[Chromosomal mosaicism in the r (15) syndrome]

Clinical, biochemical and cytogenetic description of a boy with a karyotype 46, XY, r(15) is given. The data obtained suggest that the phenotypic abnormalities of the propositus may be conditioned by the following reasons: 1) deletion of some genetic material from the chromosome 15; 2) position effect of the genes situated near the break points; 3) mosaicism of the chromosome sets owing to sister chromatid exchanges in the ring chromosome. Some clinical traits (nanism and mental retardation) of the children with a ring chromsome 15 confirm the originality of the r(15) syndrome.