High-Throughput Sequencing of mGluR Signaling Pathway Genes Reveals Enrichment of Rare Variants in Autism

Identification of common molecular pathways affected by genetic variation in autism is important for understanding disease pathogenesis and devising effective therapies. Here, we test the hypothesis that rare genetic variation in the metabotropic glutamate-receptor (mGluR) signaling pathway contributes to autism susceptibility. Single-nucleotide variants in genes encoding components of the mGluR signaling pathway were identified by high-throughput multiplex sequencing of pooled samples from 290 non-syndromic autism cases and 300 ethnically matched controls on two independent next-generation platforms. This analysis revealed significant enrichment of rare functional variants in the mGluR pathway in autism cases. Higher burdens of rare, potentially deleterious variants were identified in autism cases for three pathway genes previously implicated in syndromic autism spectrum disorder, TSC1, TSC2, and SHANK3, suggesting that genetic variation in these genes also contributes to risk for non-syndromic autism. In addition, our analysis identified HOMER1, which encodes a postsynaptic density-localized scaffolding protein that interacts with Shank3 to regulate mGluR activity, as a novel autism-risk gene. Rare, potentially deleterious HOMER1 variants identified uniquely in the autism population affected functionally important protein regions or regulatory sequences and co-segregated closely with autism among children of affected families. We also identified rare ASD-associated coding variants predicted to have damaging effects on components of the Ras/MAPK cascade. Collectively, these findings suggest that altered signaling downstream of mGluRs contributes to the pathogenesis of non-syndromic autism.

鉴定自闭症中受遗传变异影响的常见分子通路，对于理解疾病发病机制及开发有效治疗方案具有重要意义。本研究旨在验证这一假说：代谢型谷氨酸受体（metabotropic glutamate-receptor, mGluR）信号通路中的罕见遗传变异会增加自闭症的患病易感性。本研究通过两个独立的下一代测序平台，对290例非综合征性自闭症患者与300例种族匹配对照的混合样本进行高通量多重测序，以此鉴定mGluR信号通路组分编码基因中的单核苷酸变异。该分析结果显示，自闭症患者mGluR通路中罕见功能变异的富集程度显著升高。针对此前被发现与综合征性自闭症谱系障碍相关的3个通路基因TSC1、TSC2及SHANK3，自闭症患者中携带的罕见潜在有害变异的负荷更高，这表明这些基因的遗传变异同样会增加非综合征性自闭症的患病风险。此外，本研究鉴定出HOMER1作为全新的自闭症风险基因，其编码的是一种定位于突触后致密区的支架蛋白，可与Shank3相互作用以调控mGluR的活性。仅在自闭症人群中检出的罕见潜在有害HOMER1变异，会对功能关键的蛋白质区域或调控序列造成影响，且在患病家系的子代中与自闭症表型呈现紧密共分离现象。本研究还鉴定出了罕见的自闭症谱系障碍（Autism Spectrum Disorder, ASD）相关编码变异，经预测这些变异会对Ras/MAPK级联反应的组分造成损害性影响。综上，上述研究结果表明，mGluRs下游信号通路的异常改变参与了非综合征性自闭症的发病过程。