[Blood relationship].

Abstract

In every-day medical practice, blood relationship of spouses hardly ever play an important part. Mainly for genetic counselors and pediatricians the question of consanguinity of a child's parents arises when either a rare, often hereditary, disorder is diagnosed for the first time in a family, or potential parents want information on the risk for hereditary diseases. A probability calculus based on the corresponding hereditary factors of the joint ancestors establishes how likely homozygotes for hereditary diseases among the offspring of [blood]-related spouses - often cousins of the first or second degree - is. Furthermore, proof of the parents' consanguinity may explain a child's unexpected hereditary disease [especially autosomal recessive disorders] and, at the same time, it means a higher risk of repetition for the affected child's desired siblings. Incest represents a special form of genetic risk; this question arises either in connection with the adoption of a child, which was conceived by an incestuous couple, or with such a child's own family planning later on. Even the parents' descent from an ethnically, politically, religiously or linguistically isolated background may gave a similar impact on the appearance of hereditary disorders: an accumulation of rare genes has to be taken into account; factors causing disorders have to be expected among these genes, too. In the following, all major aspects of the situations described above will be given in detail.