Abstract：
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 ARSA 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 (n = 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.
摘要：
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先于早期死亡。该疾病的特征在于溶酶体芳基硫酸酯酶A（ARSA）活性不足以及由于ARSA基因中的致病性变体而导致的未降解的硫化物的积累。Atidarsageneautotemcel(arsa-cel),一项离体造血干细胞基因疗法于2021年在英国被批准用于治疗早期发病形式的症状前或早期MLD.最佳结果需要早期诊断，但在没有家族史的情况下,如果没有新生儿筛查(NBS)很难做到这一点.使用两级筛选测试算法，在英国曼彻斯特进行了预试点MLDNBS研究作为可行性研究。评估了第一层C16：0磺肽（C16：0-S）和第二层ARSA测试的预定截止值（COV）。在预试点研究之前，使用非新生儿诊断血点进行的初步测试验证表明,ARSA假性缺乏状态与年龄正常的C16:0-S结果相关(n=43),因此预计在该一级测试中不会导致假阳性结果.ARSA在血斑中的不稳定性需要在脚跟刺后7-8天内将NBS血斑从环境温度转移到-20°C储存，在这项英国预试点研究中，最早的可能。根据预先确定的COV≥170nmol/l或≥1.8倍的中位数（MoM），预试验中3687个去识别的NBS样品中有11个对C16：0-S呈阳性。所有11个样品随后测试为阴性,通过ARSACOV测定为阴性对照的平均值<20%。然而,来自MLD患者的20个NBS样本中有两个会被这个C16:0-SCOV遗漏。通过对该NBS血斑进行基因分型，进一步怀疑假阴性病例，通过单一ARSA分析进行初始测试验证，显示平均ARSA活性为4％。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。此NBS血斑的二级C16：0-S分析为150nmol/l或1.67MoM。这是迄今为止报道的最低结果，建议在未来的试点研究中使用1.65MoM的新COV。此外，这项研究的初步数据表明，C16：1-OH硫化物对MLD的特异性比C16：0-S。总之,这项预试点研究增加了建议新生儿进行MLD筛查的国际证据，使患者有可能通过早期诊断从治疗中充分受益。
