Purpose

Newborn screening (NBS) for severe combined immunodeficiency (SCID) is based on the detection of T-cell receptor excision circles (TRECs). TRECs are a sensitive biomarker for T-cell lymphopenia, but not specific for SCID. This creates a palette of secondary findings associated with low T-cells that require follow-up and treatment or are non-actionable. The high rate of (non-actionable) secondary findings and false-positive referrals raises questions about the harm-benefit-ratio of SCID screening, as referrals are associated with high emotional impact and anxiety for parents.

Methods

An alternative quantitative TREC PCR with different primers was performed on NBS cards of referred newborns (N = 56) and epigenetic immune cell counting was used as for relative quantification of CD3 + T-cells (N = 59). Retrospective data was used to determine the reduction in referrals with a lower TREC cutoff value or an adjusted screening algorithm.

Results

When analyzed with a second PCR with different primers, 45% of the referrals (25/56) had TREC levels above cutoff, including four false-positive cases in which two SNPs were identified. With epigenetic qPCR, 41% (24/59) of the referrals were within the range of the relative CD3 + T-cell counts of the healthy controls. Lowering the TREC cutoff value or adjusting the screening algorithm led to lower referral rates but did not prevent all false-positive referrals.

Conclusions

Second tier tests and adjustments of cutoff values or screening algorithms all have the potential to reduce the number of non-actionable secondary findings in NBS for SCID, although second tier tests are more effective in preventing false-positive referrals.

中文翻译：

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二级检测可减少新生儿严重联合免疫缺陷筛查中不可操作的二次发现和假阳性转诊的数量

 目的

新生儿严重联合免疫缺陷 (SCID) 筛查 (NBS) 基于 T 细胞受体切除环 (TREC) 的检测。 TREC 是 T 细胞淋巴细胞减少症的敏感生物标志物，但对 SCID 不具有特异性。这就产生了一系列与 T 细胞水平低相关的次要发现，需要随访和治疗，或者无法采取行动。高比例的（不可采取行动的）次要发现和假阳性转诊引发了人们对 SCID 筛查的危害效益比的质疑，因为转诊与父母的高情绪影响和焦虑有关。

 方法

在转诊新生儿的 NBS 卡上进行了使用不同引物的替代定量 TREC PCR（ N = 56），并使用表观遗传免疫细胞计数作为 CD3 + T 细胞的相对定量（ N = 59）。使用回顾性数据来确定较低 TREC 截止值或调整筛选算法的转诊数量的减少。

 结果

当使用不同引物进行第二次 PCR 分析时，45% 的转诊 (25/56) 的 TREC 水平高于截止值，其中包括四个假阳性病例，其中鉴定了两个 SNP。通过表观遗传 qPCR，41% (24/59) 的转诊在健康对照的相对 CD3 + T 细胞计数范围内。降低 TREC 截止值或调整筛查算法会降低转诊率，但并不能阻止所有假阳性转诊。

 结论

尽管第二层测试在防止假阳性转诊方面更有效，但第二层测试以及截止值或筛选算法的调整都有可能减少 NBS 中针对 SCID 的不可操作的二次发现的数量。