Cousin Marriage Increases the Risk of Birth Defects

Dr. Faisal Khan
Al-Dar Hospital Madina Munawara, Saudi Arabia.

Attitudes toward marriage between blood relations vary considerably across all cultures, but whatever the traditions and ethnicities of different cultures, there is a serious health concern regarding consanguinity, a relationship between blood relatives. Marriage between first cousins can more than double the risk of giving birth to a baby with a congenital anomaly such as heart or lung defects, thalassemia or down syndrome.

When parents are first cousins or close blood relatives, there is a higher risk of disease and congenital defects, stillbirths, infant mortality and a shorter life expectancy. Cousin’s marriage encouraged in all over Pakistan, accounting for more than half of all marriages, so here is a need for awareness campaign about importance of premarital blood screening to rule out risk of diseases and birth defects due to heredity & cousin’s marriage trend.

Children born to cousins have a significant higher risk of birth defects.  Studies shown the absolute risk of a birth defect is rising from 3 percent in children born to unrelated parents to 6 percent for children born to cousins. This means babies born to couples who are blood relatives have more probabilities to develop a birth defect. Marriage between blood relatives is common in all over Pakistan, so our general public needs to be provided with clear information and counseling about the increased risk of birth defects among children born to blood relatives.

In a study of more than 11,000 children within the large Pakistani community in the UK, marriages between blood relations, typically first and second cousins, were associated with a 3 to 6 percent increased risk of Down syndrome, heart and lung defects. However, these did account for nearly one-third of birth defects in babies of Pakistani origin families. Having parents who are first cousins doubles the risk of inheriting a single-gene condition, from 3 percent to about 5 percent.

But it’s harder to quantify and enumerate the risk for psychiatric illnesses because that problems typically arise from interactions among genes and environmental factors. A very recent study shows that children of cousin-parents are at higher risk for common mood disorders and other psychiatric issues. The study found that offspring from cousin’s marriage face three times increase in the possibility of taking antidepressants and two times increase in taking antipsychotics.

Technically, these all risks do not prohibit marriage to cousin and having babies, but our society have to realize importance of premarital blood screening before any cousin’s marriage. Children of non-related couples have a 2-3% risk of birth defects, as opposed to first cousins having a double or slightly more than double percentage of risk. In plain terms first cousins have at a 94% positive chances of having healthy children.

Infect we all carry different genetic defects that can lead to diseases in ourselves or in our children. Generally, this does not materialize because we have two replicas of every gene. Though, research indicates that the risk of having a child with birth defects and certain hereditary diseases increases if parents are close relatives. If there is a more percentage of DNA shared by one couple, then more chances of birth defects in their kids.

The vast majority of children born in Pakistan are healthy, but every year, some children are born with serious diseases or birth defects. The closer the blood relation between the parents, the higher the risk. If parents are cousins, the risk of having children with diseases and birth defects is twice as high as when the parents are not related.

The risk is also increased if there are many marriages between blood relatives in the family, so that the husband and the wife are related to each other in several ways. Close kinship between parents also increases the risk of stillbirths (death in mother’s womb after the 21st week of pregnancy) and infant mortality (death in the 1st year of life), and shortens life expectancy (death at all ages up to maturity).

There are many motives why offspring born with diseases and birth defects. In most of cases, the reasons are in the genes we inherit from our parents. We all carry genetic imperfections that can lead to diseases in ourselves or in our kids. Usually this does not happen because we have duplicates of every gene. If the one fails to work due to any defect, the other can generally do the job.

Both the mother and the father can have one or more genes that can lead to a disease without being ill themselves, and without any of their offspring being ill. For the children to get the disease, they have to inherit a defect in the similar gene from both parents. The risk that the mother and the father both have the same genetic defect and that it will result in disease is usually very low, but it increases when parents are close blood relatives. This is because both may have inherited the same genetic defect from their common descendants.

I want to share a case of 2 years old twin baby girls, presented to me in Rehman Medical Institute suffering from severe type of anemia. After lab tests both two girls were diagnosed as thalassemic. After getting history I found their parents are first cousins and both are carries for thalassemia.

Although all diseases and abnormalities are not inherited, but we should keep in mind that even conditions inherited due to kinship are low in ratio but often very serious. Such conditions include metabolic diseases, skin diseases, blood diseases, psychiatric diseases, physical and mental development problems, as well as problems with hearing or vision.

These conditions often caused a high risk of repetition of specific inherited diseases. During my research and medical practice in Peshawar, Bajaur, Mardan, Islamabad and even in middle east (Saudi Arabia) I have seen many cases where several children in the same family inherited the same disease. It happens when mother and father have a defect in the same gene, there is a 25 per cent chance that their children will be born with that particular disease or congenital defect. In this situation risk is the same for each pregnancy. This conditions also can lead to stillbirths, infant mortality and a shorter life expectancy.

I would like to suggest married couples, if you are blood relatives and you already have one or more children with a debilitating disease or birth defect, then you must go for genetic consultation and counseling. During the consultation, you can also discuss with your doctor, what can do if you have a child or expecting a child with a hereditary disease, whether the disease can be treated and who might be able to help the child and the family.

Genetic counselling also includes information about the possibilities for blood screening and other appropriate examinations for the husband & wife, the fetus, and any children and other family members. If the genetic defect that caused of any disease in the family is known, a gene test can determine whether or not an individual carries the defective gene. Moreover, it’s an advice for cousins who planning to marry, they should have to go for premarital blood screening including blood group compatibility test.