In order to investigate if the same apparent decrease in dystrophin negative fibers with aging observed in mouse mdx female heterozygotes also occurs in carriers of the DMD and BMD gene, we have studied the muscle of 29 DMD carriers (19 adults and 10 young daughters of obligate carriers, including 3 manifesting carriers) and 5 adult asymptomatic heterozygotes for Becker dystrophy (BMD). All young DMD possible carriers and 11 of 24 adult DMB/BMD heterozygotes had increased serum enzymes activities. A population of dystrophin negative fibers, more evident with the use of the C-terminal antibody, was seen in the three manifesting and in a 9-yr-old possible DMD carrier. In the remaining females, a positive immunohistochemical pattern of dystrophin, which did not differ from normal controls, was observed. Our results suggest that: (1) the increased population of dystrophin negative fibers reported in young mdx female heterozygotes was not seen in young DMD carriers, aged 6-17 yr; and (2) abnormalities in dystrophin immunostaining are not easily observed and are more frequent in manifesting carriers, when the muscle is grossly altered.

A deficiency or abnormality of the protein dystrophin (located at the surface membrane of muscle fibers) was recently shown to be the cause of Duchenne (DMD) and Becker (BMD) muscular dystrophies. Immunohistochemistry was used to study the dystrophin pattern in frozen sections obtained from muscle biopsies of 34 patients affected with different types of muscular dystrophies, 15 females belonging to families with DMD (11 obligate carriers and four of their daughters), three BMD obligate carriers and four normal controls. In normal muscle, a strong positive reaction was observed, in a continuous layer at the sarcolemma of the fibers. In 20 DMD patients, no reaction was seen in the majority of the fibers, although in most of the cases, a partial staining was seen in a portion of them (4 to 30%). In eight among ten patients with BMD, an apparently normal immunostain was seen, while in the remaining two the reaction seemed weaker. In four patients with limb-girdle muscular dystrophy, despite the typical histopathological abnormalities, a strong positive reaction was seen in all muscle fibers. In all females-at-risk for DMD, a normal positive strong reaction was seen in all fibers, with no difference among adult and young carriers or those with elevated serum enzymes as compared with heterozygotes with normal serum enzyme levels. The importance of these results, for differential diagnosis of some types of muscular dystrophies and for enhancing carrier detection and genetic counseling are discussed.

The localization of the protein dystrophin was studied using the immunofluorescence method, in muscle biopsies from 74 patients affected by different types of muscular dystrophy and 4 normal controls. In 15 patients with limb-girdle muscular dystrophy (LGMD) the pattern was indistinguishable from normal. Among 42 Duchenne patients (DMD), 3 were totally negative and 39 showed a variable proportion (4-30%) of partially labelled fibers. With one exception 17 Becker dystrophy patients (BMD), showed a positive sarcolemmal reaction. A diffuse reaction inside the fibers, which was not observed in normal controls, was seen in the majority of DMD and also in some of the BMD patients. Based on these observations it is suggested that in DMD, a small quantity of protein is still present or there is a cross-reaction with other proteins which share some homology with dystrophin. The present results suggest that it is possible to make a differential diagnosis between DMD and BMD through dystrophin immunohistochemistry. However, to distinguish between patients with BMD and LGMD phenotypes, or DMD and outliers, complementary immunoblot studies and quantitative determination of dystrophin are necessary.