CMT is the most common inherited peripheral neuropathy. It is also called Hereditary Motor and Sensory Neuropathy (HMSN). Hereditary neuropathy is a complex and, due to advancement in molecular biology and genetic analysis, a rapidly evolving subject. This post is only an overview of CMT.

 

What is the cause of CMT?

An abnormal gene, or a gene mutation causes CMT. Most common gene abnormality causing CMT is PMP22 gene duplication. CMT is typically an inherited disorder, but many times, there is no prior family history of inherited neuropathy.

 

How common is CMT?

It affects 1 in 2500 people. Both men and women are equally affected except the ones inherited through X-chromosome, in which case men are affected more than women. There is no particular racial difference. CMT typically starts in childhood and continues to progress in adulthood. Some forms get significantly worse in childhood resulting in young age disability.

 

Is CMT a life-threatening illness?

It can be called a life-altering illness, but the life expectancy remains about the same. Sensory and motor dysfunction leads to numbness, pain, weakness, and unsteadiness. Many patients have no or minimal disability, but more than 40% of patients can be significantly disabled.

 

What are symptoms of CMT?

In adults, it typically presents with slowly progressive weakness, unsteadiness, and numbness, usually without neuropathic pain (burning type). Children can present with delayed motor milestones, tripping, falling, ankle injuries, walking disorder, or just being clumsy.

 

What are signs of CMT?

Signs of CMT are the signs of chronic peripheral neuropathy, but some signs are peculiar to this condition. Findings may include loss of reflexes, loss of sensations, muscle atrophy (especially of foreleg and hand muscles), hammertoes, pes cavus (high arches), pes planus (flat feet), and cavovarus (high arches with inward rotation of foot). In many patients with CMT, one may find visibly thickened nerves.

 

How is CMT diagnosed?

Symptoms and signs described above can be diagnostic. EMG/NCS study can help to confirm the type of neuropathy, demyelinating or axonal, and its chronic nature. It also helps to differentiate it from other types of demyelinating neuropathies, like CIDP. In more common type of CMT, motor and sensory nerve conduction velocities are reduced, distal latencies and F responses are prolonged, without much dispersion of motor unit potentials as in CIDP.

 

What are the chances of a child getting it, if one parent has CMT?

Most CMT types are autosomal dominant with 50% odds for the child, and some are autosomal recessive resulting in odds of 25%. 10-15% of cases inherit through X-chromosome, the so-called X-linked inheritance, which can be dominant or recessive. Odds of having the disease depend upon the transmitting parent, the mother or the father, and if it is recessive or dominant type. In this type of inheritance, men are affected more than women, as they only have one copy of X chromosome. 

 

Are there different types of CMT?

Yes. A variety of gene abnormalities are implicated in causing CMT, resulting in different subtypes. This subject is much more technical and complex, is in constant evolution, and not discussed in much detail here. In brief, following are commonly known types of CMT:

1. CMT1: autosomal dominant, demyelinating neuropathy
2. CMT2: autosomal recessive, axonal neuropathy
3. Dejerne-Sottas: severe childhood form of neuropathy
4. CMTX: inherited in X-linked manner
5. CMT4: autosomal recessive, demyelinating neuropathy

 

Is there a specific treatment for CMT?

No specific treatment is available to slow down or alter the course of CMT. This is also true for most other hereditary neuropathies. There is hope that advancement in gene therapy may provide help in these intractable conditions. For example, gene therapy drugs are now available to treat neuropathy associated with familial amyloidosis, which has changed the course of this otherwise fatal illness.

While there is no cure for CMT, multiple types of interventions can help improve quality of life. This includes consultation with a formal physiatrist, physical and occupational therapy, orthopedic interventions, pain management, and appropriate treatment of commonly associated anxiety and depression. 

 

Where can I find more information about CMT?

American Academy of Neurology