**1. Introduction**

[102] Schaefer GB, Mendelsohn NJ. Genetics evaluation for the etiologic diagnosis of autism spectrum disorders. Genetics in medicine : official journal of the American College of Medical Genetics. 2008 Jan;10(1):4-12. PubMed PMID: 18197051. Epub 2008/01/17. eng.

[103] Roesser J. Diagnostic yield of genetic testing in children diagnosed with autism spec‐ trum disorders at a regional referral center. Clinical pediatrics. 2011 Sep;50(9):834-43.

PubMed PMID: 21525079. Epub 2011/04/29. eng.

320 Recent Advances in Autism Spectrum Disorders - Volume I

Autism is a neurodevelopmental disorder characterized by impaired social interaction, and verbal and nonverbal communication as well as limited and repetitive behaviours. Although symptomatology of autism may be noticed around early months, diagnosis generally occurs around 24-36 months, however in some cases diagnosis may be delayed to adulthood [1]. Since behavioural symptoms and the degree of functional impairment are variable, the au‐ tistic disorder is described as a heterogenous symptom cluster of varying etiological and pathological basis [2]. Described as a multifactorial disorder created by interaction of neuro‐ logic, immunologic, environmental, and genetic factors, autistic disorder has no definite cause [3, 4]. In many cases in whom the etiology remains unclear are diagnosed as idiopath‐ ic autism or non-syndromic autism [5, 6]. Seventy percent of cases with idiopathic autism have basic symptoms without physical abnormalities whereas 30% have complex autism in which dysmorphic features are detected such as microcephaly and/or structural brain mal‐ formations [7]. Autism is associated with other syndromes such as Fragile X syndrome, Down Syndrome, and tuberosclerosis in 5-25% of the cases ([8, 9]. Although phenotypic het‐ erogeneity is the biggest challenge for research efforts directed to identify autism etiology [10], currently it is widely accepted that environmental and genetic factors play essential role in genesis of autistic disorder thanks to a recent advance in research techniques related to biological factors and widespread studies in this field [11, 12].
