Episode 10: The genetic effect of marriage between relatives (4/5)
The second study was about the rate of chromosomal defects in children from related couples (Naguib, 1984); after the announcement of many departments, the existence of a relationship between consanguineous marriage and chromosomal defects.
He made this assumption, based on the presence of more than one individual in the same family suffering from chromosomal defects; the cause of which was attributable to the presence of a recessive gene, due to non separation of chromosomes at meiosis, and that this gene shows its impact in consanguineous marriage, which leads to (the presence) of this gene in double dose in the offspring issued from consanguineous marriages.
One hundred families were randomly selected. It was shown from (cytological) analysis that one of the family members was suffering from a chromosomal defect. The Centre carried out statistical analysis on this sample. By contrast, a hundred other families were chosen statistically as a comparative sample. It concluded the following:
Firstly: that the proportion of consanguineous marriages was 46% among patients and 34% in the comparative sample.
Secondly: there is no statistically significant difference in abortion or stillbirth, in the sample resulting from consanguineous marriages, compared to the sample resulting from marriages between non-relatives.
Thirdly: There is a statistical difference between the age of the mother, in the sample resulting from consanguineous marriages and the one resulting from exogamous marriages, and this difference is considered by many scientists as the causative in chromosomal defects.
Fourthly: The researcher analyzed these results by several statistical methods, assuming that consanguineous marriage has an effect in chromosomal defect, but the results repudiated this assumption.
From this, the researcher concluded the nonexistence of such a gene, and thus consanguineous marriage does not play an important role in such diseases, and if it had a role, it is not through the presence of a recessive gene. These results are in agreement with those reached by some scientists, such as: "Kwiterovich et al. 1966; Matsunaga, 1966; Forssman and Akesson, 1967; Stene, 1977 and Juberg and Daois, 1978)".
Then they said: “And here, it is worthwhile mentioning the importance of the period consanguineous marriages has been in practice in the community, and whether is it an ancient historic phenomenon, widely spread, or recent and infrequent? If this practice had been in existence since ancient times, then consanguineous marriage must have led – a long time ago - to the manifestation of diseases, which are often fatal; in the sense that it actually rid the society of hereditary disease-transmitters, and cleansed it over time from disease-causing genes. But if consanguineous marriage was prohibited in the society or rare, then this prohibition will lead to the survival of many individuals carrying the disease-causing genes. Therefore, the chance for possible intermarriage of two non-relatives carrying the disease-causing genes for a particular disease will be considerable; hence, the emergence of this disease in these communities. The best example of this disease is Cystic Fibrosis of the Pancreas. This disease is governed by a recessive gene, common in Britain, despite the scarcity of consanguineous marriages. This is due to the presence of a high proportion of carriers of the disease-causing gene, as explained previously, which leads to increased chance of intermarriage between the carriers of this disease, and therefore its manifestation among their progeny.