Autism and tuberous sclerosis

Autism and tuberous sclerosis

The co-occurrence of autism spectrum disorder and tuberous sclerosis complex has been recognized for decades. The prevalence of tuberous sclerosis complex in the autism spectrum disorder population is 1 to 4%, whereas features of autism spectrum disorder are present in 25 to 50% of individuals with tuberous sclerosis complex. The underlying reason for this association might be a nonspecific disruption of brain function owing to tuberous sclerosis complex, including tuber location, seizures and their effect on brain development, cognitive impairment, a disturbance in brain development in regions associated with autism spectrum disorder, or, less likely, a linkage between a TSC gene and an autism susceptibility gene. Awareness of the relationship between autism spectrum disorder and tuberous sclerosis complex is important during the evaluation of individuals with either disorder. Better delineation of the association and its causative factors is needed for the development of possible interventions.

Autistic behaviour and attention deficits in tuberous sclerosis: a population-based study

In a population-based sample of 28 individuals under the age of 20 years, autistic symptoms were present in 24 and DSM-III-R autistic disorder in 17. Many of the children and adolescents diagnosed as autistic also showed attention deficit/hyperactivity. There was no specific association between autistic behaviour and the presence of infantile spasms. Some of the children with tuberous sclerosis and autism were of near-normal intelligence. Indirectly, the results suggest that as many as 9 per cent of all children with autism may have tuberous sclerosis.

A prevalence study of autism in tuberous sclerosis

An estimate of the prevalence of autism in tuberous sclerosis (TSC) was made by interviewing the parents of 21 children between ages 3 and 11 ascertained during a previous population study of the condition in the West of Scotland. Five of the children (24%) were rated autistic and a further four (19%), all of whom were girls, had socially impaired behavior categorized as pervasive developmental disorder, without fulfilling all the DSM-III-R criteria for autism. One further boy had disruptive attention-seeking behavior that had excluded him from his normal school. The estimated prevalence from this study of autism in TSC is 1 in 4 children in general, and 1 in 2 of those with mental retardation. Tuberous sclerosis could be a significant cause of autism and pervasive developmental disorders, particularly in girls.

The neurobiology and genetics of infantile autism

Autism is a syndrome with multiple etiologies, as is made clear both by the evidence of neurobiological research and by the catalog of disorders that present with autistic behaviors. What remains unclear are the specific neuropathological mechanisms that produce autistic behaviors; for example, is there a common neuroanatomic pathology for all cases of autism, or can autistic behaviors emerge from different pathological sequences within the brain? Although it is premature to generalize, neuropathological studies appear to have identified common abnormalities in the cerebellum and limbic system of at least five autistic subjects. These subjects, with variable levels of mental retardation, demonstrated marked Purkinje cell loss in the cerebellar hemispheres, together with retained fetal neuronal circuitry in cerebellar nuclei and increased neuronal packing in specific regions of the limbic system, amygdala, and hippocampus. The architecture of the cerebral cortex was not affected. Although our knowledge of brain functioning is incomplete, alterations of the kind noted in the cerebellum and limbic system could reasonably produce autistic behaviors. For more detail, readers are directed to a review of cerebellar contributions to higher functions by Schmahmann (1991). Neuroimaging studies allow less resolution of brain structure than do neuroanatomic studies, and the reported findings from neuroimaging are somewhat contradictory. However, a number of investigators have reported structural abnormalities in ventricle size and cerebral hemispheric asymmetry using CT. MRI, which offers greater resolution, has uncovered some consistent findings, along with a variety of nonspecific abnormalities. Common abnormalities include reduced volume of cerebellar hemispheres and vermal lobules--findings not inconsistent with the above-mentioned neuropathological defects. It is also interesting to note that individuals with fragile X syndrome have similar cerebellar findings. PET and NMR studies of autism are at a preliminary stage, but these methodologies allow insight into the functioning of the brain, rather than simply brain anatomy. Recent PET studies indicating decreased association between paired regions of the brains of autistic subjects are of interest, particularly if they can be confirmed and refined by additional studies. Neurophysiological studies also offer insight into brain function, but are subject to numerous methodological criticisms. Nevertheless, recent reports of diminished P300 waves and absent NC components in autistic subjects seem to indicate fundamental defects in attention and secondary processing, which could help explain the self-stimulatory behaviors often seen in autism. The disturbances in brain development associated with autism can be produced in a number of ways, and at different times during development of the nervous system.(ABSTRACT TRUNCATED AT 400 WORDS)