibres expressing fetal myosin. In all merosin-deficien t cases the A chain was overexpressed but this was not due to immaturi ty. A secondary reduction in sarcolemmal expression of the B1 chain oc curred in five merosin-deficient cases, whilst expression in vascular tissue was normal. B1 was also reduced in one merosin-positive case of CMD, suggesting that other subunits may be involved in other forms of CMD. No differences in the expression of the B2 chain were observed i n any of the cases studied. No abnormality in laminin subunits was fou nd in controls or other neuromuscular disorders.