by Melinda Lang
Dr. Michael Shy, Director of the Charcot Marie Tooth (CMT) Clinic and Co-Director of the Neuromuscular Program at Wayne State University in Detroit, Michigan traveled to Albany, NY to address The Upstate NY CMT Support & Action group on July 30.
Dr. Shy, Chair of the Charcot-Marie-Tooth Association Medical Advisory Board, serves on the Board of Directors of the Peripheral Nerve Society (PNS) and is a member of the Medical Advisory Committee for the Muscular Dystrophy Association (MDA).
He covered some of the causes of CMT scattered throughout the genome, such as the most common type CMT1A , which is caused by a duplication of PMP 22(peripheral myelin protein). Some types are caused by a mutation in the axon, or nerve fiber, while others are caused by a mutation affecting the myelin sheath, which protects the nerve. For example, CMT Type 2 represents axonal forms. The second most common of form of CMT, type 1X, results from a gap junction beta 1 protein connected to connexin 32 on the X Chromosome. Typically, this form has onset in adolescence or childhood and often affects males more severely than females.
Currently 16 types of CMT are commercially available for genetic testing. A patient’s physician can request a kit from:
Four Biotech Park
377 Plantation Street
Worcester, MA 01605
However, testing can cost up to $16,500 and not all insurance plans cover it. Athena does, however, have a Patient Protection Plan, which can reduce a patient’s cost to 20 percent of the total cost of the test.
Next, Dr. Shy discussed some pros and cons for genetic testing.
knowing the type of CMT is important for access to clinical trails
for facilitating reproduction decisions
determining if other family members may be at risk
the cost is very expensive
concern over genetic discrimination
psychological distress with positive results
no medications are available yet
Nerve conduction velocity (NCV) tests, which measures the strength and speed of electrical signals moving down the peripheral nerves, can give a good indication of the possible type of CMT, for a more specific possible cause, thus reducing the cost of the genetic tests. Delayed responses are a sign of demyelination (type 1) and small responses are a sign of axonopathy (type 2). An electromyogram (EMG) is also used to measure the electrical signals’ strength in the muscles of the arms or legs.
Dr. Shy indicated that exercise and weight control are very important for people with CMT. Cardiovascular, and low impact forms of exercise such as; biking and swimming are preferred over jogging, which can be detrimental to joints. He recommends using caution with weight training. It’s preferable to use low weights with more repetitions. Yoga, stretching and cautious balance training can be beneficial as well. Personally, I found physical therapy to be a tremendous help in gaining strength and pool exercises have been helpful for me as well.
In Addition, Dr. Shy discussed various genetic inheritance patterns and the likelihood of passing on different types to children. For example:
The most common forms of CMT are inherited in an autosomal dominant pattern where the mutation occurs on a chromosome other than the X or Y chromosome. An affected person has one normal gene and one CMT gene in the relevant pair. So, each child has a 50/50 chance of inheriting the abnormal or CMT gene, giving them the disorder. Either boys or girls have an equal chance of inheriting the disease in this inheritance pattern. In this form, affected children can pass the CMT gene to their children, but unaffected children do not have the abnormal gene in their DNA and cannot pass CMT to their children.
Autosomal Recessive Inheritance:
The least common forms of CMT are inherited in an autosomal recessive manner as in Type 4. In autosomal recessive forms, both parents have to be “carriers” of the defective gene before a child can be affected. Neither parent shows signs of any symptoms of CMT, but the child who inherits autosomal recessive CMT gets a double dose of the defective gene causing him or her to have the disease, usually in a more severe form. Two parents each with an autosomal recessive CMT gene have a 1 in 4 chance of passing it on to their children. It can affect both males and females.
A male affected with X-linked CMT cannot pass the disorder to his sons, but all of his daughters will be carriers of the disorder. Carrier females have a 50 percent chance of passing the disorder to their sons. Unaffected children cannot pass the disorder onto their children since they don’t carry the gene.
More in next post about research developments!
- Maryland’s Patient & Family Conference Attracts International Audience (cmtnyus.wordpress.com)