Genetic Counseling in Autistic Phenotypes

Abstract

Autism is a neurobehavioural disorder that includes impairment in social interaction and language development and communication deficits accompanied by repetitive and stereotyped behaviours. More recently this term has been used to define a very broad behavioural phenotype which is classified as different disorders that comprise the Pervasive Developmental Disorders (PDD) according to the Diagnostic and Statistical Manual of Mental Disorders, 4th Edition-DSM-IV (American Psychiatric Association [APA], 1994). It contains the criteria for diagnosis and specific characteristics of each disease, including Autism, Asperger’s syndrome, Childhood Disintegrative Disorder, Rett syndrome and Pervasive Developmental Disorder Not Otherwise Specified (PDD-NOS). However, with the exception of Rett syndrome, the others make up a continuous spectrum rather than clinically defined diagnostic categories due to the wide variation of clinical signs and symptoms and the subjectivity of the criteria for differential diagnosis. For this reason these disorders have been included in a general conceptual category, Autism Spectrum Disorders (ASDs) (Snow & Lecavalier, 2011; Witwer & Lecavalier, 2008). Hence, the proposals for DSM-V, being prepared by the APA, which is scheduled to be published in 2012 or 2013, recommend that Rett syndrome is not considered among the ASDs, that the designation PDD is no longer used and that ASD is considered a single category that includes Autism, Asperger's syndrome, Childhood Disintegrative Disorder and PDD-NOS. That is, the disorders that compose the autistic spectrum would no longer have specific names (APA, 2011). Rett syndrome almost exclusively affects girls and is characterized by normal development until about six months followed by regression of motor and social skills. The triad dementiaataxia-autism is observed as is a characteristic pattern of deceleration in the rate of head growth, loss of acquired manual skills, poorly coordinated gait, involuntary movements of the hands and the trunk and autistic features. Epilepsy may be present and a abnormal respiratory pattern is typical . The prevalence among women is between 1:10,000 and 1:15,000 with most cases caused by a sporadic mutation in the MECP2 gene, located on Xq28. In some cases, the etiology is due to mitochondrial DNA mutations (Gonzales & LaSalle, 2010; Nissenkorn et al., 2010; Temudo et al., 2010). The peculiar nature and specific etiology, linked to a genetic defect with consequent brain damage, are among the reasons for not being considered within the ASDs. Childhood Disintegrative Disorder is basically characterized by normal development of children until at least two years of age followed by a process of loss of previously acquired intellectual and behavioural skills, which results in autistic behaviour (Homan et al., 2011).