Cognitive and adaptive functioning in congenital and childhood forms of myotonic dystrophy type 1: a longitudinal study.

Aim To conduct a longitudinal follow-up of the development of global cognitive abilities and adaptive skills in individuals with congenital and childhood forms of myotonic dystrophy type 1 (DM1). Method Fifty-one participants (29 males, 22 females, mean age 19y 5mo, SD 4y 11mo, range 10y 10mo-28y 11mo) were divided into severe congenital (n=16), mild congenital (n=17), and childhood DM1 (n=18) subgroups. The average time between the first and second assessments was 7 years 8 months. Adaptive skills were evaluated using the Vineland Adaptive Behavior Scales and global cognitive functioning using Wechsler scales. Results There was no statistically significant decline in cognitive abilities and adaptive behaviour. A tendency of decline regarding the level of intellectual disability was found in the congenital DM1 groups but not in the childhood group. In the congenital DM1 groups, the gap in relation to typically developing peers in cognitive and adaptive functioning increased. Predictors of change over time in adaptive skills were age and current level of intellectual disability: individuals with severe intellectual disability and younger individuals deteriorated the most. However, when raw scores were compared, no actual regression in adaptive functioning was found. Interpretation The participants had not lost any important adaptive skills. Greater cognitive and adaptive development was found in the childhood group than in the congenital groups. What this paper adds There is no absolute decline in cognitive and adaptive abilities in individuals with congenital and childhood myotonic dystrophy type 1. Pace of development is slow in comparison with normative data. The childhood group tended to show greater cognitive and adaptive development than the congenital groups.