Narrowing Down CMT Subtypes

[Guest guest]

Narrowing Down CMT Subtypes

Investigators from Wayne State University found that five genetic subtypes of

Charcot-Marie-Tooth disease accounted for more than 99 percent of diagnoses

http://quest.mda.org/news/narrowing-down-cmt-subtypes

Article Highlights:

•Charcot-Marie-Tooth disease (CMT) has more than 30 genetic subtypes, some of

which are quite rare.

•Results of genetic testing of some 1,000 people at Wayne State University has

revealed that only five genetic subtypes were found in more than 99 percent of

those in whom a genetic diagnosis was made.

•It has been proposed that these results be used to develop a flow chart for

more efficient genetic testing of CMT patients.

Results of genetic testing done at Wayne State University in Detroit of more

than 1,000 people suspected of having Charcot-Marie-Tooth (CMT) disease were

presented by MDA grantee Shy and colleagues April 14, 2010, at the

annual meeting of the American Academy of Neurology, held in Toronto.

The new results suggest that the Wayne State CMT population is representative of

the CMT population as a whole. A flow chart to guide physicians who test for CMT

can be developed based on these results, the investigators proposed.

About CMT

Charcot-Marie-Tooth disease is a disorder of the peripheral nerves, fibers that

run between the spinal cord and the periphery of the body, transmitting sensory

and motor (movement-related) information.

More than 30 forms of CMT have been identified, related to various gene defects

in the nerve fibers themselves or in a sheath made of myelin that surrounds and

insulates each nerve fiber.

Genetic diagnosis for CMT can be challenging and expensive, so there's a need

for better testing guidelines.

About the new findings

MDA grantee Shy, a professor at the Center for Molecular Medicine and

Genetics at Wayne State University in Detroit, and colleagues, examined genetic

testing results from 1,019 patients suspected of having CMT who were seen at

Wayne State.

They said 782 (77 percent) ultimately received confirmation of a CMT diagnosis.

A specific genetic diagnosis was made for 519 of the 782 (66 percent), while no

mutation was identified in 263 of the patients (34 percent).

The most common CMT subtypes were CMT1A (PMP22 gene duplications or point

mutations, chromosome 17); CMT1X (connexin 32 gene, X chromosome); HNPP (PMP22

gene deletions or point mutations, chromosome 17); CMT1B (myelin protein 0 gene,

chromosome 1); and CMT2A (mitofusin 2 gene, chromosome 1).

Fewer than 1 percent of the patients in whom a genetic diagnosis was made had

other subtypes of CMT.

Meaning for people with CMT

If a flow chart that can guide doctors to faster, more cost-effective CMT

testing can be developed, more people with CMT may benefit from such testing. As

treatments that are specific to certain genetic subtypes of CMT are developed,

the results of such tests are likely to become important in medical management

of the disease.

In the meantime, results of genetic testing can help people understand the

inheritance pattern and the likely level of severity of the disease in their

families.