Cumulative genetic risk andC9orf72repeat status independently associate with ALS status in two case-control studies

AbstractBackgroundMost amyotrophic lateral sclerosis (ALS) patients lack a monogenic mutation. This study evaluates ALS cumulative genetic risk in an independent Michigan and Spanish replication cohort using polygenic scores.MethodsALS (n=219) and healthy control (n=223) participant samples from University of Michigan were genotyped and assayed for theC9orf72hexanucleotide expansion. Polygenic scores excluding the C9 region were generated using an independent ALS genome-wide association study (20,806 cases, 59,804 controls). Adjusted logistic regression and receiver operating characteristic curves evaluated the association and classification between polygenic scores and ALS status, respectively. Population attributable fractions and pathway analyses were conducted. An independent Spanish study sample (548 cases, 2,756 controls) was used for replication.ResultsPolygenic scores constructed from 275 single nucleotide polymorphisms had the best model fit in the Michigan cohort. A standard deviation increase in ALS polygenic score associated with 1.28 (95%CI 1.04-1.57) times higher odds of ALS with area under the curve of 0.663 versus a model without the ALS polygenic score (p-value=1×10−6). The population attributable fraction of the highest 20thpercentile of ALS polygenic scores, relative to the lowest 80thpercentile, was 4.1% of ALS cases. Genes annotated to this polygenic score enriched for important ALS pathomechanisms. Meta-analysis with the Spanish study, using a harmonized 132 single nucleotide polymorphism polygenic score, yielded similar logistic regression findings (odds ratio: 1.13, 95%CI 1.04-1.23).ConclusionALS polygenic scores can account for cumulative genetic risk in populations and reflect disease-relevant pathways. If further validated, this polygenic score will inform future ALS risk models.What is already known on this topicAmyotrophic lateral sclerosis (ALS) is a complex neurodegenerative disease caused in part by genetic factors, and methods to account for ALS polygenic disease risk are needed.What this study addsAn ALS polygenic score reflects disease risk in the population and helps ascribe the magnitude of the risk.How this study might affect research, practice or policyALS polygenic scores can assign the overall distribution of genetic risk in a population and can be used to screen individuals at higher risk.