Presentation: Pregnancy at risk of Duchenne or Becker muscular dystrophy

A young, fit and healthy woman presents to her GP as she is planning a pregnancy. She has a family history of DMD and is concerned that there is a risk of a future pregnancy being affected. 

• When there is a maternal family history of Duchenne muscular dystrophy (DMD) or Becker muscular dystrophy (BMD) (this may be genetically confirmed or only clinically likely).
• Where the mother is a carrier for DMD or BMD and the pregnancy has been confirmed to be male. DMD and BMD are both X-linked recessive conditions. A male fetus will therefore have a one-in-two chance of developing the condition if their mother is a carrier.

• Collect a detailed family and personal history from the couple.
• Refer the case to clinical genetics for review by a clinical geneticist or genetic counsellor.
• The clinical genetics team will review the NHS England National Genomic Test Directory eligibility criteria to determine which tests are available to your patient. The directory itself provides a list of all available tests.
  • For those working within NHS Wales, please consult the All Wales Medical Genomics Service website for information on how to arrange testing.
• Testing options may include:
  • Carrier screening of the patient:
    • R244 Carrier testing for known familial mutation(s) – carrier screening for women who have a family history of DMD or BMD where the genetic cause has been identified (pathogenic variant). This test can currently only be requested by clinical genetics.
    • R73 Duchenne or Becker muscular dystrophy – carrier testing for women when there is a clinical diagnosis (or likely diagnosis) of DMD or BMD in the family without a genetic cause identified.
  • Prenatal testing in a pregnancy with a known familial disease-causing variant:
    • Sex determination:
      • R251 Non-invasive prenatal sexing (also called non-invasive prenatal diagnosis, or NIPD) – for fetal sex determination to inform management in pregnancy. This can be performed after seven weeks of pregnancy, but contact your local Genomic Laboratory Hub (GLH) in advance to determine the local process.
    • Testing in male pregnancies:
      • Invasive testing.
      • R310 NIPD for DMD or BMD. Non-invasive haplotype testing is available when the mother is confirmed to be a carrier of one of the conditions. This test can currently be requested by clinical genetics and fetal medicine teams. The testing laboratory must be informed in advance of the request to ensure the necessary samples and/or validation work can take place.
  • If the patient presents pre-conceptually, pre-implantation genomic testing for monogenic disorders may be available. Referral via clinical genetics is required.
• For NIPD, a blood sample in a Streck tube (or EDTA tube) is required. For many of the tests, partner samples are also needed or are helpful. Please refer to your local GLH for details of test request forms and where to send samples.
• For invasive tests, an amniocentesis or chorionic villus sample or fetal blood sample (in an EDTA tube) is required as well as a sample from the mother to test for maternal cell contamination. For many of the tests, parental samples are also needed or are helpful. Please refer to your local GLH for details of test request forms and where to send samples.
• A record of discussion form, or another appropriate local consent form, is required for testing.
• Information about patient eligibility and test indications was correct at the time of writing. When requesting a test, please refer to the National Genomic Test Directory to confirm the right test for your patient.

For clinicians

• Birmingham Women’s and Children’s NHS Foundation Trust: NIPD for Duchenne/Becker muscular dystrophies – R310.1
• NHS England: National Genomic Test Directory

For patients

• Muscular Dystrophy UK
• NHS: Muscular dystrophy