To coincide with the Dispatches When Cousins Marry, Dr Alidina (from the programme) and his colleague Dr Walji answer your questions about the medical consequences of cousins having children together.
Thank you all for your questions and interest, we will try and answer the questions as best as we can or otherwise point you towards other sources of information. Most of your questions are similar so we will answer then collectively if that is ok.
Statistics
The risks of cousin marriage genetic disorders are quoted to the about 4% in a first cousin marriage as opposed to 2% in an unrelated couple. Even though this means that you are more likely to have normal children, the risk is double if you are first cousins than if you are unrelated. The risks are even greater if there is a persistent practice of cousin marriages in the family ie if your grandparent, parents and you all marry cousins. It is also true that marriages in within a small biradari or group of people will also carry similar high risks.
Genes and inherited disorders
Why is it a problem? The answer to this lies in the genes of potential partners. We all inherit half our genes form our mothers and the other half from our fathers. The interactions between these genes usually lead to the outcome such as features, eye colour, gender and so on. Some genes are dominant whilst others are recessive, but they can be inherited from either parent so it isn't true that dominant genes are the father's or mother's only but can be either's. Most genetic conditions known to cause rare genetic conditions are thought to be autosomal recessive conditions so they interact in the following way as illustrated in the diagrams via this link [PDF]:
http://www.geneticalliance.org.uk/docs/eurogentest_RecessiveInheritance.pdf (opens in a new window)
Thalassaemia, an inherited blood disorder would be a good example of a common inherited autosomal recessive condition as would sickle cell anaemia.
Two carriers marry and have children, then there is a 25% chance of an affected child but also a 50% chance of carriers in each pregnancy. It is the latter which we would consider the silent threats as the number of carriers in the family multiply, then the chances of marrying another carrier is higher than usual if they are your cousin.
The safer relationship is that between a carrier and a non carrier (second box) resulting in no affected children but carriers like the parents or normal children. Even in this partnership, the chance of further carriers in the family is still 50% hence increasing the number of carriers within the family. This is only true for autosomal recessive conditions only.
Other forms of inheritance are outlined easily with aids of diagrams on this website
http://www.web-books.com/eLibrary/Medicine/Appendix/Inheritance.htm (opens in a new window)
Genetic counselling
Genetic counselling aims to test and calculate risks in known genetic disorders and hence pre-marital testing and counselling would be beneficial especially in most communities where termination of affected pregnancies is a taboo and forbidden.
However, we can not test for all genetic disorders and it would seem more sensible to avoid marrying cousins where genetic mutations would be common in the gene pool. I enclose a link for a patient information leaflet from Patient Uk website which gives more information about genetic testing that you may find useful:
http://www.patient.co.uk/health/Genetic-Testing.htm (opens in a new window)
Heart problems and cerebral palsy
Other conditions such as some heart problems in children and cerebral palsy are not thought to be genetic in origin but have various other causes. It would be difficult to give a definite answer without looking at the medical history of the affected person but their GPs would be able to evaluate their cases and refer to the local genetics departments at the hospital nearest to them if required.
Raising awareness without causing offence
We have to be sensitive to the cultural and personal beliefs of others too. Cousin marriages are not prohibited in Islam or incestuous in anyway. They are however not encouraged due to the above issues. Stigmatising communities for practices which are showing increased health risks due to new medical information is counterproductive and usually leads to the initial education being lost in arguments about religion and culture.
Our message is simple and non-political and we are hoping that being from amongst the community, we can raise awareness as a brothers and sons without causing offence. I firmly believe that no one wishes to have children with disability but alienating them for certain practices forces them to be defensive and takes away from the real purpose of educating them.
The Jewish community
Finally, the Jewish community has been very proactive in listing common genetic conditions affecting them and encouraging screening. I am not aware of any such lists for other ethnic groups at present. Perhaps, as our understanding of genetics increases and the community accepts the risks of genetic diseases in cousin marriages, such specific tests will become popular for particular ethnic groups in the future.
– Dr Rizwan Alidina and Dr Mohamed Walji
