Ad. Carothers et al., International variation in reported livebirth prevalence rates of Down syndrome, adjusted for maternal age, J MED GENET, 36(5), 1999, pp. 386-393
Citations number
53
Categorie Soggetti
Research/Laboratory Medicine & Medical Tecnology","Molecular Biology & Genetics
Reported livebirth prevalence of Down syndrome (DS) may be affected by the
maternal age distribution of the population, completeness of ascertainment,
accuracy of diagnosis, extent of selective prenatal termination of affecte
d pregnancies, and as yet unidentified genetic and environmental factors. T
o search for evidence of the latter, we reviewed all published reports in w
hich it was possible to adjust both for effects of maternal age and for sel
ective termination (where relevant).
We constructed indices that allowed direct comparisons of prevalence rates
after standardising for maternal age. Reference rates were derived from stu
dies previously identified as having near complete ascertainment. An index
value significantly different from 1 may result from random fluctuations, a
s well as from variations in the factors listed above. We found 49 populati
on groups for which an index could be calculated. Methodological descriptio
ns suggested that low values could often be attributed to under-ascertainme
nt. A possible exception concerned African-American groups, though even amo
ng these most acceptable studies were compatible with an index value of 1.
As we have reported elsewhere, there was also a suggestive increase in rate
s among US residents of Mexican or Central American origin. Nevertheless, o
ur results suggest that ((real)) variation between population groups report
ed to date probably amounts to no more than +/-25%. However, reliable data
in many human populations are lacking including, surprisingly, some jurisdi
ctions with relatively advanced health care systems. We Berkeley, suggest t
hat future reports of DS livebirth prevalence should routinely present data
that allow calculation of an index standardised for maternal age and adjus
ted for Berkeley, elective prenatal terminations.