RESUMO
We report in this article, analysis of the etiology of 510 observations of mental retardation seen in genetic service. The more part of our patients are children addressed to us for cytogenetic analysis or for opinion diagnosis by reason of a dysmorphic aspect. Etiological diagnosis has been determined in 441 cases. The mental retardation was chromosomal in origin in 426 cases, with in particular 398 children with Down syndrome, eleven trisomly 18, three syndromes of Wolf-Hirschhorn, one syndrome of Williams, three anomalies of gonosomes and ten chromosomal structure aberration. The mental retardation was of gentic origin in 15 patients with a transmission linked to the X chromosome in 8 cases, autosomal recessive transmission in 6 cases and autosomal dominant transmission in 1 case. The knowledge of the precise etiology of the mental retardation permits to pick up the handicapped person and especially it allows the geneticist to lavish an adequate genetic advice to the family members