Effects of consanguinity on pre-reproductive mortality: does demographic transition matter?

The aim of this study was to investigate whether there is an increase on premature deaths due to genetically determined factors at the beginning of a demographic transition. We also analyzed the effects of parental consanguinity on offspring mortality from an epidemiological viewpoint, using parish records for family reconstitution in a Basque population (1800-1990). Among the offspring of unrelated parents, 13.1% died before their first year of life (infant mortality), and 22.8% died before the age of 16 (pre-reproductive mortality). Significant increases in both infant (23.6%) and pre-reproductive (38.5%) deaths were found among the progeny of first cousins or closer relatives, 1C (F > or = 0.0625). The corresponding relative risks of mortality were 1.79 (95% confidence limits: 1.37-2.28) and 1.68 (1.38-2.01), respectively. Estimates of the population attributable risks indicate that 4% of pre-reproductive mortality is ascribable to consanguineous unions, although kinships other than 1C produced only slight increases in offspring mortality. Evidence on the relationship between the demographic transition and the increase in premature deaths due to genetic factors was obtained through a principal component analysis (95.1% of variance accounted for). During the initial stages of the demographic transition, the population experienced substantial elevations in mean family size, natural increase of the population, frequency of close consanguineous matings (1C), and death rate due to congenital anomalies and perinatal diseases. These findings are of interest for the health services of many developing societies in Asia, Africa, and Latin America, which are nowadays immersed in the demographic transition process.