Recent Advances in the Genetics of Autism Spectrum Disorders: A Minireview

Abstract

Introduction Autism is a severe neuropsychiatric pervasive developmental disorder with an early childhood onset. The condition is recognised in preschool age children but it is a lifelong disorder. Its clinical characteri-sation includes impairments in social interactions, communication or language abnormalities and restricted repetitive or stereotyped behaviour (American Psychiatric Association, 2000). The repetitive behaviour consists of repetition of words and phrases in a stereotyped way and movements of the limbs and body. These stereotypical movements may not be specific for autism because they also occur in patients with dementia, in particular, fron-totemporal dementia (Mendez et al., 2005). The communication deficit persists in children with autism (Wray et al., 2005) and hence early diagnosis of language development in autism is important. Impairment in social interactions could be due to a deficit in spatial focusing of auditory attention (Teder-Salejarvi et al., 2005). In adolescence, cognitive ability and social interaction skills may improve in some cases (McGovern and Sigman, 2005). The risk of developing autism has been consistently found to be associated with infantile microcephaly, different kinds of social impairments (Wing, 1997) and accelerated head growth in early development (Bolton et al., 2001; Dementieva et al., 2005). The clinical characteristics of the disorder closely overlap with other related conditions such as Asperger syndrome and atypical autism and hence autism is classified under a broad domain of pervasive developmental disorders. Although there is some similarity between autism and Asperger syndrome, they differ in their natural history , age of onset and sleep problems (Simpson, 2003; Polimeni et al., 2005). There are considerable variations in clinical presentation and severity of impairment in autism among affected individuals even within the same family. A variety of early developmental delays have been currently used to diagnose the autistic condition. Previous studies have reported a lower 130 incidence rate of approximately 4-10 per 10,000 individuals for autism (Smalley et al., 1988; Gillberg and Wing, 1999). However, recently it has been found that the incidence of autism is continuously rising with time (Rutter 2005). For instance, in a recent study using the International Statistical Classification of Diseases, the cumulative incidence of childhood autism in Japan is 27.2 per 10,000 (Honda et al., 2005). Similarly, according to the Danish population based study, the incidence rate and prevalence of childhood autism in children younger than 10 years is 2 per 10,000 (Lauritsen et al., 2004) and in Western Aus-tralia the incidence in children …