Geographic distribution of consanguinity in Europe.

Average consanguinity (alpha) of 20 large regional or national samples derived from Roman Catholic Dispensations or state archives shows a strong negative relationship with latitude (r = -0.738; P less than 0.001) which seems best explained by cultural-historical factors. Isolates show no such pattern and are more variable in their inbreeding levels. Two-way analysis of variance shows the sample division by population size to be significant, the division by geography to be not significant, with no significant interaction between the two factors. In a one-way analysis of variance only the mainstream samples showed significant geographic differences (P less than 0.001). There is no such geographic association in Japan which has greater cultural and historical homogeneity. The clinical patterning in average consanguinity may bias frequency estimates of rare alleles, including genetic disorders.