Charcot-Marie-Tooth disease

Although Charcot-Marie-Tooth (CMT) disease is a relatively common condition, there are no general-population screening programmes in place. Adults at risk as a result of a positive family history may be screened, but screening of asymptomatic individuals should only be performed after genetic counselling so that an informed decision can be made regarding testing.

Nerve conduction studies

Screening an at-risk individual by testing a single nerve is possible for some forms of CMT. For example, in CMT1A, if a family member has had genetic testing revealing a duplication of the PMP22 gene, the patient can have a single motor nerve (e.g., median or ulnar nerve) velocity measured. If the velocity is profoundly slowed, this provides a strong indication of CMT1A, whereas if it is normal, this excludes the possibility of CMT1A. For other forms of the condition, abnormal conditions may only be suggestive, and genetic testing may be warranted.

Genetic testing

After a patient has been diagnosed with CMT, and a specific mutation has been identified, other family members can be tested for the same mutation. The mutation should be the same throughout the family.

Genetic testing may be considered if the individual is interested in family planning, natural history information, or inclusion in clinical trials. Neurotoxic chemotherapy drugs (e.g., paclitaxel, cisplatin, and vincristine) can cause severe neuropathy and should be avoided in CMT. Therefore, if a person at risk of CMT is diagnosed with cancer, it may be reasonable to have genetic testing to determine the risk of exacerbating a neuropathy.

Not all individuals will want to have genetic testing. It is always an optional test, and individuals should only have genetic testing once informed of the implications. It is worth noting that in the US, life, disability, and long-term-care insurances can be difficult or near-impossible to obtain if a person is asymptomatic but has a positive genetic test, which indicates that the condition will appear in the future. The results of the testing will probably have an emotional impact on the individual, either through blaming the parents for passing on the condition, or feelings of guilt for passing it on to a child. Although genetic testing has become less expensive, some local funding/insurance may not cover the costs; this should always be checked before ordering the test. Genetic counsellors are knowledgeable about the process and should be consulted whenever possible, both for genetic testing and for providing information and support to people with a family history or signs of a genetic condition.

Screening of minors

Asymptomatic minors should not receive genetic testing or nerve conduction studies without careful consideration and discussion with a physician, nurse, or genetic counsellor.[21]Borry P, Stultiens L, Nys H, et al. Presymptomatic and predictive genetic testing in minors: a systematic review of guidelines and position papers. Clin Genet. 2006 Nov;70(5):374-81. http://www.ncbi.nlm.nih.gov/pubmed/17026616?tool=bestpractice.com Reasons for this include the social and psychological consequences. As there is no treatment for CMT at this time, testing minors may not provide significant medical benefit. However, if a child is symptomatic and requires therapy and bracing, it is appropriate to obtain a definitive diagnosis of CMT. This also eliminates unnecessary testing for other conditions, and assists the parents in making appropriate life plans.