Psychiatric comorbidity in multiple sclerosis: It’s not the genes

Abstract

schizophrenia (n = 22,781) and their siblings. 9 They assessed the risk of developing MS in the cohorts with psychiatric conditions, and the risk of MS associated with having a sibling with a psychiatric condition. 9 Johannson et al. 9 confirmed previous findings that depression (hazard ratio (HR) 1.86; 95% CI: 1.72-2.01) and bipolar disorder (HR 1.86; 95% CI: 1.56-2.20) were more common in the MS population than in the general population. Conversely, the risk of MS increased in people with depression (HR 1.9; 95% CI: 1.7-2.0) and bipolar disorder (HR 1.8; 95% CI: 1.6-2.2); however, the risk of having schizophrenia was reduced in persons with MS (HR 0.71; 95% CI: 0.51-1.00) and the risk of MS was reduced in individuals with schizophrenia (HR 0.6; 95% CI: 0.4-0.9). Prior studies were inconsistent with respect to the risk of psychotic disorders in MS, possibly due to differences in case definitions (all psychoses versus schizophrenia alone) and the types of study controls. 3,10 A potential concern with respect to the observed reduction in the risk of MS among individuals with schizophrenia is under-diagnosis. Having a sibling with a psychiatric condition was not associated with an increased risk of having MS. Previous studies in smaller, clinic-based populations suggest that a family history of depression is associated with an increased risk of depression in MS. 11 In the Danish population, having a first-degree relative with MS was associated with a 1.3-fold increase in the risk of schizophrenia, but no increase in the risk of bipolar disorder. 12 The findings of the present study argue against shared genetic susceptibility as an explanation for the increased burden of psychiatric comorbidity in MS. Other potential explanations include: structural brain abnormalities secondary to MS, 13 consequences of immunological and inflammatory changes second- ary to MS, 14 or consequences of therapy for MS, including corticosteroids used for relapses, disease- modifying and symptomatic therapies. 15 As more effective DMTs emerge, a relevant question is whether