There are several ocular and systemic diseases common in consanguineous population. One way to appears to reduce the morbidity and mortality is by early detection and management. Genetic counselling may be another modality. There may be some role of premarital screening to identify carrier status. What are other methods to reduce or prevent this increasing problem?
In some countries it is illegal to have a marriage within the family and it maybe the easiest way to reduce the risk. Otherwise a very expensive genetic screening may be the solution.
Ayurveda, the ancient system of medicine and science of life, believes that marriages should always be in 'Atulyagotra' i.e. from different clan. This is the only preventable measure for genetic abnormalities. Genetic screening and Preimplantation genetic diagnosis done in Artificial techniques (IVF) are other approaches but only rich can afford and also it is not available everywhere.
We still do not understand the effect of consanguinity on several of the polygenic traits, though some of the Mendelian disorders or diseases are better known e.g. HbS and these are tackled effectively, now a days, at several parts of the country and abroad, by social awareness and active role of NGOs and Scientist and government organisations. In case of single gene traits especially of autosomal nature, a community visit and local participation of their medical and other problems followed by pedigree information will reveal the potential load of the individuals at risk and their relatives. Social motivation and awareness helps the community to avoid the marriages involving risk individuals by free premdical tests. It has been so far successful in case of HbS among central, eastern regions both by government and NGOs and scientists involved.
I suggest to get the family information and detailed pedigree of the community involved, first to understand the prevalence and its occurrence. Sucn information in India is lacking. Though during early 1970 - 1980 to an extent early 1990s there were several studies to investigate the prevalence and effect of consanguinity among diverse community such activities now a days are very limited.
In this regard, it is also necessary also to remember that there are benefits of consanguineous marriages as well and there are some well investigated publications on the benefits of consanguineous marriages both soci-cultural and biological aspects. I strongly advise Dr. Jagat Ram to get these well investigated and maintain a pedigree record with medical, clinical and other relevant information. This effort has multiple advantages to get to know the prevalence, to calculate the risk factor, and imporantly the genetics of consanguinity. This in the current genome wide world will help us to understand the complex genetic nature and its possible SNPs and how they phenotypically manifest etc.
Dear Ru-Jeng Teng, I agree, marriage with in the same family and blood relation should be avoided to prevent hereditary diseases in a consanguineous population . Marriage within the same family is common in some community particularly some of the Muslim community but less common in Hindu.
Dear Jagat: I am fully aware of the the tradition. Marriage between cousins were quite common among Chinese decades ago and has been a thounsands of year tradition for high societal level families. It took two decades in my home country after changing the marriage law. I do not think changing a tradition will be easy so prenatal genetic testing maybe the only solution. But, how much we should pay for a thorough whole genome sequencing? Yes, the nex-generation whole genome sequencing is avilable but how many of us can really interpret the read-out in days although the data can be available very quickly? To my knowledge there are some patients still waiting for the interpretation 3 years after the WGS. This is especialy true when you do not know a specific gene to look into. Worst of all, I have seen so many incidences that one parent with known genetic disorder inheritance hid the truth against the other parent so the marriage could go through. Simply express my personal experience here and have no intention to start up a dabate about culture.
Would like a put another thought. Yes, there maybe societal benefit for consanguious marriage but, to the best of my knowledge, there is no proven biological benefit. In scientific study we use inbred animal, typical consanguinity, to amply a specific disease prone genetic trait. Yes, we may also create better strains but more commonly they end up with other disorders. How many of us as a physciain can actually obtain a very thorough family history for every single one of our patients? No to say how many of the family with known genetic disorders really want to elaborate their secret? Another problem is when the disease happened in a distant relative who the patient has never known for life.
Dear Teng,
We still do not understand the genetic consequences of consanguinity practices over short period and over long period of thousands of generations/years. Dr. Sanghivi, theoretical and applied population geneticist was interested in these issues in Indian context and is responsible for large scale studies both community and population wise. He also theoretically worked out the effects of consanguinity practices over generations. The theoretical expectation is that the effects gets optimised over generations (this is published in Medical Genetics in India, proceedings publications of 1977 conference). His expectation that in the long run exposure of deleterious recessive alleles in a consanguineous situation should gets wiped out of the community, unless in case of new mutation, which is supposedly a very rare event. This expectation is appears to be true theoretically as he has shown. It is true that we do get cases of traits, some of them clinically, medically undesirable and could have deleterious effect is observed in some specific families or communities, implying possible effect of consanguinity. But we still do not undersand how it manifests and can give an plausible explanation it is because of consanguinity.
As you have said, I agree, that we do not have specific concurrent scientific evidence to the biological effects of consanguinity. May be we do not have an experimental design suitable to investigating the effects of consanguinity and also the theoretical expecations of the effects of consanguinity is not well worked out. Hope some theoretical population geneticist will able to make a better statement in this regard. In India, there was a well designed prospective study conducted by Prof. PSSS Rao, (CMC, Vellore) in later part of 1970s over a large population. After a couple of years of follow up of the fertitility and mortality variables among the consanguineous and nonconsanguineous couples, the results showed no signficant differences among consanguineous and nonconsanguineous copules of the same area in the outcome of fertility and mortality schedules. These results you can get in from Annals of Human Genetics archic issues. Yes. there are also benefits of consanguineous marriages, which is not well investigated to an extent than the undesirable effects of such marriages. It is well known that some of the talents runs in families and communities and they appear to be family relatives. There are examples in mathematical sciences and music, painting, etc. We still do not how to investigate these issues and do not have a genetic hypothesis and the methodological aspects of investigation to draw for a suitbale population etc. Hope the genome wide scan among these families will help us to have a better understanding and insight of the effect of consanguinity and how it manifests.
In my opinion these are mostly settled questions. Here are some references that should help you understand why I believe this to be so:
Inconsistencies in genetic counseling and screening for consanguineous couples and their offspring: the need for practice guidelines. Bennett RL, Hudgins L, Smith CO, Motulsky AG. Genet Med. 1999 Sep-Oct;1(6):286-92.
Genetic Counseling and Screening of Consanguineous Couples and Their Offspring: Recommendations of the National Society of Genetic Counselors. Robin L. Bennett, Arno G. Motulsky, Alan Bittles, Louanne Hudgins, Stefanie Uhrich, Debra Lochner Doyle, Kerry Silvey, C. Ronald Scott, Edith Cheng, Barbara McGillivray, Robert D. Steiner and Debra Olson. Journal of Genetic Counseling, Vol. 11, No. 2, April 2002
In addition, I would explain that social psychology experiments have revealed that two factors powerfully influence human mating preference. These are proximity and similarity in roughly that order. If potential mates are co-located, they are much more likely to bond especially if they share similar values, ethnicity, beliefs, culture, social and economic class etc. A cosmopolitan life promotes genetic diversity, which is good for the species.
I do understand there are a lot of theoretical benefits for consanguineous marriage but I also experience so many patients as the product of it with severe non-treatable genetic disorders. If a culture strongly belief the societal benefit far overweighs the burden of biological concern than this is not an issue. I was trained to take thorough family history but practically how many times I can actulally get the whole story? A very common senario is "I have to ask the grandparents who live in another state and can not come for some reason". However, I do know a lot of genetic disorders run in certain ethnic group due to practice of consanguineous marriage in their culture. Yes, the chance mostly is one out of four. If a culture feels it is O.K. then there is definitely no a concern.
Dear Ru-Jeng Teng. I agree with your convincing answer such as changing the marriage law and once done it may take few years to decades to see the beneficial effect. Changing the tradition is not easy. Genetic issues are also not very simple but are important. Public awareness of problems arising from consanguineous marriage may play important role.
Dear Gold Bert, I agree with you regarding genetic Counseling and Screening of Consanguineous Couples and Their Offspring. It is correct that two factors powerfully influence human mating preference. These are proximity and similarity in roughly that order and the bond is strong is they share similar value.
It has been a great discussion among the contributors. There is no quick fix and I have no intention to convince changing the marriage laws since they are up to the societal standard and culture. Proximity and similarity are two important bonds to marriage but also because some society take them so seriously so marriage between two different societal levels, unfortunately, is banned. But, let us focus on the consanguinity and inherited genetic disorder which is what this discussion all about. Also, proximity and similarity do not happen only in consanguineous marriage. This kind of bonding can also happen in a similar societal rank, or level, from different families.
I remember recently reading of some pre-marital testing being done more or less routinely in a very insular population to try to prevent recessive disease; it may be feasible and makes the most sense when specific common genes known in the population can be tested in advance, I think it was among Samaritans. Here is an abstract of an article that I thought was thoughtfully presented on the subject: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3419292/.
Genetic testing assumes that a known disease-causing gene has been identified.
In cultures with arranged marriages where there is a high frequency of hereditary disease with known genetic basis, testing can be helpful. In cultures where in vitro fertizilation is an option, pre-implantation diagnosis is a possibility to select embryos for implantation that do not carry the family's genetic defect.
Well, if you want to be cheap about it, the DTC gene tests (e.g. 23andme) will advise on quite a few of the more common autosomal recessives for as little as $99.00 plus tax. After the fact, the ARUP SNP array and probably others will assess for and look at details in regions of homzygozity if they are large enough, but we are still seeing that most autosomal recessive disease is "luck of the draw" rather than due to actual consanguineuity.
23 and me has some advantages
- lots of data (like Wikipedia).
At present 23 and me also has many disadvantages
- much of the interpretation is incorrect (like Wikipedia)
- no quality control like that used for diagnostic tests
- no genetic counseling
Those with significant experience in genetics might find the raw data useful. A large proportion of the 23 and me associations with disease are poorly supported by data and misleading.
Beware!
Next Gen Sequencing is opening new avenues for prevention. It is becoming possible to identify a mutation if someone in the family has a condition and base further counseling on that knowledge.
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