[X chromosome-linked mental retardation with fragile X chromosome and macro-orchidism].

Description of the first Swiss family with the new syndrome of X-linked mental retardation. The three brothers described are the first of all males traced back for four generations to be affected. In two of the brothers macroorchidism and the fragile X-chromosome were demonstrated, while the third brother died before diagnosis. As expected, the fragile X was not demonstrable in the 75-year-old mother of the three brothers.