MUNC13-4 gene Polymorphisms in Macrophage Activation syndrome and Systemic Juveni

描述(申请人提供)：巨噬细胞激活综合征(MAS)是一种严重的，可能致命的全身青少年特发性关节炎的并发症。在临床实践中，迫切需要可靠的生物标志物来识别有这种并发症风险的患者。MAS是由主要涉及两种免疫细胞-巨噬细胞和T淋巴细胞的夸大炎症反应引起的。在临床相似的遗传条件下，过度的免疫反应的发展与细胞溶解细胞的功能缺陷有关。这些细胞通常杀死异常细胞，如肿瘤细胞或感染病毒的细胞。有一些证据表明，细胞溶解细胞也可能参与消除过度激活的免疫细胞。因此，如果它们功能不正常，免疫反应可能不会及时终止。这将导致在MAS中出现不受控制的炎症。此前，我们已经在Munc13-4基因中发现了几个遗传标记，这些标记是作为单个单倍型遗传的。由于Munc13-4蛋白与细胞溶解功能有关，因此这一观察结果很重要。一个重要的悬而未决的问题是，MUNC 13-4中单倍型的存在是否与Munc13-4蛋白的异常功能有关，从而直接导致患者MAS中细胞溶解功能障碍的发展。另一种可能性是，所描述的单倍型可能延伸到Munc13-4基因的上游或下游，并涉及邻近免疫相关基因的额外多态。这两种可能性将在拟议的研究中加以探讨。 公共卫生相关性：巨噬细胞激活综合征(MAS)是系统性幼年特发性关节炎(SJIA)的一种严重的、潜在的致命并发症，其特征是由T细胞和吞噬血细胞的过度激活和扩张引起的压倒性炎症反应。临床上，MAS类似于常染色体隐性遗传病家族性噬血细胞淋巴组织细胞增多症(FHLH)。在FHLH中，T细胞和巨噬细胞的不受控制的增殖与NK细胞和细胞毒细胞功能的降低有关，继发于穿孔素编码基因或Munc13-4基因的突变，Munc13-4基因的产物参与穿孔素的细胞内转运。我们的观察表明，与FHLH一样，发展为MAS的sJIA患者的NK功能严重受抑。我们最近报道了在大多数MAS患者中，作为扩展单倍型遗传的Munc13-4基因的单核苷酸多态(SNPs)。这种单倍型在健康对照组或无MAS的sJIA患者中很少见。此外，在反应性高促黄体生成素患者中，单倍型频率在统计学上也显著增加。一个重要的悬而未决的问题是，观察到的MUNC 13-4基因多态是否与Munc13-4蛋白的功能异常有关，从而直接导致患者MAS中细胞溶解功能障碍的发生。另一种可能性是，所描述的单倍型可能延伸到Munc13-4基因的上游或下游，并涉及邻近免疫相关基因的额外多态。为了解决这些问题，我们建议对JIA/MAS患者和对照组进行Munc13-4基因上游和下游的SNPs分型，以确定感兴趣的单倍型是否延伸到基因的上游或下游，并在Munc13-4基因的启动子区域或邻近基因中包括额外的SNPs。如果是这样的话，可能需要额外的测序来确定更多具有重要功能的SNP。同时，我们将确定单倍型的存在是否与Munc13-4蛋白的功能异常或位于Munc13-4基因上游或下游的基因表达水平的变化有关。这一研究途径的长期目标是确定导致sJIA中MAS发展的基因缺陷。

DESCRIPTION (provided by applicant): Macrophage activation syndrome (MAS) is a serious, potentially fatal complication of Systemic Juvenile Idiopathic Arthritis. In clinical practice, there is a strong need for reliable biomarkers that would identify patients at risk for this complication. MAS is caused by the exaggerated inflammatory response involving mainly two types of immune cells - macrophages and T lymphocytes. In clinically similar genetic conditions the development of the exaggerated immune response has been linked to defective function of cytolytic cells. These cells typically kill abnormal cells such as tumor cells or cells infected with viruses. There is some evidence that cytolytic cells may also be involved in the elimination of overly activated immune cells. Therefore, if they do not function properly, the immune response may not be terminated in a timely manner. This would lead to uncontrolled inflammation seen in MAS. Previously, we have identified several genetic markers within the MUNC13-4 gene inherited as a single haplotype. Since MUNC13-4 protein is involved with the cytolytic function this observations is important. An important unanswered question is whether the presence of the haplotype in the MUNC 13-4 is associated with abnormal function of the MUNC13-4 protein and, thus, directly contributes to the development of cytolytic dysfunction seen in patients MAS. Another possibility is that the described haplotype may extend either upstream or downstream of the MUNC13-4 gene and involve additional polymorphisms in the neighboring immunologically relevant genes. These two possibilities will be explored in the proposed study. PUBLIC HEALTH RELEVANCE: Macrophage activation syndrome (MAS) is a serious, potentially fatal complication of Systemic Juvenile Idiopathic Arthritis (sJIA) characterized by an overwhelming inflammatory reaction driven by excessive activation and expansion of T cells and hemophagocytic macrophages. Clinically, MAS is similar to the autosomal recessive disorder Familial Hemophagocytic Lymphohistiocytosis (FHLH). In FHLH, the uncontrolled proliferation of T cells and macrophages has been associated with decreased NK cell and cytotoxic cell functions secondary to mutations either in the gene encoding perforin or in the MUNC13-4 gene whose product is involved in the intracellular transport of perforin. Our observations suggest that as in FHLH, sJIA patients who develop MAS, have profoundly depressed NK function. We have recently reported an association with single-nucleotide polymorphisms (SNPs) in the MUNC13-4 gene inherited as an extended haplotype in the majority of MAS patients. This haplotype is rare in healthy controls or in patients with sJIA without MAS. Moreover, a statistically significant increase in the frequency of the haplotype was also noted in patients with Reactive HLH. An important unanswered question is whether the observed polymorphism in the MUNC 13-4 is associated with abnormal function of the MUNC13-4 protein and, thus, directly contributes to the development of cytolytic dysfunction seen in patients MAS. Another possibility is that the described haplotype may extend either upstream or downstream of the MUNC13-4 gene and involve additional polymorphisms in the neighboring immunologically relevant genes. To address these questions we propose to genotype sJIA/MAS patients and controls for additional 64 SNPs located upstream and downstream of the MUNC13-4 gene to determine whether the haplotype of interest extends up- or downstream of the gene and includes additional SNPs either in the promoter region of the MUNC13-4 gene or in the neighboring genes. If this is the case, additional sequencing may be necessary to identify additional functionally significant SNPs. In parallel, we will determine whether the presence of the haplotype is associated with either abnormal function of the MUNC13-4 protein or changes in the levels of expression of the genes located upstream or downstream of the MUNC13-4 gene. The long-term goal of this avenue of research is to define genetic defects responsible for the development of MAS in sJIA .