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Consanguineous marriage: Can marriage between cousins cause birth defects?

Consanguineous marriage: Can marriage between cousins cause birth defects?

Experts say that marriage within the family increases risks of certain life-threatening diseases.

Written by Sandhya Raghavan |Published : December 19, 2017 2:19 PM IST

Recently, a Pune family had the shock of their life when their 2-year-old's right kidney was not detected in a sonography report. They cried kidney theft and pointed the finger squarely at a doctor at Sassoon General Hospital in Pune, where the child was being treated. Here are some of the rules of living with one kidney. The boy born without an anal sphincter underwent three stages of surgery, owing to the birth defect. An inquiry committee was set up, which found that the kidney was still inside the child's body, but was too shrivelled to be detected in the sonography. The hospital explained that since the parents of the child were related to each other by blood, he was born with birth defects.

In India, many communities encourage marriage between cousins. It's called consanguineous marriage; the word is derived from "con" meaning together and "sang" meaning blood in Latin. Usually, the children of siblings belonging to the opposite sex can intermarry. In some cultures, marriage between the maternal uncle and niece is also quite common. As bizarre and revolting it may sound to the societies that are alien to the practice, consanguineous marriages normalised in certain sections of the Indian societies.For decades, the South Indian movies also played its part in glorifying love between cousins and bolstering this trend in the society.

Dr Sadhana Ghaisas, Geneticist at SDG's Genetic Centre, Vile Parle says, "Consanguineous marriages can increase the risk of genetic defects in the progeny. Defects like single-cell mutations are possible when the child is born to parents who are closely related by blood. That's why we always discourage such alliances. Irrespective of how the man and woman are related -- first or second cousins or uncle and niece -- there is a high risk of birth defects in their progeny as long as they belong to the same bloodline."

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There are many cultural reasons for promoting consanguineous marriage, which include safeguarding family wealth and maintaining the purity of the blood. Such alliances are also promoted to ensure greater stability between the husband and the wife since they will be sharing the same social relationships after marriage. It was believed that consanguinity strengthens family ties family ties.

What are the risks of consanguineous marriage?

Congenital malformations: Marriage between close cousins can cause congenital malformations in their children. Physical defects such as heart defects, cleft lip and palate, hydrocephalus and postaxial hand polydactyly are common in children born to consanguineous parents.1

Mental disorders:

Mounting evidence shows that communities that promote consanguineous marriages are at a substantial risk of developing bipolar disorder, otherwise known as manic-depressive illness. It is a serious brain disorder that causes extreme mood swings and violent behaviour.2 Some of the other common mental disorders associated with consanguinity include depression, impulse control condition, anxiety disorder, mood disorders, etc.34

Autosomal recessive diseases

Inbreeding increases the risk of developing autosomal recessive disorders such as sickle cell diseases, cystinuria, cystic fibrosis, thalassemia and congenital hepatic fibrosis. Consanguinity increases the likelihood of the offspring receiving recessive genes from their parents.5

Mental retardation and cognitive disabilities

Although the link between the two is still debated, there are is some evidence to say that history of mental retardation in the family if the parents are married consanguineously. The risk of mental retardation in the children is higher. Among all consanguineous marriages, the blood relationship of uncle-niece seems to pose the highest risk to offspring.6 Studies also point towards decline in children's cognitive abilities due to inbreeding and high frequency of mental retardation among offspring from inbred families.7

Stillbirth and infant death

Consanguinity also increases the risk of stillbirths, where the foetus dies at 20 or 28th week of pregnancy. Studies say that the risk of recurrent stillbirth and infant death is higher in children born to first cousins.8

With so many health risks, it is time this archaic practice is nipped in the bud and termed as a social evil. But if the couple has to go ahead with the alliance, ensure some precautions are taken before conception. Check for family history of autosomal recessive disorders and attend genetic counselling before you plan for a family.

References:

1 Tayebi, N., Yazdani, K., & Naghshin, N. (2010). The Prevalence of Congenital Malformations and its Correlation with Consanguineous Marriages. Oman Medical Journal, 25(1), 37 40. http://doi.org/10.5001/omj.2010.9

2 Mansour, H., Klei, L., Wood, J., Talkowski, M., Chowdari, K., Fathi, W., Nimgaonkar, V. L. (2009). Consanguinity Associated With Increased Risk for Bipolar I Disorder in Egypt. American Journal of Medical Genetics. Part B, Neuropsychiatric Genetics : The Official Publication of the International Society of Psychiatric Genetics, 150B(6), 879 885. http://doi.org/10.1002/ajmg.b.30913

3Rao, T. S. S., Prabhakar, A. K., Jagannatha Rao, K. S., Sambamurthy, K., Asha, M. R., Ram, D., & Nanda, A. (2009). Relationship between consanguinity and depression in a south Indian population. Indian Journal of Psychiatry, 51(1), 50 52. http://doi.org/10.4103/0019-5545.44906

4 Bener, A. (2017). Does consanguinity increase the risk of mental illnesses? A population based study. European Psychiatry, 41, S512.

5 Heidari, F., Dastgiri, S., Akbari, R., Khamnian, Z., Khanlarzadeh, E., Baradaran, M., ... & Tajaddini, N. (2014). Prevalence and risk factors of consanguineous marriage. European Journal of General Medicine, 11(4).

6 Madhavan, T., & Narayan, J. (1991). Consanguinity and mental retardation. Journal of Intellectual Disability Research, 35(2), 133-139.

7 Saad, H. A., Elbedour, S., Hallaq, E., Merrick, J., & Tenenbaum, A. (2014). Consanguineous Marriage and Intellectual and Developmental Disabilities among Arab Bedouins Children of the Negev Region in Southern Israel: A Pilot Study. Frontiers in Public Health, 2, 3. http://doi.org/10.3389/fpubh.2014.00003

8 Stoltenberg, C., Magnus, P., Skrondal, A., & Lie, R. T. (1999). Consanguinity and recurrence risk of stillbirth and infant death. American Journal of Public Health, 89(4), 517-523.

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