Jay P. Ross

Nuclear Receptor NR1H3 in Familial Multiple Sclerosis

Multiple sclerosis (MS) is an inflammatory disease characterized by myelin loss and neuronal dysfunction. Despite the aggregation observed in some families, pathogenic mutations have remained elusive. In this study, we describe the identification of NR1H3 p.Arg415Gln in seven MS patients from two multi-incident families presenting severe and progressive disease, with an average age at onset of 34 years. Additionally, association analysis of common variants in NR1H3 identified rs2279238 conferring a 1.35-fold increased risk of developing progressive MS. The p.Arg415Gln position is highly conserved in orthologs and paralogs, and disrupts NR1H3 heterodimerization and transcriptional activation of target genes. Protein expression analysis revealed that mutant NR1H3 (LXRA) alters gene expression profiles, suggesting a disruption in transcriptional regulation as one of the mechanisms underlying MS pathogenesis. Our study indicates that pharmacological activation of LXRA or its targets may lead to effective treatments for the highly debilitating and currently untreatable progressive phase of MS.

Identification of FUS p.R377W in essential tremor

Exome sequencing analysis has recently identified a nonsense mutation in fused in sarcoma (FUS) segregating with essential tremor (ET) within a large French‐Canadian family. Further characterization of FUS resulted in the identification of additional mutations in ET patients; however, their pathogenicity still remains to be confirmed. The role of FUS in an independent cohort of ET patients from Canada was evaluated.

Analysis of CYP27B1 in multiple sclerosis

The analysis of genetic variability in CYP27B1 and its effect on risk of multiple sclerosis (MS) has yielded conflicting results. Here we describe a study to genetically characterize CYP27B1 and elucidate its role on MS risk in the Canadian population. Sequencing CYP27B1 failed to identify mutations known to cause loss of enzymatic activity, however genotyping of p.R389H in cases and controls identified the mutation in one multi-incident family (allele frequency=0.03%) in which the p.R389H mutation segregates with disease in five family members diagnosed with MS, thus providing additional support for CYP27B1 p.R389H in the pathogenicity of MS.

Genetic variants in IL2RA and IL7R affect multiple sclerosis disease risk and progression.

Multiple sclerosis (MS) is a common demyelinating neurodegenerative disease with a strong genetic component. Previous studies have associated genetic variants in IL2RA and IL7R in the pathophysiology of the disease. In this study, we describe the association between IL2RA (rs2104286) and IL7R (rs6897932) in the Canadian population. Genotyping 1,978 MS patients and 830 controls failed to identify any significant association between these variants and disease risk. However, stratified analysis for family history of disease and disease course identified a trend towards association for IL2RA in patients without a family history (p = 0.05; odds ratio = 0.77) and a significant association between IL7R and patients who developed progressive MS (PrMS) (p = 0.002; odds ratio = 0.73). Although not statistically significant, the effect of IL2RA (rs2104286) in patients without a family history of MS indicates that the genetic components for familial and sporadic disease are perhaps distinct. This data suggests that the onset of sporadic disease is likely determined by a large number of variants of small effect, whereas MS in patients with a family history of disease is caused by a few deleterious variants. In addition, the significant association between PrMS and rs6897932 indicates that IL7R may not be disease-causing but a determinant of disease course. Further characterization of the effect of IL2RA and IL7R genetic variants in defined MS subtypes is warranted to evaluate the effect of these genes on specific clinical outcomes and to further elucidate the mechanisms of disease onset and progression.

SLC1A2 rs3794087 does not associate with essential tremor

A recent genome-wide association study of patients with essential tremor (ET) from Germany has nominated SLC1A2 rs3794087 as a novel risk factor for disease. This association was independently replicated in the Chinese population, albeit with an opposite direction of effect. To further define the role of SLC1A2 in ET, we genotyped rs3794087 in a North American series consisting of 1347 patients with ET and controls. Statistical analysis did not identify significant differences in genotype or allele frequencies between healthy controls and patients with ET (p > 0.36). These findings therefore do not support a role for SLC1A2 rs3794087 in susceptibility to ET in the North American population. Further studies in ethnically distinct populations of patients with ET are necessary to understand whether genetic variability in SLC1A2 affects disease risk for ET.

VPS35 and DNAJC13 disease-causing variants in essential tremor.

Exome-sequencing analyses have identified vacuolar protein sorting 35 homolog (VPS35) and DnaJ (Hsp40) homolog, subfamily C, member 13 (DNAJC13) harboring disease-causing variants for Parkinson disease (PD). Owing to the suggested clinical, pathological and genetic overlap between PD and essential tremor (ET) we assessed the presence of two VPS35 and DNAJC13 disease-causing variants in ET patients. TaqMan probes were used to genotype VPS35 c.1858G>A (p.(D620N)) (rs188286943) and DNAJC13 c.2564A>G (p.(N855S)) (rs387907571) in 571 ET patients of European descent, and microsatellite markers were used to define the disease haplotype in variant carriers. Genotyping of DNAJC13 identified two ET patients harboring the c.2564A>G (p.(N855S)) variant previously identified in PD patients. Both patients appear to share the disease haplotype previously reported. ET patients with the VPS35 c.1858G>A (p.(D620N)) variants were not observed. Although a genetic link between PD and ET has been suggested, DNAJC13 c.2564A>G (p.(N855S)) represents the first disease-causing variant identified in both, and suggests the regulation of clathrin dynamics and endosomal trafficking in the pathophysiology of a subset of ET patients.

Genetic modifiers of multiple sclerosis progression, severity and onset

The genetic contribution to clinical outcomes for multiple sclerosis (MS) has yet to be defined. We performed exome sequencing analysis in 100 MS patients presenting opposite extremes of clinical phenotype (discovery cohort), and genotyped variants of interest in 2016 MS patients (replication cohort). Linear and logistic regression analyses were used to identify significant associations with disease course, severity and onset. Our analysis of the discovery cohort nominated 38 variants in 21 genes. Replication analysis identified PSMG4 p.W99R and NLRP5 p.M459I to be associated with disease severity (p=0.002 and 0.008). CACNA1H p.R1871Q was found associated with patients presenting relapsing remitting MS at clinical onset (p=0.028) whereas NLRP5 p.M459I and EIF2AK1 p.K558R were associated with primary progressive disease (p=0.031 and 0.023). In addition, PSMG4 p.W99R and NLRP5 p.R761L were found to correlate with an earlier age at MS clinical onset, and MC1R p.R160W with delayed onset of clinical symptoms (p=0.010-0.041).

Analysis of CH25H in multiple sclerosis and neuromyelitis optica

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.

Analysis of Plasminogen Genetic Variants in Multiple Sclerosis Patients

Multiple sclerosis (MS) is a prevalent neurological disease of complex etiology. Here, we describe the characterization of a multi-incident MS family that nominated a rare missense variant (p.G420D) in plasminogen (PLG) as a putative genetic risk factor for MS. Genotyping of PLG p.G420D (rs139071351) in 2160 MS patients, and 886 controls from Canada, identified 10 additional probands, two sporadic patients and one control with the variant. Segregation in families harboring the rs139071351 variant, identified p.G420D in 26 out of 30 family members diagnosed with MS, 14 unaffected parents, and 12 out of 30 family members not diagnosed with disease. Despite considerably reduced penetrance, linkage analysis supports cosegregation of PLG p.G420D and disease. Genotyping of PLG p.G420D in 14446 patients, and 8797 controls from Canada, France, Spain, Germany, Belgium, and Austria failed to identify significant association with disease (P = 0.117), despite an overall higher prevalence in patients (OR = 1.32; 95% CI = 0.93–1.87). To assess whether additional rare variants have an effect on MS risk, we sequenced PLG in 293 probands, and genotyped all rare variants in cases and controls. This analysis identified nine rare missense variants, and although three of them were exclusively observed in MS patients, segregation does not support pathogenicity. PLG is a plausible biological candidate for MS owing to its involvement in immune system response, blood-brain barrier permeability, and myelin degradation. Moreover, components of its activation cascade have been shown to present increased activity or expression in MS patients compared to controls; further studies are needed to clarify whether PLG is involved in MS susceptibility.

Colony stimulation factor 1 receptor (CSF1R) is not a common cause of multiple sclerosis

Hereditary diffuse leukoencephalopathy with spheroids (HDLS) is a rare autosomal dominant disorder characterized by cerebral white-matter degeneration. The onset of disease is typically in the fourth decade of life, and involves psychiatric, neurological and somatic symptoms leading to progressive cognitive and motor dysfunction [1,2]. In MRI, HDLS initially appears as patchy asymmetrical abnormalities in cerebral white matter that become confluent and symmetrical as the disease progresses [3]. A definite diagnosis of HDLS relies on widespread loss of myelin sheaths and axonal degeneration, neuronal spheroids, gliosis and accumulation of lipid-laden macrophages at pathological examination [1]. Missense, frame-shift and splice-site mutations in colony stimulation factor 1 receptor (CSF1R) have recently been identified as the cause of HDLS [4]. Although the pathological presentation was consistent with HDLS, the clinical presentation was found to include multiple sclerosis (MS), Parkinson’s disease, Alzheimer’s disease, or frontotemporal dementia. Interestingly, a recent study identified three patients diagnosed with MS harboring CSF1R mutations [5]. Multiple sclerosis is an inflammatory disease of the CNS characterized by myelin loss, varying degrees of axonal injury, and progressive neurological dysfunction. Due to the clinical and pathological overlap between MS and HDLS, the clinical diagnosis of MS in patients with CSF1R mutations [4,5], and the biological role of CSF1R in the inflammatory response, the question of whether mutations in CSF1R are implicated in the pathological mechanisms necessary to trigger the onset of MS was evaluated (methods are provided as supplemental information; Data S1). Genetic characterization of the entire coding sequence of CSF1R in 95 probands diagnosed with MS did not identify any of the previously reported pathogenic variants for HDLS [4,5]. Similarly, novel coding substitutions, frame shifts or splice-site mutations were not observed. Detailed information for 12 previously reported CSF1R coding variants identified in this study (five missense and seven silent) is provided in Table 1. Minor allele frequencies for these variants were consistent with those previously reported in healthy controls, suggesting they are unlikely to have an effect on MS risk. The identification of CSFR1 pathogenic mutations in HDLS [4] suggested the possibility that this gene could be implicated in other more common whitematter disorders, including MS. Additional support for this hypothesis was provided by the identification of CSF1R mutations in patients clinically diagnosed with MS [5]. However, despite the clinical and pathological overlap between HDLS and MS, sequencing of CSF1R in MS patients failed to identify any of the previously described HDLS mutations or novel mutations with potentially pathogenic effects. Although the presence of CSF1R mutations could not be confirmed in a relatively small sample of MS patients, further studies in larger cohorts of MS patients, as well as other degenerative white-matter diseases, are warranted. In conclusion, our study indicates that pathogenic mutations in CSF1R are an unlikely cause of MS in the Canadian population.