Genetic Testing

For many people, M-CM can be accurately diagnosed based on clinical signs, but in some cases a genetic test may help clarify a diagnosis.

Two new clinical genetic tests have become available in 2014. These tests must be obtained through a geneticist or other doctor. Insurance coverage and sample requirements for the testing should be discussed with your doctor in advance of the test.

  • Washington University St. Louis Genomics and Pathology Services (GPS) offers somatic variant analysis by next-generation sequencing covering a range of conditions caused by somatic mosaicism. Characteristics that suggest mosaicism include asymmetry and vascular birthmarks.
  • The Megalencephaly Panel is offered by University of Washington Medicine in Seattle and covers a range of genetic changes associated with megalencephaly. Please note that the sample requirement of blood specified on this web page is unlikely to produce a result for M-CM. We strongly suggest including a tissue sample for testing for M-CM.

Testing may also be available through participation in research:

  • Research on megalencephaly conditions is being conducted by Dr. Ghayda Mirzaa at the Center for Integrative Brain Research at Seattle Children's Research Institute. If you're interested, please contact the research coordinator at for more information.
  • In the UK, research is being conducted through the Segmental Overgrowth Study, contact information can be found on the study's website.
  • The National Human Genome Research Institute at the National Institutes of Health in the United States is conducting research on overgrowth conditions. This group may accept samples from patients in the US or other countries.  Contact Ashlyn Gruber at or 301-435-6689 for more information and eligibility information.

If you are enrolling in research in order to obtain testing, be sure to discuss sample requirements and return of testing results with the research team.