Consanguineous marriages increase risk of diseases transmission to offspring- Dr. Abdulrazak Ibrahim



 Dr. Abdulrazak Ibrahim holds BSc degree in Biochemistry from Bayero University (BUK), MSc Biochemistry from Universidade Federal do Ceara (UFC), Fortaleza, Brazil, and PhD in Molecular Biology from Universidade de Brasilia (UnB), also in Brazil. He is the Editor-in-Chief of Nigerian Journal of Biotechnology.

Currently, the don is a capacity development specialist at the Forum for Agricultural Research in Africa (FARA), where he coordinates the Africa Foresight Academy and the Agricultural Research and Innovation Fellowship for Africa (ARIFA). He is a writer, commentator and promoter of scientific literacy in Africa on emerging technologies.

Sahelian Times sought the opinion of this globally acclaimed expert of molecular and evolutionary biology on potential benefits and challenges of consanguineous marriages that are prevalent in northern Nigeria. In this engaging and enlightening encounter with Ismail Auwal, the university don provides some striking insights into the unintended consequences of consanguineous marriages from the perspective of gene pooling and risk of diseases transmission.


 ST: From a scientific perspective, could you tell us about the benefits or otherwise of consanguineous marriage?

Dr. A: Although consanguineous marriage is common all over the world, its benefits are generally social or financial with a corresponding social utility such a union offers. However, from a genetics perspective, consanguineous marriages lead to an increased risk of genetic disorders among offspring.

Children of first-cousin marriages have an increased risk of autosomal recessive genetic disorders (genetic disorders that can be inherited from two parents who are carriers of a faulty gene). This is due to the expression of possible defective gene mutations inherited from a common ancestor. Normally, children inherit 50% of each of the genetic makeup of their both parents.

Through a process known as recombination (and sometimes mutation), the cells of the children will rearrange the genetic makeup inherited from both parents, creating a unique pattern of their own in those children.

Now, if any of the two parents of a child has a defective gene, the child will be fine because it can rely on a similar, but sound copy of that gene in the other parent. However, if each of the two parents of the child is a carrier of a defective gene, there is a high risk that the child will have a double dose of the defective gene, which leads to disease. So the probability that any defective gene can cause harm among people is usually much higher in populations that are already highly ethnically similar.

For example, if in a small town where carriers of the defective gene for haemoglobin, which causes sickle cell anaemia abound and people engage in consanguineous marriage, within a few generations almost everyone will have sickle cell anaemia and the population of that town will be decimated unless they start to marry from a neighboring town where the frequency of the disorder is low. So, the more related spouses are, the more likely it is that they produce offspring with deleterious gene product that can cause disease. These points underscore the disadvantages of consanguineous marriage.

ST:  Recently, we have seen uterine twins marrying themselves. Does that have any medical implication?

Dr. A: Before I answer that question, let me give you a background. Generally, the closer the biological relationship between parents, the higher the probability of their offspring inheriting identical copies of one or more detrimental recessive genes. By rule, first cousins are predicted to share 12.5% of their genes. This means that the progeny of cousins will be homozygous (that has double copies of the same gene) at 6.25% of that defective gene, which is quite high. In the case of these twins who are married to their twins, if they risk matchmaking their children, there may be a problem with their grandchildren.

Even if their embryos make it through gestation, the risks of genetic diseases are quite high.  Marriage among cousins is already risky, not to talk of children of twins, who are not only first-degree relatives but Identical twins. Barring some epigenetic differences (differences in the way the strands of DNA are folded in a cell) and a few regions, identical twins share almost 100% DNA.

This means any progeny arising from the children of the twins, is much riskier. Even if they do not carry any recessive defective gene, stillbirths and infant mortality have been reported to be slightly higher.  In essence, if children of first cousins are in danger of having the disease by a factor of X, theirs will be 2X.

ST: Are there ways to prevent gene pooling, and disease transmission in such types of marriage?

Dr. A: I think the best way is to discourage consanguineous marriage. Conversely, there’s a lot of genetic benefit in marrying someone outside your ethnic group because the offspring arising from that marriage will be unique and will possess a different form of genetic assortment that enriches the entire gene pool of the society. 

ST: What are the diseases recommended to be on the lookout for when potential couples are being screened in Nigeria?

Dr. A: Generally, this depends on the prevalence of the reference disease. For example, the haemoglobin genotype test that is now routinely conducted, to determine “genotype”, is a genetic test. Diseases such as thalassemia are also often investigated. There are several neurological diseases associated with the metabolism of amino acids also. In many countries, as soon as babies are born, there are tests to detect such diseases as anaemia, cystic fibrosis, galactosemia, glucose-6-phosphate dehydrogenase deficiency, etc. But I think genetic screening before marriage will still take some time before it’s more commonly deployed. 

ST:  Are these tests or services accessible, in terms of availability and affordability?

Dr. A:  Although some of these tests are routine elsewhere, they are not so in Nigeria. However, we already conduct the genotype tests but there are many other tests that are not readily available or affordable here.

ST:  What will you recommend to policymakers in our country?

Dr. A: It is very clear that, we need more science in the way that we do things, including in dealing with genetic risks like this. Policymakers need to really create an ecosystem and a science-policy nexus where they are better informed about the biology behind the risks, engage in a rational debate about available options while respecting human dignity and privacy, to address the risks. Additionally, there should be more awareness and follow up measures with legislative bills that would regulate consanguineous marriages on the basis of a possible genetic risk. This means health experts in relevant areas should be engaged to conduct research that to allow for  generation of sufficient data on the prevalence and risks of key genetic diseases and on that basis, advise the government on making the regulation effective.

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