In 1964 de Grouchy, Royer, Salmon, and Lamy described a deaf and mentally retarded microcephalic girl in whom the long arm of one No. 18 chromosome was about half its usual length. Since then two other microcephalic children, a boy and a girl, have been found to have this chromosome aberration (Lejeune, Berger, Lafourcade, and R6thore, 1966). Lejeune suggested on the basis of their findings tha...
