The term myopathy is derived from the Greek and it means muscle disorder
(myo = muscle, pathy = disease).
congenital myopathies are a group
of conditions which cause weakness
and wasting of the muscles. In general symptoms are present at birth but
may not be recognised until later on in childhood or even in adult life.
fibre type disproportion?
'Congenital' refers to the onset of the myopathy and means from birth. The
name 'fibre type disproportion' was first suggested in 1973 and refers to the
different size of the muscle fibres. When a normal muscle is looked at under
the microscope, two types of muscle fibres (type 1 and 2) are seen, both of
which are needed for the proper functioning of that muscle. The size of type 1
and type 2 fibres in the muscles of most young children is roughly similar. In
congenital fibre type disproportion, type 1 fibres are smaller than type 2. A
number of cases of congenital fibre type disproportion have an onset in
infancy, and may even present at birth with hypotonia (floppiness),
swallowing and breathing difficulties, joint contractures (limitation of joint
movement) or dislocation of the hips.
other cases the child may show
motor development (i.e. slow to
crawl, stand or walk). The muscle weakness is usually non-progressive or
very slowly-progressive after the age of two years. In some cases the
condition may actually improve after that time, although the degree of muscle
weakness is variable. It involves the muscles of the trunk and limbs, with
more 'proximal' involvement (proximal muscles are those that are near the
trunk such as shoulder and thigh muscles).
Because of this weakness children may
have a variety of symptoms ranging
from recurrent chest infections, drooping of the eyelids, drooling, swallowing
difficulties, and weakness of the limbs and the trunk. Children with this
condition are usually shorter than other children and in addition may develop
curvature of the spine. Some children also suffer from constipation and this
may be as a direct result of the muscles in the gut being affected, or caused
by lack of exercise and insufficient mobility. Hearing, vision and intelligence
are usually unaffected.
type disproportion an inherited disorder?
Yes, usually. Although the exact genetic cause is unknown, different patterns
of inheritance are recognised; these are known as autosomal recessive and
autosomal dominant. In the remaining cases there does not appear to be a
clear pattern of inheritance and these are described as 'sporadic' cases
which means they occur randomly, or as a one-off, with very little risk of other
children in the family being affected. However, people who are themselves
sporadic cases will be at risk of passing the condition on to their children.
autosomal recessive type may be
difficult to separate from the
autosomal dominant form, although onset is generally earlier, and the
condition may present as a 'floppy infant', or later on with severe muscle
weakness. In the recessive form both parents are carriers of the condition,
and the risk of a child of either sex being affected is 25% (1 in 4).
the autosomal dominant type of
one (either) of the two parents
is affected, may be only very mildly so, but carries the abnormal gene, and
each child (of either sex) of that affected parent has a 50% (1 in 2) chance of
fibre type disproportion myopathy diagnosed?
The diagnosis of a 'myopathy' is usually suspected from the history and
examination. However the specific diagnosis of congenital fibre type
disproportion is nearly always made by looking at a piece of muscle (muscle
biopsy). Before doing a muscle biopsy (which involves taking out a small
piece of muscle usually from the thigh muscle) a few other tests may be
done, one of which is a blood test which measures the level of a muscle
enzyme (creatine kinase or CK level), which is usually normal but may be
increased. The other is an electrical test of the muscles and the nerves
supplying the muscle; it involves the placing of a thin needle into the muscle
which then measures the electrical activity arising from that muscle. Although
this test may be able to show a 'myopathic' pattern of abnormal muscle
activity (seen in any myopathy) it is unable to define the exact type. The
muscle biopsy is therefore the important test which will make the diagnosis.
The muscle in this condition characteristically shows smaller type 1 than type
The condition is usually non-progressive or slowly progressive and the
muscle weakness may improve after the second year of life. In general
however, the earlier the onset of the myopathy the more severe and
progressive the disorder is. Some patients may become weaker in their 20s
or 30s and may eventually lose the ability to walk. Occasionally muscle
weakness may progress quite rapidly and these patients experience serious
Is there a
or a cure?
At the moment, there is no cure, nor any drug treatment for congenital fibre
type disproportion myopathy. However, other very helpful measures can be
taken such as physiotherapy (see below), the use of antibiotics to treat chest
infections, or nasogastric tube feeding when necessary.
Physiotherapy is one of the main forms of help. An initial physiotherapy
assessment at the time of the diagnosis should be followed by an exercise
programme and regular check-ups. The main aim of physiotherapy is to keep
the muscles as active as possible to prevent the formation of 'contractures'
(muscle tendon tightness causing restriction in the range of joint movement).
It is also important to provide good seating and to ensure a proper sitting and
standing posture to prevent scoliosis (curvature of the spine). The other role
of physiotherapy is to help with provision of appliances, such as splints,
calipers, standing frames (mechanical aids helping to keep children on their
feet) and wheelchairs where necessary. Children and adults are encouraged
to remain as active as possible and ensure that they do not become
overweight to limit the strain imposed on their muscles. Swimming is a
particularly good form of exercise.
Published by the Muscular
Dystrophy Campaign at: http://www.muscular-dystrophy.org
Written by Dr Paola Nicolaides, Senior Registrar and Dr Richard Appleton, Consultant Paediatric Neurologist
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