Identification and DNA sequence analysis of 15 new alpha 1-antitrypsin variants, including two PI*Q0 alleles and one...

We have investigated the molecular basis of 15 new alpha 1-antitrypsin (alpha 1AT) variants. Phenotyping by isoelectric focusing (IEF) was used as a screening method to detect alpha 1AT variants at the protein level. Genotyping was then performed by sequence analysis of all coding exons, exon-intron junctions, and the hepatocyte-specific promoter region including exon Ic. Three of these rare variants are alleles of clinical relevance, associated with undetectable or very low serum levels of alpha 1AT:the PI*Q0saarbruecken allele generated by a 1-bp C-nucleotide insertion within a stretch of seven cytosines spanning residues 360-362, resulting in a 3' frameshift and the acquisition of a stop codon at residue 376; a point mutation in the PI*Q0lisbon allele, resulting in a single amino acid substitution Thr68(ACC)-->Ile(ATC); and an in-frame trinucleotide deletion delta Phe51 (TTC) in the highly deficient PI*Mpalermo allele. The remaining 12 alleles are associated with normal alpha 1AT serum levels and are characterized by point mutations causing single amino acid substitutions in all but one case. This exception is a silent mutation, which does not affect the amino acid sequence. The limitation of IEF compared with DNA sequence analysis, for identification of new variants, their generation by mutagenesis, and the clinical relevance of the three deficiency alleles are discussed.