CLINICAL SYMPTOMS OF MYOTONIC-DYSTROPHY - EPIDEMIOLOGIC SURVEY

BACKGROUND: The presence of a local aggregation of cases of myotonic d ystrophy (MD) allows the evaluation of clinical symptoms of the diseas e in a sample in which the influence of a possible genetic heterogenei ty is decreased. METHODS: The degree of global neuromuscular handicap and the incidence and severity of four of the most characteristic symp toms (cataracts, myotonia, muscular weakness and neuropsycologic distu rbances) were studied in 183 patients with MD (146 typical adult forms , 19 neonatal, and 18 partial syndromes) in relation with the age of o nset of the symptomatology or length of disease. RESULTS: Only 8.3 % o f the patients (excluding the neonatal forms) were severely handicaped , and the degree of neuromuscular handicap depended fundamentally on t he age of onset of the disease. Cataracts and myotonia were present in 87 and 89 % of the patients, respectively. Almost all the patients ab ove the age of 40 presented cataracts. No clinical or subclinical evid ence of neuromuscular involvement was present in 11 % of the patients with MD. These patients principally corresponded to the group in whom the disease initiated over the age of 50. CONCLUSIONs: The age of onse t of the symptomatology appears to be the determining factor to establ ish both the global prognosis of neuromuscular incapacity of patients with myotonic dystrophy and the explanation of the chronology of the a ppearance of the most characteristic symptoms of the disease. The pres ence of carriers without neuromuscular symptomatology is of note, this fact reinforcing the need to incorporate DNA examination in the evalu ation of asymptomatic relatives or with exclusive ocular symptomatolog y.