Alpha-1 antitrypsin deficiency (AATD) is an inherited condition characterized by reduced levels of serum AAT due to mutations in the SERPINA1 (Serpin family A member 1) gene. The Pi*S (Glu264Val) is one of the most frequent deficient alleles of AATD, showing high incidence in the Iberian Peninsula. Herein, we describe two new alleles carrying an S mutation but producing a null phenotype: QO_Vigo and QO_Aachen. The new alleles were identified by sequencing the SERPINA1 gene in three patients who had lower AAT serum levels than expected for the initial genotype. These alleles are the result of combined mutations in cis in a PI*S allele. Sequencing detected the S mutation in cis with Tyr138Cys (S+Tyr138Cys) in two patients, whereas a third one had the S mutation in cis with Pro391Thr variant (S+Pro391Thr). When expressed in a cellular model, these variants caused strong AAT polymerization and very low AAT secretion to almost undetectable levels. The isoelectric focusing method for plasma AAT phenotyping did not show AAT protein encoded by the novel mutant alleles, behaving as null. We called these alleles PI*S-plus because the S variant was phased with another variant conferring more aggressive characteristics to the allele. The current data demonstrate that the clinical variability observed in AATD can be explained by additional genetic variation, such as dual cis-acting variants in the SERPINA1 gene. The possible existence of other unrevealed variants combined in the PI*S alleles should be considered to improve the genetic diagnosis of the patients.

Alpha-1抗胰蛋白酶缺乏症（AATD）是一种遗传性疾病，其特征是由于SERPINA1（Serpin家族A成员1）基因的突变导致血清AAT水平降低。Pi * S（Glu264Val）是AATD最常见的缺陷等位基因之一，在伊比利亚半岛显示出很高的发病率。在此，我们描述了两个带有S突变但产生无效表型的新等位基因：QO _Vigo和QO _Aachen。通过对3名AAT血清水平低于初始基因型预期水平的患者中的SERPINA1基因进行测序，确定了新的等位基因。这些等位基因是PI * S等位基因中顺式突变的结果。测序检测到顺式S突变在两名患者中使用Tyr138Cys（S + Tyr138Cys），而第三名在Pro391Thr变体（S + Pro391Thr）中具有顺式S突变。当在细胞模型中表达时，这些变体导致强烈的AAT聚合和非常低的AAT分泌至几乎不可检测的水平。血浆AAT表型的等电聚焦方法未显示出由新型突变体等位基因编码的AAT蛋白，表现为无效。我们将这些等位基因称为PI * S-plus，是因为S变体与另一种赋予该等位基因更具侵略性特征的变体阶段化。当前数据表明，在AATD中观察到的临床变异性可以通过其他遗传变异来解释，例如SERPINA1中的双顺式作用变异基因。应考虑在PI * S等位基因中组合存在其他未揭示的变体，以改善患者的遗传诊断。