title: Down's syndrome in brother and sister without evident trisomy 21.
abstract: In the present report two siblings with the typical Down's phenotype but without evident full or partial 21 trisomy are described. The finding of a regular 21 trisomy in a minority of the cells in the elder patient favors the hypothesis that both present a hardly demonstrable normal/trisomy 21 mosaicism and may be examples of a constitutional familial tendency to nondisjunction in man.
mesh_terms: D000293:Adolescent; D000328:Adult; D002904:Chromosomes, Human, 21-22 and Y; D004314:Down Syndrome / Q000235:genetics*; D005260:Female; D006801:Humans; D007621:Karyotyping; D008297:Male; D009030:Mosaicism; D010641:Phenotype; D014314:Trisomy