title: Trisomy 21 mosaicism in gonads with unexpectedly high recurrence risks.
abstract: The recurrence risk for Down syndrome (DS) is about 1% in case of a previous offspring with trisomy 21 and minimal in case of a de novo (21;21) translocation. We have monitored 1,211 pregnancies in the first and second trimester after a prior occurrence of trisomy 21. Six couples had a trisomy 21 fetus in a subsequent pregnancy. We studied their lymphocytes, fibroblasts, and in one case ovaries, to detect parental mosaicism for chromosome 21. We detected mosaicism in 2 parents with 3 and 4 pregnancies, respectively, in which trisomy 21 was found. In one it was present in 47% of cells from the ovaries. Another couple with a pregnancy monitored because of a first child with a de novo (21;21) translocation had normal chromosomes themselves and one normal child, but 2 more pregnancies with a (21;21) translocation. It is concluded that thorough cytogenetic study of parents is indicated after 2 pregnancies with regular or translocation trisomy of chromosome 21. Genetic counseling should consider the possibility of an elevated recurrence risk due to gonadal mosaicism in one parent.
authors: Department of Clinical Genetics, University Hospital Dijkzigt, Erasmus University, Rotterdam, The Netherlands.
authors: E S
authors: ES
authors: Sachs
authors: M G
authors: MG
authors: Jahoda
authors: F J
authors: FJ
authors: Los
authors: L
authors: L
authors: Pijpers
authors: J W
authors: JW
authors: Wladimiroff
mesh_terms: D000328:Adult; D000818:Animals; D004314:Down Syndrome / Q000175:diagnosis / Q000235:genetics*; D005260:Female; D006801:Humans; D008297:Male; D051379:Mice; D009030:Mosaicism / Q000235:genetics*; D010053:Ovary / Q000648:ultrastructure*; D010375:Pedigree; D011296:Prenatal Diagnosis; D012307:Risk Factors; D014178:Translocation, Genetic