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Excess of twins among affected sibling pairs with autism: implications for the etiology of autism.

ABSTRACT: It is widely accepted that genes play a role in the etiology of autism. Evidence for this derives, in part, from twin data. However, despite converging evidence from gene-mapping studies, aspects of the genetic contribution remain obscure. In a sample of families selected because each had exactly two affected sibs, we observed a remarkably high proportion of affected twin pairs, both MZ and DZ. Of 166 affected sib pairs, 30 (12 MZ, 17 DZ, and 1 of unknown zygosity) were twin pairs. Deviation from expected values was statistically significant (P<10(-6) for all twins); in a similarly ascertained sample of individuals with type I diabetes, there was no deviation from expected values. We demonstrate that to ascribe the excess of twins with autism solely to ascertainment bias would require very large ascertainment factors; for example, affected twin pairs would need to be, on average, approximately 10 times more likely to be ascertained than affected non-twin sib pairs (or 7 times more likely if "stoppage" plays a role). Either risk factors (related to twinning or to fetal development) or other factors (genetic or nongenetic) in the parents may contribute to autism.

SUBMITTER: Greenberg DA

PROVIDER: S-EPMC1274353 | biostudies-literature | 2001 Nov

REPOSITORIES: biostudies-literature

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Excess of twins among affected sibling pairs with autism: implications for the etiology of autism.

Greenberg D A DA Hodge S E SE Sowinski J J Nicoll D D

American journal of human genetics 20011002 5

It is widely accepted that genes play a role in the etiology of autism. Evidence for this derives, in part, from twin data. However, despite converging evidence from gene-mapping studies, aspects of the genetic contribution remain obscure. In a sample of families selected because each had exactly two affected sibs, we observed a remarkably high proportion of affected twin pairs, both MZ and DZ. Of 166 affected sib pairs, 30 (12 MZ, 17 DZ, and 1 of unknown zygosity) were twin pairs. Deviation fro ...[more]

PMID: 11590546

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Project description:ObjectiveConverging lines of evidence point to the existence of immune dysfunction in autism spectrum disorder (ASD), which could directly affect several key neurodevelopmental processes. Previous studies have shown higher cytokine levels in patients with autism compared with matched controls or subjects with other developmental disorders. In the current study, we used plasma-cytokine profiling for 25 discordant sibling pairs to evaluate whether these alterations occur within families with ASD.MethodsPlasma-cytokine profiling was conducted using an array-based multiplex sandwich ELISA for simultaneous quantitative measurement of 40 unique targets. We also analyzed the correlations between cytokine levels and clinically relevant quantitative traits (Vineland Adaptive Behavior Scale in Autism (VABS) composite score, Social Responsiveness Scale (SRS) total T score, head circumference, and full intelligence quotient (IQ)). In addition, because of the high phenotypic heterogeneity of ASD, we defined four subgroups of subjects (those who were non-verbal, those with gastrointestinal issues, those with regressive autism, and those with a history of allergies), which encompass common and/or recurrent endophenotypes in ASD, and tested the cytokine levels in each group.ResultsNone of the measured parameters showed significant differences between children with ASD and their related typically developing siblings. However, specific target levels did correlate with quantitative clinical traits, and these were significantly different when the ASD subgroups were analyzed. It is notable that these differences seem to be attributable to a predisposing immunogenetic background, as no other significant differences were noticed between discordant sibling pairs. Interleukin-1β appears to be the cytokine most involved in quantitative traits and clinical subgroups of ASD.ConclusionsIn the present study, we found a lack of significant differences in plasma-cytokine levels between children with ASD and in their related non-autistic siblings. Thus, our results support the evidence that the immune profiles of children with autism do not differ from their typically developing siblings. However, the significant association of cytokine levels with the quantitative traits and the clinical subgroups analyzed suggests that altered immune responses may affect core feature of ASD.

Project description:Cell-free DNA (cfDNA) in the human blood circulation has been under investigation since its initial observation in 1948. Plasma cfDNA is known to be significantly elevated in diseased people. Due to possible variation in the population, evaluating cfDNA as a non-invasive biomarker at disease onset alone may not be sensitive enough to accurately diagnose diseases, particularly early stage cancers on a personal level. To understand the factors that define the cfDNA levels on the personal level and for better use as a non-invasive biomarker, we isolated cfDNA from the plasma of healthy individuals with varying degrees of genetic and/or environmental similarities (monozygotic twins, dizygotic twins, sibling pairs, and unrelated individuals) as well as from patients with varying stages of breast and ovarian cancer undergoing treatment. Cell-free DNA levels were quantified by a fluorometer (ng/ml) and/or real-time PCR (copies/ml). The associations between individuals with various degrees of genetic and/or environmental similarities and their plasma cfDNA levels were evaluated. The ACE model (A = additive genetic, C = common environment, and E = specific environmental factors) was used to determine the proportion of each factor on the cfDNA levels. We found a high correlation (r = 0.77; p < 0.0001) in plasma cfDNA levels between monozygotic twins (n = 39). However, the correlation was gradually reduced to moderate (r = 0.47; p = 0.016) between dizygotic twins (n = 13) and low correlation (r = 0.28; p = 0.043) between sibling pairs (n = 26). The ACE model analysis showed that the plasma cfDNA level of a given healthy individual is influenced both by genetic and the environmental components in similar proportions (53% and 47%, respectively; A = 53%, C = 22.5%, E = 24.5%). Moreover, while age had no effect, gender significantly influenced the individual's plasma cfDNA level. As expected, cfDNA levels were significantly higher in both breast (n = 26) (p<0.0001) and ovarian (n = 64) (p<0.0001) cancer patients compared to the healthy individuals. Our study demonstrated that both genome and environmental factors modulate the individual's cfDNA level suggesting that its diagnostic sensitivity may be improved only if the person's cfDNA level is known prior to disease presentation.

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Excess of twins among affected sibling pairs with autism: implications for the etiology of autism.

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Excess of twins among affected sibling pairs with autism: implications for the etiology of autism.

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