Acute splenic sequestration crisis (ASSC) is one of the earliest acute clinical manifestations of sickle cell anemia (SCA), with a median age at first episode of 1.8 years [range: 0.4–12.9] as reported for our recently published regional longitudinal newborn cohort, beginning with the introduction of newborn screening (1986) and ending just before the introduction of preventive intensification with hydroxyurea (HU) in 2015.¹ Early predictive biomarkers have been identified for ASSC, but little is known about the impact of early ASSC on disease severity.² Unlike early dactylitis, early ASSC was not found to be associated with an increase in the risk of adverse outcomes, including death, stroke, frequent vaso-occlusive crisis (VOC), and recurrent acute chest syndrome (ACS), in a cohort of newborns with SCA.³

Our main objective here was to determine, from our SCA birth cohort, whether children experiencing early ASSC have a higher disease burden. In addition, we aimed to update clinical information on ASSC and confirm the prognostic factors identified in previous studies. Consistent with the French standards of care, for the whole cohort, disease-modifying therapies (DMT) were started only after the occurrence of complications: transfusion program (TP) was mainly implemented for stroke prevention, and HU was prescribed only to children over the age of 3 years for low hemoglobin (Hb) levels and/or recurrence of VOC/ACS. Specifically at our center, TP was offered for frequent VOC/ACS or anemia despite HU, or in children younger than 3 years, and hematopoietic stem cell transplantation (HSCT) to patients with cerebral vasculopathy or frequent VOC/ACS with a human leukocyte antigen-identical sibling. In our cohort-study, the use of DMT was thus considered a surrogate for disease severity.

ASSC was defined as splenic enlargement (increase of at least 2 cm from baseline) measured below the costal margin and associated with acute anemia (decrease in Hb concentration >2 g/dL relative to the previous measurement). Early and late ASSC were defined as a first episode of ASSC occurring before or after the age of 2 years respectively. During ASSC, standard management was prompt transfusion to restore effective circulating volume. After the resolution of a first ASSC, local guidelines recommended watchful waiting, unless children had another reason for receiving TP or HU. After the second or third episode, then either splenectomy or a temporary prophylactic TP were considered, to prevent ASSC recurrence. The age at which splenectomy was considered (usually after 3 years of age) and the indication for splenectomy after TP (only if persistent splenomegaly during TP or systematic) varied over time.

Children were classified into two groups on the basis of the timing of the first ASSC: before 2 years (early ASSC group), or after 2 years or no ASSC (other group). Descriptive statistics were used to summarize the data and groups were compared using Student's t-tests and Fisher's exact tests. Multivariate logistic regression analyses with stepwise selection identified significant factors predictive of early ASSC. Kaplan–Meier (KM) estimates and Hazard Ratios (HRs) were provided for SCA complications and initiation of DMT. Incidence rates were compared between ASSC groups using a Poisson regression.

Our severe sickle cell genotype cohort consisted of 292 subjects: 280 with HbSS, nine with HbSβ⁰, and three with HbS-Dpunjab (HbSD) genotypes. During the study period, 105 children, 56 (53%) boys and 49 girls experienced a first episode of ASSC, resulting in two- and 5-year probabilities of 21% [95% CI:16–25%] and 31% [95% CI:25–36%], respectively.¹ The first ASSC occurred before and after the age of 2 years in 61 and 44 children, respectively. Hundred children were not receiving any DMT when first ASSC occurred whereas four were taking HU, and one child had initiated TP. They all experienced first ASSC episode after 2 years of age.

During the first ASSC episode, mean Hb and platelet levels dropped to 6.0 ± 1 g/dL and 148 ± 77G/L, respectively, with no significant difference between the two age groups (6.0 ± 1 vs. 6 ± 0.1 g/dL; and 143 ± 67 vs. 155 ± 87G/L respectively, p = 0.91 and 0.53) suggesting similar severity in the two age groups. Approximately 104 children received a blood transfusion during their first ASSC. After the resolution of the first ASSC, watchful waiting was applied for 95 (90%) children, 43 (41%) of whom experienced no further episode. A temporary TP was used for four children. All had additional reasons for receiving blood transfusions. Only one child was started on HU because of recurrent VOCs. Five children underwent splenectomy.

Sixty-two of the 105 children (59%) experienced more than one episode: 40 of the 61 with a first ASSC before the age of 2 years and 22 of the 44 children with a first ASSC after the age of 2 years. There were 238 episodes in total, with a global incidence of 6.9/100 patient-years (PY). None of the episodes were fatal or accompanied by stroke. The median interval between the first and second episodes was 116 days [range 66–293 days] overall, 112 days [range: 63–288] and 131 days [range: 71–291] for children experiencing a first ASSC before and after the age of 2 years, respectively.

Overall, a temporary TP was used in 31/105 (30%) children, mostly in those with recurrent ASSC (28/62 (45%)). The median duration of the TP was 25 months [range: 16–35 months]. Sequestration recurred during the TP in 12 cases (39%), a median of 14.5 months after TP initiation [range: 7–27]. Splenectomy was performed in 39/105 (37%) patients overall, and in 15/31 (48%) children initially placed on a TP. Median age at splenectomy was 4.5 years [range: 3.6–6.8] overall, and 4.5 years [3.3–5.5] and 4.8 years [3.8–7.5] in the subgroups of children with and without prior TP, respectively.

We then focused on early ASSC, to identify prognostic markers of early ASSC occurrence among baseline blood parameters and before any DMT, and to determine whether early ASSC occurrence was predictive of adverse outcomes throughout childhood. We restricted analysis to the 287 children with more than 2 years' follow-up (FU). We thus compared the group of 60 children with early ASSC and a group of 227 children with first ASSC after 2 years (late ASSC) or no ASSC.

Mean FU was 13.7 ± 4.6 years in the early ASSC group and 13.4 ± 4.9 years in the other patients. In univariate analysis, early ASSC was significantly associated with being male, β-globin Bantou/Bantou haplotype, alpha-thalassemia (including one or two α-chain gene deletion), lower baseline Hb and HbF levels and higher baseline reticulocyte, leukocyte and neutrophil counts (Table S1). In the multivariable analysis, low HbF level (OR 0.88, 95% CI 0.83–0.94; p < .0001), high leukocyte count (OR 1.11, 95% CI 1.03–1.19; p < .007), and alpha-thalassemia (OR 2.11, 95% CI 1.02–4.38; p < .004) were independently associated with early ASSC.

We next investigated whether children with early ASSC experienced more severe disease by performing log-rank tests to compare KM estimates for sickle complications. KM curves showed that early ASSC was associated with a significantly higher cumulative risk of conditional transcranial Doppler (TCD) velocities, but did not increase the risk of abnormal TCD velocities, overt stroke, silent cerebral infarcts (SCI), or extracerebral cumulative organ damage, including a high tricuspid regurgitation velocity (TRV≥2 m/s), sickle nephropathy, and retinopathy (Table 1A). As expected, early ASSC was significantly associated with a higher cumulative risk of requiring transfusion, acute exacerbation of anemia (AEA), splenectomy, initiation of a TP, and HSCT. Interestingly, early ASSC was not associated with a higher cumulative risk of hydroxyurea use.

We then compared incidence rates to determine whether children with early ASSC had a higher vaso-occlusive burden. Early ASSC predicted a modest but significant increase in the numbers of both VOC (74.4 vs. 61.4/100 PY) and ACS episodes (19.6 vs. 15.3/100 PY) during FU. Interestingly, ACS rates increased only for ACS developing during the clinical course of a VOC (11.9 vs. 7.3/100 PY), not for ACS in the form of acute pneumonia episodes (7.8 vs. 8.1/100 PY) (Table 1B).

In conclusion, this single-center cohort study of 238 episodes of ASSC in 105 children with SCA, with no concomitant strokes or deaths, confirms the benefits of a well-developed healthcare system providing newborn screening, parental education, and early access to comprehensive sickle cell disease referral centers. As previously reported, high baseline HbF levels provided the strongest protection against early ASSC in multivariate analysis (p < .0001). We also show, for the first time, that alpha-thalassemia is independently predictive of early ASSC.

This is the first study to evaluate the prognostic significance of early ASSC for disease severity throughout childhood. We found that children with early ASSC did not have higher rates of neurological complications other than conditional cerebral velocities. This finding was unexpected because early ASSC was significantly associated with a higher cumulative risk of AEA in our cohort, and AEA was identified as a significant independent risk factor for SCI in other cohorts.⁴ These findings may reflect the protective effect of alpha-thalassemia against cerebral vasculopathy,⁵ as the prevalence of alpha-thalassemia was significantly higher in the group of children with early ASSC. Alternatively, our data may attest to the protective effect of the DMT widely used in our SCA genotype group, particularly for HSCT (probability of 83.1% [95% CI: 78.3–87.4%] overall and of 16.7% [95% CI: 12.4–21.5%] for HSCT by the age of 10 years).¹ Interestingly, no abnormal TCD velocities or SCI developed after transplantation in any of the 56 children undergoing HSCT median age at HSCT: 4.8 years (range: [2.6–17.3] for the 17 children with early ASSC, and 7.3 years [3.2–19.7] for the other 39 children).

Interestingly, early ASSC increased the odds of more frequent VOCs and more frequent ACSs throughout childhood. Our data argue for a broader use of HU, even in children with ASSC complications, as HU did not influence ASSC occurrence rates in the Baby-hug randomized trial,⁶ because many of these children experience recurrent vaso-occlusive complications. Some of the strongest predictors of splenic function preservation in children treated with HU included younger age at initiation of HU therapy, shorter time to reach the maximum tolerated dose (MTD), and a larger increase in HbF levels relative to baseline.⁷ Additional studies in real-life conditions are warranted because HU may delay the development of functional asplenia, and it is important to investigate the effects of introducing HU earlier and of the dose escalation to the MTD, on ASSC risk over time.

急性脾隔离危象 （ASSC） 是镰状细胞性贫血 （SCA） 最早的急性临床表现之一，首次发作的中位年龄为 1.8 岁 [范围：0.4-12.9]，正如我们最近发布的区域纵向新生儿队列所报道的那样，从引入新生儿筛查（1986 年）开始，到 2015 年引入羟基脲 （胡） 预防性强化之前结束。¹ 已经确定了 ASSC 的早期预测性生物标志物，但对早期 ASSC 对疾病严重程度的影响知之甚少。² 与早期指（趾）炎不同，在一组患有 SCA 的新生儿中，未发现早期 ASSC 与不良结局风险增加相关，包括死亡、中风、频繁的血管闭塞危象 （VOC） 和复发性急性胸部综合征 （ACS）。³

我们在这里的主要目标是从我们的 SCA 出生队列中确定经历早期 ASSC 的儿童是否具有更高的疾病负担。此外，我们旨在更新 ASSC 的临床信息并确认先前研究中确定的预后因素。与法国护理标准一致，对于整个队列，疾病修饰疗法 （DMT） 仅在并发症发生后才开始：输血计划 （TP） 主要用于预防中风，胡 仅用于 3 岁以上儿童的低血红蛋白 （Hb） 水平和/或 VOC/ACS 复发。特别是在我们中心，TP 被用于频繁的 VOC/ACS 或贫血，尽管有 胡，或 3 岁以下的儿童，以及造血干细胞移植 （HSCT） 用于脑血管病变或频繁的 VOC/ACS 患者与人类白细胞抗原相同的兄弟姐妹。在我们的队列研究中，因此使用 DMT 被认为是疾病严重程度的替代指标。

ASSC 被定义为在肋缘以下测量的脾肿大 （从基线增加至少 2 cm） 并与急性贫血 （Hb 浓度相对于之前的测量降低 >2 g/dL） 相关。早期和晚期 ASSC 定义为 ASSC 的首次发作分别发生在 2 岁之前或之后。在 ASSC 期间，标准管理是及时输血以恢复有效循环容量。在解决第一个 ASSC 后，当地指南建议观察等待，除非儿童有其他原因接受 TP 或 胡。在第二次或第三次发作后，考虑脾切除术或临时预防性 TP，以防止 ASSC 复发。考虑脾切除术的年龄 （通常在 3 岁以后） 和 TP 后脾切除术的适应证 （仅当 TP 期间持续性脾肿大或全身性） 随时间变化。

根据第一次 ASSC 的时间将儿童分为两组： 2 岁前 （早期 ASSC 组），或 2 年后或无 ASSC （另一组）。使用描述性统计来总结数据，并使用 Student t 检验和 Fisher 精确检验对各组进行比较。逐步选择的多变量 logistic 回归分析确定了预测早期 ASSC 的重要因素。为 SCA 并发症和 DMT 的开始提供了 Kaplan-Meier （KM） 估计值和风险比 （HRs）。使用 Poisson 回归比较 ASSC 组之间的发病率。

我们的严重镰状细胞基因型队列由 292 名受试者组成：280 名 HbSS，9 名 HbSβ^0,3 名 HbS-Dpunjab （HbSD） 基因型。在研究期间，105 名儿童、56 名 （53%） 男孩和 49 名女孩经历了 ASSC 的首次发作，导致 2 年和 5 年概率分别为 21% [95% CI：16-25%] 和 31% [95% CI：25-36%]。¹ 第一次 ASSC 分别发生在 61 名和 44 名儿童的 2 岁之前和之后。当第一次 ASSC 发生时，100 名儿童没有接受任何 DMT，而 4 名儿童正在服用 胡，1 名儿童开始了 TP。他们都在 2 岁后经历了第一次 ASSC 发作。

在第一次 ASSC 发作期间，平均 Hb 和血小板水平分别降至 6.0 ± 1 g/dL 和 148 ± 77G/L，两个年龄组之间无显著差异 （6.0 ± 1 vs. 6 ± 0.1 g/dL;和 143 ± 67 vs. 155 ± 87 G/L，p = 0.91 和 0.53），表明两个年龄组的严重程度相似。大约 104 名儿童在第一次 ASSC 期间接受了输血。在第一次 ASSC 解决后，对 95 名 （90%） 儿童进行了观察等待，其中 43 名 （41%） 没有进一步发作。四个孩子使用了临时 TP。他们都有接受输血的其他原因。由于反复出现的 VOCs，只有一名儿童开始接受 胡。5 名儿童接受了脾切除术。

105 名儿童中有 62 名 （59%） 经历了不止一次发作：61 名儿童中有 40 名在 2 岁之前首次发生 ASSC，44 名儿童中有 22 名在 2 岁后首次发生 ASSC。总共有 238 次发作，全球发病率为 6.9/100 患者年 （PY）。没有一次发作是致命的或伴有中风。第一次和第二次发作之间的中位间隔总体为 116 天 [范围 66-293 天]，2 岁之前和之后首次经历 ASSC 的儿童分别为 112 天 [范围：63-288] 和 131 天 [范围：71-291]。

总体而言，31/105 （30%） 的儿童使用了临时 TP，主要是复发性 ASSC 的儿童 （28/62 （45%））。TP 的中位持续时间为 25 个月 [范围：16-35 个月]。12 例 （39%） 在 TP 期间复发，中位为 TP 开始后 14.5 个月 [范围：7-27]。总共 39/105 （37%） 的患者和 15/31 （48%） 最初接受 TP 的儿童进行了脾切除术。脾切除术的中位年龄总体为 4.5 岁 [范围：3.6-6.8]，既往有和无 TP 的儿童亚组分别为 4.5 岁 [3.3-5.5] 和 4.8 岁 [3.8-7.5]。

然后，我们专注于早期 ASSC，以确定基线血液参数中和任何 DMT 之前早期 ASSC 发生的预后标志物，并确定早期 ASSC 的发生是否能预测整个儿童期的不良结局。我们将分析限制在 287 例随访超过 2 年的儿童 （FU） 中。因此，我们比较了 60 名早期 ASSC 儿童组和一组 227 名 2 年后首次 ASSC （晚期 ASSC） 或无 ASSC 的儿童。

早期 ASSC 组的平均 FU 为 13.7 ± 4.6 年，其他患者的平均 FU 为 13.4 ± 4.9 年。在单变量分析中，早期 ASSC 与男性、β-珠蛋白 Bantou/Bantou 单倍型、α-地中海贫血（包括一个或两个α链基因缺失）、较低的基线 Hb 和 HbF 水平以及较高的基线网织红细胞、白细胞和中性粒细胞计数显著相关（表 S1）。在多变量分析中，低 HbF 水平 （OR 0.88,95% CI 0.83-0.94;p < .0001）、高白细胞计数 （OR 1.11,95% CI 1.03–1.19;p < .007） 和 α-地中海贫血 （OR 2.11,95% CI 1.02–4.38;p < .004） 与早期 ASSC 独立相关。

接下来，我们通过进行对数秩检验来比较镰状并发症的 KM 估计值，调查早期 ASSC 患儿是否经历更严重的疾病。KM 曲线显示，早期 ASSC 与条件经颅多普勒 （TCD） 速度的累积风险显著升高相关，但不会增加 TCD 速度异常、显性中风、无症状脑梗死 （SCI） 或颅外累积器官损伤的风险，包括高三尖瓣反流速度 （TRV≥2 m/s）、镰状肾病和视网膜病变（表 1A）。正如预期的那样，早期 ASSC 与需要输血、贫血急性加重 （AEA）、脾切除术、TP 开始和 HSCT 的较高累积风险显著相关。有趣的是，早期 ASSC 与羟基脲使用较高的累积风险无关。

然后，我们比较了发病率，以确定早期 ASSC 患儿是否具有更高的血管闭塞负荷。早期 ASSC 预测 FU 期间 VOC （74.4 vs. 61.4/100 PY） 和 ACS 发作次数 （19.6 vs. 15.3/100 PY） 的数量略有增加。有趣的是，仅在 VOC 临床病程中发生的 ACS 发生 ACS 发生率增加（11.9 对 7.3/100 PY），而急性肺炎发作形式的 ACS 则没有增加（7.8 对 8.1/100 PY）（表 1B）。

总之，这项单中心队列研究对 105 名 SCA 患儿的 238 次 ASSC 发作进行了研究，没有伴随中风或死亡，证实了提供新生儿筛查、父母教育和早期进入综合镰状细胞病转诊中心的良好医疗保健系统的好处。如前所述，在多变量分析中，高基线 HbF 水平对早期 ASSC 提供了最强的保护 （p < .0001）。我们还首次表明 α-地中海贫血可以独立预测早期 ASSC。

这是第一项评估早期 ASSC 对整个儿童期疾病严重程度的预后意义的研究。我们发现，早期 ASSC 患儿除了条件性脑速度外，神经系统并发症的发生率并不高。这一发现是出乎意料的，因为在我们的队列中，早期 ASSC 与 AEA 的较高累积风险显著相关，而 AEA 在其他队列中被确定为 SCI 的重要独立危险因素。⁴ 这些发现可能反映了 α-地中海贫血对脑血管病变的保护作用，⁵ 因为早期 ASSC 儿童组的 α-地中海贫血患病率明显更高。或者，我们的数据可能证明我们的 SCA 基因型组中广泛使用的 DMT 的保护作用，特别是对 HSCT （总体概率为 83.1% [95% CI： 78.3–87.4%] 和 16.7% [95% CI： 12.4–21.5%] 到 10 岁时 HSCT）。¹ 有趣的是，56 名接受 HSCT 的儿童在移植后没有出现异常的 TCD 速度或 SCI，HSCT 的中位年龄：4.8 岁（范围：17 名早期 ASSC 患儿为 [2.6-17.3]，其他 39 名患儿为 7.3 岁 [3.2-19.7]）。

有趣的是，早期 ASSC 增加了整个儿童期更频繁的 VOC 和更频繁的 ACS 的几率。我们的数据表明，即使在患有 ASSC 并发症的儿童中，胡 也应该得到更广泛的使用，因为 胡 在 Baby-hug 随机试验中不会影响 ASSC 发生率，⁶ 因为这些儿童中的许多人会出现复发性的血管闭塞并发症。接受 胡 治疗的儿童脾功能保留的一些最强预测因素包括 胡 治疗开始时年龄较小、达到最大耐受剂量 （MTD） 的时间较短以及 HbF 水平相对于基线的更大增加。⁷ 有必要在现实生活中进行额外的研究，因为 胡 可能会延迟功能性无脾的发展，重要的是要调查早期引入 胡 和剂量递增到 MTD 对 ASSC 风险随时间的影响。