tag:blogger.com,1999:blog-5548560205914833324.post3710766239219989402..comments2023-04-23T00:16:48.148+01:00Comments on Questioning Answers: On the broader autism phenotypePaul Whiteleyhttp://www.blogger.com/profile/14288851488012254897noreply@blogger.comBlogger4125tag:blogger.com,1999:blog-5548560205914833324.post-77317134413700650922012-03-10T11:40:29.775+00:002012-03-10T11:40:29.775+00:00How the broader autism phenotype may be a backgrou...How the broader autism phenotype may be a background genetic effect has been demonstated in Downs Syndrome with or without co-occurring autism. Ghaziuddin compared a group of Downs Syndrome children with or without co-occurring autism. In Downs Syndrome with co-occurring autism there was an excess of first degree relatives who met the description of BAP features compared to first degree relatives in children with Downs Syndrome without co-occurring autism who did not meet the description of BAP features. None of the first degree relatives in Downs Syndrome with co-occurring autism were diagnosed either with Downs Syndrome or autism ( Ghaziuddin M ) (Ghaziuddin1997 ).<br /><br />http://www.ncbi.nlm.nih.gov/pubmed/11079353<br /><br />http://www.ncbi.nlm.nih.gov/pubmed/9089464RAJhttps://www.blogger.com/profile/17686665037607780553noreply@blogger.comtag:blogger.com,1999:blog-5548560205914833324.post-69255867763838897692012-03-10T11:24:01.198+00:002012-03-10T11:24:01.198+00:00Thanks RAJ.
I agree that the 1995 twin study does...Thanks RAJ.<br /><br />I agree that the 1995 twin study does perhaps seem a little 'dated' in light of the subsequent research on the complexity of the genetics of autism and the introduction of epigenetics on to the scene.<br /><br />I'm glad you referenced Fransesca Happe's paper and the important conclusion that they (and everyone else) have come to on autism heterogeneity and how using behavioural 'markers' as a starting point really hasn't cut the mustard in terms of elucidation of underlying biological processes.Paul Whiteleyhttps://www.blogger.com/profile/14288851488012254897noreply@blogger.comtag:blogger.com,1999:blog-5548560205914833324.post-80569678670022827332012-03-10T11:18:59.008+00:002012-03-10T11:18:59.008+00:00As far as the twin studies are concerned, twin stu...As far as the twin studies are concerned, twin studies were introduced by Sir Francis Galton more than one hundred years ago long before the discovery of DNA. Researchers continue to believe that you can calculate a heritability estimate based on the assumption that the genetic effect seen in MZ twins are always inherited. Based on early European twin studies there isn't a research paper that does not reference these early twin studies and state that autism is the most heritable of the developmental disorders based on the concordance rate in MZ twins compared to DZ twins. Not so. The concordance rates seen in MZ twins with Downs Syndrome is nearly 100% and the concordance rates in DZ twins are nearly 0% which paradoxically would make Downs Syndrome, not autism the most 'heritable' of all the developmental disorders.<br />The 1995 British autism twin study, the most referenced twin study ever published excluded twin pairs where one or both twins had an identifiable medical cause. Three twin pairs were excluded, one pair each with Down's Syndrome, Williams Syndrome and congenital rubella syndrome. None of those syndromes are inherited.<br />The classical twin studies does not control for de novo gene mutations and will always overstate the 'heritability' of autism.RAJhttps://www.blogger.com/profile/17686665037607780553noreply@blogger.comtag:blogger.com,1999:blog-5548560205914833324.post-17145718179179408392012-03-10T10:18:13.825+00:002012-03-10T10:18:13.825+00:00Unaffected siblings have been found to have simila...Unaffected siblings have been found to have similar results to their ASD diagnosed siblings in comparison to typically developing controls. As reported by Dalton et al 2007: 'The siblings gaze fixations and brain activation patterns during the face processing task were similar to that of the autism group and showed decreased gaze fixation along with diminished fusiform activation compared with the control group. Furthermore, amygdala volume in the siblings was similar to the autism group and was significantly reduced compared with the control group'.<br /> <br />These findings suggest that what is inherited in these families is not autism as such but rather the broader autism phenotype. The prevelance of severe to moderate BAP features in general population children is about 10% suggesting that the BAP is far too frequently present in the general population to be considered as a causal mechanism rather than a risk factor of small effect. Happe, Arnold and Plomin 2006 on the prevelance of the BAP in general population child "Around 10% of all children showed only social impairment, only communicative difficulties or only rigid and repetitive interests and behavior, and these problems appeared to be at a level of severity comparable to that found in children with diagnosed ASD in our sample'.<br /> <br />Dalton et al 2007.Gaze-fixation, brain activation, and amygdala volume in unaffected siblings of individuals with autism.<br /> <br />http://www.ncbi.nlm.nih.gov/pubmed/17069771 <br /><br />Happe, Arnold & Plomin 2006. Time to give up on a single explanation for autism.<br /> <br />http://dept.wofford.edu/neuroscience/neuroseminar/pdfFall2011/4-explaining-autism.pdfRAJhttps://www.blogger.com/profile/17686665037607780553noreply@blogger.com