Inherited Chronic Obstructive Pulmonary Disease: New Selective-Sequencing Workup for 1-Antitrypsin Deficiency Identifies 2 Previously Unidentified Null Alleles

disposes individuals to chronic obstructive pulmonary disease (COPD) and/or liver disease. Phenotyping of the protein by isoelectric focusing is often used to char-acterize 1AT deficiency, but this method may lead to misdiagnosis (e.g., by missing null alleles). We evalu-ated a workup that included direct sequencing of the relevant parts of the gene encoding 1AT, SERPINA1 [serpin peptidase inhibitor, clade A (alpha-1 antipro-teinase, antitrypsin), member 1], for patients with 1AT concentrations1.0 g/L. METHODS: During a 5-year period, we identified 66 pa-tients with 1AT concentrations 1.0 g/L and ampli-fied and sequenced exons 2, 3, and 5 of the 1AT gene in these patients. To ensure that no relevant geno-types were missed, we sequenced the same exons in 48 individuals with 1AT concentrations between 1.0 and 1.5 g/L. RESULTS: Sequence analysis revealed 18 patients with combinations of disease-associated 1AT alleles: 8 homozygous for the deficient Z allele and 10 com-pound heterozygotes for various deficient or null al-leles. We identified and named 2 new null alleles, Q0soest (Thr 1023delA, which produces a TGA stop sig-nal at codon 112) and Q0amersfoort (Tyr 1603stop). No relevant disease-associated allele combinations were missed at a 1.0-g/L threshold. CONCLUSIONS: Up to 22 % of the alleles in disease-asso-ciated1AT allele combinationsmay bemissed by con-ventional methods. Genotyping by direct sequencing of samples from patients with 1AT concentrations 1.0 g/L detected these alleles and identified 2 newnull alleles