Questions About Muscular Dystrophy

Q1. What is muscular dystrophy?

A. Muscular dystrophy is the name applied to a group of diseases that are, for the most part, genetically determined and that cause gradual wasting of muscle with accompanying weakness and deformity.

Q2. Are these diseases contagious?

A. No.

Q3. What is the common kind of muscular dystrophy, the type that affects young boys?

A. This form of the disease is called Duchenne muscular dystrophy. Symptoms usually appear between the ages of two and six. It was first described by Duchenne, a french physician, in 1861.

Q4. What are the first clinical signs of Duchenne muscular dystrophy?

A. The first signs of weakness usually are (1) delayed onset of walking, (2) difficulty in performing a standing jump, (3) a waddling gait, (4) difficulty in rising from the floor.

Q5. What are some of the later clinical signs of weakness in Duchenne muscular dystrophy .

A. Later signs of weakness included (1) difficulty in rising from a chair, (2) inability to climb stairs in a normal manner, (3) wide gait with difficulty in balance.

Q6. How is muscular Dystrophy transmitted?

A. Musular dystrophy is transmitted from a parent (or parents) through an affected gene. In limb-girdle dystrophy, both parents carry such a gene, though neither has the disease. This type of muscular dystrophy can be transmitted to either a male or female child. The technical term for the inheritance pattern in limb-girdle dystrophy is “autosomal recessive”.

In facioscapulohumeral dystrophy and myotonic dystrophy, at least one parent has to have the disease in order to transmit it (“autosomal dominant: inheritance pattern). This type can also be inherited by a male or female.

In Duchenne muscular dystrophy, the defective gene is carried by the female and the disease is transmitted to the male (recessive “X-linked” inheritance pattern). Each male child born to such a mother stands 50 percent risk of inheriting the disease, and each female a 50 percent risk of becoming a carrier. It should be noted that it is the father’s genetic contribution that determines the sex of the child.

Q7. Is muscular dystrophy always hereditary?

A. We don’t know for sure. According to many investigators, one-third of all boys with classic Duchenne muscular dystrophy are “sporadis cases”, having no familial history of the disease.

Q8. What are the chances of a mother without a family history of Duchenne muscular dystrophy having a son with the disease?

A. In the population at large, the risk of Duchenne muscular dystrophy in a male child is about 1 in 3,200 live male births. The risk of a sporadic (non-hereditary) case is approximately 1 in 12,000.

Q9. Can the carrier state be detected in the mother or sister of a young boy with Duchenne Muscular Dystrophy

A. Using tests for muscle enzyme levels in the blood as well as other examinations (electromyogram, manual muscle tests, muscle biopsy), approximately 70 to 80 percent of all carriers can be identified. The younger the subject is when these tests are performed, the better the chance of detection.

Q10. What is the classification of carriers of Duchenne muscular Dystrophy?

A.”Definite carriers” are mothers who have an affected son and who also have an affected brother, maternal uncle, sister’s son, or other male relatives in the female line of inheritance, or who are also mothers of a second affected son by a different father not related by blood to the first. “Probable carriers” are mothers who have two or more sons with muscular dystrophy and no other affected relatives. A “possible carrier” is a mother of an isolated case, or a sister or other female relative, such as a maternal aunt, of an affected male.

Q11. If a known carrier decides to have her own children, is there some way of determining whether or not she is carrying a child with Duchenne muscular dystrophy?

A.Although there is yet no way of telling whether she is carrying a child with muscular dystrophy, the sex of the fetus can be determined by the sixteenth week of pregnancy by removing and analyzing specimen of amniotic fluid. If the child is a boy, there is a 50 percent chance of him having muscular dystrophy.

Q12. If the mother of one son with Duchenne muscular dystrophy has a normal blood level of the muscle enzyme creatine kinase (CPK), what is the risk of her daughter, who also has a normal CPK, of bearing a son with Duchenne muscular dystrophy?

A. A normal CPK level is increasingly less meaningful for carrier detection as a girl gets old, so we will assume that the daughter’s CPK is determined at a fairly early stage. In that case, the risk is approximately 1 in 52 that a daughter whose CPK is normal, whose mother’s CPK is normal, and whose brother has Duchenne muscular dystrophy will give birth to a dystrophic son.

Q13. If the mother of a son with Duchenne muscular dystrophy has an elevated CPK but her daughter’s CPK in normal, what then is the risk to the daughter of bearing a son with Duchenne muscular dystrophy.

A.. If the mother’s CPK tests is elevated, the risk that the daughter will give birth to a son with Duchenne dystrophy rises to 1 in 16, even though the daughter’s CPK is normal.

Q14. Is there a late-occurring type of childhood muscular dystrophy?

A. Yes. Becker muscular dystrophy is a comparatively benign form of juvenile dystrophy with onset between 5 and 25 and relatively slow progression.

Q15. Is muscular dystrophy strictly a disease of children?

A. No. For example, limb-girdle dystrophy usually has its onset in late adolescence, and the facioscapulohumeral and myotonic types usually start in adulthood. These forms of muscular dystrophy are slower in their progression and less disabling than the childhood forms.

Q16. What are some of the early signs of adult muscular dystrophy?

A. A weak smile and inability to pucker the lips or whistle occur early in facioscapulohumeral dystrophy. Subtle weakness in the shoulders and hips occurs early in limb-girdle dystrophy. Weakness of the feet and hands and difficulty in relaxing the grip are early signs of myotonic dystrophy.

Q17. What is the incidence of muscular dystrophy (neuromuscular disease)?

A. The incidence of “Muscular Dystrophy” is estimated to be 100 per 100,000 head of population. Based on current figures (1995), it is estimated that there would be in excess of 20,000 people in Australia who have some form of neuromuscular disease. The incidence of Duchenne muscular dystrophy (DMD) is estimated to be 1 in 4,000 live male births is by far the most common form of neuromuscular disease.

Q18.In what part of the world is muscular dystrophy most common?

A.. There is no area of the world where muscular dystrophy is more prevalent than anywhere else.

Q19.What percentage of body weight is made up of muscle tissue? How much muscle tissue has to be lost before function is affected?

A. Muscle makes up 40 percent of the total body weight. Approximately 33 percent of muscle mass has to be lost for function to be impaired in large postural muscles.

Q20.What muscles are affected in muscular dystrophy?

A.. Different muscles are affected in different forms of muscular dystrophy. Although any of the 434 voluntary muscles can be affected, spinal musculature and that of the limb-girdles (shoulders and hips) are involved most frequently and, when involved, are affected earliest and most profoundly.

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