Journal of Prenatal Diagnosis and TherapyJournal of Prenatal Diagnosis and Therapy
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Year : 2010  |  Volume : 1  |  Issue : 1  |  Page : 14-19

Genetic counseling in chromosomal abnormalities

1 Department of Obstetrics and Gynecology, Nowrosjee Wadia Maternity Hospital, Mumbai, Maharashtra, India
2 Mediscan System and Fetal Care Research Foundation, Chennai, India
3 Surendar Genetic Laboratory & Research Centre, Chennai, Tamil Nadu, India

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Flat No 9, Vaitarna Building, Anushaktinagar, Mumbai, Maharashtra 400 088
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DOI: 10.4103/0976-1756.62136

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Pure trisomy due to nondysjunction of chromosome 21 is responsible for 96% of Downs with a recurrence risk of less than 1%. Parental karyotype is not required in nondysjunction type of trisomies. Majority of fetuses with Trisomy 13, 18, monosomy XO and triploidy display major malformations on USG. Recurrence for all of the above nondysjunction numerical aberration is low. Hence, pregnancies with previous history of any of the above confirmed on fetal karyotype, can be followed up by serial ultrasound scans. Translocation of chromosome 21 (4% of Downs), the recurrence risk varies between 10-25% if one parent is a carrier of a translocation. The risk of unbalanced translocation in the offspring will depend on the type of translocation in the parents, which parent is involved and whether translocation is between homologous or non homologous chromosome. Once an unbalanced translocation in the fetus / child has been identified, parental karyotype is essential. More than 50% of translocations in fetus occur denovo. So if parents have a normal karyotpe, no matter what the translocation in the fetus, recurrence risk is minimal <1%.

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