There is not much information on the juvenile form of CMyD. Here is what I have found.  This information is from a study by:

Steyaert, A Study of the cognitive and psychological profile in 16 Children with congenital or juvenile myotonic dystrophy. Clinical Genetics 1997: 52:135-141

No major problems were noted in these problems at birth. Of the 14 patients with Juvenile CMD, five of them had feeding problems, these early problems were diagnosed with myotonic dystrophy before age 8.  Based on:

The mean age for diagnosis is 8.1 years. This is for all of the 14 subjects. So if you are just finding out about this disease for a child it may be that the symptoms need to develop before a clinical diagnosis is made. Learning difficulties are the primary reason most parents seek medical help.

Intelligence Information

Three subjects had mental retardation. Five subjects had borderline intelligence. Five subjects had learning disabilities with IQ between 85-100. Nine of the 14 subjects were in special education programs.

This study included information about the CTG repeats. Steyaert states that the repeat length does not permit the prediction of variation within one diagnostic group but there is a correlation between repeat length and FSIQ (full scale IQ) Thus Steyaert states that roughly the longer the repeat the lower the FSIQ

All 14 were hypotonic and presented facial weakness, myotonia in the face and hands. Delayed fine motor movement was noted in 5 subjects and somnolence (sleepiness) in  4 Most of the Subjects needed long nights rest with over 75% needing 10 or more hours of sleep.

Behavioral Issues

Issues with behavior were noted using the Child Behavior Check List with the main concerns:

• withdrawal
• social problems
• attention problems
• Depression (2 individuals)
• Anxiety Disorders
• Attention Deficit and Hyperactivity Disorder (ADHD)

Clinically 5 individuals were diagnosed with ADHD. However, more showed symptoms of this disorder. The patients showed presented symptoms of mainly relating to attention deficit and impulsivity and very few to hyperactivity.

The prevalence of ADHD in the general population in 1-3%. In this study it was 25% and higher if you consider that the subjects do not show the classical hyperactivity symptoms

The children reporting depression were reported to be teased at school. This aspect deserves special attention of parents and educators. Steps must be taken with other students to educate and instruct them on how to interact with kids with CMyD if this is possible.