Human and Molecular Genetics Center, The Medical College of Wisconsin, Milwaukee 53226, USA.
Genet Med. 2011 Mar;13(3):255-62. doi: 10.1097/GIM.0b013e3182088158.
We report a male child who presented at 15 months with perianal abscesses and proctitis, progressing to transmural pancolitis with colocutaneous fistulae, consistent with a Crohn disease-like illness. The age and severity of the presentation suggested an underlying immune defect; however, despite comprehensive clinical evaluation, we were unable to arrive at a definitive diagnosis, thereby restricting clinical management.
We sought to identify the causative mutation(s) through exome sequencing to provide the necessary additional information required for clinical management.
After sequencing, we identified 16,124 variants. Subsequent analysis identified a novel, hemizygous missense mutation in the X-linked inhibitor of apoptosis gene, substituting a tyrosine for a highly conserved and functionally important cysteine. X-linked inhibitor of apoptosis was not previously associated with Crohn disease but has a central role in the proinflammatory response and bacterial sensing through the NOD signaling pathway. The mutation was confirmed by Sanger sequencing in a licensed clinical laboratory. Functional assays demonstrated an increased susceptibility to activation-induced cell death and defective responsiveness to NOD2 ligands, consistent with loss of normal X-linked inhibitor of apoptosis protein function in apoptosis and NOD2 signaling.
Based on this medical history, genetic and functional data, the child was diagnosed as having an X-linked inhibitor of apoptosis deficiency. Based on this finding, an allogeneic hematopoietic progenitor cell transplant was performed to prevent the development of life-threatening hemophagocytic lymphohistiocytosis, in concordance with the recommended treatment for X-linked inhibitor of apoptosis deficiency. At >42 days posttransplant, the child was able to eat and drink, and there has been no recurrence of gastrointestinal disease, suggesting this mutation also drove the gastrointestinal disease. This report describes the identification of a novel cause of inflammatory bowel disease. Equally importantly, it demonstrates the power of exome sequencing to render a molecular diagnosis in an individual patient in the setting of a novel disease, after all standard diagnoses were exhausted, and illustrates how this technology can be used in a clinical setting.
我们报告了一名 15 个月大的男性患儿，最初表现为肛周脓肿和直肠炎，随后进展为全层结肠炎伴结肠直肠瘘，符合克罗恩病样疾病。鉴于其发病年龄和严重程度，提示存在潜在的免疫缺陷；然而，尽管进行了全面的临床评估，我们仍未能明确诊断，从而限制了临床管理。
我们通过外显子组测序试图确定致病突变，以提供临床管理所需的必要补充信息。
测序后，我们共发现 16124 个变异。进一步分析发现，X 连锁凋亡抑制因子基因存在一个新的半合子错义突变，导致一个高度保守且功能重要的半胱氨酸被酪氨酸取代。X 连锁凋亡抑制因子以前与克罗恩病无关，但通过 NOD 信号通路在促炎反应和细菌感知中发挥核心作用。该突变通过许可临床实验室的 Sanger 测序得到确认。功能检测显示，细胞凋亡和 NOD2 信号的激活诱导细胞死亡的敏感性增加，以及对 NOD2 配体的反应性受损，与正常 X 连锁凋亡抑制蛋白功能丧失一致。
基于该病史、遗传和功能数据，该患儿被诊断为 X 连锁凋亡抑制因子缺乏症。基于这一发现，为预防危及生命的噬血细胞性淋巴组织细胞增生症的发生，进行了异基因造血祖细胞移植，与 X 连锁凋亡抑制因子缺乏症的推荐治疗方案一致。移植后 >42 天，患儿可以进食和饮水，且未再出现胃肠道疾病，提示该突变也导致了胃肠道疾病。本报告描述了一种新型炎症性肠病的病因。同样重要的是，它展示了外显子组测序在排除所有标准诊断后，为个体患者在新发病例中提供分子诊断的能力，并且说明了该技术如何在临床环境中使用。
