Rare variant and polygenic analyses of amyotrophic lateral sclerosis in the French-Canadian genome.

PURPOSE: The genetic etiology of amyotrophic lateral sclerosis (ALS) includes few rare, large-effect variants and potentially many common, small-effect variants per case. The genetic risk liability for ALS might require a threshold comprised of a certain amount of variants. Here, we tested the degree to which risk for ALS was affected by rare variants in ALS genes, polygenic risk score, or both.METHODS: 335 ALS cases and 356 controls from Québec, Canada were concurrently tested by SNP-chip genotyping and targeted sequencing of ALS genes known at the time of study inception. ALS GWAS summary statistics were used to estimate an ALS polygenic risk score (PRS). Cases and controls were subdivided into rare variant heterozygotes and non-heterozygotes.RESULTS: Risk for ALS was significantly associated with PRS and rare variants independently in a logistic regression model. While ALS PRS predicted a small amount of ALS risk overall, the effect was most pronounced between ALS cases and controls that were not heterozygous for a rare variant in the ALS genes surveyed.CONCLUSION: Both PRS and rare variants in ALS genes impact risk for ALS. PRS for ALS is most informative when rare variants are not observed in ALS genes.