Metachromatic leukodystrophy (MLD) is a devastating rare neurodegenerative disease. Typically, loss of motor and cognitive skills precedes early death. The disease is characterised by deficient lysosomal arylsulphatase A (ARSA) activity and an accumulation of undegraded sulphatide due to pathogenic variants in the gene. Atidarsagene autotemcel (arsa-cel), an ex vivo haematopoietic stem cell gene therapy was approved for use in the UK in 2021 to treat early-onset forms of pre- or early-symptomatic MLD. Optimal outcomes require early diagnosis, but in the absence of family history this is difficult to achieve without newborn screening (NBS). A pre-pilot MLD NBS study was conducted as a feasibility study in Manchester UK using a two-tiered screening test algorithm. Pre-established cutoff values (COV) for the first-tier C16:0 sulphatide (C16:0-S) and the second-tier ARSA tests were evaluated. Before the pre-pilot study, initial test validation using non‑neonatal diagnostic bloodspots demonstrated ARSA pseudodeficiency status was associated with normal C16:0-S results for age ( = 43) and hence not expected to cause false positive results in this first-tier test. Instability of ARSA in bloodspot required transfer of NBS bloodspots from ambient temperature to −20°C storage within 7–8 days after heel prick, the earliest possible in this UK pre-pilot study. Eleven of 3687 de-identified NBS samples in the pre-pilot were positive for C16:0-S based on the pre-established COV of ≥170 nmol/l or ≥ 1.8 multiples of median (MoM). All 11 samples were subsequently tested negative determined by the ARSA COV of <20% mean of negative controls. However, two of 20 NBS samples from MLD patients would be missed by this C16:0-S COV. A further suspected false negative case that displayed 4% mean ARSA activity by single ARSA analysis for the initial test validation was confirmed by genotyping of this NBS bloodspot, a severe late infantile MLD phenotype was predicted. This led to urgent assessment of this child by authority approval and timely commencement of arsa-cel gene therapy at 11 months old. Secondary C16:0-S analysis of this NBS bloodspot was 150 nmol/l or 1.67 MoM. This was the lowest result reported thus far, a new COV of 1.65 MoM is recommended for future pilot studies. Furthermore, preliminary data of this study showed C16:1-OH sulphatide is more specific for MLD than C16:0-S. In conclusion, this pre-pilot study adds to the international evidence that recommends newborn screening for MLD, making it possible for patients to benefit fully from treatment through early diagnosis.

中文翻译：

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提高异染性脑白质营养不良的新生儿筛查测试性能：一项预试验研究的建议，该研究确定了一个晚期婴儿病例的治疗方法

异染性脑白质营养不良（MLD）是一种毁灭性的罕见神经退行性疾病。通常，运动和认知技能的丧失会导致早逝。该疾病的特征是溶酶体芳基硫酸酯酶 A (ARSA) 活性缺陷以及由于基因致病性变异导致未降解的硫苷脂积累。Atidarsagene autotemcel (arsa-cel) 是一种离体造血干细胞基因疗法，于 2021 年在英国获批用于治疗早发型症状前或早期 MLD。最佳结果需要早期诊断，但在没有家族史的情况下，如果不进行新生儿筛查 (NBS)，则很难实现这一目标。预试点 MLD NBS 研究是在英国曼彻斯特使用两层筛选测试算法进行的可行性研究。对第一层 C16:0 硫苷脂 (C16:0-S) 和第二层 ARSA 测试的预先设定的截止值 (COV) 进行了评估。在预试验研究之前，使用非新生儿诊断血斑进行的初步测试验证表明，ARSA 假性缺陷状态与年龄 (= 43) 的正常 C16:0-S 结果相关，因此预计不会在该第一级研究中导致假阳性结果测试。由于血斑中 ARSA 不稳定，需要在足跟采血后 7-8 天内将 NBS 血斑从环境温度转移至 -20°C 储存，这是英国预试点研究中最早的可能。根据预先确定的 COV ≥170 nmol/l 或≥中位数 (MoM) 的 1.8 倍，预试验中的 3687 个去识别 NBS 样本中有 11 个 C16:0-S 呈阳性。随后，所有 11 个样本均呈阴性，ARSA COV 小于阴性对照平均值的 20%。然而，来自 MLD 患者的 20 个 NBS 样本中有两个会被这种 C16:0-S COV 遗漏。通过对该 NBS 血斑的基因分型证实了进一步疑似假阴性病例，该病例通过用于初始测试验证的单次 ARSA 分析显示出 4% 的平均 ARSA 活性，并预测了严重的晚期婴儿 MLD 表型。这导致当局批准对这个孩子进行紧急评估，并在 11 个月大时及时开始 arsa-cel 基因治疗。该 NBS 血斑的二次 C16:0-S 分析结果为 150 nmol/l 或 1.67 MoM。这是迄今为止报告的最低结果，建议未来的试点研究采用 1.65 MoM 的新 COV。此外，本研究的初步数据表明，C16:1-OH 硫苷对 MLD 的特异性比 C16:0-S 更高。总之，这项预试点研究增加了建议新生儿 MLD 筛查的国际证据，使患者能够通过早期诊断从治疗中充分受益。