MET and autism susceptibility: family and case-control studies

Further evidence for the role of MET in autism susceptibility

MET receptor tyrosine kinase (MET)-mediated signaling has been implicated in multiple aspects of neocortical and cerebellar neuronal growth and maturation. A promoter functional SNP (rs1858830) that disrupts the transcription of MET has been reported to be strongly associated with autism spectrum disorders (ASD) in the Caucasian population. Here, we performed a trio association study of MET with ASD in Japanese subjects (n=126 trios). Based on the HapMap data on the Japanese population, 15 SNPs were chosen for the association study. One SNP located in intron 1, rs38841, showed a nominal association with autism (p=0.044; OR=1.61) when analyzed using the transmission disequilibrium test. To the best of our knowledge, this is the first replication study of the association of MET with autism, in any non-Caucasian population. Association of rs38841 with autism was further confirmed in 252 Caucasian trios from AGRE (p=0.0006). An interesting observation is that all three SNPs of MET (rs1858830, rs38845 and rs38841) shown to be associated with autism in three independent studies including the present one, are located towards the 5'end of the gene at a span of 9.4 kb. Our results provide further evidence for a possible role of MET in the pathogenesis of ASD.

Association of MET with social and communication phenotypes in individuals with autism spectrum disorder

Autism is a complex neurodevelopmental disorder diagnosed by impairments in social interaction, communication, and behavioral flexibility. Autism is highly heritable, but it is not known whether a genetic risk factor contributes to all three core domains of the disorder or autism results from the confluence of multiple genetic risk factors for each domain. We and others reported previously association of variants in the gene encoding the MET receptor tyrosine kinase in five independent samples. We further described enriched association of the MET promoter variant rs1858830 C allele in families with co-occurring autism and gastrointestinal conditions. To test the contribution of this functional MET promoter variant to the domains of autism, we analyzed its association with quantitative scores derived from three instruments used to diagnose and describe autism phenotypes: the Autism Diagnostic Interview-Revised (ADI-R), the Autism Diagnostic Observation Schedule (ADOS), and both the parent and the teacher report forms of the Social Responsiveness Scale (SRS). In 748 individuals from 367 families, the transmission of the MET C allele from parent to child was consistently associated with both social and communication phenotypes of autism. Stratification by gastrointestinal conditions revealed a similar pattern of association with both social and communication phenotypes in 242 individuals with autism from 118 families with co-occurring gastrointestinal conditions, but a lack of association with any domain in 181 individuals from 96 families with ASD and no co-occurring gastrointestinal condition. These data indicate that the MET C allele influences at least two of the three domains of the autism triad.

The genetics of autism: key issues, recent findings, and clinical implications

Autism spectrum disorders (ASDs) are highly heritable. Gene discovery promises to help illuminate the pathophysiology of these syndromes, yielding opportunities for the development of novel treatments and understanding of their natural history. Although the underlying genetic architecture of ASDs is not yet known, the literature demonstrates that it is not a monogenic disorder with mendelian inheritance, rather a group of complex genetic syndromes with risk deriving from genetic variations in multiple genes. This article reviews the origins of the common versus rare variant debate, highlights recent findings in the field, and addresses the clinical implications of common and rare variant discoveries.

Genetics of autistic disorders: review and clinical implications

Twin and family studies in autistic disorders (AD) have elucidated a high heritability of AD. In this literature review, we will present an overview on molecular genetic studies in AD and highlight the most recent findings of an increased rate of copy number variations in AD. An extensive literature search in the PubMed database was performed to obtain English published articles on genetic findings in autism. Results of linkage, (genome wide) association and cytogenetic studies are presented, and putative aetiopathological pathways are discussed. Implications of the different genetic findings for genetic counselling and genetic testing at present will be described. The article ends with a prospectus on future directions.

Similarities in features of autism and asthma and a possible link to acetaminophen use

Autism and autism spectrum disorders are enigmatic conditions that have their origins in the interaction of genes and environmental factors. In this hypothesis, genes statistically associated with autism are emphasized to be important in inflammation and in innate immune pathways, including pathways for susceptibility to asthma. The role of acetaminophen (paracetamol) in an increased risk for asthma is described and a possible similar link to an increased risk for autism is suggested.

Further evidence that the rs1858830 C variant in the promoter region of the MET gene is associated with autistic disorder

Previous studies in three independent cohorts have shown that the rs1858830 C allele variant in the promoter region of the MET gene on chromosome 7q31 is associated with autism. Another study has found correlations between other alterations in the MET gene and autism in two unrelated cohorts. This study screened two cohorts, an Autistic Disorder cohort from South Carolina and a Pervasive Developmental Disorder (PDD) cohort from Italy, for the presence of the C allele variant in rs1858830. A significant increase in the C allele variant frequency was found in the South Carolina Autistic Disorder patients as compared to South Carolina Controls (chi(2)=5.8, df=1, P=0.02). In the South Carolina cohort, a significant association with Autistic Disorder was found when comparing the CC and CG genotypes to the GG genotype (odds ratio (OR)=1.64; 95% confidence interval (CI)=1.12-2.40; chi(2)=6.5, df=1, P=0.01) in cases and controls. In the Italian cohort, no significant association with PDD was found when comparing the CC or CG genotype to the GG genotype (OR=1.20; 95% CI=0.56-2.56; chi(2)=0.2, df=1, P=0.64). This study is the third independent study to find the rs1858830 C variant in the MET gene promoter to be associated with autism.

Decreased Serum Hepatocyte Growth Factor (HGF) in Autistic Children with Severe Gastrointestinal Disease

Aim:

To assess serum Hepatocyte Growth Factor (HGF) levels in autistic children with severe gastrointestinal (GI) disease and to test the hypothesis that there is a relationship between GI pathology and HGF concentration.

Subjects and Methods:

Serum from 29 autistic children with chronic digestive disease (symptoms for a minimum of 6–12 months), most with ileo-colonic lymphoid nodular hyperplasia (LNH—markedly enlarged lymphoid nodules) and inflammation of the colorectum, small bowel and/or stomach), and 31 controls (11 age matched autistic children with no GI disease, 11 age matched non autistic children without GI disease and 9 age matched non autistic children with GI disease) were tested for HGF using ELISAs. HGF concentration of autistic children with GI disease was compared to GI disease severity.

Results:

Autistic children with GI disease had significantly lower serum levels of HGF compared to controls (autistic without GI disease; p = 0.0005, non autistic with no GI disease; p = 0.0001, and non autistic with GI disease; p = 0.001). Collectively, all autistic children had significantly lower HGF levels when compared to non autistic children (p < 0.0001). We did not find any relationship between severity of GI disease and HGF concentration in autistic children with GI disease.

Discussion:

These results suggest an association between HGF serum levels and the presence of GI disease in autistic children and explain a potential functional connection between the Met gene and autism. The concentration of serum HGF may be a useful biomarker for autistic children, especially those with severe GI disease.

The genetic and neurobiologic compass points toward common signaling dysfunctions in autism spectrum disorders

Autism spectrum disorder (ASD) is a common neurodevelopmental disorder with high heritability. Here, we discuss data supporting the view that there are at least two distinct genetic etiologies for ASD: rare, private (de novo) single gene mutations that may have a large effect in causing ASD; and inherited, common functional variants of a combination of genes, each having a small to moderate effect in increasing ASD risk. It also is possible that a combination of the two mechanisms may occur in some individuals with ASD. We further discuss evidence from individuals with a number of different neurodevelopmental syndromes, in which there is a high prevalence of ASD, that some private mutations and common variants converge on dysfunctional ERK and PI3K signaling, which negatively impacts neurodevelopmental events regulated by some receptor tyrosine kinases.