Abstract
Reed (1954) suggested the investigation of children from incestuous unions as a method for calculation of the detrimental heterozygosity of man. Some studies of latent genetics load in man have been based on the comparison of health status of incestuous children with their half-sibs born to the same mothers in matings with nonconsanguineous partners (Adams and Neel, 1967; Seemanova, 1971).
These studies were limited to the detection of autosomal-recessive genes leading to abnormal phenotypes or mental deficiency in homozygotes. The highest coefficient of inbreeding in human beings is 1/4 in offspring of incestuous matings: hence, the high proportion of affected homozygotes and low incidence of affected individuals among their maternal half-sibs.
Mental deficiency in incestuous children represents not only cases of simple recessive inheritance. Recently, we observed three incestuous families in which fragile X syndrome was detected.