Glutamatergic Pathway and Axonal Guidance Signaling Genes As Candidate for ASD Etiology

Background: The Autism Spectrum Disorders (ASD) are neuropsychological disorders, characterized by repetitive and stereotyped behavior, inability to communicate, lack of reciprocal social interaction and, sometimes, cognitive impairment. These disorders affect about 1/150 children, being currently considered a public health problem. It has recently been shown that de novoand mostly rare copy number variations (CNVs) accounts for about 10-15% of the autism cases.

Objectives: Identify new genes possibly candidate for ASD and verify what biological pathways can be significantly involved in these disorders.

Methods: It was analyzed 101 sporadic autism cases by custom-designed microarray CGH with a high probe density targeted to exon of genes previously reported as candidate for ASD and others involved in the same metabolic pathways of these genes. We included only patients with no history of complications during pregnancy, negative Fragile X result and without congenital malformations or facial dimorphisms. To assess whether detected alterations can be pathogenic, CNVs from ASD cases were compared to dataset from apparently healthy individuals (DGV) and 200 matched controls subjects analyzed by the same array platform. Only alterations not viewed in unaffected subjects were considered putative pathogenic and were validated using quantitative PCR, SNP array 500K from Affymetrix or CGH-array 180K from Agilent Tchenologies.The parents were also evaluated in order to verify the mutation origin.

Results: We detected 12 different CNVs possibly pathogenic in DNA samples from 17 autistic individuals. We observed enrichment of de novo deletions in genes whose proteins interact directly or indirectly with the neurotransmitter glutamate (4/12 - 33,3%). Among the functions performed by these proteins we emphasize: release of glutamate in the synaptic cleft, metabotropic glutamate receptor, catalyzing the production of gamma-aminobutyric acid from L-glutamic acid and glutamate transport into the pre-synaptic vesicle. Several other glutamatergic pathway genes have been reported as ASD candidates. We propose that dysregulation of these genes leads to an imbalance between excitatory and inhibitory synapses with consequent impairment of neuronal maturation and plasticity. We also observed enrichment of de novo deletions and duplications in genes involved in Axonal Guidance Signaling (3/12 – 25%). The roles performed by proteins of these genes are actin filament and cytoskeleton reorganization, dendritic spine morphogenesis and neurite outgrowth.  Dsyregulation of these genes can lead to synapse impairment.

Conclusions: Using the strategy of analyzing genes belonging to the same pathway of others already reported as associated to autism was possible to identify novel candidate genes. Furthermore, our results corroborate with the involvement of glutamatergic pathway and Axonal Guidance Signaling in the etiology of this disorder.

FAPESP/CNPq