Hemophagocytic lymphohistiocytosis (HLH), particularly primary HLH (pHLH), is a rare, life-threatening disease. Germline genetic deficiency of 12 known HLH genes impairs cytotoxic degranulation in natural killer (NK) cells or cytotoxic T lymphocytes (CTLs) and contributes to pHLH development. However, no pathogenic mutations in these HLH genes are found in nearly 10% of HLH patients, despite a strong suspicion of pHLH, suggesting that the underlying genetic basis of HLH is still unclear. To discover novel susceptibility genes, we first selected 13 children with ppHLH (presumed primary HLH patients in the absence of detectable known HLH gene variants) and their parents for initial screening. Whole-genome sequencing (WGS) in one trio and whole-exome sequencing (WES) in twelve trios revealed that two ppHLH patients carried biallelic NBAS variants, a gene that is involved in Golgi-to-endoplasmic reticulum (ER) retrograde transport upstream of the degranulation pathway. Additionally, two candidate genes, RAB9B and KLC3, showed a direct relationship with known HLH genes in protein-protein interaction (PPI) network analysis. We analyzed NBAS, RAB9B, KLC3 and known HLH genes in an independent validation cohort of 224 pediatric HLH patients. Only biallelic NBAS variants were identified in three patients who harbored no pathogenic variants in any of the known HLH genes. Functionally, impaired NK-cell cytotoxicity and degranulation were revealed in both NBAS biallelic variant patients and in an NBAS-deficient NK-cell line. Knockdown of NBAS in an NK-cell line (IMC-1) using short hairpin RNA (shRNA) resulted in loss of lytic granule polarization and a decreased number of cytotoxic vesicles near the Golgi apparatus. According to our findings, NBAS is the second most frequently mutated gene (2.11%) in our HLH cohort after PRF1. NBAS deficiency may contribute to the development of HLH via a dysregulated lytic vesicle transport pathway.

中文翻译：

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NBAS 是一种参与细胞毒性脱粒的基因，在小儿噬血细胞性淋巴组织细胞增多症中反复发生突变

噬血细胞性淋巴组织细胞增多症 (HLH)，尤其是原发性 HLH (pHLH)，是一种罕见的危及生命的疾病。12 个已知 HLH 基因的种系遗传缺陷会损害自然杀伤 (NK) 细胞或细胞毒性 T 淋巴细胞 (CTL) 中的细胞毒性脱粒，并有助于 pHLH 的发展。然而，尽管强烈怀疑 pHLH，但在近 10% 的 HLH 患者中未发现这些 HLH 基因的致病突变，这表明 HLH 的潜在遗传基础仍不清楚。为了发现新的易感基因，我们首先选择了 13 名 ppHLH 儿童（在没有可检测到的已知 HLH 基因变异的情况下假定为原发性 HLH 患者）及其父母进行初步筛查。一个三人组中的全基因组测序 (WGS) 和十二个三人组中的全外显子组测序 (WES) 显示，两名 ppHLH 患者携带双等位基因 NBAS 变体，参与脱粒途径上游的高尔基体至内质网 (ER) 逆行转运的基因。此外，在蛋白质-蛋白质相互作用 (PPI) 网络分析中，两个候选基因 RAB9B 和 KLC3 与已知的 HLH 基因有直接关系。我们在 224 名儿童 HLH 患者的独立验证队列中分析了 NBAS、RAB9B、KLC3 和已知的 HLH 基因。在 3 名在任何已知 HLH 基因中均无致病性变异的患者中，仅鉴定出双等位基因 NBAS 变异。在功能上，在 NBAS 双等位基因变异患者和 NBAS 缺陷 NK 细胞系中均发现 NK 细胞细胞毒性和脱粒受损。使用短发夹 RNA (shRNA) 在 NK 细胞系 (IMC-1) 中敲除 NBAS 导致裂解颗粒极化丧失和高尔基体附近的细胞毒性囊泡数量减少。根据我们的研究结果，在我们的 HLH 队列中，NBAS 是继 PRF1 之后第二个最常见的突变基因（2.11%）。NBAS 缺乏可能通过失调的溶解囊泡运输途径促进 HLH 的发展。