P phenotype observed in two generations of Tunisian family with a high rate of inbreeding.

A p phenotype was discovered in a Tunisian woman and in three of her seven children. This paradoxical result challenges the known hypotheses on this phenotype, which generally recognise that it is determined by the existence of a very rare allele in a double dose. The computation of the coefficient of inbreeding of these subjects showed that repeated intermarriages increased the coefficient of kinship of the propositus and her husband to 0.116 (if unknown women of the ancestry were assumed to be different for each child) through 0,1362 (if unknown women of the ancestry were assumed to be the same for sibs). Therefore inbreeding was proved to be so high as to induce the presence of a recessively defined phenotype in two successive generations. Moreover, the search for probability of origin of genes of the last generation showed that the BCH ancestor was probably the carrier of the p allele.