Tr David-Padilla, Carmencita Cutiongco-de la Paz, Eva Maria Chiong, Mary Anne D. Charcos, Grace S. Cadag, Nene S. text monographic eng

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A review of the results at the Medical Genetics Unit, University of the Philippines (UP) College of Medicine (1991-1999) and at the Institute of Human Genetics, National Institutes of Health (IHG-NIH), University of the Philippines Manila (1999-2007) showed that Down Syndrome (DS) or Trisomy 21 accounted for 68.0% of all abnormal results detected. Trisomy 21 is caused by the presence of an extra chromosome 21 and the risk increases with advancing maternal age. There are 3 types of DS- full trisomy 21, mosaic trisomy 21 and translocation DS accounting for 88.3%, 7.2% and 3.3%, respectively. About 25% of translocation DS are familial and 75% are de novo. The familial cases are offspring of parents who are carriers of a balanced translocation involving chromosome 21 and another chromosome. This confers an increased risk of recurrence in subsequent pregnancies and the identification of such families is crucial. If the mother is a balanced carrier of a t(13/14/15/22;21), there is about a 12% risk for another DS child to be born in each subsequent pregnancy. If the father is the carrier, the observed risk drops to about 3% for DS. However, for translocation of 2 chromosome 21 [t(21:21)] which accounted for 50.0% of translocations detected, the implications will be different. A parent who is a balanced carrier of a t(21:21) will only have 2 outcomes for the pregnancy, unbalanced translocation DS and a lethal monoscomy. Carmencita David-Padilla [and four others] In: Acta Medica Philippina, 2009 vol 43 (1) pages: 12-15 Down Syndrome Translocation, Genetic 210220 20210716145605.0 D0001J000090