Proximal spinal muscular atrophy (SMA), a leading genetic cause of infant death worldwide, is an early-onset motor neuron disease characterized by loss of α-motor neurons and associated muscle atrophy. SMA is caused by deletion or other disabling mutations of survival motor neuron 1 (SMN1) but retention of one or more copies of the paralog SMN2. Within the SMA population, there is substantial variation in SMN2 copy number (CN); in general, those individuals with SMA who have a high SMN2 CN have a milder disease. Because SMN2 functions as a disease modifier, its accurate CN determination may have clinical relevance. In this study, we describe the development of array digital PCR (dPCR) to quantify SMN1 and SMN2 CNs in DNA samples using probes that can distinguish the single nucleotide difference between SMN1 and SMN2 in exon 8. This set of dPCR assays can accurately and reliably measure the number of SMN1 and SMN2 copies in DNA samples. In a cohort of SMA patient–derived cell lines, the assay confirmed a strong inverse correlation between SMN2 CN and disease severity. We can detect SMN1–SMN2 gene conversion events in DNA samples by comparing CNs at exon 7 and exon 8. Partial deletions of SMN1 can also be detected with dPCR by comparing CNs at exon 7 or exon 8 with those at intron 1. Array dPCR is a practical technique to determine, accurately and reliably, SMN1 and SMN2 CNs from SMA samples as well as identify gene conversion events and partial deletions of SMN1.

近端脊髓性肌萎缩症 (SMA) 是全球婴儿死亡的主要遗传原因，是一种早发性运动神经元疾病，其特征是 α 运动神经元的丧失和相关的肌肉萎缩。SMA 是由运动神经元存活 1 ( SMN1 )的缺失或其他致残突变引起的，但保留了一个或多个旁系同源物SMN2 的副本。在 SMA 群体中，SMN2拷贝数 (CN)存在很大差异；一般来说，那些具有高SMN2 CN 的SMA患者病情较轻。由于SMN2作为疾病调节剂，其准确的 CN 测定可能具有临床意义。在这项研究中，我们描述了阵列数字 PCR (dPCR) 的发展，以量化使用可以区分外显子 8 中SMN1和SMN2之间单核苷酸差异的探针检测 DNA 样品中的SMN1和SMN2 CN 。这组 dPCR 检测可以准确可靠地测量DNA 样品中SMN1和SMN2 的拷贝数。在一组 SMA 患者来源的细胞系中，该测定证实SMN2 CN 与疾病严重程度之间存在强烈的负相关。我们可以通过比较外显子 7 和外显子 8的 CNs来检测DNA 样本中的SMN1–SMN2基因转换事件。SMN1 的部分缺失也可以通过 dPCR 检测外显子 7 或外显子 8 的 CN 与内含子 1 的 CN。阵列 dPCR 是一种实用技术，可准确可靠地确定SMA 样本中的SMN1和SMN2 CN，以及识别基因转换事件和部分SMN1 的缺失。