A study on the frequency of the different alpha-1-antitrypsin phenotypes in a population from Barcelona, Spain

BACKGROUND: Severe alpha-1-antitrypsin (AAT) deficiency is caused by homozygous inheritance of gene Z, and is associated with a high risk of developing pulmonary emphysema. Determination of frequencies of different genes associated with the deficiency (especially S and Z) gives a clue to estimate the number of individuals homozygous PiZZ, carrying a high risk for pulmonary disease, in any given population. PATIENTS AND METHODS: Pi phenotypes of 440 healthy individuals were determined by means of isoelectrofocusing in polyacrylamide gel. Seric values of AAT were determined by immunonephelometry. Mean age of participants was 30 years (range 18-49 yrs.). Results are compared with other published series. RESULTS: Distribution of phenotypes was: PiMM 333 individuals (75%), PIMS 84 (19%), PiMZ 14 (3%), PiSS 4 (0.9%), PiM 3 (0.6%), PiMF 1 (0.2%), PiMP 1 (0.2%). The corresponding gene frequencies were Pi*M 87%, Pi*S 10.4%, and Pi*Z 1.5%. Normal values of AAT (phenotype PIMM) established in our laboratory were 116-232 mg/dl (21-41 micromol/l) (mean +/- 2 SD). According to Hardy-Weinberger ecuation, expected frequency of PiZZ individuals in our area would be 225 per milion. CONCLUSIONS: The frequency of Z gen individuals observed in our study is one of the highest in the Iberian Peninsula, but lower than the frequency in nothern Europe. According to these results, AAT deficiency (PiZZ) is not a rare condition in contrast with the small number of patients diagnosed. The gen frequency of the S variant is higher than that of the rest of Europe, and similar to others found in some Spanish populations.