BACKGROUND: Familial factors influence susceptibility to @entity15 ( @entity15 ) but it is unknown whether there are additional effects on the natural history of the disease. METHOD: We evaluated 1,083 families with > or =2 first-degree relatives with @entity15 for concordance of age at onset, clinical course, and disease severity and investigated transmission patterns of these clinical features in affected parent- @entity1 pairs. RESULTS: There is concordance for age at onset for all families (correlation coefficient 0.14; p < 0.001), as well as for affected siblings (correlation coefficient 0.15; p < 0.001), and affected parent- @entity1 pairs (correlation coefficient 0.12; p = 0.03) when each is evaluated separately. Concordance for year of onset is present among affected siblings (correlation coefficient 0.18; p < 0.001) but not the parent- @entity1 group (correlation coefficient 0.08; p = 0.15). The clinical course is similar between siblings (kappa 0.12; p < 0.001) but not affected parents and their @entity1 (kappa -0.04; p = 0.09). This influence on the natural history is present in all clinical subgroups of relapsing-remitting, and primary and secondary progressive @entity15 , reflecting a familial effect on episodic and progressive phases of the disease. There is no concordance for disease severity within any of the considered family groups (correlation coefficients: all families analyzed together, 0.02, p = 0.53; affected sibling group, 0.02, p = 0.61; affected parent- @entity1 group, 0.02, p = 0.69). Furthermore, there are no apparent transmission patterns of any of the investigated clinical features in affected parent- @entity1 pairs and no evidence for anticipation or effects of genetic loading. CONCLUSION: Familial factors do not significantly affect eventual disease severity. However, they increase the probability of a progressive clinical course, either from onset or after a phase of relapsing remitting disease. The familial effect is more likely to reflect genetic than environmental conditions. The results are relevant for counseling @entity1 and have implications for the design of studies seeking to identify factors that influence the natural history of the disease.

Familial effects on the clinical course of XXXX .

@entity1 :: ('9606', 'Species') :: ['children', 'patients', 'child'] @entity15 :: ('MESH:D009103', 'Disease') :: ['multiple sclerosis', 'MS']
@entity15 :: (MESH:D009103,Disease) :: ['multiple sclerosis']
