To examine patterns of autism spectrum disorder (ASD) inheritance and other features in twin pairs by zygosity, sex, and specific ASD diagnosis.
Internet-based autism registry for US residents.
Survey results from 277 twin pairs (210 dizygotic [DZ] and 67 monozygotic [MZ]) aged 18 years or younger with at least 1 affected twin.
Zygosity and sex.
Concordance within twin pairs of diagnosis, natural history, and results from standardized autism screening.
Pairwise ASD concordance was 31% for DZ and 88% for MZ twins. Female and male MZ twins were 100% and 86% concordant, respectively, and DZ twin pairs with at least 1 female were less likely to be concordant (20%) than were male-male DZ twin pairs (40%). The hazard ratio for ASD diagnosis of the second twin after a first-twin diagnosis was 7.48 for MZ vs DZ twins (95% confidence interval, 3.8-14.7). Affected DZ individual twins had an earlier age at first parental concern and more frequent diagnoses of intellectual disability than did MZ twins; MZ twins had a higher prevalence of bipolar disorder and Asperger syndrome and higher concordance of the latter. Results of autism screening correlated with parent-reported ASD status in more than 90% of cases.
Our data support greater ASD concordance in MZ vs DZ twins. Overall higher functioning, psychiatric comorbidity, and Asperger syndrome concordance among affected MZ vs DZ twins may also suggest differential heritability for different ASDs. For families in which one MZ twin is diagnosed with ASD, the second twin is unlikely to receive an ASD diagnosis after 12 months. In addition, Internet parent report of ASD status is valid.
"This is because the primary differences between MZ and DZ twins, aside from nonshared factors (e.g., experiences outside the home, friends, etc.), are genetically mediated. Twin studies to date yield heritability estimates of ASD between 70 and 80%   . Aside from one recent study suggesting a significant contribution of shared environmental factors to ASD (experiences that are common to both twins, e.g., socioeconomic status and parental mental health problems ), these studies have generally reported small or nonsignificant shared environmental effects. "
[Show abstract][Hide abstract] ABSTRACT: Neurodevelopmental disorders represent a broad class of childhood neurological conditions that have a significant bearing on the wellbeing of children, families, and communities. In this review, we draw on evidence from two common and widely studied neurodevelopmental disorders-autism spectrum disorder (ASD) and attention-deficit hyperactivity disorder (ADHD)-to demonstrate the utility of genetically informed sibling designs in uncovering the nature and pathogenesis of these conditions. Specifically, we examine how twin, recurrence risk, and infant prospective tracking studies have contributed to our understanding of genetic and environmental liabilities towards neurodevelopmental morbidity through their impact on neurocognitive processes and structural/functional neuroanatomy. It is suggested that the siblings of children with ASD and ADHD are at risk not only of clinically elevated problems in these areas, but also of subthreshold symptoms and/or subtle impairments in various neurocognitive skills and other domains of psychosocial health. Finally, we close with a discussion on the practical relevance of sibling designs and how these might be used in the service of early screening, prevention, and intervention efforts that aim to alleviate the negative downstream consequences associated with disorders of neurodevelopment.
BioMed Research International 08/2015; 2015:672784. DOI:10.1155/2015/672784 · 2.71 Impact Factor
"( Fombonne , 2003 ) and affects approximately 1% of the population ( Centers for Disease Control and Prevention , 2012 ) . Recent studies have provided overwhelming evidence for genetic involvement in ASD ( Bishop , Maybery , Wong , Maley , & Hallmayer , 2006 ; Constantino et al . , 2006 ; Constantino , Zhang , Frazier , Abbacchi , & Law , 2010b ; Rosenberg et al . , 2009 ; Taniai , Nishiyama , Miyachi , Imaeda , & Sumi , 2008 ; Veenstra - VanderWeele , Christian , & Cook , 2004 ) . The risk of having a child with ASD increases with a family history of ASD , with heritability estimates ranging between 37% and 70% ( Constantino et al . , 2013 ; Hallmayer et al . , 2011 ) . First degree relatives of childr"
[Show abstract][Hide abstract] ABSTRACT: Head circumference growth in individuals with an Autism Spectrum Disorder (ASD) has been well characterized in the first two to three years of life and reflects a period of acceleration followed by a period of deceleration when compared with their typically developing (TD) peers. While this altered growth trajectory has been consistently found for head circumference, it is less clear if an abnormal growth trajectory also exists across measures of height and weight. Moreover, most studies have focused on infancy and early childhood, and no longitudinal data have been collected in older children with ASD. This review focuses on the physical growth trajectory of individuals with ASD, and proposes that a general growth dysregulation is present in ASD, and that an endophenotype within ASD may exist that is characteristic of extreme overgrowth. Two possible explanations for a general growth dysregulation are suggested: (1) a connective tissue disorder, which is frequently associated with increased height and disproportionate body ratios; and (2) a dysregulation of the hypothalamic–pituitary–adrenal (HPA) axis, which regulates growth hormones. The existence of a general growth dysregulation, and possible endophenotype, may serve as a potential biological marker in ASD.
"The measured ASD monozygote concordance rate using the IAN database varies from 41/60 = 0.683 (2014) to 59/67 = 0.881 or somewhere between 68.3% and 88.1%. What does the multimutation model predict the monozygote concordance rate to be? "
[Show abstract][Hide abstract] ABSTRACT: Whether autism spectrum disorder (ASD) is caused by genetics, environmental factors, or a combination of both is still being debated today. To help resolve this issue, a genetic multimutation model of ASD development was applied to a wide variety of age-of-onset data from the USA and Canada, and the model is shown to fit all the data. Included in this analysis is new, updated data from the Interactive Autism Network (IAN) of the Kennedy Krieger Institute in Baltimore, Maryland. We find that the age-of-onset distribution for males and females is identical, suggesting that ASD may be an autosomal disorder. The ASD monozygote concordance rate in twin data predicted by the genetic multimutation model is shown to be compatible with the observed rates. If ASD is caused entirely by genetics, then the ASD concordance rate of a cohort of monozygote twins should approach 100% as the youngest pair of twins in the cohort passes 10 years of age, a prediction that constitutes a critical test of the genetic hypothesis. Thus, by measuring the ASD concordance rate as a cohort of monozygote twins age, the hypothesis that this disorder is caused entirely by genetic mutations can be tested.
International Scholarly Research Notices 01/2015; 2015:1-10. DOI:10.1155/2015/519828
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