Is it conceivable that a large number of these genes may be mutated

or play a role in autism? Gene variants at a significant number of these loci may contribute to autism in a complex genetic fashion. Regarding the vast genetic heterogeneity that may be at play in autism, it is worth considering the genetic architecture of intellectual disability (ID). Of course, ID may be related to autism in many cases, as approximately 38% of children with autism also have co-occurring ID.2 ID is caused by a large variety of mutations, including chromosomal as well as many monogenic mutations such as X-linked loci. Indeed, greater that 10% of the genes on the X chromosome may Inhibitors,research,lifescience,medical be associated with ID.23 By the lessons of ID, there are genetic mutations that would perturb just about all steps

of neurodevelopment (Figure 1): however, if we restrict the clinical scope to “non-syndromic” intellectual Inhibitors,research,lifescience,medical disability (ie, cognitive effects without structural brain or medical effects), the mechanisms may be more refined to synaptic structure and in particular dendritic spine abnormalities.24 Here, we also contend that those steps of neurodevelopment that are involved in autism are find more similarly constrained, and we will argue here that they are constrained to those Inhibitors,research,lifescience,medical steps that affect the formation of neuronal circuitry, ie axon and dendrite growth and arborization, and experience-dependent synaptic modification. Heterogeneous gene mutations in autism Genetic studies in ASD have made substantial progress in the last decade. Numerous, individual mutations, largely corresponding to rare genetic variants, have been Inhibitors,research,lifescience,medical discovered.4,25 These studies have elucidated a

variety of genetic loci and pathways regarding the genetic architecture of autism. No single locus in question appears Inhibitors,research,lifescience,medical to be found in greater than 1%, and the majority of loci are recurrent at a much lower Parvulin rate, and some representative of private (single mutations). The nature of the rare mutations include gross chromosomal anomalies, copy number variants, single nucleotide variants, particularly de novo variants.26-30 These mutations have pinpointed a heterogeneous group of genes and loci that may contribute to the pathobiology of autism. These mutations appear to affect a range of mechanisms (Table I) including those that regulate: (i) gene expression; (ii) pre-mRNA splicing; (iii) protein localization, translation, and turnover; (iv) synaptic transmission, such as synaptic vesicle release and membrane excitability; (v) cell signaling; (vi) cytosketal and scaffolding proteins particularly at the postsynaptic membrane; and (vii) neuronal cell adhesions molecules.