Burden of rare coding variants in an Italian cohort of familial multiple sclerosis

Background: Multiple Sclerosis (MS) is a chronic inflammatory and neurodegenerative demyelinating disease of the central nervous system. It is a complex and heterogeneous disease caused by a combination of genetic and environmental factors, and it can cluster in families. Objective: to evaluate at gene-level the aggregate contribution of predicted damaging low-frequency and rare variants to MS risk in multiplex families. Methods: We performed whole exome sequencing (WES) in 28 multiplex MS families with at least 3 MS cases (81 affected and 42 unaffected relatives) and 38 unrelated healthy controls. A gene-based burden test was then performed, focusing on two sets of candidate genes: i) literature-driven selection and ii) data-driven selection. Results: We identified 11 genes enriched with predicted damaging low-frequency and rare variants in MS compared to healthy individuals. Among them, UBR2 and DST were the two genes with the strongest enrichment (p = 5 × 10⁻⁴ and 3 × 10⁻⁴, respectively); interestingly enough the association signal in UBR2 is driven by rs62414610, which was present in 25% of analysed families. Conclusion: Despite limitations, this is one of the first studies evaluating the aggregate contribution of predicted damaging low-frequency and rare variants in MS families using WES data. A replication effort in independent cohorts is warranted to validate our findings and to evaluate the role of identified genes in MS pathogenesis.