FREEZE-FRACTURE ANALYSIS OF MUSCLE PLASMA-MEMBRANE IN BECKERS MUSCULAR-DYSTROPHY

The intramembranous particle (IMP), orthogonal array (OA) and orthogon al array subunit particle (GASP) densities in skeletal muscle plasma m embranes from eight patients with Becker's muscular dystrophy (BMD) we re analysed by the freeze-fracture technique. The results showed almos t normal IMP density with the significant decrease of OA and OASP dens ities in BMD. The group mean densities +/- SE of IMPs on the protoplas mic faces with and without OASPs, and on extracellular faces/mu m(2) w ere 2137 +/- 207, 1839 +/- 68 and 895 +/-108, respectively in controls ; whereas those of BMD were 1989 +/- 259, 1837 +/- 203 and 900 +/- 239 , respectively (P > 0.1 by two-tailed t-test). The group median densit y of OAs and their pits/mu m(2) was 4.89 with mid-ranges (25 similar t o 75% values of the counts) of 2.66 similar to 10.18 in controls; wher eas that in BMD was 2.15 with mid-ranges of 1.14 similar to 4.31 (P < 0.01 by Wilcoxon rank-sum test). The group mean density +/- SE of OASP s in controls was 15.99 +/- 1.83; whereas that in BMD was 13.47 +/- 1. 07 (P < 0.01 by two-tailed t-test). However, the diminution of OA and OASP densities in BMD muscle plasma membranes was not as severe as in Duchenne's muscular dystrophy. There was a relationship between OA den sity and clinical severity in BMD patients; the decrease of OA density in a severe BMD patient was more marked than that in mildly affected BMD patients. Therefore, it seems that marked depletion of OA density may lead to the severe disability in muscular dystrophies.