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Example clinical scenario

A full-term neonate, born via normal vaginal delivery, is now 48 hours old and has yet to pass their first stool. The mother had an uneventful pregnancy with normal antenatal scans. The newborn’s abdominal X-ray shows multiple dilated loops of bowel.

When to consider genomic testing

  • Genomic testing should be considered if:
    • Hirschsprung disease is diagnosed clinically; or
    • there is a structural bowel malformation and/or other congenital anomalies suggestive of a syndromic diagnosis.
  • Cystic fibrosis should be investigated if meconium ileus is suspected or diagnosed.

What do you need to do?

  • Consult the National Genomic Test Directory. From here you can access the rare and inherited disease eligibility criteria, which provides information about individual tests and their associated eligibility criteria. You can also access a spreadsheet containing details of all available tests.
  • To find out which genes are included on different gene panels, see the NHS Genomic Medicine Service (GMS) Signed Off Panels Resource.
  • Decide which of the panels best suits the needs of your patient or family. For failure to pass meconium, there are a number of available panels.
    • R177 Hirschsprung disease. Consider this test if there is a clinical diagnosis of Hirschsprung disease.
    • R27 Paediatric disorders. Consider this test if there is structural bowel malformation and/or other congenital malformation suggestive of a syndromic diagnosis.
    • R184 Cystic fibrosis diagnostic test. This is the full cystic fibrosis variant test (not just the common CFTR pathogenic variant test), and should be considered if meconium ileus is diagnosed and sweat test results are abnormal or there is an additional urgent prenatal situation for the parents or for a close relative and the urgent sweat test is not available.
  • For tests that are undertaken using whole genome sequencing (WGS), including R27, you will need to:
    • submit parental samples alongside the child’s sample (this is trio testing) to aid interpretation, especially for the larger WGS panels (where this is not possible, for example because the child is in care or the parents are unavailable for testing, the child may be submitted as a singleton).
  • For tests that do not include WGS, including R177 and R184:
    • parental samples may be needed for interpretation of the child’s result. Parental samples can be taken alongside that of the child, and their DNA stored, or can be requested at a later date if needed.
  • The majority of tests are DNA based, and an EDTA sample (purple-topped tube) is required. Exceptions include karyotype testing and DNA repair defect testing (for chromosome breakage), which require lithium heparin (green-topped tube).
  • R27 is a large WGS ‘super panel’ (a panel comprised of several different constituent panels forming one large panel), and requesting it currently requires authorisation from clinical genetics services.
  • 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.

Resources

For clinicians

References:

For patients

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  • Last reviewed: 29/03/2024
  • Next review due: 29/03/2025
  • Authors: Dr Alexander Ross
  • Reviewers: Dr Amy Frost, Dr Eleanor Hay, Dr Emile Hendriks, Dr Hannah Massey, Dr Chinthika Piyasena