What is a myopathy?
The term myopathy is derived from the Greek language and means muscle disorder.
What is Bethlem myopathy?
Bethlem myopathy (BM) is a little known muscle disorder, which is named after the Dutch doctor who first described the condition in 1976. Diagnosis and recognition of it has improved over the past few years following work done by a number of researchers around the world on the identification of the protein involved. The protein is called collagen VI. A fault in any of the three genes for collagen VI can give rise to BM.
How does the disease present?
First symptoms of BM can present at any time from birth through to adulthood and are very variable. In childhood these symptoms can be hypotonia (floppiness), muscle weakness, delayed motor milestones (for example when a baby first sits up unaided or learns to walk), talipes (clubfoot), torticollis (stiff neck) and contractures (tightness) in the ankles, hips, knees and elbows. The contractures are often quite variable and can come and go over time.
Adults with BM can have tight tendons at the back of their ankles, as well as tightness of various other joints (elbows, knees, joints in the back) and especially some of the muscles in the hands. Other symptoms such as poor stamina / poor exercise tolerance and difficulties walking upstairs or doing tasks which require lifting the arms above the head are related to the subtle muscle weakness that tends to go with Bethlem myopathy.
In addition, the skin of some people with BM can be unusual. Over the outer surfaces of the arms and legs especially it can feel rough or dry to touch and has been described as looking like “plucked chicken skin”. Other patients might find that they scar in an unusual way, either by forming keloids (raised, rather angry looking scars) or thin silvery “cigarette paper scars”.
How is Bethlem myopathy diagnosed?
The diagnosis of BM is usually suspected from the symptoms and examination, paying special attention to the features described above. Because it is a rare disorder not very many doctors have experience of these features and people with Bethlem myopathy may often have had other diagnoses suggested in the past.
It is often necessary to do a blood test and a muscle biopsy to exclude other conditions that can present in a similar fashion. The muscle biopsy is studied through a microscope to check how the muscle is put together and whether there is any evidence of it being damaged. In BM the muscle fibres, instead of being evenly sized, show some variation but no significant damage or scarring. With special stains we can also check for a special protein called laminin beta 1, which can sometimes be reduced. However this only provides additional evidence, as these findings are not entirely specific to BM. At present the diagnosis of BM is usually made by collating the information gathered from history, clinical examination with the laboratory findings.
In some cases it is possible for us to prove the specific diagnosis by demonstrating a fault in one of the genes encoding for collagen VI. This can be done using a skin biopsy or a blood sample. At present it is available on a research basis only and results take months to years to come through. However, we are hoping this will change in the future.
Is Bethlem myopathy inherited?
BM is inherited in what we call an autosomal dominant way. This means that there is a 50% (one in two) chance for the children of a person affected by BM to inherit the faulty gene and be affected by BM themselves. This is independent of how mildly the parent might be affected. Sometimes when people are diagnosed as having BM, neither of their parents seems to be affected. In this case the fault in the gene may have arisen for the first time in the affected person, which is quite a common situation.
Are patients at risk from developing any complications?
The main complications we look out for at the regular check ups in the muscle clinic are contractures (muscle tightness causing restriction in the range of joint movement) and chest problems. People with BM can be prone to chest infections if their cough is not strong due to weakness of their breathing muscles and in some cases overnight sleep studies may be required to assess breathing. From what we know so far the heart, although a muscle, is usually not affected by BM.
Does the condition get worse?
For most patients with BM the weakness and contractures are known to get worse over the years, however, this usually only happens very slowly. Whereas some adults remain unaware of any muscle weakness and only have very slight contractures which do not pose them any functional problems others need to make use of practical home aids to work around their muscle weakness and contractures. A proportion of adults over the years might need aids to help movement outside the house (i.e. cane, crutches or wheelchair) and might also experience breathing problems for which they require treatment.