Myotubular Myopathy: Centronuclear Myopathy

Myotubular Myopathy is a congenital myopathy, one of a group of conditions causing weakness and wasting of the muscles with symptoms usually present at birth. The name 'myopathy' means muscle disorder and comes from the Greek words 'myo' meaning muscle and 'pathy' meaning disease.

Myotubular Myopathy is so called because the affected muscle fibres look like myotubes (muscle cells found only during fetal development when the fetus is between twelve to twenty weeks old). The condition is also known as 'centronuclear myopathy' because the nuclei of affected muscle cells are found in the centre of each cell instead of the periphery or edge of the cells (as occurs in healthy muscle cells).

There are at least three different types of this condition. The types are defined by the way in which it has been inherited. The most severe form, which typically affects boys, presents at birth or even before birth, in contrast to the other two and milder forms which present later in childhood. The most severe type is called ‘X-linked recessive’ type and the milder types are called ‘autosomal recessive’ and ‘autosomal dominant’. In all types, but particularly the severe type, the mother may notice a reduction in fetal movements during the pregnancy, or the doctors might have said that there was too much fluid (water) around the baby. The baby may also have a low birth-weight.

At birth, the symptoms are Hypotonia, breathing and swallowing difficulties. In the very severely affected cases, the baby may not survive for more than a few days or weeks. In others, there appears to be slowly progressive muscle weakness that affects the face, limbs and muscles involved in breathing. The affected muscles are weak and cannot function as well as normal (unaffected) muscles. As a result, children may have a variety of symptoms, including drooping of the eyelids, reduced movements of their eyes, drooling, swallowing difficulties and weakness of limbs and trunk. Some children are constipated and this may be as a direct result of the muscles in the gut being affected or caused by poor mobility. Hearing, vision and intelligence are usually unaffected.

Diagnosis of Myotubular Myopathy can only really be made by doing a muscle biopsy – which means taking a piece of muscle, usually from the outer part of the thigh or sometimes from the upper arm and looking at this under a microscope (called histological diagnosis). In addition there is a genetic test that may be undertaken on blood that may diagnose the most severe type of myotubular myopthay – the X-linked type – the one that generally only affects boys. This genetic test looks for an abnormality in the MTM1 gene that is located on the X chromosome (MTM1 stands for ‘myotubularin’ which is the protein that is very important for making normal muscles).

The condition may be non-progressive, progress slowly or progress moderately quickly. In general the earlier the onset of the disease the more severe and progressive the disorder appears to be. In the form that presents at birth, there may be life-threatening breathing difficulties and severe hypotonia (floppiness). However, in most cases the disease is only slowly progressive and most patients become weaker in late adolescence or early adult life and may eventually lose the ability to walk. They may also develop droopy eyelids and the muscles that move the eyeballs may also be affected. Occasionally muscle weakness may progress quite rapidly and these patients experience serious breathing problems.

There is currently no cure for Myotubular Myopathy. However, there are other helpful measures which can certainly improve a person’s quality of life and how they can live with this disorder. These include physiotherapy, the use of antibiotics to treat chest infections and nasogastric or feeding gastrostomy tubes if normal feeding is difficult. There is also treatment to help those children and teenagers who have problems with their breathing, particularly at night; this is called ‘non-invasive ventilation’ and may be very beneficial and make people feel better during the day. Regular but non-strenuous exercise such as swimming and cycling may help. It is also very important not to become overweight.

Inheritance patterns
Myotubular Myopathy can be inherited in X-linked recessive, autosomal recessive and autosomal dominant types while some cases are sporadic. The X-linked recessive type that affects boys only typically presents at birth. The autosomal and autosomal dominant types affect boys and girls equally.

Prenatal diagnosis
This is only possible in those families where a previous child has been found to have the most severe type, ‘X-linked recessive’ myotubular myopathy and where the gene mutation has been found in this previously affected child.

Medical text written September 2002 by Contact a Family from information supplied by Dr R Appleton. Approved September 2002 by Dr R Appleton. Last Updated September 2007 by Dr R Appleton, Consultant Paediatric Neurologist, Alder Hey Children's Hospital, Liverpool, UK

Further Online Resources
Medical texts in The Contact a Family Directory are designed to give a short, clear description of specific conditions and rare disorders. More extensive information on this condition can be found on a range of reliable, validated web sites and links to them are included in the CD-ROM version of this Directory. Further information on these resources can be found in our Medical Information on the Internet article.

There is an online support group for this condition, The Information Point for Centronuclear and Myotubular Myopathy, Web: http://www.centronuclear.org.uk e-mail: centronuclear.org@btinternet.com (information about the use of online groups is available in our 'Medical Information on the Internet: Seeking Quality' article). This group is moderated and refers affected adults, children and their families to relevant and trusted sources of information it also puts families in touch with one another. They produce a newsletter three times a year for the Centronuclear and Myotubular Myopathy community which is also distributed to medical professionals, charities and other organisations. If you do not have internet access, please telephone our freephone helpline on 0808 808 3555.

Group details last updated February 2007.