[The 48,XXXX syndrome: study of psychomotor development from birth to 11 years of age and review of the literature].

A child with four X chromosomes is described. This case and the literature review allow to underline the mental retardation and some other "major" but inconstant signs that are extremely helpful for the early clinical diagnosis. They are hypertelorism, epicanthal fold and genital anomalies. The mental evolution is assessed on an eleven year period. The bad results concern particularly the child's use of language and the complicated works. They become worse with time. The additional X chromosomes Mary Lyon inactivation, perhaps incomplete, is discussed because its determinism. Enzymatic measuring out is our approach to this problem.