Genetic Testing

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CMT genetic testing is used to confirm a diagnosis and to pinpoint the subtype (responsible gene mutation = subtype). Different genetic tests examine different sets of genes, and laboratories offer different CMT tests. Genetic testing for CMT is not a single test but a set of options available to your provider.

Benefits of CMT Genetic Testing

Genetic testing can:

  • Confirm or clarify a clinical diagnosis
  • Identify the specific genetic subtype
  • Identify inheritance patterns for informing family planning
  • Identify other family members who may be at risk
  • Support participation in research or future trials: clinical trials typically require genetic confirmation

Genetic testing also has limitations. Not every CMT-related gene is known, and current methods do not detect all possible gene variants (mutations). Even when a genetic change is identified, it may require a deep, sophisticated analysis to determine whether it’s responsible for the individual’s CMT.

Types of Genetic Tests Used in CMT

Several types of genetic tests are available for CMT. These tests differ in scope and in the types of genetic changes they can detect.

  • Single-gene testing
    Examines one specific gene when a particular CMT subtype is strongly suspected or already identified in a family.
  • Multi-gene panel testing (most commonly ordered genetic test in CMT)
    Looks at multiple genes at the same time. Panel size and specific genes included vary by laboratory and panel. Panels may change over time.
  • Whole-exome sequencing (WES)
    Attempts to look at the coding regions of all genes to identify variants that may be missed on standard panels.
  • Whole-genome sequencing (WGS)
    Looks at all coding and non-coding regions of DNA to potentially identify the unknown genetic cause of one’s CMT. This approach is more commonly used in research and specialized diagnostic settings than in routine clinical testing (not a test most providers would order).
  • Copy number testing (e.g., gene duplication or deletion testing)
    Looks for missing or extra copies of genes and chromosome segments that may be missed with gene panel testing (many CMT gene panels include copy number variant (CNV) testing for certain genes, such as the PMP22 gene).
  • Advanced sequencing approaches (e.g., long-read sequencing)
    Newer advanced technology to detect complex genetic changes that are difficult to identify with conventional methods. Read more about long-read sequencing (LRS).

Frequently Ordered Genetic Tests for CMT

Many clinical laboratories offer CMT genetic testing. Various panels are commonly ordered. Each varies in the number and composition of the genes it includes. This list is provided for informational purposes only. This list is not intended to be exhaustive but to provide an example of tests your provider might order.

What If a Genetic Test Is Negative or Inconclusive?

Genetic testing in CMT doesn’t always return a positive result. Inconclusive/negative results are fairly common. Often, the results show what’s called a variant of unknown or uncertain significance (VUS). A VUS is a type of mutation in which scientists don’t yet know if it causes something such as CMT or if it’s benign and harmless, and more data are needed.

Whether inconclusive because of a VUS or negative because the test found no variants, the result does not mean it’s not CMT. A result like this means only that the gene with the responsible variant was not looked at or the testing technology used is not yet advanced enough. As many as half of all who have CMT fall into this diagnostic gap. Learn more about this diagnostic gap: Error 404: Gene Not Found.

Self-Ordered Testing

Many companies offer genetic sequencing (testing) without a healthcare provider’s order. This is called direct-to-consumer (DTC) sequencing. These can provide a lot of information, but the companies do not resolve reported variants into clinical relevance. They don’t provide the information providers need to interpret what the variants might mean.

DTC sequencing should not be used to make medical decisions, including diagnoses. DTC sequencing can sometimes help a provider narrow where to look, but clinical genetic testing (genetic testing ordered by a healthcare provider) would still be needed to confirm a CMT diagnosis.

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CMT Classifications
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