COPENHAGEN, Denmark — A higher cumulative genetic burden for depression is associated with an increased risk for relapse and worsening disability in people with multiple sclerosis (MS), early results of a new study showed.
Unlike the previous research, the current analysis used polygenic risk scores for depression, which summarize the estimated effect of genetic variants to determine the potential association with MS disease activity, so results are less likely to be explained by reverse causality.
This study increases awareness of the link between depression and MS, study investigator Kaarina Kowalec, PhD, assistant professor, College of Pharmacy, Rady Faculty of Health Sciences, University of Manitoba, Winnipeg, Manitoba, Canada, told Medscape Medical News. "We're starting to understand how depression affects relapses and disability progression in MS," she said.
The findings were presented on September 20 at the 40th Congress of the European Committee for Treatment and Research in Multiple Sclerosis (ECTRIMS) 2024.
Common Comorbidity
Depression is a common comorbidity in patients with MS and is associated with increased relapse and disability progression. Depression risk is partly polygenic in nature, involving numerous common genetic variants, said Kowalec.
The case-control study included 3420 relapsing-onset MS cases of European ancestry from four existing cohorts in three countries.
The Canadian cohort included those enrolled in a prospective longitudinal study of psychiatric comorbidity in chronic immune-mediated inflammatory disease (IMID), including MS; the Swedish cohort was an MS registry (SSReg) that encompasses 64 MS clinics (the cohort was split into two groups); and the US cohort was enrolled in a clinical trial of combined therapy with interferon and glatiramer acetate (CombiRx) in patients with MS.
The median follow-up in these cohorts ranged from 3 to 5 years.
Not surprisingly, most participants were women (from 71% in one of the Swedish cohorts to 83% in the Canadian cohort), and the age at MS onset ranged from 29 years in the Canadian cohort to 35 years in one of the Swedish cohorts.
The median baseline Expanded Disability Status Scale (EDSS) score was higher in the Canadian cohort (3.5) than in the Swedish (1.5) and US (2.0) cohorts, "reflective of the Canadian cohort being slightly more progressed," said Kowalec.
Inherited Variants
To measure depression heritability, researchers generated a polygenic risk score in whole-genome imputed genotypes. The score reflects the number of inherited common genetic variants, weighted by effect sizes.
Researchers investigated the association between depression polygenic risk scores (top 20% vs bottom 80%) with annualized relapse rate and worsening disability in MS measured by the rate of change in EDSS score. In the US cohort, they also explored the association between depression polygenic risk scores and time to relapse and confirmed EDSS worsening.
Covariates included use of disease-modifying therapy, age, sex, and the first five genetic ancestry principal components. The latter was done to capture residual stratification by genetic ancestry, although Kowalec stressed analyses were done only in those of European ancestry.
Investigators found a higher depression polygenic risk score was associated with relapse risk (incident rate ratio, 1.23; 95% CI, 1.01-1.49).
"Essentially, for every one standard deviation increase in the depression polygenic score, we found a significant increased hazard of 23% for experiencing a relapse over the follow-up period," said Kowalec, who is also affiliated with the Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden.
She noted the Canadian cohort did not have many relapses, while the US and Swedish cohorts "had an increased rate."
Other analyses examined the risk of having a relapse or worsening disability. Every one SD increase in the depression polygenic risk score was significantly associated with a 2.2 greater risk of experiencing relapse (hazard ratio [HR], 2.20; 95% CI, 1.35-3.60) and a 51% increased risk for confirmed EDSS progression (HR, 1.51; 95% CI, 1.03-2.22).
'An Ideal Marker'
Use of polygenetic risk scores reduces the possibility of reverse causation, noted Kowalec. "These markers are fixed at birth and don't change over your lifespan, so they're really an ideal marker."
The results suggest polygenetic risk scores represent a potential biomarker for risk stratification in people with MS, said Kowalec. Although depression polygenic risk scores are not currently available in clinical practice, "I would hope this would change in the next 3-4 years," she said.
Asked by a delegate if confounding by a third variable is possible, Kowalec said because genetic markers don't change over time, there is a hint that the direction is causal and that depression is driving the outcome. However, she added, further confirmation is needed.
Kowalec noted that there were no data on antidepressant use but noted that about half of the Canadian and US cohorts — and likely the same number in the Swedish cohorts — self-reported depression.
A limitation of the study was that it included only participants of European ancestry.
Commenting on the research for Medscape Medical News, Lauren Gluck, MD, program director, Montefiore Multiple Sclerosis Center, Bronx, New York, described the study as "fascinating" but noted that it's unclear how to use this new information in clinical practice.
"Clinicians frequently ask people with MS about mood symptoms and offer interventions like antidepressants and referrals to therapists. However, genetic testing is not routine, so we don't yet know who to target based on these data."
Preexisting depression or more severe depression could be viewed as a "red flag" for risk for more disease activity in the future, she said.
"This could encourage clinicians to use more highly effective therapy in these patients, similar to our strategies for people with MS with frequent attacks and more disease burden on MRIs."
Note: This article originally appeared on Medscape.
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