Presentation: Child with suspected lymphoproliferative syndrome with absent SAP expression (X-linked lymphoproliferative disease type 1)

A six-year-old boy presents to paediatrics from primary care. He has a significant history of recurrent lower respiratory tract infections and, on two occasions, has required hospital admission for intravenous antibiotics. He has palpable lymph node enlargement with splenomegaly. He is found to have low immunoglobulin levels with normal B and T cell count. There is a family history of lymphoma affecting one of his maternal uncles.

Genomic testing with R17 should only be undertaken if X-linked lymphoproliferative syndrome with absent SAP expression is suspected. Features include:

• haemophagocytic lymphohistiocytosis (HLH), hypogammaglobulinaemia or other lymphoproliferative conditions affecting males consistent with SAP-related disease; and
• low or absent SAP expression.

R15 Primary immunodeficiency or monogenic inflammatory bowel disease should be used where features are less specific and the broader diagnosis of a lymphoproliferative condition and/or immunodysregulation is suspected.

Note that the related condition X-linked lymphoproliferative disease type 2, which is distinguished by low/absent XIAP instead of SAP, should be investigated via R18 Haemophagocytic syndrome with absent XIAP expression. If there is uncertainty, the R15 indication will test for both conditions, along with many other monogenic causes of immunodeficiency, inflammatory bowel disease and autoimmunity.

R17 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 lymphoproliferative conditions with SAP deficiency, consider:
  • R17 Lymphoproliferative syndrome with absent SAP expression (single gene sequencing of ADA).
• For conditions in which the broader diagnosis of lymphoproliferation and/or HLH is suspected (including lymphoproliferative syndrome type 2), consider:
  • R15 Primary immunodeficiency and monogenic inflammatory bowel disease. This will investigate causes of severe combined immunodeficiency, and includes a whole genome sequencing (WGS) panel of all genes known to cause immune conditions.
• For tests that do not include WGS, including R17:
  • 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 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
• GeneReviews: X-linked lymphoproliferative disease
• Jeffrey Modell Foundation: 10 warning signs of primary immunodeficiency

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

For patients

• Immunodeficiency UK
• Jeffrey Modell Foundation