EP07.05: A case of double Trisomy (T21 and T18)

Abstract

It is estimated that as much as 60% of first-trimester pregnancy losses are chromosomally abnormal and that single trisomies comprise the majority of these. In comparison, the occurrence of double aneuploidy in the same individual is a relatively rare phenomenon, and estimated to occur in only 0.21 to 2.8% of karyotyped spontaneous abortions. Pregnancy losses with double trisomies are reported to occur at an earlier gestational age and at an older maternal age than single trisomic losses. Various combinations of double trisomy in more than fifty cases have been described in the literature. The common double trisomies were the combinations of 48,XXY, +21 and 48,XXX,+18; 20 and 16 cases were reported, respectively. There was only one case report published by Grosse and Schwanitz [1977] regarding a liveborn female with double trisomy of the autosomes 18 and 21 (48,XX,+18,+21), exhibiting the clinical features of mongolism. We describe a case of double trisomy of the autosomes 18 and 21 (48,XX,+18,+21) noted from the cytogenetic studies of products of conception. A 42-year-old lady G1P0 was referred to the fetal medicine unit at approximately 11 weeks gestation with cystic hygroma. She had NIPT which showed high risk for T13 and T18. Unfortunately, she had spontaneous miscarriage, and subsequently had evacuation of retained products of conception. The cytogenetic studies of the products of conceptions showed 48,XX,+18,+21. Recurrence risk following a single trisomic pregnancy is approximately 1%. Currently, the recurrence risk following double trisomy is unknown. Case control studies are needed to determine recurrence risk following double or triple trisomic pregnancies. A significantly greater recurrence risk than that for single trisomy would have implications for genetic counselling.