It would have been pretty annoying, starting with the fact that Duf 1220 has changed names three times and is not even a full protein, so it was already difficult to find out the exact sequences I was going to look for. I was already gearing up to find out how to extract the copy numbers directly from the genome data. The 1000 Genomes Project has collected whole genome sequencing data from more than 2000 persons coming from a few dozen different populations. There is data out there to test this hypothesis. If they are strongly correlated with IQ and some groups just have more copies, that would be it. Duf 1220 copy numbers provide an absolute scale. Because they were calculated on the basis of a particular population, there is always the possibility that other populations just have other causal variants, or maybe the same causal variants but tagged by different non-causal variants. This is something polygenic scores cannot do fully convincingly. For better or for worse, it might give an undeniable genetic underpinning to IQ differences between ethnic groups. There is another major thing Duf 1220 exploration might bring about. So if a significant part of the genetic variation in IQ is due to copy number variation, the upcoming polygenic scores for IQ will miss out on that. SNP-data, however, doesn’t give you copy numbers. Such polygenic scores are expected to capture almost all of the genetic variation in one of the upcoming studies, as the data sets approach a million genomes and more. These polygenic scores are computed on the basis of SNP-sequencing, so basically a couple of hundred thousand known genetic variants are looked up for hundreds of thousands of people and then these variants are correlated with a measure of IQ. This could present a major roadblock for polygenic scores for IQ that capture a significant part of the variation. There also hasn’t been a try yet to replicate this result, though the whole genome sequencing data that UK biobank is aggregating in 2018/19 should be ideal for that, so hopefully it is only a matter of time. So it is hard to say how this would generalize to the population at large. There is a caveat here, that the populations had been selected for unusual brain sizes, apparently because Duf 1220 mutations have also been implicated in cases of microcephaly and macrocephaly. IQ points (CON2 copy numbers varied from 26 to 33). And while the correlation is not very strong, the effect size is pretty big: A one copy increase is associated with a rise of 3.3. There is a 2014 paper that shows a correlation between CON2 copy number and IQ, as well as between CON2 copy number and mathematical aptitude in two different populations. The more interesting finding, however, concerns CON2. This is a data point in favor of a hunch many people seem to have, that autism and schizophrenia are to a certain degree opposites. More copies increase the severity of autism symptoms, but ameliorate the symptoms of schizophrenia. CON1 copy number variation has been correlated with symptom severity in both autism and schizophrenia. ![]() There are several slightly different versions of Duf 1220: Three versions conserved in mammals, CON1, CON2, CON3, and three human lineage specific versions, HLS1, HLS2, HLS3. ![]() Humans underwent rapid copy number expansion since our split from Chimpanzees, so it might just be an essential part of what made us human. It correlates with brain size and number of neurons in the neocortex. The number of Duf 1220 copies rises with increasing cognitive sophistication of the animal. a conserved part of a protein, and mammals generally have several copies of its coding sequence.
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