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Congenital Myotonic Dystrophy

Background

Congenital myotonic dystrophy is a serious form of myotonic dystrophy type 1 (DM1). DM1 usually affects adults, but can affect individuals of all ages and both sexes. Congenital means it is present from birth, myotonic means muscle stiffness, and dystrophy means wasting and weakening.

Credits

Medical text written November 2011 by Dr D Wilcox, Senior Lecturer and Honorary Consultant, Ferguson-Smith Centre for Clinical Genetics, Glasgow, UK. Last updated by Darren Monckton, Professor of Human Genetics, University of Glasgow, Glasgow, UK, October 2019.

Although great care has been taken in the compilation and preparation of all entries to ensure accuracy, we cannot accept responsibility for any errors or omissions. Any medical information is provided for education/information purposes and is not designed to replace medical advice by a qualified medical professional.

What are the symptoms?

In babies
At birth, babies with congenital myotonic dystrophy usually do not have muscle stiffness, but are usually very floppy due to delayed muscle development. Their feet might be deformed, they may not be able to breathe or feed properly, and they may need treatment in an intensive care unit (ICU). Women with DM1 should ideally have their baby in a hospital that has a neonatal ICU. The first few weeks are very critical for affected babies, but later on, the outcome is often better than was initially feared.

In children
As they grow, children with congenital myotonic dystrophy might not learn to sit, walk and talk as quickly as other children and they might have facial weakness. They may have learning difficulties, with a short attention span and poor motivation, and tire easily. Their muscles seem to be less affected in childhood than might be expected from their weakness at birth. Some anaesthetics and sedatives are dangerous for children with congenital myotonic dystrophy, so you should always tell the doctors about it.

What are the causes?

It is an inherited (genetic) condition, which is caused by a change (mutation) in the genetic material (DNA) that is passed on from one generation to the next. In DM1 this mutation is not stable and tends to increase in size with each generation often leading to an earlier onset of the disease in successive generations.

How is it diagnosed?

The condition may be suspected from the symptoms, and confirmed by genetic testing (usually using a blood sample). If other members of the family already have a diagnosis of DM1, diagnosis is likely to be quicker. However, in many families the birth of a congenitally affected child may be the first clear sign of the disease and diagnosis may take longer.

How is it treated?

There is no cure, but much can be done to help. After intensive support following birth, children with congenital myotonic dystrophy may need extra educational help. Physiotherapists, occupational and speech and language therapists can also help. Affected children should attend a neuromuscular clinic at least once a year, to ensure each child gets the help they need.

Inheritance patterns and prenatal diagnosis

Inheritance patterns
Each of an affected person's children has a 50% chance of inheriting DM1. However, it is usual for a baby with congenital myotonic dystrophy to inherit it from its mother rather than from its father. By the time a baby with congenital myotonic dystrophy is born in a family, DM1 will often have affected people in the previous generations. As DM1 is very variable, it might not have been recognised in previous generations, so the baby with congenital myotonic dystrophy might be the first person in the family to be diagnosed.

Prenatal diagnosis
Options for prenatal diagnosis include testing a pregnancy to see if the foetus has inherited DM1. Although these tests are good at telling if a foetus has inherited DM1, they are not so good at telling whether the child will develop congenital myotonic dystrophy or might not develop symptoms until adult life.In vitro fertilisation (IVF) and preimplantation genetic diagnosis may be available to couples at risk of having an affected child.

Is there support?

Myotonic Dystrophy Support Group

Helpline: 0115 987 0080 
Email: contact@mdsguk.org
www.myotonicdystrophysupportgroup.org

The Group is a Registered Charity in England and Wales No. 1134499. It provides information and support to those affected by Myotonic Dystrophy. The Group runs a helpline and has a network of regional contacts throughout the UK, and also has links abroad.

Group details last reviewed October 2019.

Muscular Dystrophy UK

Helpline: 0800 652 6352
Email: info@musculardystrophyuk.org
www.musculardystrophyuk.org

The Charity is a Registered Charity in England and Wales No. 205395, and Scotland No. SC039445. It provides information and support for anyone affected by muscular dystrophy and other muscle-wasting conditions. Muscular Dystrophy UK also provide grants towards the cost of specialist equipment.

Group details last updated September 2017.