8 May 2014 updated 17 May 2014
I have long been conscious of the genetic risks of marrying one’s first cousin. Sadly many people are unaware of them, or fail to understand what they mean or sometimes even deny that there are any genetic risks.
That led me to write my piece “Playing Russian roulette with my baby's health: the health risks of marrying one's first cousin”. It starts with a fable to explain what the risks mean, and then links to a number of scientific papers which establish beyond doubt that the genetic risks are real and measurable.
Since I wrote it on 26 September 2010 the page has been viewed 7,927 times as of today. Indeed it is the most visited page on my website after the "Home" and the "About me" pages.
It is sobering to reflect that if even 1% of visitors to the page have been deterred from marrying their first cousin that will represent 79 first cousin marriages that have not taken place. With a roughly 3% incremental risk of a genetically damaged baby if one marries a first cousin, statistically my publishing the page will have saved between two and three couples from having such a baby with the devastating consequences that follow for both the baby and its parents.
Accordingly, when I learned of the publication of this book in 2012, I immediately bought it. However due to time pressures, I was only able to complete reading it earlier this year.
It is a relatively short book, 318 pages including the index. The simplest way of giving an overview of the book is to reproduce the table of contents.
The author, Alan H. Bittles is Adjunct Professor and Research Leader in the Centre for Comparative Genomics, Murdoch University, Australia and also Adjunct Professor of Community Genetics in the School of Medical Sciences, Edith Cowan University, Australia.
As one would expect from the author's background and the table of contents reproduced above, the book is extremely comprehensive.
The scientific literature is well referenced as one would expect from the author's scientific background. However the author has been equally detailed in researching the social history aspects of the subject. For example he explains clearly the detailed history of how it came about that the Coptic Orthodox Church permits consanguineous unions while the Greek and Russian Orthodox Churches do not.
The scientific coverage in the book will be challenging for people to read unless they have a strong scientific background. Even though I have a degree in mathematics, studied sciences at A-level, and have subscribed to "Scientific American" magazine for over 30 years, in places I found it heavy going.
Accordingly I recommend that readers who do not have a scientific or medical background should give this book a miss as large parts of it will not be accessible to them.
Conversely, for those readers who are comfortable with reading scientific material, I recommend the book very strongly as it provides an excellent comprehensive and objective summary of the subject.
Bittles is very fair and precise in pointing out the genetic risks from marrying one's first cousin, and also other consanguineous unions. The risk factors he mentions are essentially the same as in my website article. That is to be expected since in some cases we are referencing the same original scientific papers.
When I posted this review originally, I made the comment:
Where I find the author’s writing unsatisfactory is that he appears to downplay the significance of the genetic risks while over-emphasising the claimed social benefits of consanguinity. I believe that in doing so he suffers from excessive cultural sensitivity.
Due to a happy coincidence, I have since made contact with Professor Bittles by email. In our correspondence, he made me realise that in the above comment I took an excessively "advanced country" centric view. An extra 3% risk of a genetically damaged baby matters far more in an environment with good healthcare where life expectancy at birth may be approaching 80 years, than it does in an environment with poor healthcare and high informant mortality, where many babies may not even live to the age of one. The social benefits may be roughly the same in both environments, while the the genetic risks are proportionately much more significant in the advanced country.
However as most readers of this website live in advanced countries, and standards of healthcare are developing rapidly even in poor countries such as China, India and African countries, I believe that it remains right to treat the genetic risks of consanguinity as being very serious.
The encouraging news is that as levels of education and urbanisation increase, the levels of consanguinity diminish.