Clinical variability of facioscapulohumeral muscular dystrophy in Russia.

One hundred forty-two patients (66 men and 76 women) from 20 autosomal-dominant pedigrees and 3 families including 5 "sporadic" cases were examined. A great similarity of clinical manifestations among those affected was noted. Clinical variability of phenotypes reflecting various phases of the disease and different expressions of the mutant gene were always within the limits of the identical final phenotype of the disease, namely the facio-scapulo-humero-peroneal-femoro (posterior group of the muscles)-gluteal (gluteus maximus). Thus, the clinically and genetically homogeneous group of patients with autosomal-dominant descending with a "jump" form of facioscapulohumeral dystrophy (FSHD), called facioscapuloperoneal dystrophy (FSPD), was examined. Among the observed cases we did not come across any having the autosomal-dominant gradually descending form of FSHD, called facioscapulolimb dystrophy (FSLD), in which the pelvic and proximal lower limb muscles get weak earlier than in the peroneal group (anterior tibial) muscles. We could not reveal the "pure" facioscapulohumeral phenotype of muscle weakness in 142 examined patients. A "pure" FSHD does not exist as a nosological entity. It represents only the syndrome which characterizes the initial phase of FSLD, but not of the FSPD. It is quite probable that FSPD and FSLD which may be differentiated clinically are two different diseases connected with the mutation of allelic or even different genes. Linkage studies in FSPD and FSLD mapping genes would confirm this data.