Autism is heterogeneous with respect to clinical symptoms and etiology. A significant limitation in research of the neurobiology and treatment of autism has been the lack of attention to this heterogeneity. A dimensional approach to the study of autism is valuable in linking key symptoms to the neurobiology and treatment of the disorder in a clinically meaningful way. In this article, we outline a dimensional approach to the autism spectrum, discuss the three core dimensions of autism and their neurobiology, and review the possible links of serotonin, anterior cingulate gyrus activity, and the immune marker D8/17 to the repetitive behavior/compulsivity dimensions.

Autism and related disorders occur in as many as one in 500 children. Recognizing the need for uniform recommendations to help guide the initial diagnostic evaluation and referrals in this area, an initial working group of the Cure Autism Now Foundation promulgated the following consensus guidelines for autism screening and diagnostic referral. Although these recommendations were formulated using the best information currently available, they are likely to be modified as the results of additional studies become available; however, they provide a useful tool for clinicians involved in the management of children with autism and related developmental abnormalities.

To date, research regarding the neurobiological basis of autism has produced only the most preliminary of data. Although some advances have been made, the need for more definitive knowledge is crucial to more fully understand and treat this disorder.

In this review, the autistic spectrum is discussed in terms of its defining symptoms. These symptoms are explained based on current understanding, and the need for more information regarding the bases of these abnormalities is noted. The critical needs of research are discussed, with an emphasis on areas in urgent need of analysis.

Autism spectrum disorder (ASD) is a neurobiological developmental symptom complex characterized by early onset of deficits in verbal and nonverbal communication skills, socio-communicative function, and repetitive behaviors. The well-documented increased frequency of seizures and abnormal electroencephalographic (EEG) findings in ASD support the concept that the central nervous system dysfunction has a neurobiological basis. We review the prevalence of seizures and EEG abnormalities in children with ASD and explore the possible clinical significance of this correlation.

Autism is a severe developmental disorder likely resulting from a combination of biologic and genetic mechanisms including an environmental stimulus. This article presents an immunologic theory for the development of some cases of autism and circumstantial biologic evidence in support of this theory. A summary of some of the latest related findings obtained in the laboratory of the author is also presented. The intent of this article is to stimulate interest in the concept that abnormalities of the immune system are involved in autistic symptoms and to provide an impetus for additional studies in this area. Such studies may provide a novel approach to the treatment of some autistic individuals.

Although the precise etiological nature of autism—the most common development disorder—remains elusive, two main biological factors have been suggested. One is related to a possible neurochemical dysfunction at the level of the serotonergic system; the other underlines the presence of neuroanatomical abnormalities in different areas, in particular, in the cerebellum.

The authors propose a unifying hypothesis linking serotonin (5-hydroxytryptamine, or 5-HT) to the cerebellum on the basis of the observation of a specific 5-HT receptor subtype, 5-HT5A, in this area. The 5-HT5A receptors may be involved in the pathophysiology of autism, and perhaps, in autism-related disorders, since they are mainly expressed in Purkinje's cells. Future studies with specific drugs that interact with 5-HT5A receptors should permit the testing of this hypothesis through the evaluation of the receptors themselves in autopsied brain samples or in vivo by positron emission tomography. Theoretically, such compounds might prove effective in the treatment of autism.