Inherited Chronic Obstructive Pulmonary Disease: New Selective-Sequencing Workup for α1-Antitrypsin Deficiency Identifies 2 Previously Unidentified Null Alleles

Abstract

AbstractBackground: α1-Antitrypsin (α1AT) deficiency predisposes individuals to chronic obstructive pulmonary disease (COPD) and/or liver disease. Phenotyping of the protein by isoelectric focusing is often used to characterize α1AT deficiency, but this method may lead to misdiagnosis (e.g., by missing null alleles). We evaluated a workup that included direct sequencing of the relevant parts of the gene encoding α1AT, SERPINA1 [serpin peptidase inhibitor, clade A (alpha-1 antiproteinase, antitrypsin), member 1], for patients with α1AT concentrations ≤1.0 g/L.Methods: During a 5-year period, we identified 66 patients with α1AT concentrations ≤1.0 g/L and amplified and sequenced exons 2, 3, and 5 of the α1AT gene in these patients. To ensure that no relevant genotypes were missed, we sequenced the same exons in 48 individuals with α1AT concentrations between 1.0 and 1.5 g/L.Results: Sequence analysis revealed 18 patients with combinations of disease-associated α1AT alleles: 8 homozygous for the deficient Z allele and 10 compound heterozygotes for various deficient or null alleles. We identified and named 2 new null alleles, Q0soest (Thr102→delA, which produces a TGA stop signal at codon 112) and Q0amersfoort (Tyr160→stop). No relevant disease-associated allele combinations were missed at a 1.0-g/L threshold.Conclusions: Up to 22% of the alleles in disease-associated α1AT allele combinations may be missed by conventional methods. Genotyping by direct sequencing of samples from patients with α1AT concentrations ≤1.0 g/L detected these alleles and identified 2 new null alleles.