Search for ethnic, geographic, and other factors in the epidemiology of Down syndrome in South America: Analysis of data from CLAMC Project, 1967-1997

We have analyzed data on 3,157 cases of Down syndrome (DS) from nine South American countries in consecutive series of hospital live births over a 30- year period, with particular emphasis on possible ethnic or geographic vari ations in maternal age-adjusted incidence. The data constitute the largest series of DS cases assembled to date from an area lacking advanced health c are systems. Absolute incidence rates were estimated from total hospital li ve births; relative rates were estimated from matched case-control data usi ng conditional logistic regression. Maternal age-adjusted rates were closel y similar to those reported elsewhere, and showed little or no dependency o n other factors investigated, including paternal age, birth order, ancestra l origin, country of birth, maternal educational level, maternal ABO and Rh esus blood groups, interval to and outcome of mother's previous pregnancy, and parental consanguinity. The absence of an effect of high birth order wa s particularly notable because of the relatively large number of grand mult ipara resulting from high fertility in this population. The study adds to a body of evidence suggesting that maternal age-adjusted DS rates vary littl e across human populations, and are therefore unlikely to be greatly influe nced by genetic or environmental factors that differ between them. An unusu al finding was of a markedly lower sex ratio (98 males per 100 females) tha n has been reported in other DS samples. (C) 2001 Wiley-Liss, Inc.