PTPRC (CD45) is not associated with multiple sclerosis in a large cohort of German patients

BACKGROUND: Since contradictory results have been reported, we reanalysed the 77C→G transition in exon 4 of the protein-tyrosine phosphatase receptor-type C (PTPRC also known as CD45) in a large cohort of German MS patients and controls. Different isoforms of the protein are expressed, depending on alternative splicing of exons 4 (CD45RA), 5 (CD45RB) and 6 (CD45RC) (CD45RO, exons 4–6 spliced out). The 77C→G transition does not change the amino acid sequence, but it is probably part of a motif necessary for splicing leading to the isoform CD45RA. The expression of CD45RA is increased in 77C/G heterozygous individuals. The aim of the study was to clarify the importance of the PTPRC 77C→G transition in our German cohort of MS patients. METHODS: PCR products of exon 4 were digested using endonuclease MspI. The resulting restriction fragments of the wildtype C allele are 198 and 62 bp in length. In the G allele an additional restriction site is present yielding fragments of 114 and 84 bp. RESULTS: The G allele was identified in 10 of the 347 controls (1.4%) and in 7 of 454 MS patients (0.8%; Table 1). No homozygous individuals were found either in the control or in the patient group. Genetic association between the PTPRC 77C→G transition and MS susceptibility was excluded in the MS cohort. In addition, subgrouping patients according to differences in the clinical course of MS or according to HLA-DRB1*15 status did not yield significant differences. CONCLUSIONS: The 77C→G transition in exon 4 of the PTPRC gene may contribute to MS susceptibility only in very few families, if at all, but it is not relevant for the majority of MS cases, including virtually all German patients.

研究背景：鉴于已有研究报道了相互矛盾的结果，我们对一大队列德国多发性硬化（Multiple Sclerosis, MS）患者与对照人群中蛋白酪氨酸磷酸酶受体型C（protein-tyrosine phosphatase receptor-type C, PTPRC，亦称CD45）的第4外显子77C→G碱基转换进行了重新分析。该蛋白存在多种剪接异构体，具体取决于外显子4（对应CD45RA）、5（对应CD45RB）以及6（对应CD45RC）的可变剪接；CD45RO则为外显子4至6均被剪接移除的异构体。77C→G碱基转换并不会改变氨基酸序列，但它可能属于调控CD45RA异构体剪接所必需的基序。在77C/G杂合个体中，CD45RA的表达水平会升高。本研究旨在明确PTPRC基因77C→G碱基转换在我们的德国MS患者队列中的临床意义。
研究方法：对第4外显子的聚合酶链式反应（Polymerase Chain Reaction, PCR）产物采用限制性内切酶MspI进行酶切消化。野生型C等位基因的酶切片段长度分别为198 bp与62 bp；而G等位基因则存在额外的酶切位点，酶切后得到114 bp与84 bp的片段。
研究结果：在347名对照人群中共检出10例G等位基因携带者（占比1.4%），在454名MS患者中检出7例（占比0.8%；详见表1）。对照人群与患者组均未发现纯合突变个体。本MS队列的分析结果排除了PTPRC 77C→G碱基转换与MS易感性之间存在遗传关联的可能。此外，根据MS临床病程差异或HLA-DRB1*15基因型状态对患者进行亚组分析，也未得到具有统计学意义的组间差异。
研究结论：PTPRC基因第4外显子的77C→G碱基转换即便真的对MS易感性存在影响，也仅可能在极少数家族中发挥作用，而对于绝大多数MS病例（几乎涵盖所有德国MS患者）而言，该位点与MS发病并无临床相关性。