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Thursday, May 12, 2016

Are Genetic Studies Revealing Consanguinamory is Common?

Someone commenting on this blog linked to this article at nature.com from the European Journal of Human Genetics, to which I only subscribe for the annual swimsuit issue. But seriously, the article is extremely technical. Those of you who are somewhat educated in the sciences, especially Biology in general or genetics in particular, may be able to decipher what's being said, but I think I understand what the Abstract said.

Abstract

Copy neutral segments with allelic homozygosity, also known as regions of homozygosity (ROHs), are frequently identified in cases interrogated by oligonucleotide single-nucleotide polymorphism (oligo-SNP) microarrays. Presence of ROHs may be because of parental relatedness, chromosomal recombination or rearrangements and provides important clues regarding ancestral homozygosity, consanguinity or uniparental disomy. In this study of 14574 consecutive cases, 832 (6%) were found to harbor one or more ROHs over 10Mb, of which 651 cases (78%) had multiple ROHs, likely because of identity by descent (IBD), and 181 cases (22%) with ROHs involving a single chromosome. Parental relatedness was predicted to be first degree or closer in 5%, second in 9% and third in 19%. Of the 181 cases, 19 had ROHs for a whole chromosome revealing uniparental isodisomy (isoUPD). In all, 25 cases had significant ROHs involving a single chromosome; 5 cases were molecularly confirmed to have a mixed iso- and heteroUPD15 and 1 case each with segmental UPD9pat and segmental UPD22mat; 17 cases were suspected to have a mixed iso- and heteroUPD including 2 cases with small supernumerary marker and 2 cases with mosaic trisomy. For chromosome 15, 12 (92%) of 13 molecularly studied cases had either Prader–Willi or Angelman syndrome. Autosomal recessive disorders were confirmed in seven of nine cases from eight families because of the finding of suspected gene within a ROH. This study demonstrates that ROHs are much more frequent than previously recognized and often reflect parental relatedness, ascertain autosomal recessive diseases or unravel UPD in many cases.
Taking a closer look...
"Parental relatedness was predicted to be first degree or closer in 5%, second in 9% and third in 19%"
Now, "parental relatedness" being "first degree" means someone's genetic parents were parent and child or full siblings. That's for 5% of the population, or, 1 out of every 20 people.

"Second degree" means uncle and niece, aunt and nephew, grandparent and grandchild or half-siblings. That's 9%, or almost 1 out of every 10 people having such parentage.

"Third degree" means first cousins or some similar distance. That 19%, or nearly 1 out of every 5.
"This study demonstrates that ROHs [regions of homozygosity] are much more frequent than previously recognized and often reflect parental relatedness..."
Unless I'm reading that wrong, these scientists are saying more people in the population have close relatives for parents than previously thought.

It is important to remember that these do not all reflect CONSENSUAL (to be redundant) sex. At least some are, no doubt, the result of rape. Still, the indication is that...

1) A significantly large percentage of the population has genetic parents who are first cousins or closer, and most of them do not have severe genetic problems, or a whole lot more people would have such problems;

2) Even if we only count consensual relationships that are producing children (and we know that many consanguineous relationships don't because either they can't or choose not to), there's a lot of consanguinamory going on out there.


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4 comments:

  1. Anon who posted the article here.

    I am not a geneticist, nor a scientist, but a common problem is that while the sample size is large it could be biased in a particular way. One might imagine the sample includes a subset of the population who had their genes scanned because they had what was thought to be a genetic problem.

    What this might be saying is that if you have a genetic issue there is a higher probability of it being caused by a recessive trait.

    Another possibility is that recessive genes are far more common than thought. This could be true too, as that is a large sample size (intuitively).

    ReplyDelete
    Replies
    1. Yeah, when I read the beginning of the methodology/methods sections, which describes how studies are done, it said that they did the study based on people who already showed problems.

      Delete
  2. Oops! Just rechecked & it says methods and materials not methodology/methods.

    ReplyDelete
    Replies
    1. So in people with problems, the majority of problems were not caused by he parents being closely related.

      Delete

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