Familial Hemophagocytic Lymphohistiocytosis (FHL)
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About the Disorder | Genes Tested | Indications | Specimen l Testing Methodology l Sensitivity l Turnaround Time l Cost l CPT Codes l Shipping l Results l Contact Us
About the Disorder
Hemophagocytic lymphohistiocytosis (HLH) is a disorder of widespread accumulation of lymphocytes and mature macrophages, sometimes with hemophagocytosis, primarily involving the spleen, lymph nodes, bone marrow, liver and cerebral spinal fluid. The diagnostic criteria for HLH, based on the recommendations of the Histiocyte Society, include at least five of the eight following findings:
- Fever
- Splenomegaly
- Cytopenias affecting at least two of three cell lineages in peripheral blood
- Hypertriglyceridemia and / or hypofibrinogemia
- Hemophagocytosis in bone marrow, spleen or lymph nodes
- Low or absent natural killer (NK) cell function activity
- Hyperferritinemia
- High levels of soluble IL-2r
HLH can either occur sporadically (secondary HLH), or can be inherited as the autosomal recessive condition known as familial hemophagocytic lymphohistiocytosis (FHL). The incidence of FHL is about 1-in-50,000 live births. The age of onset of FHL is typically in infancy or young childhood, although presentation in young adulthood has been observed. FHL is generally fatal, unless treated with hematopoietic stem cell transplantation. Both familial and secondary HLH can be triggered by infections and are clinically indistinguishable.
Three genes have been specifically associated with FHL. Perforin 1 (PRF1), one of the causative genes of FHL, maps to 10q21-q22. Mutations in the PRF1 gene are identified in approximately 30% of individuals with FHL worldwide and in about 50% of individuals with FHL in the United States. PRF1 mutations are very commonly identified in children with HLH who are of African American and / or Hispanic descent. PRF1 encodes a 376 amino acid protein known as perforin. Perforin inserts into the membrane of a target cell and creates a pore, allowing the entry of granzyme B and inducing cell death. Mutations in PRF1 interfere with pore formation. The gene consists of three exons (exon 1 is noncoding). Mutations involving both coding exons have been described. NK cell function is typically abnormal in individuals with PRF1 mutations and the biochemical production of perforin and granzyme B is often decreased in symptomatic individuals with PRF1 mutations.
A second gene for familial HLH, MUNC13-4, maps to 17q25 and has been identified in an additional 30% of individuals with HLH. The gene consists of 32 exons and 31 introns and encodes for a 3273 amino acid protein which is essential for normal secretion of cytolytic granules. Mutations in MUNC13-4 interfere with normal secretion of cytolytic granules leading to widespread accumulation of lymphocytes and mature macrophages, sometimes with hemophagocytosis. Mutations in most of the exons have been identified. NK function may be normal or abnormal in individuals with MUNC13-4 mutations. Perforin and granzyme B are often upregulated in individuals with MUNC13-4 mutations. At this time, there is no specific functional assay for the MUNC13-4 protein.
A third gene for familial HLH, Syntaxin 11 (STX11), maps to 6q24 and has been identified only in a small inbred Turkish-Kurdish population. Mutations in STX11 have not been identified in other populations (Western European, Japanese) studied to date. A thorough analysis of North American patients has not yet been completed. The gene consists of one exon. NK cell function may be normal or abnormal in individuals with STX11 mutations. At this time, there is no specific functional assay for the STX11protein.
A fourth gene for FHL has been tentatively identified on the basis of linkage analysis [9q21-3-22 (Ohadi et al 1999)], but specific mutations in this region have not yet been reported. Additional genes for FHL are also suspected, but have not yet been identified. In addition, X-linked lymphoproliferative disease (XLP) should be considered in all males presenting with hemophagocytic lymphohistiocytosis not attributable to mutations in PRF1, MUNC13-4 or STX11.
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Genes Tested
- PRF1
- MUNC13-4 (UNC13D)
- SYNTAXIN 11
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Indications
- Confirmation of in a symptomatic individual
- Presymptomatic testing of at-risk siblings
- Carrier identification in individuals with a family history of HLH
- Prenatal diagnosis of an at-risk fetus, after confirmation of biallelic mutations in the parents (by prior arrangement only)
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Specimen
At least 5 mls whole blood in purple top (EDTA) tube. Label tube with patient's name, birth date and date of collection. Buccal samples are required for analysis in patients who have undergone bone marrow transplantation and may facilitate DNA isolation in patients undergoing chemotherapy or in individuals with leukopenia. Please call for a free buccal (cytobrush) collection kit.
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Testing Methodology
Testing is performed by PCR-based sequencing of the entire coding regions and intron/exon boundaries of the PRF1, MUNC13-4, or STX11 genes. Testing may be ordered sequentially or tandemly.
Perforin expression and granzyme B analysis by flow cytometry may be helpful in determining the most cost-effective order of tests. Please contact the Diagnostic Immunology Laboratory at 513-636-4769 for more information about these tests.
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Sensivitity
The sensitivity of DNA sequencing is over 99% for the detection of nucleotide base changes, small deletions, and insertions in the regions analyzed. Multiple exon deletions, large insertions and genetic recombinational events may not be identified using these methods. Large deletions have been reported in STX11 and are suspected in MUNC13-4.
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Turnaround Time
- 1 month for PRF1
- 2 months for MUNC13-4
- 1 month for Syntaxin 11
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Cost
Please call 1-866-450-4198 for current pricing information or with any billing questions.
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CPT Codes
| PRF1 |
83890, 83898x3, 83894x3, 83891x2, 83904x12, 83912 |
| MUNC13-4 |
83890, 83898x22, 83894x5, 83891x22, 83904x44, 83912, 84378 |
| STX 11 |
83890, 83898, 83894, 83891, 83904 x6, 83912 |
| Family specific mutation analysis |
83890, 83898, 83894, 83891, 83904, 83912 |
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Shipping Instructions
Please enclose test requisition with sample. All information must be completed before sample can be processed. Place samples in styrofoam mailer and ship at room temperature by overnight Federal Express to arrive Monday through Friday.
Ship to
Cytogenetics and Molecular Genetics Laboratories
3333 Burnet Avenue NRB 1042
Cincinnati, OH 45229
Phone 513-636-4474
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Results
Results will be reported to the referring physician or their designee as specified on the requisition form.
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Contact Us
For additional inquiries, contact us:
Phone 513-636-4474
Fax 513-636-4373
Email moleculargenetics@cchmc.org
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