[The evolution of epilepsy in the most common genetic forms with mental retardation (Down's syndrome and the fragile X syndrome)].

Some chromosomal abnormality syndromes carry a higher risk of seizures than that found in the general population. Down's syndrome is considered to be the first and the most frequent chromosomal abnormality causing mental retardation. In spite of numerous reports and epidemiological surveys, the outcome of epileptic syndromes in patients with Down's syndrome (DS) is still largely unknown. We retrospectively studied 34 DS patients with epilepsy (14M; 20F). Epileptic syndromes were classified as: infantile spasms, 10 cases, i.e. 31%; Lennox-Gastaut syndrome, 5 cases, 15.5%; symptomatic generalized epilepsy, 1 case; idiopathic generalized epilepsy, 6 cases, 17.6%; partial symptomatic epilepsy, 10 cases, i.e. 31%. In 2 patients the epilepsy was unclassifiable. In all the patients the following evolutive particularities were noted: a) the infantile spasms to have a relatively mild prognosis, as 8/10 patients remained seizure-free, 3 of whom without treatment; b) no patient experienced febrile convulsions prior to the onset of epilepsy; c) Lennox-Gastaut syndrome had a relatively late onset (mean age 10 years, range 8-11.5); d) 7 patients (20.6%) developed reflex seizure. The fragile X syndrome is considered to be the second most frequent chromosomal abnormality causing mental retardation. The prevalence of epilepsy varies from 9.1% to 45% in the different series. In order to evaluate the prevalence rate of epilepsy and the previously hypothesized association with a particular electroclinical picture, we retrospectively studied 90 fragile X syndrome patients (80M, 10F) aged 4 to 25 years (mean age 13y6m).(ABSTRACT TRUNCATED AT 250 WORDS)