[Two long-living brothers of dystrophin-related muscular dystrophy with an in-frame deletion of exon 3 of the dystrophin gene--clinical features and diagnosis].

Two long-living brothers of dystrophin-related muscular dystrophy with an in-frame deletion of exon 3 of the dystrophin gene were described. Weakness of the lower extremities and pseudohypertrophy of calf muscles began at the age of 2 years in the elder brother and 4 years in the younger brother, respectively. Clinical symptoms progressed rapidly and both of them lost ambulation and became wheelchair bound at the age of 11-12 years. However, the progression of the disease process slowed in late teens, and now at the age of 36 and 33 years, respectively, they do not have respiratory or cardiac insufficiency, although they are disabled severely. Southern blotting with the entire dystrophin cDNAs, cDNA 1-2a, 2b-3, 4-5a, 5b-7, 8, and 9-14, revealed a single deletion of exon 3 in the 2 brothers. The mother was shown to be a heterozygote for this mutation. The unique clinical features of these brothers were presumed due to the following 2 factors: (1) a single deletion of exon 3 is an in-frame deletion of the dystrophin gene, and (2) exon 3 corresponds to a unique domain of the dystrophin molecule; the amino-terminal region which is highly homologous to the actin-binding-region of alpha-actinin. We consider that these 2 brothers are compatible with the so-called frame-shift hypothesis of Duchenne/Becker muscular dystrophy (DMD/BMD) phenotype, although they are diagnosed DMD by the classification method based on the patients' age of becoming permanently wheelchair bound.