- Cousin Marriages: Between Tradition, Genetic Risk and Cultural Change ed. by Shaw Alison, Raz Aviada
As the title suggests, this book offers a “hybrid perspective” on the notion of consanguinity. The authors begin with a strict scientific definition: consanguinity is the relatedness between descendants of a common ancestor as measured by “what is usually described as their coefficient of inbreeding (F)”, expressed by the probability that two alleles on one of an individual’s chromosomally located genes will be an identical copy of the corresponding allele of a common ancestor. For example – and this is the most frequently encountered case in human populations – the F coefficient for individuals born to parents who are first cousins is 0.0625, meaning that they “will have inherited identical genes at 1/16 of gene loci” by way of the ancestor their parents share. This condition is called “homozygosity”. Once these basic facts have been presented, the book offers a series of contributions that discuss various aspects of consanguinity.
One of them is consanguineous marriage, known to increase the risk of genetic disorders. Two main factors are discussed in this connection: insularity and preferential marriage. Insularity refers to a situation in which there is very little migration-related exchange or where spousal choice is limited to a relatively closed group of individuals likely to belong to the same line. Preferential marriage is a response to cultural considerations and hopes or expectations that union between kin will bring social or economic benefits. The book offers well-documented in-depth studies of Mediterranean and Middle Eastern populations; that is, societies where consanguineous marriage is frequent and results in relatively high frequencies of such genetic disorders as sickle-cell disease and β-thalassaemia.(1)
Another aspect covered in detail is the public health strategies that different countries develop to deal with the demographic and economic problems caused by genetic disorders. The examples of Cyprus and Sardinia are of particular interest. β-thalassamaeia prevalence has fallen considerably since the implementation of programmes for detecting individual carriers of mutated alleles. The programmes primarily consist in genetic counselling for couples at risk of having a sick child, to enable them to make reproductive choices. Another compelling example is the programme in Israel for Orthodox Jewish communities where marriages are family-arranged and abortion is prohibited. These groups are affected by Tay-Sachs disease, a deadly genetic disorder that usually appears in early childhood.(2) The programme was set up in the early 1980s and involves prenuptial genetic testing in which the rabbinical authorities have a role to play; it has resulted in a clear reduction of Tay-Sachs among Ashkenazi Jews. [End Page 368]
One of the major strengths of Shaw and Raz’s book – in addition to the clarity of the contributors’ presentations and the diversity of situations discussed – is to show that programmes to combat consanguinity-related genetic disorders can only be successful if they integrate local cultural factors and popular beliefs into what are very often highly technical medical procedures. [End Page 369]
1. Sickle-cell disease and β-thalassaemia are genetic diseases affecting the blood. In the first, the shape of red blood cells changes; in the second, not enough haemoglobin is produced.
2. Tay-Sachs disease is a genetic disorder affecting metabolism. Insufficient production of a particular enzyme leads to abnormal accumulation of a particular lipid in the nervous system.