Abstract：
X-linked agammaglobulinemia (XLA) is caused by mutations in the Bruton tyrosine kinase) BTK) gene. Affected patients have severely reduced amounts of circulating B cells. Patients with atypical XLA may have residual circulating B cells, and there are few studies exploring these cells\' repertoire. We aimed to study the B cell repertoire of a novel hypomorphic mutation in the BTK gene, using the next generation sequencing (NGS) technology. Clinical data was collected from our clinical records. Real-time PCR was used to determine KREC copies, and NGS was used to determine the immunoglobulin (Ig) heavy chain (IgH) repertoire diversity. Both patients had a relatively mild clinical and laboratory phenotype, residual BTK protein expression, and the same novel mutation in the BTK gene, c.1841 T > C, p. L614P. Signal-joint kappa-deleting recombination excision circles (sj-KREC) for both patients were completely absent reflecting lack of naïve B cells. The intron RSS-Kde coding joints (cj) were significantly reduced, reflecting residual replicating B cells. NGS displayed restricted IgH repertoire with highly uneven distribution of clones, especially for Pt2. We report a novel BTK mutation, c.1841 T > C (p. L614P) that is associated with a relatively mild phenotype. We conclude that the IgH repertoire in atypical XLA is restricted with highly uneven distribution of clones. This phenomenon may be explained by extremely reduced to non-existent levels of BTK in B cells. This report sheds further light on atypical cases of XLA.
摘要：
X-连锁丙种球蛋白血症（XLA）是由Bruton酪氨酸激酶）BTK基因突变引起的。受影响的患者的循环B细胞量严重减少。非典型XLA患者可能有残留的循环B细胞，很少有研究探索这些细胞库。我们旨在研究BTK基因中一种新的低态突变的B细胞库，使用下一代测序（NGS）技术。从我们的临床记录中收集临床数据。实时PCR用于确定KREC拷贝，和NGS用于确定免疫球蛋白(Ig)重链(IgH)库的多样性。两名患者的临床和实验室表型相对较轻，残余BTK蛋白表达，和BTK基因中同样的新突变，c.1841T>C，p.L614P。两名患者的信号联合κ缺失重组切除环（sj-KREC）完全不存在，反映出缺乏原始B细胞。内含子RSS-Kde编码接头(cj)显著减少,反映残留的复制B细胞。NGS显示出限制的IgH库，克隆分布高度不均匀，尤其是Pt2。我们报告了一个新的BTK突变，c.1841T>C（p。L614P）与相对温和的表型相关。我们得出的结论是，非典型XLA中的IgH库受到限制，克隆的分布高度不均匀。这种现象可以通过B细胞中BTK的极度降低到不存在的水平来解释。本报告进一步阐明了XLA的非典型病例。
