Autism-associated missense genetic variants impact locomotion and neurodevelopment in Caenorhabditis elegans.

Autism spectrum disorder (ASD) involves thousands of alleles in over 850 genes, but the current functional inference tools are not sufficient to predict phenotypic changes. As a result, the causal relationship of most of these genetic variants in the pathogenesis of ASD has not yet been demonstrated and an experimental method prioritizing missense alleles for further intensive analysis is crucial. For this purpose, we have designed a pipeline that uses Caenorhabditis elegans as a genetic model to screen for phenotype-changing missense alleles inferred from human ASD studies. We identified highly conserved human ASD-associated missense variants in their C. elegans orthologs, used a CRISPR/Cas9-mediated homology-directed knock-in strategy to generate missense mutants and analyzed their impact on behaviors and development via several broad-spectrum assays. All tested missense alleles were predicted to perturb protein function, but we found only 70% of them showed detectable phenotypic changes in morphology, locomotion or fecundity. Our findings indicate that certain missense variants in the C. elegans orthologs of human CACNA1D, CHD7, CHD8, CUL3, DLG4, GLRA2, NAA15, PTEN, SYNGAP1 and TPH2 impact neurodevelopment and movement functions, elevating these genes as candidates for future study into ASD. Our approach will help prioritize functionally important missense variants for detailed studies in vertebrate models and human cells.

Conserved missense variant in ALDH1A3 ortholog impairs fecundity in C. elegans.

Accumulating evidence demonstrates that mutations in ALDH1A3 (the aldehyde dehydrogenase 1 family, member A3) are associated with developmental defects. The ALDH1A3 enzyme catalyzes retinoic acid biosynthesis and is essential to patterning and neuronal differentiation in the development of embryonic nervous system. Several missense mutations in ALDH1A3 have been identified in family studies of autosomal recessive microphthalmia, autism spectrum disorder, and other neurological disorders. However, there has been no evidence from animal models that verify the functional consequence of missense mutations in ALDH1A3. Here, we introduced the equivalent of the ALDH1A3 C174Y variant into the Caenorhabditis elegans ortholog, alh-1, at the corresponding locus. Mutant animals with this missense mutation exhibited decreased fecundity by 50% compared to wild-type animals, indicating disrupted protein function. To our knowledge, this is the first ALDH1A3 C174Y missense model, which might be used to elucidate the effects of ALDH1A3 C174Y missense mutation in the retinoic acid signaling pathway during development.