A Pro → Leu substitution in codon 369 of the alpha-1-antitrypsin deficiency variant PI MHeerlen

Abstract

The molecular defect has been elucidated in the alpha-1-antitrypsin (PI) gene of a patient with a serum level of only 5 mg/100 ml and a PI M-like phenotype, designated PI MHeerlen. The restriction fragment patterns obtained by probes covering the whole gene and flanking sequences were normal, suggesting no major rearrangements. The nucleotide sequence of the exons, intron/exon junctions, and a part of the promoter region is similar to that of a PI M1(Ala213) gene except for an C----T mutation in codon 369, causing a Pro----Leu substitution. Haplotype analysis and oligonucleotide hybridization studies demonstrated the homozygous state of the mutation in the index case. It is most likely that the Pro369----Leu substitution is responsible for the low serum alpha-1-antitrypsin concentration of the patient because this mutation is solely confined to the PI MHeerlen allele and no other relevant mutations could be revealed. As proline is important for the secondary and tertiary structure of proteins, the mutation may cause an abnormal processing of the nascent polypeptide. The same mutation was observed in two unrelated subjects known to carry a PI allele giving a low serum alpha-1-antitrypsin level.

Molecular characterisation of the defective α1-antitrypsin alleles PI Mwürzburg (Pro369Ser), Mheerlen (Pro369Leu), and Q0lisbon (Thr68lle)

“…We observed the deficiency allele PI Mheerlen described by Hofker et al 16 in heterozygous form, together with the nonexpressing PI Q0granite falls allele, 20 in one of our patients with severe COPD and an extremely low α1AT serum level of 0.7 mM (3.7 mg/dl). 31 The 42-year-old patient had smoked until the age of 36.…”

“…We have observed the PI Mheerlen allele 16 in a COPD patient in combination with the non-expressing allele PI Q0granite falls. 31 The patient was the only affected member of a three-generation family and suffered from rapidly progressive COPD causing his death at the age of 42 years.…”

“…24 We characterise a new defective allele PI Mwürzburg (Pro369Ser) associated with intracellular α1AT accumulation. In addition, we show that the previously identified allele Mheerlen 16 which carries a different amino acid substitution (Pro369Leu) in the same position as Mwürzburg, also causes complete retention of the mutant protein in the ER. In contrast to the complete transport block associated with these two mutations the deficiency allele PI Q0lisbon (Thr68Ile) 25 is shown to be associated with reduced secretion of α1AT from the cell.…”

“…Only a few of the deficiency alleles are also associated with liver disease, among them the most common defective α1AT allele PI Z 14,15 which has an allele frequency of 2% in Northern Europe. Other rare alleles associated with liver dysfunction are PI Mmalton 16,17 and Mduarte. 18 All alleles associated with liver disease show intracellular α1AT accumulation.…”

Simple method for α1-antitrypsin deficiency screening by use of dried blood spot specimens

“…All the a 1 -AT exons (II±IV) were amplified and the PCR products sequenced, as previously described [12]. Analysis of the DNA sequence showed a change from CCC to TCC at codon 369 in exon V. This substitution is characteristic of the heerlen PIM (PIMheerlen) a 1 -AT variant [15]. On the basis of genotyping, the patient was classified as heterozygous PIMMheerlen.…”