The substantial degree of familial clustering with ASD could be due predominantly to genetics, or shared genetic and environmental factors, but cannot be explained predominantly by environmental factors. Epidemiological studies of concordance of ASD in same-sex twins favor a predominantly genetic explanation, with heritability of at least 90% under a multi-factorial threshold model . By contrast, a recent twin study [12•] estimated heritability to be 37% for strict autism and similar for ASD, albeit
with a wide confidence interval (8–84%). Selleckchem Ceritinib For various reasons, including the relatively low population prevalence of ASD and the relatively high frequency of de novo DNA alterations that can affect risk, interpretation of these twin studies is not straightforward. We expand on the issue of de novo variants in subsequent discussion. Concordance for a phenotype of either autism or milder cognitive and social deficits was 82% among monozygotic (MZ) twins, compared with ≈10% in DZ twin pairs [7, 9 and 13]. This finding suggests that the ASD phenotype extends beyond the traditional diagnostic boundaries to a subclinical realm: the so-called broader autism phenotype . Family studies have similarly shown a marked increase in subclinical cognitive or behavioral features among the relatives of autistic individuals, compared with those of controls. Considering these data, and the striking similarity between autism
and the milder social deficits seen in some children, autism is now seen to
encompass a spectrum of similar, often genetically related disorders, and as a result the Diagnostic and Statistical Manual PI3K Inhibitor Library solubility dmso of Mental Disorders edition V (DSM-V) plans to group them under the single entity of ASD (Figure 1). As we shall discuss, Flucloronide various genes certainly have an important role in ASD, and there has been incremental progress toward their identification, enhancing clinical definition and diagnostic tools [3, 15, 16, 17 and 18]. Approximately 10% of individuals with ASD have an identifiable Mendelian condition or genetic syndrome. Fragile X syndrome (≈1–2% of ASD cases), tuberous sclerosis (≈1%), Rett syndrome (≈0.5%) and neurofibromatosis (NF1; <1%), are the most commonly cited. Other rare microdeletion or single gene defects have been associated with ASD including those found in Williams–Beuren, Sotos, Cowden, Moebius, Smith-Lemli-Opitz, and Timothy syndromes. ASD can also occur in some mitochondrial diseases and untreated phenylketonuria. A recent review  identified over 103 disease genes and 44 genomic loci among subjects with ASD or autistic behavior. These genes have all been causally implicated in intellectual disability, indicating that these two neurodevelopmental disorders often share a common genetic basis [20••]. High-resolution karyotyping reveals cytogenetically visible chromosome rearrangements in ∼5% of individuals with ASD. Our previous survey  found such abnormalities in 129/1749 ASD cases (7.4%).