A ring D chromosome in association with Down's syndrome-like phenotype.

The first ring chromosome was described by Morgan (1933) 9 and originated from a crossing-over between attached X-chromosomes containing an inversion in Drosophila. Since then ring chromosome have been studied specially in Drosophila, maise and Man. Interest on ring chromosomes arises from the fact that some information may be disclosed regarding mechanism of chromatid splitting during mitosis and meiosis as well as on sister-strand crossing-over (McClintock, 1 9 3 8 7 ; Smith White et al., 1 9 6 3 1 0 ) . In man, ring chromosomes might be valuable in assigning loci to specific chromosomes not only because of the original deletion involved in the formation of the ring but also because of the deficiencies and duplications that might arise during mitotic divisions (Lejeune, 1967) 6 . Thus, studying patients with a ring D chromosome, the locus that determines the synthesis of the alpha chain of haptoglobin has been shown to belong to the chromosome 13 (Gerald et al . 4 , 1967; Bloom et al. 2 , 1967). The present paper reports on a patient with Down's syndrome-like characteristics and whose caryotype analysis revealed a mosaicism involving a ring D chromosome.