Myotonic Dystrophy (DM)

Congenital DM1

Estimates of the incidence of congenital DM vary widely, ranging from about 2 to 28 per 100,000 live births in different studies.^{23, 24} When DM 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 is likely that the symptoms of adult-onset DM1 will appear.

Congenital DM has been observed only in DM1. To learn more, see Energy, Dedication, Hope Help Parents of Children with Congenital DM1, part of Quest's In Focus: Myotonic Dystrophy series.

When a child is born with congenital DM1, the mother usually has adult-onset DM1, even though her symptoms may be so mild that she did not know she had the disorder. Mothers with DM also can pass on the adult-onset form. A child can inherit the disease from the father, but it is almost always the adult-onset form. These unusual features are not seen in other genetic disorders.^{25, 26} For more, see Causes/Inheritance.

Respiratory involvement is common and is the leading cause of death in the neonatal period. Mechanical ventilation is required for 70% to 80% or more of patients.^{27, 24} Feeding difficulties are also common, with many children requiring a nasogastric or gastric feeding tube. Both sucking and swallowing are related to muscle weakness in the face and the throat area.

The overall mortality rate is approximately 15% to 20% percent and approaches 40% in severely affected infants.²⁷

Cognitive disabilities in congenital DM

Infants born with congenital DM often have serious cognitive disabilities, although this is not always the case. Intellectual disability is present in 50% to 60% of the children who survive.²⁷ 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 DM also could be a contributing factor to the cognitive problems seen in these babies.

Outgrowing congenital DM

Cognitive difficulties do not improve but 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 DM will very likely develop the adult form of DM when they reach adolescence or adulthood.

Speech, hearing and vision difficulties

The muscles involved in talking often are affected in congenital DM. Hearing also can be impaired. The eye muscles are affected and are not always aligned, a condition called strabismus.

Cataracts, common in adult-onset DM, are not a feature of congenital DM during early childhood. However, children with congenital DM are likely to develop them later.²

Weak muscles

Babies with congenital DM1 have very weak muscles and a lack of muscle tone (hypotonia) rather than myotonia. They appear floppy, have trouble breathing, and suck and swallow poorly.

In the past, many infants with congenital DM did not 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.

Babies with congenital DM1 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 DM1 do not have myotonia at first but develop it later in life.²⁷

References

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