Demographic information for the healthy controls, siblings and patients.

aGroups were compared with an analysis of variance (ANOVA) and did not differ significantly (p = 0.62).
bLevel of education was defined according to scoring system of Verhage [57] (ordinal scale). Group differences for gender and education were tested with a chi-square and kruskal-wallis test, respectively. Neither gender (p = 0.23) nor level of education (p = 0.72) differed between groups.