Of defects in the genes

inbreeding

Of defects in the genes

Consanguineous marriages or blood-related marriages are a common practice followed across many parts of our country. When you marry biologically-related people or blood relatives, then it is a consanguineous marriage. It is most common amongst first cousins. Another type of marriage is where a maternal uncle marries his niece (sister’s daughter).

Theoretically, the risk of having a genetically-defective child is higher in the latter. Most of us do not even recognise the pros and cons of such marriages. Research and studies have shown that cousins who marry among themselves run double the risk of having birth defects in their children. The genetic or chromosomal abnormalities often found in such kids can have long-standing consequences.

Connected by genes

Blood-related marriages that continue for generations in a family or inbreeding leads to deafness, blindness and other congenital defects. According to a study, people who marry within their kith and kin are 13 times more prone to having a genetically-abnormal child. This reiterates the need to completely stop this practice. 

While assessing the consequences of consanguineous against non-consanguineous marriages, several scientific studies have shown that consanguinity leads to death of infants before, during or immediately after birth, an increased incidence of birth defects, genetic diseases including blinding disorders, blood cancer (acute lymphocytic leukemia), breathing problems at birth (apnea), increased susceptibility to disease and many more.

Babies born out of such wedlock could have many congenital problems: heart problems, still births, lung issues, nervous disorders, and other genetic abnormalities like Down syndrome etc.

The problem in such ‘close relative’ marriages surfaces when one of the partners carries a defect in any of the genes associated with some form of illness.

Unfortunately, people’s mindsets regarding this issue is one of the major causal factors. Many people believe that marrying their cousin is a better idea due to many reasons: it’s the same family, no burden of searching for a groom or bridegroom, less financial burden, and the family property remains undivided.

Similar genetic pool

Due to inheritance, parents and children, brothers and sisters, commonly share 50% of their genetic system. Similarly, uncle and niece share 25% of their genetic system, and first cousins 12.5% of their inherited genetic material, as it originates from a common ancestor. In such situations, if there are any ‘silent’ genetic defects, then such errors manifesting as a disease in the child of a consanguineous parents is high.

When you marry within the community, with one who may also have such a family defect, the child inherits two copies of this faulty gene, and thus has the defect. But when you marry outside the community, you bring in genes from a much larger gene pool, and the odds that the child will inherit the problem reduce remarkably.

A vast majority of problems are caused by recessive genes. Everyone carries some abnormal recessive genes, but most people don’t have a defect because the normal gene overrules the abnormal one. But if the couples have abnormal recessive genes being related to each other as cousins, almost two in every four babies are likely to have chromosomal abnormalities.

(The author is director & head of reproductive medicine, Manipal Fertility)

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