What Is Hereditary Motor and Sensory Neuropathy?
Hereditary Motor and sensory neuropathy is a genetic disability (passed on from parent to child) where the protective myelin sheath which covers the nerves, erodes away. This means that messages to the brain are 'scrambled', resulting in decreased sensitivity to heat, cold and pain. Sometimes there may be a numbness in the feet. It occurs because of a chromosomal abnormality.
Around 23,000 people suffer from HMSN in the UK, so it is a fairly rare condition. It is also known as Charcot Marie Tooth disease (CMT), named after the doctors who discovered it, and peripheral neuropathy.
There are different types of HMSN. The first and most common type is HMSN 1a. This is the demyelinating neuropathy. The second most common type is HMSN type 2, also known as axonal HMSN. Axons are the nerve fibres, and in this type the nerves themselves are damaged, rather than the protective sheath covering them, as in type 1.
There is a third type which is much more rare, called Spinal HMSN, or Distal Spinal Muscular Atrophy. In this type, only the motor nerves are affected and not the peripheral nerves.
When Will It Develop?
People who are disabled by HMSN are born abled. As the disability involves the gradual damage of the nerves, symptoms are not usually apparent for a number of years. In type 1, onset usually occurs in early childhood, around the age of 3 to 5 years. In other types, it can coincide with adolesence. In some cases it can be triggered or made worse by a viral infection such as the flu (only in those people with the defective gene).
What Symptoms Are There?
One of the earliest symptoms are curling toes. This may cause balance problems and the person may fall over frequently. There may be abnormally high arches in the feet. The muscles of the arms and legs will waste, making the person look quite thin. This muscle wastage can cause the bones to move out of place. This usually requires surgery to re-position bones. Joints wear out more quickly due to lack of muscle so re-constructive operations may be done to help (eg. hip replacement).
There is usually decreased sensation in the hands and feet so the affected person may not feel heat, cold and pain quite as sharply as a healthy person. They may also suffer from cramping and excessive tiredness.
The disability is degenerative which means it will get worse over time, leading the person to require a walking aid or in severe cases, a wheelchair.
What Is The Long Term Outcome?
There is a 50% chance for an affected person to pass on the condition to a child they have, but the condition is not life threatening in any way and people with HMSN can lead independent lives and have a normal life expectancy.
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