Neurological Disorders: Muscular Dystrophy (MD)

What is MD?

Muscular dystrophy, unofficially sometimes abbreviated as MD, is a group of myopathies (muscle diseases) that are genetic (hereditary) in nature.

There are myriad types of Muscular dystrophy, and characteristically these genetic disorders are all progressive in nature, however the degree of progression varies considerably from type to type.

Some are progressive and serious to the extent they are invariably fatal (e.g. Duchenne MD), and some other are minimally progressive and result in some motor handicap and are almost never fatal themselves. Some are early onset while some others are late onset. Some involve only boys or men and the women/girls are only carriers. Duchenne muscular dystrophy is a good example for above both (only men/boys are affected and the women/girls are the carriers).

What kind of genetic is involved with MD?

MDs are always genetic diseases by definition. The inheritance varies and includes;

• AD (autosomal dominant)
• AR (autosomal recessive)
• X linked

AD type hereditary disease:

• Presence of disease or abnormal gene in only one parent is enough for the kids to get it

• If a parent is affected then each child has 50% chance of catching the disease
• Both male & female children of the affected parent can contract this disease

AR type hereditary disease:

• Presence of disease or abnormal gene in both parents is necessary for the kids to get it

• If both parents are affected then each child has 25% chance of catching the disease
• Both male & female children of the affected parent can contract this disease

X inked type hereditary disease:

• Boys (men) are usually the victims. Girls (women) are usually the carriers. If father has a bad gene in is X chromosome then since all his X goes to daughters, a father can transmit X linked disease only to his daughters

• A mother can transmit her X linked disease o both daughters and sons

• Generally girls/women are not much affected by X chromosome disease as they have 2 X chromosomes and the normal X tries to compensate for the defect in the other X. Boys/men have only one X so the disease invariable manifests in them

• That is why with X linked diseases male gender is the sufferers and female gender is the carriers.

How the genetic defect triggers MD?

With the advent of advance in medical field, especially at the molecular level, our understanding of the pathology at the cellular level has improved considerably.

For many of these MDs the genetic mutation (abnormality) causes an abnormal gene product. Genes are basic units of DNA (and RNA) and they generally code for the production of a protein called as a gene product. This protein could be an enzyme, or other cellular proteins and mediate important body functions.

With MDs these proteins are generally constituents of the cell membrane. They give stability to the cell and its absence, or a defect can cause muscle damage. Dystrophin is one such gene product or protein that is necessary for integrity of muscle cell membrane. Its absence or deficiency causes MD like Duchenne and Becker muscular dystrophies respectively.

Types of MD

These are some of the well defined MDs;

• Duchenne & Becker MD
• FSH (Facioscapulohumeral MD)
• OPD (Oculopharyngeal MD)
• LGM (Limbgirdle MD)
Myotonic Dystrophy
• Emery Dreifus MD
• Congenital MD
• Distal MD etc

Please note that the abbreviations like FSH, OPD, LGM are not official it is used only for convenience (easy to remember as FSH rather the full name).

How patient presents?

Within the skeletal muscle domain:

• Progressive muscle weakness (progressive)
• Progressive muscle wasting (thinning or atrophy)
• Walking difficulties
• Waddling gait (like a duck walks)
• Delayed or regressive motor milestones in a child
• Drooping of eye lids
• Contracture of joints
• Pseudohypertrophy (not true bulk increase)

Out side the skeletal muscle domain:

• Heart muscle involvement (irregular heart beats, heart failure etc)
• GI (gastrointestinal) muscle involvement
• Sexual organ/gonadal dysfunction
• Endocrine abnormalities (e.g. diabetes)
• Eye problems
• Intellectual problems etc.

Please note that not the same muscular dystrophy patient will develop all these above manifestations.

Diagnosis

Many of the MDs now-a-days have genetic test available and they are generally confirmatory.

Other tests that may be employed include;

• Blood CPK, LDH
• EMG/NCS (electromyography and nerve conduction study)
• Muscle biopsy & staining etc

Treatment

At this moment none of the MDs have a curative treatment so the management is mostly symptomatic & supportive. This would include physical, occupational, speech therapies, assistive devices, wheel chairs, orthopedic surgeries etc.

For Duchenne Muscular Dystrophy steroids can be tried as they slow down the muscle degeneration, but of course do not cure the disease. Steroid side effects are major concerns.

Experimental therapies like gene or stem cell therapy etc appears to be the hopes for the future.

A neurologist is usually involved in the care of these patients.



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