Identification and distribution of rare and new mutations of Alpha-1-antitrypsin in Germany

Rational: Mutations in the SERPINA-1 gene encoding the alpha-1-antitrypsin (AAT) antiprotease are a risk factor for the development of a chronic obstructive pulmonary disease (COPD). The Z- and the S-Allele are the most frequent mutations that lead to AAT-deficiency. Besides these mutations, numerous alleles have been identified, that lead to AAT-deficiency. The aim of this study was the identification of patients with rare or unknown mutations from a AAT-screening program. Methods: Individuals with a suspected AAT-deficiency were genotyped by PCR-analysis and isoelectric focusing (IEF) of serum. In individuals with low serum levels and the absence of the S or the Z allele, we performed exon sequencing of the 3 non-coding (Exon Ia-c) and 4 coding exons. To identify rare and unknown mutations, we compared the patients sequence with a reference sequence and all published rare mutations. Results: Out of 16180 analyzed individuals 98,6 % could be identified by PCR-analysis and IEF. We analyzed 1,4 % by exon sequencing and found 25 new mutations. Out of the 237 sequenced people 34% were heterozygous for PiZ plus a rare at risk mutation and 5% had a combination of PiZ and Q0. 13,5 % carried a rare base allele and neither Z or Q0 and 5,3% had a combination of PiZ and a rare base allele. Among the new mutations we found 5 potential stop mutations. The most common rare at risk mutations we found were M-Heerlen (18%) followed by M-Procida (9,5%). Conclusion: Allel-specific PCR and isoelectric focusing are proven and reliable methods to diagnose AAT-deficient patients. Genomic sequencing and subsequent genetic analysis are the most powerful additions to identifiy rare and unknown mutations.