When MMD symptoms manifest at birth, life-threatening complications ensue. However, once this critical period is past, improvement is likely during early childhood. Later, as a child approaches adolescence, it's likely that the symptoms of adult-onset MMD1 will appear.
Congenital MMD only has been observed in MMD1. To learn more, see Energy, Dedication, Hope Help Parents of Children with Congenital MMD1, part of Quest's In Focus: Myotonic Muscular Dystrophy series.
When a child is born with congenital MMD1, it’s almost always found that the mother has adult-onset MMD1 — even though her symptoms may be so mild that she didn’t even know she has the disorder.
Mothers with MMD also can pass on the adult-onset form. A child can inherit the disease from the father, but it’s almost always the adult-onset form. These unusual features aren’t seen in other genetic disorders. For more, see Causes/Inheritance.
Cognitive disabilities in congenital MMD
Infants born with congenital MMD often have serious cognitive disabilities, although this isn’t always the case. The condition seems to be related to abnormal development of parts of the brain, presumably caused by genetic abnormalities.
Some experts have suggested that the very high incidence of labor and delivery complications in mothers with MMD also could be a contributing factor to the cognitive problems seen in these babies.
Outgrowing congenital MMD
Infants and children with MMD1 symptoms may “outgrow” many of the muscle-related aspects of the disorder as they 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. See Medical Management.
However, despite early gains during childhood, children with congenital MMD will very likely develop the adult form of MMD when they reach adolescence or adulthood.
Speech, hearing and vision difficulties
The muscles involved in talking often are affected in congenital MMD. Hearing also can be impaired. The eye muscles are affected and can cause the eyes not to work together, a condition called strabismus.
Cataracts, common in adult-onset MMD, aren’t a feature of congenital MMD during early childhood. However, children with congenital MMD are likely to develop them later.
Babies with congenital MMD1 have very weak muscles and a lack of muscle tone (hypotonia). They appear floppy, have trouble breathing, and suck and swallow poorly.
In the past, many infants with congenital MMD didn’t survive. Today, with special care in neonatal intensive care units, such children have a much better chance of survival, although they still will face multiple challenges in childhood.
Children with congenital MMD1 have facial muscle weakness, leading to a bland expression and an upper lip that comes to a point — known as a tented upper lip.
Babies with congenital MMD1 often are born with clubfeet — a curvature of the feet and lower legs. The problem may be due to abnormal muscle development in the lower legs and feet during fetal life.
Infants with MMD1 don’t have myotonia at first but develop it later in life.