Rare diseases in disabled children: an epidemiological survey

AIM: To estimate the contribution of rare diseases (RD) to severe impairment in 7-year-old children. METHODS: Data from a morbidity register of childhood impairments in a single French region were used. Impairments were classified as a mental, sensorial, neuromuscular (skeletal or movement-related) impairment (MSNI) according to the International Classification of Functioning. Details of children born from 1980 to 1994 and resident in the county under study when they were 7 years old were recorded. A rare disease was defined as a prevalence rate of <1 per 2000 general population. RESULTS: 26% of children with severe MSNI had a rare disease; in 36% the MSNI was of unknown origin. The proportion of impairments that were due to a rare disease varied according to the type of impairment: 3. 3% for severe psychiatric disorders; 16. 0% for intellectual impairment; 37. 2% for hearing impairment; 41. 2% for neuromuscular, skeletal and movement impairment; and 81. 1% for visual impairment. The overall prevalence rate of rare diseases was 2. 1 per 1000 (459/218 283), and it increased significantly over time (p = 0. 003). The latter increase was not associated with a decrease in the proportion of impairments of unknown origin, indicating an improvement in the survival of the children with a rare disease. CONCLUSIONS: In this study, a rare disease was at the origin of 26% of cases of severe MSNI. This proportion remained stable over time, whereas the prevalence rate, as well as the prevalence rate of MSNI disability, increased over time.