title: Tandem duplication chromosome 21 in the offspring of a ring chromosome 21 carrier.
abstract: A direct tandem duplication chromosome 21 was found in a boy with Down's syndrome. The proband's mother and grandmother both carried a ring chromosome 21. The observed duplication chromosome in the child may be explained either by recombination between the maternal ring and the mother's normal chromosome 21 or by break of a double-sized ring chromosome 21.
mesh_terms: D002675:Child, Preschool; D002869:Chromosome Aberrations; D002891:Chromosomes, Human, Pair 21; D004314:Down Syndrome / Q000235:genetics*; D006579:Heterozygote; D006801:Humans; D008297:Male; D010375:Pedigree; D012303:Ring Chromosomes