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Consanguinity - a common human heritage? The effects on the health and well-being of Indian populations

Rao, N.A., Savithri, H.S., Devi, A.R.R. and Bittles, A.H. (1998) Consanguinity - a common human heritage? The effects on the health and well-being of Indian populations. In: Balasubramaniam, D. and Rao, N.A., (eds.) The Indian Human Heritage. Universities Press (India) Limited, Hyderabad, India, pp. 11-21.

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Th etopic of inbreeding in human populations has long fascinated geneticists, sociologists and philosophers. Among the populations throughout North and sub-Saharan Africa, the Middle East, and Central and South Asia, marriages between couples related as second cousins or closer, still account for 20% to over 50% of all unions. By comparison, in Western societies generally negative views on close kin marriages have predominated, due mainly to historical, social and religious prejudices. As a result, unions of this type are rare in the West.

It can be predicted that autosomal recessive traits will be more common in the progeny of consanguineously related parents, since they have a greater chance of inheriting identical copies of a mutant gene or genes from a common ancestor. However, in communities with a long and unbroken history of consanguineous unions, it has been hypothesised that deleterious genes would have been substantially eliminated from the gene pool. In addition, there is the suggestion that factors such as changing family structure and urbanisation would result in a large decrease in close kin marriages.

We have attempted to assess the effect of consanguinity on the prevalence of genetic disorders, and more generally on reproductive behaviour and post natal mortality. Between 1980 and 1989, we examined some 107,500 newborn children in Bangalore and Mysore as part of a systematic neonatal screening programme. In addition, mentally retarded and sick children referred to us with suspected genetic disorders were investigated. Contrary to earlier prediction, consanguinity was still widely prevalent among Hindus (33.5%) with a mean inbreeding coefficient (F) of 0.0333, Muslims (23.7%) with F=0.0160, and Christians (18.6%) with an F value of 0.0173. The comparative value for industrialised Western populations is less than 1% consanguineous marriage, with an approximate F value of 0.0003.

Surprisingly, the prevalence of inherited amino acid disorders in Karnataka was of the same magnitude as in outbred populations, and a simple statistical analysis of the data on numbers of liveborn and living children by consanguinity class failed to reveal a significant consanguinity effect. Multivariate analysis did indicate that excess mortality was associated with consanguinity in a minority of families and a separate analysis of data collected on sick children also revealed the adverse influence of consanguinity. Paradoxically, among Vysas who do not practise consanguinity, the incidence of the autosomal disorder pseudocholinesterase deficiency was high.

It is apparent that in many earlier studies into the effects of consanguinity on fertility and prenatal and postnatal mortality, adequate allowance for socio-demographic variables was not made. Our studies have emphasised the social, cultural and economic benefits of consanguineous marriage in regions such as South India and, in assessing the needs of the minority of consanguineous families with genetic disorders, due attention should be given to these benefits. At the same time, there is an urgent need for the rapid development of appropriate medical care and genetic counselling for consanguineous and non-consanguineous couples alike.

Publication Type: Book Chapter
Publisher: Universities Press (India) Limited
Copyright: 1998 Universities Press (India) Limited
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