Genetic susceptibility to multiple sclerosis. A co-twin study of a nationwide series
E. Kinnunen, J. Juntunen, L. Ketonen, S. Koskimies, Y. T. Konttinen, T. Salmi, M. Koskenvuo and J. Kaprio
Clinical Neurosciences, Institute of Occupational Health, Helsinki, Finland.
The problems of differentiation between environmental and genetic
influences on the development of multiple sclerosis are well known. Twin
studies may provide valuable information on this question. However, most
published twin series are selected and no through clinical twin studies
based on epidemiologic series have been carried out. In this study, all
available same-sex twin pairs with clinically definite multiple sclerosis
derived from the Finnish Twin Cohort of 15815 pairs were studied by
clinical evaluation, magnetic resonance imaging, and visual and auditory
evoked responses. The mean length of follow-up of the pairs after the onset
of symptoms of multiple sclerosis was 20 years. Two of the seven
monozygotic pairs were concordant; one was definitely so, and in the other,
the co-twin of the index case had, in addition to clinical findings, white
matter changes suggestive of multiple sclerosis in magnetic resonance
imaging and abnormal visual evoked responses. All six dizygotic pairs were
discordant. The frequency of the HLA antigen DR2 in probands (69%) was
significantly increased, but the distribution among the healthy subjects
and patients showed nonsignificant differences. The results indicate a
genetic influence on the susceptibility to multiple sclerosis, although
still unknown genetic determinants are possible involved.
