The health risks of marrying your first cousin

The genetic consequences of marrying a close relative, especially a first cousin, blight the health of many people of Pakistani and Arab origin.

A fable

I want you to come on an imaginary journey with me, going 30 years back in time.

It is a hospital in Manchester and after a long labour my first child, Ibrahim, has just been born. I have been sent away from the delivery room to the hospital waiting room while the nurses clean up my wife and baby and both get some rest. While I'm sitting in the armchair in the waiting room, exhausted and emotionally drained myself, a strange guy walks in.

He is dressed the way you only see in films and television. Tall, wearing a white suit with his hair slicked back. In his right hand he is carrying a suitcase and in his left hand a shopping bag. He wears a solid gold Rolex encrusted with dazzling diamonds, a gold neck chain and on every one of his fingers there is a jewel encrusted gold ring. As if this was not enough jewellery, he also wears a diamond tie pin! He has dark glasses and I assume that if hospital rules did not prohibit smoking, he would have had a large Cuban cigar in his mouth.

The stranger puts the suitcase onto the low coffee table, grabs my right hand and shakes it vigorously. “Good afternoon Mr Amin. Many congratulations on the birth of your son Ibrahim!”

I am so tired that all I can do is mumble: “Who are you? How did you know my name? Even more, how did you know what my wife and I are going to call our son when we haven't told anybody yet?”

He responds “Mr Amin, the name is Maverick, Bart Maverick. I have my methods regarding information! Don't worry about that. I have come to you with the proposition of a lifetime. This proposition is so valuable that it will take your breath away. I warn you now that if you turn it down, I'm going to walk straight out of the door and you will never see me again or get another chance to accept the proposition.”

All I can do is reply “I'm too tired to care but go-ahead. What's your pitch?”

Mr Maverick reaches into the shopping bag in his left hand and pulls out a large revolver. He sees me flinch. “Don't worry, it's not loaded and the safety catch is on. This is a very special revolver, let me show it to you.”

He opens the revolver so that I can see the barrel. It is not a six shooter; instead the barrel has very small chambers but lots of them. Mr Maverick tells me that there are 100 chambers. From the shopping bag, Mr Maverick takes out two boxes of bullets, tiny bullets to match the size of the small chambers of the revolver.

Mr Maverick continues “Do you see these grey bullets Mr Amin? These bullets are blanks and I'm loading 97 of them into the chambers. The blanks are completely harmless. Now this smaller box contains red bullets and I'm only going to load three of them. These red bullets are very special and come in lots of different types. Some of them will lead to death in a matter of days, others can lead to blindness, kidney failure or cause a person to grow up severely mentally retarded. There are lots of different types of red bullets and I can't even keep track of them all myself, but as you can see I've only loaded three into the revolver. Now Mr Amin, I want you to take this revolver, go into the room where your baby is sleeping and just fire the revolver once at your baby.”

Suddenly I am wide awake as his comments have led to an adrenalin rush after the shock of hearing his words. “Do you think I'm crazy? Why on earth should I fire that revolver at my newborn son?”

Mr Maverick continues: “Of course I don't think you're crazy Mr Amin. I haven't told you the full proposition yet.”

Mr Maverick opened the suitcase which is full of large neat bundles of new £50 notes. “Mr Amin, I have here a large amount of money, and if that is not enough there is more money in the boot of my car outside. I want you to tell me how much I need to pay you to go and fire that revolver at your son. I warn you against asking for too much; if you do we are going to have to haggle. If we can't strike a deal, I'm going to walk out of here with the revolver and the money and you will have blown the opportunity of a lifetime by being too greedy.”

What should I do?

To be completely honest, I can imagine circumstances where I would accept Mr Maverick's offer.

For much of the last quarter century, the eastern region of Zaire / Democratic Republic of the Congo was wracked by a brutal civil war that killed millions. Imagine that my wife and I are refugees somewhere in the Congolese rainforest. She has just given birth behind a tree, and our lives are in danger from tropical diseases, starvation and the killers from the warring faction who are hunting us. From seeing what happened to the children of our friends, I know that Ibrahim has a less than 50/50 chance of living to his first birthday, and if he does survive he faces the same life of flight and danger that my wife and I are experiencing now.

In that situation, Mr Maverick’s money would transform our lives, giving us the chance to come and live in the UK perhaps. Even from my son's perspective, the offer is a bargain. Without the offer, he has a bigger than 50% chance of dying before he reaches 12 months; with the offer he has a 97% chance of coming to the UK and growing up to be just like any other citizen of this country.

However, those were not my circumstances 30 years ago. My wife and I were living in the UK, both of us were University graduates and had middle-class professions. The UK is a safe society. We have the National Health Service and a social security system. While nobody can predict the future except God, 30 years ago I had every reason to expect a safe and happy life for my newborn son. In those circumstances, I can honestly say that there is no amount of money that Mr Maverick could have offered me to play his game.

However writing the above paragraph raises another ethical issue. Even if our family did not need Mr Maverick’s money to survive, by taking it I could use it to save the lives of helpless refugees overseas, for example the hypothetical couple mentioned above. Is it selfish of me to refuse to take a 3% risk with my newborn son when playing Mr Maverick’s game could allow me to save so many other people's lives?

I cannot give a definitive resolution to that ethical question. However I am still certain that if Mr Maverick had appeared with his revolver and suitcase full of money, I would have turned him down.

Why is this fable relevant?

Mr Maverick is of course an imaginary character you will never meet. If he turned up at a hospital, expect him to be arrested for carrying a revolver in breach of UK gun laws!

However, you play the same odds that Mr Maverick is offering above if you choose to marry your first cousin. Most of the time, your babies will be fine. However, some of the time they will have serious genetic defects which can cause death, blindness, severe retardation and other crippling or fatal diseases. The scientific evidence is that the risk varies depending upon the total amount of intermarriage within a social group. Even if you marry a completely unrelated person, there is always some risk of birth defects, but it is quite low. Marrying your first cousin raises that background risk very significantly, in many cases doubling it. An extra 3% risk is a reasonable way of looking at the science.

Nobody would play Mr Maverick's game unless he offered them money. Similarly, knowing the scientific facts, nobody would choose to marry their first cousin unless they believed that there were other benefits from doing so which outweighed the genetic dangers.

Some of the other benefits which I often hear are that your first cousin will relate better to your parents since he or she already knows them. If there are problems between the married couple, since their parents contain a brother or sister pairing, the two families can cooperate better to sort out the difficulties between the married couple. Finally, if the families are rich, it can keep the money inside the family.

I accept that the advantages mentioned above do arise from time to time. However many years of seeing cousin marriages both succeed and fail, and when they fail poisoning relations between rest of the the blood relatives, have taught me to be sceptical about the benefits.

However, the key question which each person has to answer for himself or herself is "How big do the benefits of first cousin marriages have to be to make me voluntarily take the 3% risk of crippling or even killing the children that my first cousin and I are going to have." Remember that both in English law and in Islamic law, marriage is a voluntary contract and nobody, absolutely nobody, can order you to get married to anyone.

The science

It may be that you are not aware of the genetic risks of first cousin marriages. Nobody is born knowing science, and the way to remedy the gap in your knowledge is to learn about simple genetics.

The website Jewish Genetic Disorders UK is run by a charity. While it is aimed at the Jewish community and genetic diseases which are more commonly found amongst Jews, reading the material on the site will be informative for most people.

Lower down, I have included links to some scientific papers. As these are research papers written by scientists to be read by other scientists and not for laymen, you may find some of them hard going if you are not used to reading scientific literature. However, please have a look at them, since it is much better for you to look at the hard evidence for yourself rather than being told by other people that the risks are not real or exaggerated.

If you are familiar with the scientific results but do not believe them, then you are simply in denial. There is no point in me asking you to read anything further until you are prepared to open your closed mind.

When white non-Muslim politicians raise this subject, they are often accused of being racist or anti-Muslim. Similarly, most of the research mentioned below (apart from the Jerusalem and Spanish gypsy studies) refers to Arabs and Pakistanis. There is a simple reason for this; those are the societies where consanguineous marriages are most common. The map below illustrates this:

First cousins are not the only sources of risk

It is easiest to explain the genetic risks with the example of first cousins, because everyone is aware that first cousins have a common grandparent, and can therefore see how faulty recessive genes might be inherited by both spouses and come together in their child. As first cousins are genetically closer than second cousins (who share a common great-grandparent) the risks are greater; the more remote your relative the lower the risk should normally be.

However this simple example is based upon there being only one source of a faulty gene, namely a single ancestor, and there being no other inter-marriage within the descendants.

In practice, there are groups which practice a much higher level of endogamy, which is the custom of marrying only within the limits of a local community, clan, or tribe. Examples are communities from villages which are remote from other people, castes and sub-castes amongst Hindus in India, marriage within Arab tribes, and Pakistani relationship groups known as "biraderi" (a form of clan system which is obviously derived from the Hindu caste system.)

Where a group practices high levels of endogamy, the genetic risks are increased. Even though your intended spouse may not appear to be a family member, you and your intended spouse may have many common ancestors, which significantly increases the risk that both of your carry the same faulty recessive genetic disorder.

Short video presentation

On 11 March 2019, the Conservative Muslim Forum held an event "The genetic risks of cousin marriage." I spoke to summarise the science and what I believe people should do.

"But Islam does not prohibit marrying your first cousin!"

Each of Judaism, Christianity and Islam have religious rules prohibiting marriage with certain close relatives; for example all of them prohibit marrying your sister or brother. However, neither Judaism nor Islam prohibit marrying your first cousin. (The position is more complicated with Christianity, with some Christian subdivisions permitting first cousins to marry, other banning it, while the Roman Catholic Church requires the intending first cousin spouses to obtain special permission from the Church.)

The fact that Islam does not prohibit marrying your first cousin is often used by Muslims as evidence that the practice must be perfectly satisfactory. In particular, proponents of cousin marriage invoke the Islamic principle that humans cannot prohibit something that God has permitted, citing texts such as Quran 16.114-116 (Muhammad Asad translation):

Such an objection completely misses the point. As far as I am aware, nobody is proposing making first cousin marriages illegal, or contending that people who enter into such marriages are committing a sin.

In Islam, God has not forbidden you from marrying your first cousin; nor has He commanded you to do so. Instead the decision is left to you to make on pragmatic grounds. From a practical perspective, the key point is that such a marriage does add significantly to the risk of genetic defects in your children.

Therefore why take the extra risk unless there are major positive benefits from choosing to marry your first cousin which outweigh the extra risk to your children? Hence the fable of Mr Maverick above. It is not a theological issue, any more than deciding to always wear a seat belt when driving a car, or avoiding excessive salt in your diet. If something is dangerous, why do it?

Genetic screening

Finally, if you are still keen on marrying your first cousin, a sensible precaution is for both of you to have genetic screening. While our ability to identify dangerous recessive genes is imperfect, genetic screening will tell you if you and your cousin share known recessive genes that would impair your children's health and you can decide whether or not to proceed with getting married knowing more of the facts.

I have been informed by genetics specialists that the usual approach is to take the family history, identify any obvious conditions that have already occurred which may therefore be at particular high risk, discuss haemoglobinopathy and carrier screening, and cystic fibrosis screening as there are easy tests for these common recessive conditions. Haemoglobinopathy includes beta-thalassaemia and sickle cell disease. These are both recessive conditions although beta-thalassaemia is much more serious than sickle cell disease. Carriers can be detected by their haemoglobin level rather than looking for genetic mutations. Carriers of sickle cell disease may be mildly symptomatic themselves.

Screening in USA aimed at Jews

There is a very worthwhile initiative operated by the Chicago Centre for Jewish Genetic Disorders, aimed at the Ashkenazi Jewish community called Dor Yeshorim. As an individual Ashkenazi Jew, you can pay $200 and have your genome tested for a number of genetic disorders. You are issued with a "ticket number" but with no results. This means that you do not have the psychological challenges or possible stigma of learning that you may be a carrier for certain genetic disorders. Their website explains:

Screening in UK aimed at Jews

There is a charity in the UK, Jnetics, dedicated to improving the prevention, diagnosis and management of Jewish genetic disorders in the UK. It focuses on genetic conditions that, though not exclusively Jewish, are of particular relevance to people of Jewish ancestry.

Screening aimed at British Muslims

I am not aware of any such initiative amongst any Muslim community, such as British Muslims of Pakistani origin, but it would be a worthwhile community initiative to launch.

If you are already married to a first cousin and expecting a baby, it is possible to have extra tests done during pregnancy. However there is little point in this unless you are willing to consider an abortion if the news is bad.