Inbreeding and Genetic Disease
In January, scientists found that humans and chimps have a higher than expected number of genetic mutations due to inbreeding. Inbreeding isn’t necessarily limited to matings between people who are close relatives, it can also refer to matings between members of a small population where the genetic variation is small. Some well-known recessive diseases that can arise from inbreeding are hemophilia and Tay Sachs disease.
In modern life, inbreeding is still a concern in some populations. Public health experts in western Galilee have begun a project to educate citizens in areas with large Arab populations about the dangers of inbreeding. (Jerusalem Post, August 15, 2005)
Such consanguineous marriages [inbreeding], Dr. Avshalom Strulov of the University of Haifa’s Faculty of Social Welfare and Health Studies and of the Health Ministry’s Northern District health office writes, “are not part of the Islamic religion” and are indeed harmful since they lead to the conception of fetuses with serious inherited diseases.
The truth is, most first cousin marriages are at only slightly greater risk of producing children with genetic disorders - children of non-related couples have a 2-3% risk of birth defects, as opposed to first cousins having a 4-6% risk and second cousins have little to any increase in risk of having children with genetic disorders.* It all comes down to the kinds of defective genes parents carry which could be passed down to their children. And that occurs even when parents come from families which do not overlap for many generations. (All our families overlap at some point in the past even if it is hundreds or thousands of years ago.)
Genetic testing would be a more straightforward way to address this issue and is the standard in most industrialized countries. Genetic counseling is offered to couples–related or not–who have a family history of inherited diseases. The National Society of Genetic Counselors official recommendation for consanguineous couples is:
…beyond a thorough medical family history with follow-up of significant findings, no additional preconception screening is recommended for consanguineous couples. Consanguineous couples should be offered similar genetic screening as suggested for any couple of their ethnic group. During pregnancy, consanguineous couples should be offered maternal-fetal serum marker screening and high-resolution fetal ultrasonography. Newborns should be screened for impaired hearing and detection of treatable inborn errors of metabolism.
Maybe genetic testing is still too expensive to be incorporated into medical care in western Galilee. Until DNA analysis becomes widely available, affordable, and routine, some Arab couples in love and wishing to marry will have to deal with the disapproval of healthcare professionals and others in their community.
I guess love doesn’t conquer all.
Pointer from Blogging Baby.
*Thanks to reader Brad for the correction. Cousin Couples has facts about cousin marriages.
ETA: Reader Razib brings up some excellent points about Arab culture in his post on the subject at Gene Expression. For example, marrying close relatives within the same Arab clan is more common than in most other cultures and thus would lead to a higher frequency of congenital diseases. Razib also has a more technical discussion complete with equations if you are so inclined.
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4 opinions for Inbreeding and Genetic Disease
Brad
Aug 17, 2005 at 10:11 pm
Your statement that "most first cousin marriages are at no greater risk of producing children with genetic disorders" seems misleading to me. I agree that most people probably don’t have any recessive genes for genetic disorders, but among those who do, their first cousins are significantly more likely to share that gene with them compared to a non-relative, and therefore children of such a marriage would be at a far greater risk of genetic disorders than if those same people had married non-cousins. Considering that few (if any) of us can say with 100% confidence that we have zero recessive genes for genetic disorders, it seems that practically everyone would be at <i>some</i> elevated risk for having children with genetic disorders if they were to procreate with a first cousin.
I hope that makes sense. I do know where you’re coming from, but until each of us knows our entire genome, I’m not sure we can say with any confidence that having children with a first cousin doesn’t carry any greater risk.
Lei
Aug 17, 2005 at 10:21 pm
Brad, I stand corrected. Research has shown that children of matings between first cousins are only at slightly elevated risk of genetic diseases - children of non-related couples have a 2-3% risk of birth defects, as opposed to first cousins having a 4-6% risk and second cousins have little to any increase in risk of having children with genetic disorders. Genetic counselors agree that this small increase in risk could easily be managed with proper genetic counseling.
(I’ll go make the edit now.)
» Implications of the Dog Genome Genetics and Health
Dec 8, 2005 at 5:37 am
[…] A list of 2.5 million common genetic differences between dogs has been compiled, which will make it easier to understand the effects of intensive inbreeding and selection for specific traits. […]
Genetics and Health » Inbreeding and Diabetes in Norfolk, UK
Aug 14, 2006 at 11:36 am
[…] Rob at Diabetes Notes has already written about Dr. Ian Gibson’s comment on BBC Radio that the higher incidence of type 1 diabetes in Norfolk, UK may be partially explained by inbreeding. The Spoof! has more. Dr Gibson, 67, stood by his comments yesterday, to achieve this he had them enlarged and placed on a poster, and insisted that he had not meant to cause offence. “If you have a high frequency of genes with a predisposition to type 1 diabetes, then you have to ask why that is,” he said. […]
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