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Multiple sclerosis (MS) is an inflammatory disease of the central nervous system characterized by myelin loss and neuronal dysfunction. Although the majority of patients do not present familial aggregation, Mendelian forms have been described. We performed whole-exome sequencing analysis in 132 patients from 34 multi-incident families, which nominated likely pathogenic variants for MS in 12 genes of the innate immune system that regulate the transcription and activation of inflammatory mediators. Rare missense or nonsense variants were identified in genes of the fibrinolysis and complement pathways (PLAU, MASP1, C2), inflammasome assembly (NLRP12), Wnt signaling (UBR2, CTNNA3, NFATC2, RNF213), nuclear receptor complexes (NCOA3), and cation channels and exchangers (KCNG4, SLC24A6, SLC8B1). These genes suggest a disruption of interconnected immunological and pro-inflammatory pathways as the initial event in the pathophysiology of familial MS, and provide the molecular and biological rationale for the chronic inflammation, demyelination and neurodegeneration observed in MS patients., Competing Interests: The authors have declared that no competing interests exist.

The implementation of exome sequencing technologies has started to unravel the genetic etiology of familial multiple sclerosis (MS). A homozygote p.G587S mutation in NLRP1 has been suggested as potentially causative for the onset of MS in an affected sibling pair, who later developed malignant melanoma. To validate the proposed role of recessive NLRP1 mutations in the pathological mechanisms of MS, we examined exome sequencing data from 326 MS patients from Canada for the identification of NLRP1 missense and nonsense variants. This analysis did not identify the previously described p.G587S mutation; however, three patients with potential NLRP1 compound heterozygote mutations were observed. Haplotype and segregation analyses indicate that the variants observed in these patients were inherited in cis, and do not segregate with disease within families. Thus, the analysis of MS patients from Canada failed to identify potentially pathogenic mutations in NLRP1, including the previously described p.G587S mutation. Further studies are necessary to confirm a role of NLRP1 in the pathophysiology of MS.

Genetic variants in the purinergic receptors P2RX4 and P2RX7 have been shown to affect susceptibility to multiple sclerosis (MS). In this study, we set out to evaluate whether rare coding variants of major effect could also be identified in these purinergic receptors. Sequencing analysis of P2RX4 and P2RX7 in 193 MS patients and 100 controls led to the identification of a rare three variant haplotype (P2RX7 rs140915863:C>T [p.T205M], P2RX7 rs201921967:A>G [p.N361S], and P2RX4 rs765866317:G>A [p.G135S]) segregating with disease in a multi-incident family with six family members diagnosed with MS (logarithm of odds = 3.07). Functional analysis of this haplotype in HEK293 cells revealed impaired P2X7 surface expression (P < 0.01), resulting in over 95% inhibition of adenosine triphosphate (ATP)-induced pore function (P < 0.001) and a marked reduction in phagocytic ability (P < 0.05). In addition, transfected cells showed 40% increased peak ATP-induced inward current (P < 0.01), and a greater Ca 2+ response to the P2X4 135S variant compared with wild type (P < 0.0001). Our study nominates rare genetic variants in P2RX4 and P2RX7 as major genetic contributors to disease, further supporting a role for these purinergic receptors in MS and the disruption of transmembrane cation channels leading to impairment of phagocytosis as the pathological mechanisms of disease., (© 2017 Wiley Periodicals, Inc.)

Identifying rare genetic variants that drive the onset of disease is challenging, even before considering the additional genetic and environmental influences that likely exist in complex diseases. We recently published a study proposing a rare variant in the NR1H3 gene (p.R415Q, rs61731956) as responsible for the onset of multiple sclerosis (MS) in two multi-incident families (Wang et al., 2016). This publication has generated much discussion, and fortunately the possibility to validate a finding or prove it spurious can occur rapidly in genetic studies. All novel discoveries must be replicated, and best efforts should be made to ensure that these replications use the appropriate samples and approach, and provide the correct interpretation of the results. This Matters Arising Response paper addresses the Minikel and MacArthur (2016) and The International Multiple Sclerosis Genetics Consortium (2016) Matters Arising papers, published concurrently in Neuron., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Oxysterols produced by CH25H during cholesterol metabolism have been shown to play an important role in the immune response. In this study we report the genetic characterization of CH25H in patients diagnosed with multiples sclerosis (MS) or neuromyelitis optica (NMO), for the identification of genetic variants affecting disease susceptibility and course. Exome analysis in 212 MS and 14 NMO patients identified a rare CH25H p.Q17H mutation in two NMO patients of Asian ancestry. In addition, association analysis of common CH25H variants identified a nominally significant association with MS patients presenting a clinical course consistent with primary progressive disease., Competing Interests: The authors declare that they have no conflict of interest., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Background: Genetic epidemiological studies suggest both genetic and environmental factors have a role in multiple sclerosis (MS). Environmental effects are strongly suggested from geographical gradients, migration data, and discordance rates in twins. In epidemiological studies, risk of MS in offspring of small families and in those with an early birth-order position has been reported and interpreted in the context of the hygiene hypothesis, which is that infections at an early age, introduced by older siblings, are protective. We aimed to study the effect of birth order on MS risk., Methods: A longitudinal, population-based sample of individuals with MS and their healthy siblings were identified from the Canadian Collaborative Project on Genetic Susceptibility to MS. Data were grouped according to single (simplex) or multiple (multiplex) siblings with MS in a sibship. Separate analyses were done for each sibship size., Findings: We studied 10 995 individuals with MS and 26 336 healthy siblings, and found no relation between MS risk and birth-order position. In simplex sibships of at least seven siblings, slightly more siblings who were born late in the birth order had MS; the same was found for the first-born sibling with MS in a multiplex sibship. Siblings with MS were slightly younger (p<0.0001) than those without MS, contrary to the expected age at onset bias., Interpretation: These findings do not support the hygiene hypothesis and could be due to a cohort effect resulting from increasing MS incidence. Birth order has no effect on MS risk in most families, and there is no support for the hypothesis that having older siblings protects against MS.