CONSANGUINITY

All human societies in existence, prohibit the matings of first - degree relatives (incest). Marriages between relatives further than brothers. sisters and parents is not necessarily prohibited, but the dividing line between legal and illegal varies between countries. In certain countries like the USA, Uncle - Niece, Aunt - Nephew and first cousin marriages are forbidden by law. In some countries like India, Pakistan, Japan and the Middle East it is even encouraged and about 30% of all marriages are such unions. In Sri Lanka the laws prohibit incest and marriages between certain blood relatives like Uncle and Niece and Aunt and Nephew and those with step brothers and sisters but not those between first cousins.

A consanguineous couple are at an increased risk for autosomal recessive and multifactorial traits, including several congenital malformations. The usual risk of a serious disease or major malformation is 5% which is double the population risk. Such marriages should be discouraged and in the case of a pregnancy in such a union, detailed ultrasound scanning may have to be considered. Special screening may be suggested in the case of a previous history of a particular problem or factors like ethnic origin. If an autosomal recessive problem is present in a previous pregnancy the relevant recurrence risks of 25% will have to be given.