title: Structural chromosome abnormalities in Down syndrome: a study of two families.
abstract: Two families were ascertained through a proband with Down syndrome and a structural rearrangement involving two chromosomes 21. It is suggested that in one patient the chromosome is an isochromosome formed by misdivision of the centromere of a maternal telocentric chromosome 21 and that in the other a Robertsonian translocation involving chromosome 21 was inherited from the mother, who is a 46,XX/46,XX, -21,+t(21q21q) mosaic. The origin of the mosaicism is discussed and considered to be likely to be the result of breakage and reunion at the chromatid, rather than the chromosome, level.
mesh_terms: D000328:Adult; D002904:Chromosomes, Human, 21-22 and Y; D004314:Down Syndrome / Q000235:genetics*; D006801:Humans; D007962:Leukocytes / Q000648:ultrastructure; D008297:Male; D009030:Mosaicism; D010375:Pedigree; D014178:Translocation, Genetic