Alternative titles; symbols
HGNC Approved Gene Symbol: UNC13D
Cytogenetic location: 17q25.1 Genomic coordinates (GRCh38) : 17:75,827,225-75,844,404 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 17q25.1 | Hemophagocytic lymphohistiocytosis, familial, 3 | 608898 | Autosomal recessive | 3 |
By coimmunopurification of GTP-RAB27A (603868)-interacting proteins in platelets, followed by sequence analysis, database analysis, and PCR of a bone marrow cDNA library, Shirakawa et al. (2004) cloned full-length UNC13D, which they called MUNC13-4. The deduced 1,090-amino acid protein contains 2 calcium-binding C2 domains and 2 Munc13 homology domains, but it lacks the N-terminal region containing a phorbol ester-binding C1 domain present in other Munc13 proteins, such as UNC13B (605836). MUNC13-4 distributed between the cytosol and membrane fractions in permeabilized platelets.
Using Northern blot analysis, Feldmann et al. (2003) detected a 4.5-kb UNC13D transcript that was highly expressed in spleen, thymus, and peripheral blood leukocytes. Faint expression was detected in small intestine, prostate, ovary, and colon. RT-PCR analysis showed high expression of UNC13D in all hematopoietic tissues and cells examined. In nonhematopoietic tissues, strong expression of UNC13D was detected only in lung and placenta, with weak expression in brain, heart, skeletal muscle, and kidney.
Secretion of the contents of cytolytic granules at the immunologic synapse is a highly regulated process essential for lymphocyte cytotoxicity. This process requires the rapid transfer of perforin (170280)-containing lytic granules to the target cell interface, followed by their docking and fusion with the plasma membrane. Feldmann et al. (2003) found that expressed tagged UNC13D localized with cytotoxic granules at the immunologic synapse. Using UNC13D-deficient cells, they determined that UNC13D is essential for the priming step of cytolytic granule secretion preceding vesicle membrane fusion.
Shirakawa et al. (2004) found that MUNC13-4 bound GTP-RAB27A and GTP-RAB27B (603869) in vitro, but not other GTPases, and it enhanced platelet secretion in an in vitro assay.
Feldmann et al. (2003) determined that the UNC13D gene contains 32 exons.
By genomic sequence analysis, Feldmann et al. (2003) mapped the UNC13D gene to chromosome 17q25.1.
Feldmann et al. (2003) identified 6 mutations in the UNC13D gene in patients with hemophagocytic lymphohistiocytosis-3 (FHL3; 608898). They found that UNC13D deficiency resulted in defective cytolytic granule exocytosis, despite polarization of the secretory granules and docking with the plasma membrane.
Noting that mutations in the perforin gene (PRF1; 170280) account for only about 40% of cases of hemophagocytic lymphohistiocytosis, Santoro et al. (2006) sequenced the UNC13D gene in 30 probands with hemophagocytic lymphohistiocytosis who did not have mutations in PRF1. In 15 families, 12 novel and 4 known mutations were found, spread throughout the gene (see, e.g., 608897.0001, 608897.0006, and 608897.0009). The mutations were homozygous in 8 families and compound heterozygous in 7.
Variant Studies
Noori et al. (2023) developed an in vitro assay to determine the clinical relevance of mutations in the UNC13D, STXBP2 (601717), PRF1 (170280), and STX11 (605014) genes identified in patients with HLH, with the goal of distinguishing patients with familial hemophagocytic lymphohistiocytosis from patients with nonfamilial hemophagocytic lymphohistiocytosis. In this assay, the mouse homolog of the relevant mutated gene was removed by Cas9 ribonucleoprotein in naive murine CD8+ T cells, and then the cells were transduced with cDNA of the human homolog containing the patient's mutation to be studied. The cells were then tested for cytotoxicity and degranulation capacity. Noori et al. (2023) tested mutations previously identified in patients with HLH and found that biallelic mutations resulting in complete loss of function were identified in infants or very young children with HLH, whereas partial loss of function mutations in one or more alleles were identified in older children or adults with HLH. Interestingly, the authors found that the level of protein expression resulting from a gene mutation did not necessarily correlate to the level of residual function. Meyer and Nichols (2023) commented that this assay may not appropriately characterize dominant-negative mutations or biallelic mutations with complementary effects.
Crozat et al. (2007) described Jinx, an N-ethyl-N-nitrosourea-induced murine cytomegalovirus (MCMV) susceptibility mutation in C57BL/6 mice. They identified the Jinx mutation as an insertion of 53 nucleotides from intron 26 into exon 26 of the Unc13d gene, resulting in a 20-amino acid insertion, followed by premature termination after amino acid 859. In addition to increased MCMV viral titers and lethality comparable to that observed in susceptible BALB/c mice, Jinx mice produced high levels of Ifng (147570) and Ifna (147660)/Ifnb (147640) after infection, but they were unable to kill natural killer (NK) target cells. Both NK and cytotoxic T lymphocytes failed to degranulate in Jinx mice. Jinx mice showed no increased susceptibility to Listeria monocytogenes. Jinx mice developed an FHL3-like phenotype after infection with lymphocytic choriomeningitis virus (LCMV), but not after infection with MCMV. One exception to the FHL3-like phenotype was that instead of neutropenia, Jinx mice developed neutrophilia after infection with LCMV. Crozat et al. (2007) concluded that development of hemophagocytic lymphohistiocytosis in mice is conditional and proposed that there may also be a specific infectious trigger of FHL3 in humans.
Using Jinx mice to analyze platelet granule release and secretion, Ren et al. (2010) observed complete ablation of release from dense granules and compromised activity from alpha granules and lysosomes. Platelets from Jinx mice showed attenuated aggregation, and Jinx mice had prolonged bleeding times. Defective release was rescued by addition of recombinant human UNC13D to permeabilized Jinx platelets. Unc13d levels correlated directly with the extent of granule release from wildtype and Jinx heterozygous mouse platelets. Ren et al. (2010) concluded that UNC13D is a limiting factor required for platelet secretion and hemostasis.
In patients with familial hemophagocytic lymphohistiocytosis-3 (FHL3; 608898) from 3 Moroccan families, Feldmann et al. (2003) identified homozygosity for a 12-bp deletion at nucleotide 1822 within exon 20 of the UNC13D gene. The mutation resulted in the deletion of amino acids 608 to 611.
In a Moroccan patient with FHL, Santoro et al. (2006) identified homozygosity for the 1822del12 mutation in the UNC13D gene.
In patients with familial hemophagocytic lymphohistiocytosis-3 (FHL3; 608898) from a Pakistani family, Feldmann et al. (2003) identified homozygosity for a deletion of nucleotide 214C in exon 3 of the UNC13D gene, resulting in a frameshift after codon 72.
In an Arabian patient with familial hemophagocytic lymphohistiocytosis-3 (FHL3; 608898), Feldmann et al. (2003) identified homozygosity for an insertion of T at nucleotide 1755 in exon 20 of the UNC13D gene, resulting in a frameshift after codon 586.
In a French patient with familial hemophagocytic lymphohistiocytosis-3 (FHL3; 608898), Feldmann et al. (2003) identified homozygosity for a G-to-A transition at the donor splice site of intron 15 of the UNC13D gene, resulting in abnormal splicing and frameshift after codon 464.
In patients with familial hemophagocytic lymphohistiocytosis-3 (FHL3; 608898) from a French family, Feldmann et al. (2003) identified compound heterozygosity for a C-to-T transition at nucleotide 766 in exon 10 of the UNC13D gene, resulting in an arg256-to-ter (R256X) substitution, and a G-to-T transversion at the donor splice site of intron 9 (608897.0006), resulting in abnormal splicing and frameshift after codon 252.
For discussion of the G-to-T transversion at the donor splice site of intron 9 in the UNC13D gene that was found in compound heterozygous state in patients with familial hemophagocytic lymphohistiocytosis-3 (FHL3; 608898) by Feldmann et al. (2003), see 608897.0005.
In 3 unrelated Italian patients with FHL, Santoro et al. (2006) identified compound heterozygosity for the +1G-T transversion in intron 9 of the UNC13D gene and another mutation in UNC13D (see, e.g., 608897.0009).
In a Turkish patient who had primary hemophagocytic lymphohistiocytosis (FHL3; 608898), Zur Stadt et al. (2006) found homozygosity for a leu403-to-pro (L403P) mutation in the UNC13D gene. The family was consanguineous, and the diagnosis in the patient had been made at the age of 2 years.
In an Italian family with primary hemophagocytic lymphohistiocytosis (FHL3; 608898), Santoro et al. (2006) identified compound heterozygosity for mutations in the UNC13D gene: a 2570T-G transversion in exon 27, resulting in a phe857-to-cys (F857C) substitution, and a splice site mutation (608897.0006).
Crozat, K., Hoebe, K., Ugolini, S., Hong, N. A., Janssen, E., Rutschmann, S., Mudd, S., Sovath, S., Vivier, E., Beutler, B. Jinx, an MCMV susceptibility phenotype caused by disruption of Unc13d: a mouse model of type 3 familial hemophagocytic lymphohistiocytosis. J. Exp. Med. 204: 853-863, 2007. Note: Erratum: J. Exp. Med. 205: 737 only, 2008. [PubMed: 17420270] [Full Text: https://doi.org/10.1084/jem.20062447]
Feldmann, J., Callebaut, I., Raposo, G., Certain, S., Bacq, D., Dumont, C., Lambert, N., Ouachee-Chardin, M., Chedeville, G., Tamary, H., Minard-Colin, V., Vilmer, E., Blanche, S., Le Deist, F., Fischer, A., de Saint Basile, G. Munc13-4 is essential for cytolytic granules fusion and is mutated in a form of familial hemophagocytic lymphohistiocytosis (FHL3). Cell 115: 461-473, 2003. [PubMed: 14622600] [Full Text: https://doi.org/10.1016/s0092-8674(03)00855-9]
Meyer, L. K., Nichols, K. E. Deciphering genetic uncertainty in familial HLH. Blood 141: 2288-2290, 2023. [PubMed: 37166930] [Full Text: https://doi.org/10.1182/blood.2023019713]
Noori, T., Rudd-Schmidt, J. A., Kane, A., Frith, K., Gray, P. E., Hu, H., Hsu, D., Chung, C. W. T., Hodel, A. W., Trapani, J. A., Voskoboinik, I. A cell-based functional assay that accurately links genotype to phenotype in familial HLH. Blood 141: 2330-2342, 2023. Note: Erratum: Blood 143: 562 only, 2024. [PubMed: 36706356] [Full Text: https://doi.org/10.1182/blood.2022018398]
Ren, Q., Wimmer, C., Chicka, M. C., Ye, S., Ren, Y., Hughson, F. M., Whiteheart, S. W. Munc13-4 is a limiting factor in the pathway required for platelet granule release and hemostasis. Blood 116: 869-877, 2010. [PubMed: 20435885] [Full Text: https://doi.org/10.1182/blood-2010-02-270934]
Santoro, A., Cannella, S., Bossi, G., Gallo, F., Trizzino, A., Pende, D., Dieli, F., Bruno, G., Stinchcombe, J. C., Micalizzi, C., De Fusco, C., Danesino, C., Moretta, L., Notarangelo, L. D., Griffiths, G. M., Arico, M. Novel Munc13-4 mutations in children and young adult patients with haemophagocytic lymphohistiocytosis. (Letter) J. Med. Genet. 43: 953-960, 2006. [PubMed: 16825436] [Full Text: https://doi.org/10.1136/jmg.2006.041863]
Shirakawa, R., Higashi, T., Tabuchi, A., Yoshioka, A., Nishioka, H., Fukuda, M., Kita, T., Horiuch, H. Munc13-4 is a GTP-Rab27-binding protein regulating dense core granule secretion in platelets. J. Biol. Chem. 279: 10730-10737, 2004. [PubMed: 14699162] [Full Text: https://doi.org/10.1074/jbc.M309426200]
Zur Stadt, U., Beutel, K., Kolberg, S., Schneppenheim, R., Kabisch, H., Janka, G., Hennies, H. C. Mutation spectrum in children with primary hemophagocytic lymphohistiocytosis: molecular and functional analyses of PRF1, UNC13D, STX11, and RAB27A. Hum. Mutat. 27: 62-68, 2006. [PubMed: 16278825] [Full Text: https://doi.org/10.1002/humu.20274]