Cognition and adaptive skills in myotonic dystrophy type 1: a study of 55 individuals with congenital and childhood forms

Aims To investigate cognitive abilities and adaptive skills in children and adolescents with myotonic dystrophy type 1 (DM1) and correlate the findings to the cytosine-thymine-guanine (CTG) repeat expansion size. Method Cognitive level was assessed in 55 children and adolescents with DM1 (31 males, 24 females; mean age 12y 1mo, SD 5y 1mo; range 2y 7mo-21y 5mo) divided into the following categories: severe congenital DM1 (n=19), mild congenital DM1 (n=18), and childhood DM1 (n=18). The Griffiths Mental Developmental Scale, the Wechsler Scales, and the Vineland Adaptive Behavior Scales (VABS) for adaptive skills were used for this purpose. Results Learning disability was found in 95% of the severe congenital group, 83% of the mild congenital group, and 89% of the childhood DM1 group. The more severe the form of DM1, the lower the full-scale IQ (FSIQ; r(s)=0.28, p=0.044). The individuals with severe congenital and childhood DM1 had a significantly higher verbal IQ than performance IQ (severe congenital: mean difference 5.7, SD 5.7, p=0.008; childhood DM1: mean difference 9.8, SD 18.0, p=0.038). CTG repeat expansion correlated negatively with FSIQ (r(s)=-0.63, p < 0.006). Almost all participants showed poor results on the VABS. There was a positive relationship between cognitive level and adaptive skills in the mild congenital (r(s)=0.95, p < 0.01) and childhood DM1 groups (r(s)=0.92, p < 0.01). Interpretation Children and adolescents with DM1 exhibit significant cognitive and adaptive problems.