Validating absolute lymphocyte count and plasma sphingosine-1-phosphate as disease biomarkers of sphingosine phosphate lyase insufficiency syndrome in anticipation of a pyridoxine clinical trial

鞘氨醇磷酸裂解酶不足综合征(SPLIS)是一种遗传性儿童代谢综合征 由SGPL1的隐性突变引起。受影响的儿童表现出类固醇抗药性肾病综合征 迅速进展为终末期肾病、肾上腺功能不全、神经缺陷和淋巴细胞减少。一个 观察到了严重程度的范围，受影响最严重的患者在宫内死亡，而其他人活着 到成年，尽管需要透析或肾移植。重要的是，SPLIS没有特效的治疗方法， 因此，迫切需要开发新的安全有效的治疗方法。SGPL1编码 鞘氨醇磷酸裂解酶(SPL)，一种导致不可逆疾病的重要胞内酶 鞘磷脂代谢的最后一步中鞘氨醇-1-磷酸(S1P)的分解。S1P是一种生物活性 通过其5个G蛋白偶联的S1P受体来调节淋巴细胞转运和其他 生理过程。SGPL1突变削弱SPL活性并导致鞘磷脂堆积导致 器官功能障碍和衰竭。此外，SPLIS儿童S1P信号异常会导致淋巴细胞减少 与淋巴细胞出口的缺陷有关。SPL的活性依赖于维生素B6作为辅因子。独立于其作为 作为160多个酶反应中的辅酶，维生素B6还可以作为伴侣，稳定维生素 依赖B6的酶。以B6维生素形式存在的维生素B6的药理剂量有 证明对涉及B6依赖酶的先天代谢错误有效。基于鼓舞人心 两名服用维生素B6补充剂的SPLIS患者的初步研究结果，我们正准备 评价维生素B6补充剂作为SPLIS首个特效治疗药物的安全性和有效性。 开发一种可靠的方法监测SPLIS患者血液样本中SPL活性的挑战 使对疾病生物标记物的依赖成为SPLIS任何临床试验的关键组成部分。我们假设 淋巴细胞绝对计数(ALC)和血浆S1P水平将作为反映SPLIS的可靠生物标志物 疾病状况。不幸的是，儿科对血浆S1P和其他主要鞘脂的参考范围 到目前为止还没有报道。此外，还没有研究全面分析中国的循环免疫细胞群 据报道，SPLIS。为了证实我们的假设并克服这些障碍来推进治疗 对于患有SPLIS和其他鞘脂代谢紊乱的儿童，我们将确定主要的血浆特征 SPLIS儿童和健康儿童及健康儿童的鞘脂和血液免疫功能标记物 成人对照队列。为了实现我们的特定目标，我们将验证血浆S1P和ALC是否为稳健的SPLIS 疾病生物标志物。我们将建立一套全面的血浆鞘脂的参考范围 健康的儿科和青年队列，将在未来用于诊断、监测和 在广泛的鞘磷脂疾病中进行临床试验。我们的结果将特别有助于临床 测试补充维生素B6辅因子治疗SPLIS的安全性和有效性的试验准备情况。

Sphingosine phosphate lyase insufficiency syndrome (SPLIS) is an inherited metabolic childhood syndrome caused by recessive mutations in SGPL1. Affected children exhibit steroid-resistant nephrotic syndrome with rapid progression to end stage renal disease, adrenal insufficiency, neurological defects and lymphopenia. A range of severity has been observed, with the most severely affected patients dying in utero, while others live to adulthood, albeit requiring dialysis or kidney transplantation. Importantly, there is no specific cure for SPLIS, and thus there is a dire need for the development of novel safe and effective treatments. SGPL1 encodes sphingosine phosphate lyase (SPL), an essential intracellular enzyme responsible for the irreversible breakdown of sphingosine-1-phosphate (S1P) in the final step of sphingolipid metabolism. S1P is a bioactive lipid that signals through its five G protein coupled S1P receptors to regulate lymphocyte trafficking and other physiological processes. SGPL1 mutations impair SPL activity and cause sphingolipid accumulation leading to organ dysfunction and failure. In addition, aberrant S1P signaling in SPLIS children leads to lymphopenia due to a defect in lymphocyte egress. SPL activity depends on vitamin B6 as a cofactor. Independent of its role as a coenzyme in over 160 enzymatic reactions, vitamin B6 can also function as a chaperone, stabilizing vitamin B6-dependent enzymes. Pharmacological doses of vitamin B6 in the form of the B6 vitamer pyridoxine have proven effective in inborn errors of metabolism involving B6-dependent enzymes. Based on encouraging preliminary findings in two SPLIS patients treated with vitamin B6 supplementation, we are preparing to evaluate the safety and efficacy of vitamin B6 supplementation as the first specific treatment for SPLIS. Challenges to developing a reliable assay for monitoring SPL activity in blood samples from SPLIS patients make reliance on disease biomarkers a critical component of any clinical trial in SPLIS. We hypothesize that absolute lymphocyte count (ALC) and plasma S1P levels will serve as reliable biomarkers that reflect SPLIS disease status. Unfortunately, pediatric reference ranges for plasma S1P and other major sphingolipids have not been reported to date. Further, no study comprehensively profiling circulating immune cell populations in SPLIS has been reported. To confirm our hypothesis and overcome these obstacles to advancing treatments for children with SPLIS and other sphingolipid metabolic disorders, we will characterize the major plasma sphingolipids and blood markers of immune function in children with SPLIS and a healthy pediatric and young adult control cohort. In accomplishing our Specific Aims, we will validate plasma S1P and ALC as robust SPLIS disease biomarkers. We will establish reference ranges for a comprehensive set of plasma sphingolipids in a healthy pediatric and young adult cohort that will be useful in the future for diagnosis, monitoring and conducting clinical trials in a broad range of sphingolipid disorders. Our results will specifically facilitate clinical trial readiness for testing the safety and efficacy of vitamin B6 cofactor supplementation to treat SPLIS.