Autism spectrum disorders in tuberous sclerosis: pathogenetic pathways and implications for treatment

Autism and cancer risk

A literature review was conducted on the genetic and developmental bases of autism in relation to genes and pathways associated with cancer risk. Convergent lines of evidence from four types of analysis: (1) recent theoretical studies on the causes of autism, (2) epidemiological studies, (3) genetic analyses linking autism with mutations in tumor suppressor genes and other cancer-associated genes and pathways, and (4) contrasts with schizophrenia, Parkinson's, and Alzheimer's disease indicate that autism may involve altered cancer risk. This evidence should motivate further epidemiological studies, and it provides useful insights into the nature of the genetic, epigenetic, and environmental factors underlying the etiologies of autism, other neurological conditions, and carcinogenesis.

Children with autism spectrum disorders (ASD) who exhibit chronic gastrointestinal (GI) symptoms and marked fluctuation of behavioral symptoms exhibit distinct innate immune abnormalities and transcriptional profiles of peripheral blood (PB) monocytes

Innate/adaptive immune responses and transcript profiles of peripheral blood monocytes were studied in ASD children who exhibit fluctuating behavioral symptoms following infection and other immune insults (ASD/Inf, N=30). The ASD/Inf children with persistent gastrointestinal symptoms (ASD/Inf+GI, N=19), revealed less production of proinflammatory and counter-regulatory cytokines with stimuli of innate immunity and marked changes in transcript profiles of monocytes as compared to ASD/no-Inf (N=28) and normal (N=26) controls. This included a 4-5 fold up-regulation of chemokines (CCL2 and CCL7), consistent with the production of more CCL2 by ASD/Inf+GI cells. These results indicate dysregulated innate immune defense in the ASD/Inf+GI children, rendering them more vulnerable to common microbial infection/dysbiosis and possibly subsequent behavioral changes.

Autism in tuberous sclerosis: are risk factors identifiable and preventable?

Evaluation of: Numis AL, Major P, Montenegro MA, Muzykevicz DA, Pulsifer MB, Thiele EA. Identification of risk factors for autism spectrum disorder in tuberous sclerosis complex. Neurology 76(11), 981–987 (2011). Autism spectrum disorders (ASDs) are much more frequent in individuals with tuberous sclerosis complex (TSC) than in the general population. However, the underlying reasons for this association remain largely unclear. This study aimed to identify some risk factors leading to autism in children with TSC. The authors analyzed epidemiological, genetic, electrophysiological and neuroanatomical risk factors in a cohort of 103 TSC patients. ASDs were diagnosed in 41 of the TSC patients (40%). Individuals with ASD had earlier age at seizure onset and a lower IQ (p < 0.001). There was a trend for patients with ASD to have the largest tuber burden in the left temporal lobe and mutations inactivating the hamartin domain of the TSC2 gene. They concluded that autism in TSC may be associated with early and persistent seizure activity in specific brain regions, particularly in the left temporal lobe, where areas responsible for social communication are localized. Cyst-like tubers were more common in TSC patients with ASD.

Altered ultrasonic vocalizations in a tuberous sclerosis mouse model of autism

Tuberous sclerosis (TSC) is an autosomally dominant neurocutaneous disease notable for its high comorbidity with autism in human patients. Studies of murine models of tuberous sclerosis have found defects in cognition and learning, but thus far have not uncovered deficits in social behaviors relevant to autism. To explore social communication and interaction in TSC2 heterozygous mice, we recorded ultrasonic vocalizations (USV) and found that although both wild-type (WT) and heterozygous pups born to WT dams showed similar call rates and patterns, baseline vocalization rates were elevated in pups born to heterozygous dams. Further analysis revealed several robust features of maternal potentiation in all but WT pups born to heterozygous dams. This lack of potentiation is suggestive of defects in mother-pup social interaction during or before the reunion period between WT pups and heterozygous dams. Intriguingly, male pups of both genotypes born to heterozygous dams showed particularly heightened call rates and burst patterns. Because our maternal retrieval experiments revealed that TSC2(+/-) dams exhibited improved defensive reactions against intruders and highly efficient pup retrieval performance, the alterations in their pups' USVs and maternal potentiation do not appear to result from poor maternal care. These findings suggest that a pup's interaction with its mother strongly influences the pup's vocal communication, revealing an intriguing dependence of this social behavior on TSC2 gene dosage of both parties involved. Our study of this murine model thus uncovers social abnormalities that arise from TSC haploinsufficiency and are suggestive of autism.