LATE-ONSET (or MILD) MYOTONIC DYSTROPHY
Symptoms start after the age of 50 years. Symptoms are often mild, with cataract (opaque spots in the lenses of the eyes; see eyes). Some musle weakness may occur, e.g. droopy eyelids (ptosis). Life expectancy is usually within the normal range.

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ADULT-ONSET (or CLASSICAL) MYOTONIC DYSTROPHY
Symptoms start between the age of 10 and 50 years. Initially, myotonia occurs, which is the inability to relax skeletal muscles after contraction. Muscle weakness is slowly progressive, and involves especially muscles in the face, chewing and swallowing muscles, and neck muscles. Frequently occurring symptoms are fatigue and lack of initiative. Several aspects of physical and mental functioning can be affected due to involvement of other organs, such as the brain, the heart, lungs, eyes, and the digestive tract. Weakness in facial muscles, fatigue and lack of initiative may affect communication. Life expectancy is ususally shortened and is mainly the result of heart and lung problems.

JUVENILE-ONSET MYOTONIC DYSTROPHY
Complaints start between the first year of life and 10 years of age. The most prominent features at young age are speech problems (unclear or blurry speech) and learning problems. Children are often clumsy. Besides the learning disabilities, also issues with attention and concentration, increased sleepiness and behavioural problems may occur. Gastrointestinal complaints are very frequent. As the child matures into adulthood, typical features of adult-onset DM1 usually emerge.

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CONGENITAL MYOTONIC DYSTROPHY
When myotonic dystrophy symptoms manifest at birth, life-threatening complications ensue. However, once this critical period is past, improvement is likely during early childhood. In children with congenital myotonic dystrophy, the disease is almost excluvely transmitted by the mother, although her symptoms may be so mild that she didn’t even know she has the disorder. Babies with congenital myotonic dystrophy have very weak muscles and a lack of muscle tone (hypotonia). They appear floppy, have trouble breathing, and suck and swallow poorly. Club feet (a curvature of the feet and lower legs) are often present. Many of the muscle-related aspects of the disorder improve as the children mature. Although cognitive difficulties don’t improve, they generally do not worsen either, and children can learn when given the right tools, instruction and environment. Gastrointestinal complaints can occur.
When children with congenital myotonic dystrophy reach adolescence or adulthood, they usually will develop the adult form of myotonic dystrophy.
For more information, see the brochure congenitale vorm (in Dutch).