Background: Investigation of coaffected sib pairs is one method to determine the genetic influence on the clinical presentatio n of many complex diseases, such as multiple sclerosis (MS). Investigation of the clinical concordance in coaffected sib pairs may be a prerequisite to identify genes that modify the clinical outcome. The aim of this study was to investigate a possible genetic influence on selected demographic and clinical variables among familial Scandinavian MS cases. Material and methods: We identified 136 C aucasian Scandinavian families with MS coaffected sib pairs from Denmark, Norway, and Sweden. C ohen’s kappa coefficient and the intraclass correlation coefficient were used to assess concordances in sib pairs. Furthermore, clinical features and HLA-DR2 carrier status were compared among the probands of sib pairs. Results: We found significant concordance of the disease course (k=0.28, PB-0.001) and adjusted age of onset (r =0.23, P=0.028). Among probands of sib pairs, HLA-DR2 carrier patients had a younger age of onset (P=0.024). Conclusion: A nalyses of Scandinavian coaffected sib pairs suggest that disease course and age of onset are partly under genetic control. Furthermore, HLA-DR2 in probands of sib pairs suggests importance for age of onset.
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