Asymptomatic subjects differ less from their twin siblings with MS than from healthy controls in cognitive functioning. A Finnish Twin Cohort study.

Background: Cognitive impairment develops in some MS patients at any time during the course of the disease regardless of whether the patients have neurological disability or not. Underlying causes for the MS related cognitive decline are yet poorly understood but both genetic and environmental risk factors have been proposed.

Objectives: To assess whether the cognitive performance differs between subjects with multiple sclerosis (MS) and their asymptomatic co-twins.

Methods: Nineteen twin pairs discordant for MS recruited from the Finnish Twin Cohort were studied neurologically and with a comprehensive neuropsychological test battery. Control group included twenty age and education matched healthy subjects.

Results: Compared with the control subjects, the asymptomatic co-twins of MS patients performed significantly less well in tests of naming, verbal reasoning, visuospatial performance, processing speed, attention, verbal memory and learning. The twins with MS performed significantly less well than their co-twins in the SDMT evaluating processing speed, in visual learning and in word fluency.

Conclusions: The lack of significant difference in majority of neuropsychological tests between the MS patients and their co-twins as well as considerable differences between asymptomatic co-twins and healthy controls may suggest that the cognitive performance may be partly developmental and regulated both by genes and shared environmental factors.