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

描述（由申请人提供）：巨噬细胞激活综合征（MAS）是系统性幼年特发性关节炎的一种严重的、可能致命的并发症。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是由过度的炎症反应引起的，主要涉及两种免疫细胞-巨噬细胞和T淋巴细胞。在临床上类似的遗传条件下，过度免疫反应的发展与细胞溶解细胞的功能缺陷有关。这些细胞通常会杀死异常细胞，如肿瘤细胞或感染病毒的细胞。有证据表明，细胞溶解细胞也可能参与消除过度活化的免疫细胞。因此，如果它们不能正常工作，免疫反应可能无法及时终止。这将导致MAS中不受控制的炎症。在此之前，我们已经确定了MUNC13-4基因中的几个遗传标记，这些遗传标记作为单个单倍型遗传。由于MUNC13-4蛋白参与细胞溶解功能，这一观察结果是重要的。一个重要的未解决的问题是，MUNC13-4中单倍型的存在是否与MUNC13-4蛋白功能异常有关，从而直接导致MAS患者出现细胞溶解功能障碍。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性。这两种可能性将在拟议的研究中加以探讨。

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 .