Consanguineous marriage is the name given to the marriage of people who are related to each other by blood. The couple whose mother or father is a sibling is called 1st degree consanguineous marriage, while the marriage of a couple whose grandparent is a sibling is called 2nd degree consanguineous marriage.
Although these types of marriage, which are considered taboo all over the world and are prohibited in many countries, have been common throughout history, they are extremely dangerous for the child to be born. Let’s take a closer look at why children born from this type of marriage, in which genetically inherited diseases are highly likely to be transmitted to children, cause some diseases.
Stillbirth rates in consanguineous marriages are double that of normal marriages.
According to studies, miscarriage, stillbirth and newborn losses as a result of consanguineous marriages are twice as high as in normal marriages. At the same time, this type of marriage increases the risk of birth defects and causes autosomal recessive diseases in children born.
Consanguineous marriage leads to the transmission of two defective genes of the same type to offspring
Before we move on to why consanguineous children often have genetic diseases, we need to take a closer look at the genes that two parents pass on to their children.
Inherited diseases occur as a result of mutations in genetics, and two-dose mutations (recessive gene) in this hereditary material called a gene cause autosomal recessive diseases.
Individuals who are related by blood also share common genetic characteristics thanks to this bond, and the probability of two recessive genes coinciding in consanguineous marriages is much higher than in normal marriages.
In this situation, which is completely caused by blood ties, if there is any hereditary disease in the individuals in the pedigree, the parents can pass this gene directly to the child to be born, even if they are not sick.
Let’s give an example from cystic fibrosis, which affects the mucus and sweat glands in the digestive, respiratory and production systems from birth. Caused by a mutation in the CFTR gene, this disease can lead to excessive fluid loss, various heart diseases, diabetes, and even infertility, but it takes two of the same mutated genes to have the disease.
In cases where one of the parents is only a carrier and there is no such disease in the genetics of the other side, there is no possibility of the child to be born with cystic fibrosis. However, even if both parties are only carriers, this gene is inherited directly to the child with a 50% probability.
Another disease that we can give an example on this subject is phenylketonuria, which is a disease that causes severe mental retardation. A child with phenylketonuria, a familial disease, has two genes, one normal and one mutated, in his parents. If this disease is present in the pedigree of consanguineous marriages, the child born will have inherited two recessive genes and is born with congenital phenylketonuria.
Before giving birth to children in consanguineous marriages, doctors need to do pedigree checks
Children born as a result of consanguineous marriage are highly likely to have hereditary diseases, but it is also possible for the child to be born healthy. In order to be sure about this issue, parents should definitely have a pedigree check before deciding to have a child.
In this control, experts examine the family tree of the mother and father candidates, including 4 generations. If there is any risk in the resulting pedigree, parents should be warned about this issue. At the same time, if the prospective mother and father come from a region where consanguineous marriages are common and recessive genes are common, they are subjected to screening tests.
Many diseases, especially mental retardation, can be seen in children born as a result of consanguineous marriage.
There are many types of autosomal recessive diseases, but the most common disorders seen as a result of consanguineous marriages include developmental disorder, mental retardation, cystic fibrosis and multiple system disease.
At the same time, let’s not go without saying that the risk of miscarriage in first and second cousin marriages is much higher than in normal pregnant women, and the probability of the child born to have some hereditary disorders such as hypertension is extremely high compared to other children.
Consanguineous marriages also lead to hereditary depression
A scientific article published in 2018 revealed that children born as a result of consanguineous marriages are much more likely to have mood disorders and psychosis than children born from normal marriages.
In this study, which included 363,960 people, it was observed that being the child of related parents increased the use of antidepressant-like drugs when they reached adulthood. According to the study, children of first-degree consanguineous parents are three times more likely to receive medication for mood disorders and psychosis than children of normal parents.
Source 1, Source 2, Source 3, Source 4
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