1) Charcot-Marie-Tooth Disease (CMT) is also known as:
a. Inflammatory Nerve and Muscle Syndrome
b. Hereditary Motor and Sensory Neuropathy
c. Funky Foot Disorder
d. Chronic Tendinopathy with fatigue
2) How many different inheritance patterns does CMT have?
d. Too many to count.
3) Can CMT skip generations?
4) Can CMT appear in a child if the parents’ DNA is normal?
5). Is CMT a type of Muscular Dystrophy?
6). What type of pain might you experience with CMT?
a. Neuropathic or nerve pain
b. Muscle pain
c. Joint pain
d. All of the above.
7). CMT is a heterogeneous disease. What does heterogeneous mean?
a. CMT is an inherited disease.
b. CMT is usually related to having a very high IQ.
c. CMT is caused by many different gene mutations.
d. CMT affects both men and women equally.
8). Can a person have 2 types of CMT?
9). Is HNPP a type of CMT?
10). CMT has no cure. But, non-medicinal treatments include:
a. Physical and Occupational therapies
b. AFOs or leg braces
c. Orthopedic surgery
d. All of the above
#1 – b
Hereditary Motor and Sensory Neuropathy (HMSN) Hereditary means that the disease tends to run in families and causes problems with the sensory and motor nerves, the nerves that run from the arms and legs to the spinal cord and brain.
#2 – c : 3
The 3 types of inheritance are Autosomal Dominant, Autosomal Recessive and X-Linked. Autosomal Dominant – the faulty gene is located on one of the numbered, or non-sex, chromosomes. Humans typically have 46 chromosomes or 23 pairs of chromosomes. The first 22 chromosomal pairs are called autosomes. Autosomal dominant conditions affect men and women equally, and both men and women have a 50% chance in each pregnancy of passing on the condition.
If a child inherits the mutation, that child will have CMT and will have a 50% chance of passing it on again. If the child does not inherit the change, that child will not have CMT, will not have symptoms, and will not be able to pass on the change that is in the family in the future.
Autosomal Recessive – 2 copies of the mutation are needed to cause the disease, meaning neither copy of the gene is working properly. In almost all cases, the changes in the gene were inherited from the parents. Each parent has one copy of the gene with a change, but because that person has one copy of the gene without a change, that person does not have symptoms of CMT and is called a “carrier.” Only people with autosomal recessive forms of CMT in the family can be considered carriers. Both males and females are affected equally with autosomal recessive conditions, and there is an equal chance of passing it on to a child, no matter the sex. If two people are carriers of an autosomal recessive form of CMT, there is a 1 in 4, or 25%, chance of both passing down the copies of the genes that do not work to a child in each pregnancy. It is only the child that inherits two copies of the gene that have mutations that will have CMT. For a person who has a recessive type of CMT, that person will pass on one of the copies of the gene with the mutation to all of that person’s children. However, only if that person’s partner is also a carrier of a mutation in this gene will it be possible to have a child that is affected with the condition. If the partner is not a carrier, it is not possible to have children affected with a recessive form of CMT, but all children will be carriers.
X-Linked – the last pair of chromosomes is called sex chromosomes. the Y and the X. For a person with an X-linked form of CMT, the inheritance is different depending on the sex of the person affected. X-linked forms of CMT (such as CMT1X) are caused by a mutation in a gene carried on the X chromosome. Recall that females have two X chromosome and males have an X and a Y chromosome. If a female has a mutation in an X chromosome gene, she will have a 50% chance of passing on that mutation to each of her children, no matter the sex of the child. However, if a male has a mutation in an X chromosome gene, the sex of the child does make a difference. As males pass on their X chromosome to their daughters and their Y chromosome to their sons, all of the daughters of a male with an X-linked mutation will inherit the condition, and none of the sons will. Source: https://www.rarediseasesnetwork.org/cms/inc/Charcot-Marie-Tooth/What-is-CMT
CMT does not skip generations.
Sometimes the parents’ DNA is normal and the CMT variation happens when the child’s DNA is forming. This is called a new or spontaneous mutation.
#5. No No, CMT is not a type of muscular dystrophy.
CMT is primarily a disease of the peripheral nerves. CMT causes weakness and impaired sensory perception because the signal can’t get to and from the brain to muscle and skin, among other things. The muscles atrophy because they aren’t getting the proper signals, but the muscles themselves are not directly diseased, per se. Muscular dystrophy is a group of diseases of the muscle itself, which causes weakness of varying degrees (there are many forms of MD).
Sometimes the heart is involved because it is a muscle too. The lungs can also be affected because the breathing muscles are weak (similar to CMT, although in CMT it is because the phrenic nerves are affected, which in turn weakens the diaphragm, our main breathing muscle). So, in summary, CMT is a genetic neuropathy which is of course a neuromuscular disorder (The euro part of the word comes from nerve). When they were expanding the MDA early one, they included 41 of the neuromuscular diseases, including Muscular Dystrophy, CMT, Spinal Muscular Atrophy, Myasthenia Gravis and so on. The thing to remember is that when nerves stop sending the correct signals, muscles atrophy and you wind up with similar problems to those experienced by someone with a “muscle disease” like MD.
# 6. D – All the above.
Over 100 different genes have been identified as causing CMT (and counting).
The statistic is that about 1.5 percent of people will have two types of CMT. Not all variants are disease-causing. In many cases, the results of the genetic tests are often very difficult to decipher and seeing a trained CMT expert who also performs a physical exam is key for an accurate diagnosis.Please see a licensed genetic counselor (www.nsgc.org) to better understand your genetic testing results.
Yes, HNPP is a form of CMT. There are three different types of CMT associated with PMP22. People with a duplication of PMP22 have CMT1A, people with a deletion of PMP22 have HNPP, and people with a missense mutation (single letter mutation changing an amino acid) in the PMP22 gene have CMT1E. All are hereditary forms of peripheral neuropathy, and as CMT is the umbrella name for all forms of hereditary peripheral neuropathy, that would include HNPP. (Written by genetic counselor, Shawna Feely)
CMT has no cure and treatments are supportive. Foot orthotics and braces (ankle-foot-orthotics, AFOs) are commonly prescribed to help with foot deformity and foot drop. Surgery to correct foot alignment or to lengthen or transfer tendons is often performed. Physical and occupational therapies are instrumental in providing long lasting quality of life. There is no cure for CMT nor any drug or vitamin known at this time to make CMT better.