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The Pros and Cons of Consanguineous Marriages

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The Pros and Cons of Consanguineous Marriages
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In the beginning of mankind’s humble existence, humans had very few options about who they could have children with. Our ancestors procreated with their close family members in order for life as we know it to carry on. Many European royal families bred within their bloodlines to safeguard their power and keep it in the family. At the present time, having children with biological relatives is still a widely accepted and practiced phenomenon, yet it is also widely condemned. We take a look at this controversial subject and explore the pros and cons of consanguineous marriage.

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What Does Consanguineous Mean?

The word consanguineous is derived from the Latin roots of com, meaning “together” and sanguineus, meaning, “of blood”. A consanguineous marriage is the union of two people who share an ancestor, specifically first cousins or more distantly related.

In 2002, the Royal Free and University College Medical School published a study stating that 20 percent of the world’s population live in communities that favor consanguineous marriage. They are particularly prevalent in the Middle East and South Asia, specifically countries such as Pakistan, India, and Sri Lanka, as well as parts of Africa. So, what makes consanguineous unions so popular?

The Pros

The potential benefits of consanguineous marriage are mostly related to social factors:

  • Two people and their families already know each other well.
  • A high degree of compatibility in marriage.
  • Less stress of marital problems, particularly financial issues.
  • Assets are kept within the family.
  • Increased chance of the marriage surviving.
  • Stability conducive to the raising of a well-adjusted family.
  • Cultural values are successfully passed on and preserved.

A study called Born in Bradford (BiB) surveyed pregnant Pakistani women in consanguineous relationships in the English city Bradford, well known for its high rates of consanguinity. They found that socially, economically, culturally and in terms of health, the women in consanguineous relationships fared as well as those in non-consanguineous relationships, and sometimes better.

In an interview with the BBC, the co-author of the BiB study, Professor Neil Small, said “…the vast majority of babies born to couples who are blood relatives are absolutely fine, and whilst consanguineous marriage increases the risk of birth defect from 3 to 6 percent, the absolute risk is still small.”

Shiraz University’s Department of Biology conducted a study investigating the association between consanguinity in marriage and the risk of divorce in the city of Shiraz, Iran. They found that consanguineous marriages can act as a defensive mechanism against divorce and, furthermore, that there is an increased chance of the marriage surviving.

Many well-known people have married their first cousins, including the eminent scientist Albert Einstein, Indian filmmaker Satyajit Ray, English naturalist Charles Darwin, the American writer Edgar Allan Poe and the American presidents Thomas Jefferson and Franklin Delano Roosevelt.

The Cons

The potential drawbacks of consanguineous marriage are mostly linked to health factors. These relate to how genes are affected by people who share a similar biological lineage. When one parent has a recessive gene this usually has no detrimental effect when passed on to children. However when parents are as closely related as first cousins, there is an increased chance that they both pass on these recessive genes to their children, which may result in a genetic condition such as heart or lung defects, or Down’s syndrome.

There is a doubled risk of birth defects in consanguineous offspring compared to non-consanguineous offspring, as mentioned in the Born in Bradford study. However, this risk is still relatively small. There is also a notable 4.4 percent increase in the chance of pre-reproductive mortality. With each successive generation of consanguineous offspring the risk of birth defects increases, as shown in the table below.

Relationship Shared Genes Risk of birth defects above population background risk
First cousins 1 Eighth 1.7% – 2.8%
First cousins once removed
Half first cousins
1 Sixteenth 0.85% – 1.4%
Second cousins 1 Thirty-second 0.425% – 0.7%

Genetics and Epigenetics

There is also increased risk of mental health problems for diseases which have a genetic link, such as schizophrenia. A study lead by Professor Abdulbari Bener of Hamad Medical Corporation looked at whether or not the risk of schizophrenia is increased by consanguinity. They studied Qataris with a family history of the disorder and parental consanguinity and found that schizophrenia occurred more often in the offspring of consanguineous parents than in those of non-consanguineous parents.

However, many diseases and mental health issues are heavily influenced by environment in addition to genetics, this includes: family and peer influences; food and exercise; behavioral responses to stress; and many more elements. The impact of environment on the genetic expression of disease states is a relatively new branch of scientific research called epigenetics. This promising new area looks specifically at changes in gene expression as a result of external factors, providing hope for many. Even if a specific trait is inherited, its effect can be influenced and reduced. For example if there is a family history of bowel cancer and individuals work at reducing their risk, through diet, exercise and stress reduction, the risk can be vastly diminished.

A study published in 2015 in the Journal of Translational Medicine found two genetic susceptibilities to obesity in the Qatari population. For our ancestors who lived thousands of years ago, these genes had an evolutionary advantage: promoting fat storage and preventing starvation. Unfortunately, when cousins marry, any susceptible genes like this become amplified and their impact increased. However, this doesn’t mean obesity is predetermined, it simply means it is more likely in a given environment, for example one of food abundance.

While there are certainly social advantages to marrying within the family, it can be equally argued that there is value in marrying outside of it. Culture is preserved in consanguineous marriages, yet when people of different ancestry come together and marry this creates new culture and more diversity, expands social bonds and promotes harmony between people of different backgrounds.

In an interview with UAE’s The National, Dr Mahmoud Taleb Al Ali embodied the conflict between the pros and cons of consanguinity: “I am a geneticist, I know every principle in genetics and I am married to my cousin. If you ask me as a scientist, I would say not to allow consanguineous marriages. If you ask me as a person in my culture, I would encourage it. It is part of our identity.”

Taking Precautions and Avoiding Problems

As we have seen, the risks of problems in the offspring of consanguineous marriages depend upon how closely the parents share genes and the specific genetics involved. From this perspective, consanguineous marriages between some relatives can be a strong foundation to build a family, amplifying positive genetic traits. However, for others this amplification effect can compound problems by increasing genetic illnesses and the likelihood of birth defects. It is important for couples who are related to be very well informed if they are thinking about having children.

A study published in the Journal of Bioscience determined that in Qatar the rate of cousin marriages has increased from 41.8 percent to 54.5 percent in one generation, specifically showing an increase in the rate of double first cousin marriages (parents and offspring in first-cousin marriages). A 2014 study published in the Journal of Human Heredity found that hereditary hearing loss (congenital deafness) affects 5.2 percent of the population of Qatar and is much more common in offspring of double cousin marriages. Several genetic mutations that cause the loss of hearing appear to be specific mutations, found only in Qatar, which have been inherited over repeated generations of consanguineous marriages.

Genetic counselling is the easiest way to estimate the possible risks. This includes obtaining a medical family history spanning 3 to 4 generations and taking into account ethnicity, as specific disorders are prevalent among different populations. With the right knowledge, consanguineous couples can then make informed and responsible decisions about starting a family.