Introduction
Consanguineous marriage, a prevalent tradition in regions like North Africa, the Middle East, and West Asia, involves unions between close relatives. Approximately one billion individuals live in communities favoring such marriages, constituting a significant global population. These regions' primary healthcare providers often receive inquiries from consanguineous couples seeking preconception counseling. This article will explore the genetic and reproductive consequences of consanguineous marriages. Continue reading further to know more about it.
What Is Consanguineous Marriage?
Consanguineous marriage is also known as cousin marriage or intra-family marriage. It is very popular in some countries, especially the greater Middle East region. Cousin marriage is the marriage between two closely related family members (blood-related), like first cousins. In other words, a marriage between two people whose grandparents are the same is called a cousin or consanguineous marriage.
What Are the Genetic Risks of Cousin Marriage?
Cousin marriages are not safe, as they can lead to multiple miscarriages, an increased risk of birth defects, stillbirth, the risk of early childhood death, or a higher risk of offspring having genetic disorders that are running in their families. A child always carries 50 percent of genetic material from the mother and 50 percent from the father. When marriage happens within the same family, the mother and father are already carriers of that disease. Therefore, the chances of passing that disease to the offspring increase significantly. Hence, sometimes, the child will be born with birth defects or genetic disorders that can be fatal, and it becomes difficult for the baby to survive. In cousin marriages, the genetic disorders will be inherited by the offspring and passed on to every generation.
Furthermore, the child will be more likely to have autosomal recessive disorders. Autosomal recessive disorders are genetic disorders in homozygous individuals for a particular recessive gene mutation. This means carrying two copies or alleles of the same gene.
Which Inherited Disorders Are Often a Product of a Consanguineous Marriage?
As discussed earlier, consanguineous marriages can lead to autosomal recessive disorders in the child. The common autosomal recessive disorders that are inherited are
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Cystic Fibrosis: Cystic fibrosis is a genetic disorder affecting the respiratory, digestive, and reproductive systems.
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Fanconi Anemia: Fanconi anemia is a rare genetic disorder characterized by bone marrow failure, congenital anomalies, and an increased risk of cancer.
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Thalassemia: A group of inherited blood disorders affecting the production of hemoglobin, leading to anemia.
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Phenylketonuria: Phenylketonuria is a metabolic disorder caused by a deficiency of the enzyme phenylalanine hydroxylase.
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Sickle Cell Anemia: A hereditary blood disorder characterized by abnormal hemoglobin, causing red blood cells to become rigid and assume a sickle shape.
Out of these disorders, thalassemia and sickle cell anemia are the most common. Thalassemia is a blood disorder in which a child needs multiple blood transfusions, which can increase the risk of death. Multiple blood transfusions can have several side effects like liver enlargement, spleen enlargement, cardiac issues, joint issues, retarded growth, low life span, etc. The increased risk of genetic disorders in consanguineous marriages is presented below.
Congenital anomalies:
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Nervous system defects (spina bifida).
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Congenital heart disease.
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Oral or facial cleft like cleft lip or palate.
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Digestive abnormalities.
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Musculoskeletal abnormalities.
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Abdominal wall, urinary, genital, and limb abnormalities.
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Blood disorders like hemophilia.
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Genetic diseases.
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Major mood disorders like anxiety or depression.
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Psychotic disorders like schizophrenia.
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Down syndrome.
All these defects and disorders are more likely to occur in consanguineous marriage.
Is There Any Way to Prevent the Genetic and Reproductive Consequences of Marriage?
If someone is going to get married to their blood-related family members, then they should take genetic counseling before marriage. Consanguineous marriages may require advanced fertility treatments to assess genetic abnormalities. Advanced fertility treatments like pre-genetic testing can help identify any genetic or hereditary disorders before embryo freezing. Pre-genetic testing involves a biopsy of the embryonic cells to assess for abnormalities and is of three types.
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Pre-genetic testing helps identify hereditary disorders in embryos.
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Different types of pre-genetic testing include testing for structural rearrangements and mutations.
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PGTA, or pre-genetic testing for aneuploidy, determines if the embryo has chromosomal abnormalities.
Testing embryos can help avoid hereditary disorders in consanguineous marriages. Transferring normal embryos provides a 100 percent chance of preventing hereditary disorders in the family lineage. Genetic testing is crucial for couples marrying blood relatives to avoid passing on hereditary disorders. Consanguineous marriage can lead to birth defects. Prenatal testing like amniocentesis and chorionic villus sampling can detect birth defects in babies.
Furthermore, treatment options are available to find out if the baby has birth defects. Preconception evaluation can prevent birth defects. Pre-genetic evaluation ensures 100 percent certainty of no hereditary diseases or chromosomal abnormalities. Prevention through evaluation is better than trying to cure the problem after conception.
Does Consanguinity Increase Susceptibility to Infectious Diseases in Humans?
Consanguinity strongly correlates with heightened susceptibility to specific infectious diseases in human populations. Notably, West Africans, particularly Gambians engaged in first-cousin marriages at a frequency of approximately 30 percent, demonstrate a significant association with susceptibility to tuberculosis (TB) and persistent hepatitis B virus infection. In contrast, populations with lower consanguinity levels, like Italians, do not show a notable association with persistent hepatitis in genome scans. Instances where affected individuals, particularly in populations with high consanguineous marriages, display increased evidence of inbreeding compared to unaffected controls, further emphasizing the impact of kinship on infectious diseases.
An exception to this pattern is observed in leprosy cases in India, where despite high consanguinity levels, the disease's unique genetic architecture suggests potential oligogenicity or genetic purging due to persistent, strong inbreeding. The affected sib-pair design effectively controls biases related to population stratification.
Conclusion
To conclude, consanguineous marriages should be avoided in the first place, as they increase the risk of high-risk pregnancies and genetic disorders. However, if individuals want to marry a blood relative, they must go for genetic counseling to reduce the genetic and reproductive consanguineous marriage. It is important to make it a priority to avoid marrying a blood relative, even though this can help reduce the risk.
