Muscular dystrophy is a group of inherited muscle disorders characterised by gradually increasing weakness and degeneration of the muscles that control voluntary bodily movement. The most common type, Duchenne muscular dystrophy (about 95% of cases), results from a lack of the protein dystrophin required for proper muscle function.Muscle tissue weakens and progressively wastes away and is replaced by connective and fatty tissue. In most cases, the arms, legs and spine become deformed.Duchenne type affects mostly boys from the age of five and up. Types of muscular dystrophy are distinguished from one another both by the symptoms and severity and by the way they’re inherited.
There are eight other known forms of muscular dystrophy:
- Becker muscular dystrophy. The onset may be as late as young adulthood and symptoms are less severe than with the Duchenne type, but similar. Life expectancy may even be normal.
- Limb-girdle muscular dystrophy may only show up in adulthood, when problems in terms of walking or lifting the arms become noticeable.
- Facioscapulohumeral muscular dystrophy. The onset may only occur in adulthood and life span may be normal. Early warning signs include lack of facial mobility.
- Distal muscular dystrophy.
- Emery-Dreifuss muscular dystrophy.
- Fukuyama congenital muscular dystrophy.
- Oculopharyngeal muscular dystrophy.
- Ophthalmoploegic muscular dystrophy.
What are the causes?
Chemically speaking, the two most common forms of muscular dystrophy, Duchenne and Becker, are caused by a genetically inherited deficiency of the dystrophin protein (in the most common type).
Other less common types for which the causes are less well understood are caused by faulty segments in the genes, which result in the lack of other vital proteins.
To understand the causes in broader terms requires an understanding of genetic inheritance and how gender- or sex-linked dominant genes or recessive genes affect our physical characteristics.
How genetic inheritance of muscular dystrophy works
Muscular dystrophy is a result of inherited faults in genes.
When a foetus is formed, he or she receives 23 chromosomes – tiny threadlike structures that carry genes – from each parent, making a total of 46. These chromosomes pair off, each carrying genes for the same purpose. A total of 22 of these pairs or genes are identical in males and females. The composition of the 23rd pair determines the sex of the unborn child. If the pair consists of one “X” chromosome from the mother and another “X” from the father, the child will be female. If the pair is made up of an “X” from the mother and a “Y” chromosome from the father, the child will be male.
The genes packed together in precise locations on these chromosomes may, for only partly understood reasons, be flawed or lost. When this is the case, a genetic disorder – one of which is muscular dystrophy – may result.
Who risks inheriting muscular dystrophy?
Because the faulty gene may be located in the X or Y chromosome, the gender of the child is relevant in assessing the risk inheritance for all members of the extended family. The way that the disorder is inherited may vary from one type of muscular dystrophy to another.
Autosominal dominant inheritance:
It doesn’t skip generations because the genetic errors may be present in any one of the 46 chromosomes that carry the genes, except for the sex chromosomes. Only one parent needs to transmit the abnormal gene, so the child has a 50% chance of inheriting the disorder.
Types of muscular dystrophy inherited this way include faciocapulohumeral dystrophy and myotonic dystrophy.
Autosominal recessive inheritance:
Disorders inherited this way usually appear in only one generation – there may be no family history of genetic disorders as the parent who carries the gene shows no symptoms of illness. There is a 25% chance that each child of the affected couple will receive the faulty recessive gene and be affected, and a 50% chance that they will become a carrier of the disorder.
Limb-girdle muscular dystrophy is inherited this way.
X-linked recessive inheritance:
The disorder is carried by the X chromosome. When the mother is the carrier, boys have a 50% chance of being affected and girls a 50% chance of being carriers. Men who are carriers of this type of disorder cannot pass it on to their sons (as they only provide the Y chromosome for a male baby), but all daughters will be carriers.
The most common forms of muscular dystrophy, Duchenne and Becker types, are inherited via the X chromosome.
Not all genetic disorders are initially inherited. Gene mutation may occur unpredictably, apparently at random, and develop an altered or faulty characteristic. This creates an inheritable form of muscular dystrophy.
Some research indicates that about a third of boys who develop Duchenne muscular dystrophy develop it as a result of an apparently spontaneous gene mutation.
Autosominal dominant inheritance:
Disorders inherited this way don’t skip generations and children have a 50% chance of inheriting the disorder.
Symptoms and signs of muscular dystrophy
Initial symptoms of muscular dystrophy include:
- A tendency to fall
- Difficulty getting up after lying down or even sitting
- A waddling action when walking or running
- Enlarged calf and/or other muscles
- Contracted or “shortened” muscles, resulting in deformities
- Unusually high levels of the muscle enzyme creatine kinase in the blood
- Decreased muscle tone (hypotonia)
- Skeletal deformities and scoliosis (a crooked spine)
- Drooping eyelids and lack of facial expression (in some forms of the disease)
- Intellectual retardation (also only present in some forms)
How is muscular dystrophy diagnosed?
Medical doctors initially diagnose muscular dystrophy using:
- A physical examination for typical symptoms.
- A family medical and genetic disorder history if any is available, particularly in order to determine from which type of muscular dystrophy the patient is suffering.
- Diagnostic tests aid in diagnosis to determine muscular dystrophy and to find out what type the patient might be affected by.
- Blood tests are used to detect abnormal levels of certain enzymes, such as creatine kinase, creatine phosphokinase or AST in the blood. Elevated levels of these enzymes assist towards a firm diagnosis of muscular dystrophy.
- DNA testing from blood samples can also be performed so that the genetic material (DNA) can be studied for disease diagnosis. Potential carriers may also be tested and their DNA studied.
- An electromyogram may be carried out. In this procedure, small electrodes are inserted into the muscle and electrical activity patterns monitored to detect patterns characteristic of muscular dystrophy.
- A muscle biopsy. The surgical removal of a small piece of the patient’s muscle tissue for examination under a microscope can also provide clues useful in diagnosis. This is often the primary test.
- Straining for a protein (or lack of it) may be performed to confirm diagnosis of forms of muscular dystrophy such as the Duchenne/Becker type, in which the problematic protein is known.
- Muscular dystrophy may alter the results of urine, serum, isoenzyme related and adolase tests.
Can muscular dystrophy be prevented?
Muscular dystrophy is a genetic disorder and may be present in genes without parents realising it. For example, women may be carriers but be asymptomatic. The genes that cause it, may be recessive – in other words, they may skip one or more generations.
It can only be successfully prevented if all the genetic information about parents, such as family medical history, is available to the medical practitioner. This can partly be obtained through tests, and partly through genetic counselling.
The most common form, Duchenne muscular dystrophy, can be detected through genetic studies during pregnancy, allowing the parents to decide whether to continue with the pregnancy or terminate on medical grounds.
How is muscular dystrophy treated?
Two main types of treatment are currently available:
- Physiotherapy and occupational therapy
Physiotherapy and occupational therapy
Physiotherapy and occupational therapy can help keep people living with muscular dystrophy independent for longer and improve quality of life.
These types of therapy include taught exercises and manipulation by physiotherapists to maintain strength and maximise range of motion. They may also include routine assisted or unassisted stretching exercises to delay deformities and improve mobility.
The physiotherapist will help the patient and his/her family to determine the best exercises for the patient to do, or to be assisted in performing.
An occupational therapist will help the patient overcome daily difficulties by finding alternative ways for them to physically accomplish daily tasks, for example by finding more useful seating positions, or ways to use a computer in order to write. The occupational therapist may also assist wheelchair-bound patients in use of devices that enable them to participate more fully in recreational activities as well as in daily work and home activities.
As muscles weaken, contractures or shortened muscles and tendons may make movement difficult and painful. Some surgical procedures may improve quality of life and even prolong a patient’s life span.
Possible surgical treatments include:
- Tendon release: In the most common type of procedure, the tendon connecting the large calf muscle with the ankle joint is severed to relieve side effects of muscle shortening. A similar procedure can be carried out on tendons in the hips, knees and other joints. This procedure is then backed up by casts, braces and physiotherapy that assist the patient in maintaining mobility.
- Correction of spinal curvature or scoliosis, which may be worsened by use of a wheelchair, resulting in problems breathing. A luque procedure and spinal fusion are the most common examples of procedures, which are carried out by an orthopaedic surgeon.
- Myotonic dystrophy may result in cataracts or opacities on the lens of the eye. An opthalmologist can surgically remove these growths and improve vision.
What is the outcome of treatment?
Muscular dystrophy limits life span and is incurable at present.
Depending on living circumstances and availability of treatment, the current life span of most patients who suffer from the more common forms of muscular dystrophy, Duchenne muscular dystrophy, is limited to their 20s.
The course of the illness varies from patient to patient but when children become symptomatic around or before five years of age, a wheelchair is usually needed by age 12. Mental impairment may occur and respiratory failure may be fatal.
The latest research
Research has succeeded in identifying the gene for Duchenne muscular dystrophy and identifying the lack of the protein dystrophin as the cause of the condition.
Other research has identified the nature and location of the gene that causes myotonic muscular dystrophy. Some of the genetic errors that cause forms of limb-girdle muscular dystrophy have also been identified.
Problematic genes are frequently discovered along with the missing or altered protein that causes muscular dystrophy.
Although there’s no cure for muscular dystrophy at present, research is ongoing.
When to call a doctor
Consult a medical practitioner and ensure that appropriate tests are carried out if you detect any symptoms or signs of muscular dystrophy.
Doctors may refer people living with muscular dystrophy to:
- Neurologists, who specialise in studying and treating disorders that affect the nervous system, which is made up of nerves and muscles. Muscular dystrophy affects the peripheral nervous system.
- Geneticists, who specialise in the study and treatment of genetic disorders such as muscular dystrophy. They’ll advise parents who think they may have a family history of muscular dystrophy.
- Physiotherapists, who can make living with muscular dystrophy easier.
- Support groups.