Clustering of trisomy 18 in Kuwait: Genetic predisposition or environmental?

Background: This study describes 59 newborns with regular trisomy 18 (Edwar ds' syndrome, T18) who were ascertained clinically and cytogenetically at t he Kuwait Medical Genetic Centre from 1994 to 1997, out of 118 T18 cases id entified from 1980 to 1997. Materials and Methods: T18 cases were ascertained clinically and cytogeneti cally shortly after birth. In addition to assessing the T18 birth prevalenc e rate and confidence limits during the years 1994-1997, we investigated th e possible etiological factors by a case-control study with normal healthy newborns. Studied factors included gender, parental age, birth order, abort ion, clinical variables (presentation, amniotic fluid and mode of delivery) , and survival. Results: The average T18 birth prevalence rate during the period was 8.95 p er 10,000 live births (95% confidence limits 6.66-11.23). The T18 cases wer e mostly females, with a male:female ratio of 1:2.1, and the majority (53%) died before the second week of life. Maternal age above 30 years was found to be a significant factor for T18. Conclusion: This high T18 birth prevalence rate suggests clustering of T18 in the highly inbred population of Kuwait. Such clustering may indicate a p ossible environmental, and to a lesser extent, genetic predisposition to an euploidy nondisjunction.