Presentation: Child with haemophagocytic lymphohistiocytosis syndrome with absent perforin expression

A five-year-old girl presents acutely to hospital with deranged liver enzymes and pancytopenia. She is found to have jaundice with marked hepatosplenomegaly. Laboratory findings include elevated serum ferritin, triglycerides and lactate dehydrogenase. The patient’s bone marrow aspiration shows extensive haemophagocytosis. Perforin expression studies find absent (<5%) levels compared to control samples.

• Genomic testing with R232 should only be undertaken if the patient is suspected to have haemophagocytic lymphohistiocytosis (HLH) with low or absent perforin expression.
• R15 should be used where the broader diagnosis of HLH and/or immunodysregulation are suspected.
• R232 and R15 testing should typically be requested by immunology, haematology or clinical genetics teams.

• Consult the National Genomic Test Directory. From here you can access the rare and inherited disease eligibility criteria, which contains information about individual tests and their associated eligibility criteria. You can also access a spreadsheet containing details of all available tests.
  • For information about how to arrange testing in Wales, Scotland or Northern Ireland, see Genomic testing in the devolved nations.
• For information about the genes that are included on different gene panels, see the NHS Genomic Medicine Service (GMS) Signed Off Panels Resource.
• For HLH with low/absent perforin deficiency, consider:
  • R232 Haemophagocytic syndrome with absent perforin expression (single gene sequencing of PRF1).
• For conditions in which the broader diagnosis of severe or combined immunodeficiency is suspected, consider:
  • R15 Primary immunodeficiency. This will investigate causes of severe combined immunodeficiency, and includes a whole genome sequencing (WGS) panel of many genes associated with immune conditions.
  • R15.5 Semi-rapid testing (singleton whole exome sequencing panel) may be requested for acutely unwell children or adults highly likely to have a severe monogenic inflammatory condition where a diagnosis would have immediate management implications, such as confirming a diagnosis of HLH prior to considering haemopoietic stem cell transplant.
• For tests that do not include WGS, including R232 and R15.5 (semi-rapid testing only):
  • you can use your local Genomic Laboratory Hub test order and consent (record of discussion (RoD)) forms; and
  • 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.
• For tests that are undertaken using WGS, including R15, you will need to:
  • complete an NHS GMS test order form with details of the affected child (proband) and their parents, including details of the phenotype (using human phenotype ontology (HPO) terms) and the appropriate panel name(s) with associated R number (see How to complete a test order form for WGS for support in completing WGS-specific forms);
  • complete an NHS GMS record of discussion (RoD) form for each person being tested – for example, if you are undertaking trio testing of an affected child and their parents, you will need three RoD forms (see How to complete a record of discussion form for support); and
  • submit parental samples alongside the child’s sample 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).
• Most tests are DNA based, and an EDTA sample (typically a purple-topped tube) is required. There are a few tests for which a different type of tube is used; see Samples for genomic testing in rare disease.
• If you are discussing genomics concepts with your patients, you may find it helpful to use the visual communication aids for genomics conversations.
• 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

• European Society for Immunodeficiencies: Diagnostic criteria PID

References:

• Bousfiha A, Moundir A, Tangye SG and others. ‘The 2022 Update of IUIS Phenotypical Classification for Human Inborn Errors of Immunity‘. Journal of Clinical Immunology 2022: volume 42, issue 7, pages 1,508–1,520. DOI: 10.1007/s10875-022-01352-z
• Schulert GS and Cron RQ. ‘The genetics of macrophage activation syndrome‘. Genes & Immunity 2020: volume 21, issue 3, pages 169–181. DOI: 10.1038/s41435-020-0098-4

For patients

• Immunodeficiency UK
• Jeffrey Modell Foundation