Increased [32P]-phosphorylation of tryptic peptides of erythrocyte spectrin in Duchenne muscular dystrophy

Altered distribution of protein kinase C in dystrophic muscle cells and its modulation by liposome-delivered phospholipids

The activity and subcellular distribution of the calcium-phospholipid dependent protein kinase (protein kinase C) were studied in normal and dystrophic muscle cells in vitro. Clonal strains of satellite cells, isolated from normal and dystrophic (C57BL/6J/dydy) mice, differentiate in vitro at a comparable level (over 80% of fusion). Differentiated myotubes were homogenized and separated into a soluble and a particulate fraction. The activity of protein kinase C was assayed in both fractions, and was found to be mainly in the cytosol of normal cells, whereas it was mainly associated to the membrane fraction of dystrophic cells. This altered distribution of the enzyme was likely consequent to alterations in the phospholipid composition of the dystrophic cell membrane, since it was possible to partially revert the situation by modifying the membranes with liposome-delivered phospholipids. Splenic lymphocytes from dystrophic mice showed an altered distribution of protein kinase C similar to that observed in muscle cells. The possible biochemical basis and the functional consequences of this altered distribution of the enzyme in the dystrophic cells are discussed.

The genetic status of mothers of isolated cases of Duchenne muscular dystrophy

Classical genetic theory, based on assumed equal mutation rates in males and females, predicts that one-third of all cases of Duchenne muscular dystrophy (DMD) in a generation are born as new mutants to non-carrier mothers. Furthermore, less than half the mothers of apparently isolated cases appear to be carriers on the basis of raised serum creatine kinase levels. We have analysed the pedigrees of 61 families of DMD boys seen in the Duke Neuromuscular Research Clinic and 45 DMD families followed at the University of Virginia. The frequency of affected boys among the next born male sibs of 37 initially isolated DMD cases in two clinic populations was significantly greater than predicted by Haldane's theory (p = 0.029) and the estimated proportion of new mutant cases in the combined clinic population of 106 families was 0.127 (SE 0.111). The absence of affected males in earlier generations in families of isolated cases may be explained in part by a high ratio of male to female stillbirths and infant deaths, which was more than three times that of the normal population in this study. These data suggest that new mutant cases are less common than expected and current predictions may underestimate genetic risks in mothers of isolated cases.