Hair and eye colour, skin reactivity, and melanin production gene mutations as risk factors for multiple sclerosis: a case-control study in Sweden
Author(s): ,
K.A. Smith
Institute of Environmental Medicine (IMM)
I. Kockum
Department of Clinical Neuroscience (CNS); Center for Molecular Medicine (CMM), Karolinska Institutet, Stockholm, Sweden
T. Olsson
Department of Clinical Neuroscience (CNS); Center for Molecular Medicine (CMM), Karolinska Institutet, Stockholm, Sweden
L. Alfredsson
Institute of Environmental Medicine (IMM)
A.-K. Hedström
Institute of Environmental Medicine (IMM); Department of Clinical Neuroscience (CNS)
ECTRIMS Online Library. Smith K. Oct 12, 2018; 228838
Kelsi Alexandra Smith
Kelsi Alexandra Smith
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Abstract: P996

Type: Poster Sessions

Abstract Category: Clinical aspects of MS - Epidemiology

Introduction: The etiology of Multiple sclerosis (MS) involves both genetic and environmental factors. MS affects Northern European Caucasians at a higher frequency compared to most other populations. However, it is unestablished whether pigmentation phenotype, skin reactivity to sunlight or mutations in the gene controlling melanin production, affect MS risk.
Aim: To determine if hair or eye color, skin reactivity to sunlight, or mutations in the melanin producing melanocortin-1 receptor (MC1R) gene are associated to MS risk, and whether sex modifies these potential associations.
Methods: This population-based case-control study was based on the Epidemiological Investigation of Multiple Sclerosis. Incident MS cases (n=1473) in Sweden between 2009-2015 were matched by age, sex, and residential area to randomly selected controls (n=3229). Individuals were classified by self-reported pigmentation phenotype, skin reactivity, and by high or low penetrance MC1R SNPs. Unconditional logistic regression models were used to calculate odds ratios (OR) with 95% confidence intervals (CI) of developing MS among participants with light pigmentation, compared to those with dark pigmentation, and by MC1R SNPs compared to wild-type. Potential confounding variables such as ancestry, sunlight exposure, HLA-DRB1*15:01 and HLA-A*02:01 status, were considered.
Results: Hair and eye colour showed no association with MS risk. Compared to having low skin reactivity to sunlight, high skin reactivity increased MS risk in females (adjusted OR 1.4, CI 1.1-1.9), but not in males (adj. OR 1.1, CI 0.8-1.6). High penetrance MC1R SNPs increased MS risk in females (adj. OR 1.5, CI 1.0-2.2), but not in males (adj. OR 0.5, CI 0.3-1.1). An interaction analysis restricted to females indicated a synergistic effect between high penetrance MC1R SNPs and presence of HLA-DRB1*15:01 with MS risk (adj. OR 5.05, CI 2.8-9.2). Low penetrance MC1R SNPs were not associated with MS risk.
Conclusions: High skin reactivity to sunlight and high penetrance MC1R mutations seem to independently increase MS risk in females. The MC1R SNP results should be interpreted with caution due to limited sample sizes. Further studies elucidating the interplay between MC1R SNPs, HLA-DRB1*15:01 status, sun exposure, and sex with respect to MS risk are warranted.
Disclosure: KS: Nothing to disclose.
IK: Nothing to disclose.
TO: Tomas Olsson has received funding from Swedish Research Council and the Swedish Brain foundation in addition to unrestricted MS research grants and/or lecture advisory board compensations from Biogen, Novartis, Genzyme, and Roche Merck.
LA: Nothing to disclose.
AKH: Nothing to disclose.

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