the Genetics of it

[Guest guest]

,

This is a link with good information on CMT genetics.

http://www.mayoclinic.com/health/charcot-marie-tooth-disease/DS00557/DSECTION=3

CMT is an inherited genetic disease. A unique form of the disease develops

depending on the particular gene mutation. Genes produce the proteins that are

essential to functions of the body. In CMT, defective genes affect the proteins

involved in the structure and function of your peripheral nerves or the myelin

sheath. Deterioration of your peripheral nerves or the myelin sheath can send

only weak signals to the muscles in your legs, arms, hands and feet, causing

weakness and numbness.

CMT can be inherited in various ways:

X-linked. In X-linked inheritance, the genetic defect (mutation) is located on

the X chromosome. X-linked diseases are passed from mother to son through one of

the mother's genes in a pattern called X-linked recessive inheritance. A boy

inherits an X chromosome from his mother and a Y chromosome from his father. The

X-Y combination makes him male. A girl inherits two X chromosomes, one from her

mother and one from her father. The X-X combination makes her female. Women who

have a defective gene that causes a disorder are simply carriers and exhibit no

signs or symptoms of the disease. The disease can skip a generation until

another son inherits the defective gene on the X chromosome.

Autosomal dominant. When the genetic defect occurs on a chromosome other than X

or Y, CMT affects males and females the same. Autosomal dominant inheritance of

CMT results when one copy of the defective gene is enough to cause the disease.

If either parent carries the defective gene for CMT, there's a 50 percent chance

the disorder will be passed along to a child.

Autosomal recessive. Autosomal recessive inheritance occurs when two copies of

the defective gene are required to cause CMT. One copy is inherited from each

parent, neither actually having CMT.

Some types of CMT can pass from generation to generation and affect males and

females equally. In other cases of CMT, the disease arises from a new or

spontaneous mutation in a gene rather than from an inherited defective gene,

meaning there's no previous family history of the disorder.

CMT occurs in many forms. Scientists have determined a number of genes that are

involved in CMT, each linked to a specific type of the disease. The most common

forms of CMT include:

CMT1. The most common type, CMT1 results from defective myelin genes, those

involved in the structure and function of the insulation covering your nerves

(myelin sheath). Defective myelin genes can cause a breakdown of myelin

(demyelination), causing the myelin sheath to deteriorate and expose the

peripheral nerves.

CMT2. This form of CMT is less common and is caused by abnormalities in the

peripheral nerves as opposed to the myelin sheath.

CMT3. Also known as Dejerine-Sottas disease, CMT3 is a severe form of CMT that

develops during infancy and affects the myelin sheath.

CMT4. This is the most complicated form of CMT. It involves several subtypes of

demyelinating nerve damage, with each subtype caused by a different gene defect.

CMTX. The defective gene that causes CMTX is located on the X chromosome. CMTX

usually affects males more than females. This is because females have two X

chromosomes that can usually compensate for a defective copy of the gene on one

chromosome with a normal copy on the other.

[Guest guest]

,

I forgot we have a section on Genetics in our Files area. You might

want to read through that information also.

Gretchen