Fig. 1

Age at onset of the disease (study cohort). For 77 % of probands included in the study the data about the age at onset of the disease were available. These are represented in the graph Age at Onset. For 23 % of probands these data were not readily available (N.A./ not available), however, age at referral for these probands is shown, as this may also be a useful surrogate (graph Age at referral). Each block in the graph represents a different age group; age groups are described as intervals in years, and percentage of probands with onset/referral is shown. From probands included in the study, 60 % of them had onset of the disease before the age of 20 years