Alpha 1-antitrypsin deficiency

A 39-year-old female patient, an ex-smoker with an 8-pack-year smoking history and severe pulmonary emphysema of early onset, received a diagnosis of [[alpha].sub.1]-antitrypsin (AAT) deficiency and proved to be a carrier of a new deficient variant, YBARCELONA, derived from the normal MI variant with two substitutions: one in exon III and the other in exon V. AAT genotype of eight members of the same family and study of lung function of the index ease and family members at baseline and after 6 years of follow-up were performed. Five subjects were PiYM, with intermediate serum AAT concentrations and normal pulmonary function. No changes were observed over 6 years in pulmonary function of the PiYM patients who were nonsmokers; however, the PiYY index ease presented worsening of pulmonary function with FE[V.sub.1] of 33%. The heterozygotes PiYM have AAT concentrations similar to the PiMZ and, at 6 years, the nonsmokers presented no worsening in pulmonary function. The risk associated with this variant in its heterozygous form may be similar to that described for PiMZ.

Key words: [[alpha].sub.1]-antitrypsin deficiency; pulmonary emphysema; YBARCELONA

Abbreviation: AAT = [[alpha].sub.1]-antitrypsin

**********

Severe [[alpha].sub.1]-antitrypsin (AAT) deficiency is a co-dominant autosomal hereditary disorder that manifests clinically as the appearance of pulmonary emphysema at young ages, particularly in smokers. In general, severe AAT deficiency is associated with detection in serum of the PiZZ homozygote phenotype, although other, less frequent alleles, associated with a decrease in serum concentrations of the protein, have also been described.

CASE REPORT

The index case is a female patient; at the time of diagnosis, she was 39 years old, an ex-smoker with an 8-pack-year smoking history, with pulmonary emphysema (FE[V.sub.1] of 920 mL or 38% predicted, and transfer factor for carbon monoxide of 58% predicted), and serum AAT concentrations of 6.6 [micro]mol/L. A phenotype determination at our center failed to show the Z band. Genomic analysis of the AAT gene showed it to present two substitutions from the normal Mi genotype (Va1213): a transversion from GAT to GTT in exon III of the codon for residue 256, which resulted in a change from amino acid Asp256 to Val256, and a transversion from CCC to CAC in exon V of the codon for residue 391, which resulted in a change from amino acid Pro391 to His391. This new deficient variant had not been described previously and was named YBARCELONA. (1)

After diagnosis, respiratory function tests were carried out in both the index case and the other eight members of the family. Serum AAT concentrations were determined by immunonephelometry. The AAT proteinase inhibitor phenotype was determined by isoelectrofocusing technique in polyacrylamide gel as previously described. (2,3) Analysis of the AAT gene was later performed by polymerase chain reaction techniques and DNA sequencing with the technique described previously. (4) Eight primers were synthesized, in accordance with the gene sequence determined by Long et al, (5) to perform amplification of exons II-IV of the AAT gene. Amplification was carried out in a thermocycler (PCB System 9600; Perkin-Elmer Cetus; Norway, CT). The product obtained from amplification of exons II, III, IV, and V was visualized by electrophoresis in 1.5% agarose. Direct amplified DNA sequencing was performed using a nonradioactive cyclic technique (Taq DyeDeoxy Therminator kit; Perkin-Elmer Cetus) following the instructions of the manufacturer. (1)

Serum AAT concentrations of each relative studied and respiratory function test values at baseline are detailed in Table 1. Five members of the family were carriers of the YBARCELONA allele in heterozygote form; serum AAT concentrations in heterozygote individuals were intermediate and similar to those described for heterozygote carriers of the Z gene, oscillating between 14.2 [micro]mol/L and 21.4 [micro]mol/L.

The family members who were PiYM were nonsmokers, except for one brother with an accumulated tobacco consumption of only 5 pack-years, and they were asymptomatic with normal spirometric results. After 6 years of follow-up, pulmonary function of the index case had deteriorated: FE[V.sub.1] of 793 mL (33% predicted). Her relatives remained asymptomatic, and spirometric values were within normal limits. These data are summarized in Table 2.

DISCUSSION

Severe AAT deficiency is a co-dominant autosomal hereditary disorder that manifests clinically as the appearance of pulmonary emphysema at young ages, particularly in smokers. (6) The AAT gene is located in chromosome 14 and consists of seven exons, four of which (II, III, IV, and V) codify this protein. AAT has wide polymorphism; > 75 variants have been described, most of which are differentiated by a change in one polypeptide chain amino acid and denominated according to their mobility in electrophoresis gel. (7) The most frequent variants are M (considered normal) and S and Z, which are considered to be deficient variants. (7) In general, severe AAT deficiency is associated with detection in serum of the PiZZ homozygote phenotype, although other, less frequent alleles, associated with a decrease in serum concentrations of the protein, have also been described. (8)

The PIYBARCELONA phenotype in its homozygote form causes severe AAT deficiency with very low serum AAT concentrations and which is clinically indistinguishable from the PiZZ homozygote form. The patient identified had severe pulmonary emphysema of early onset despite having smoked only 8 packs-years. The severity of the lung damage cannot be explained by the smoking consumption and suggests that the PIYBARCELONA is, at least in smokers, a risk factor for the development of emphysema.

The heterozygote carriers of this new deficient variant presented intermediate serum AAT concentrations and pulmonary function measured by spirometry, static pulmonary volumes, and carbon monoxide diffusion within normal limits. After 6 years of follow-up, pulmonary function in the index case has deteriorated slightly; however, three heterozygote relatives maintain unaltered pulmonary function, probably favored by their being nonsmokers. We cannot evaluate the importance of being a heterozygote carrier of the Y variant, but the resemblance of the homozygote form to the PiZZ phenotype and plasma concentrations similar to those of PiMZ heterozygote individuals lead us to believe that these carriers may have a risk for lung disease similar to that of PiMZ subjects. In this respect, a recent study (9) estimated the relative risk of having COPD to be 1.5 for carriers of the PiMZ phenotype vs carriers of the normal PiMM phenotype.

We consider it of interest to detect family carriers of heterozygous forms of these lesser known deficient variants to prevent them from smoking or stimulate them to stop, thereby avoiding the early onset of lung disease; however, it is important to have a reference laboratory for analysis of the AAT genotype in patients with nonconclusive results from isoelectrofocusing analysis. (10,11) Consequently, it will be possible to identify unknown AAT variants. Furthermore, prospective follow-up should be made of eases and carriers of these less frequent deficient variants to better understand the natural history of AAT deficiency. To this end, national (12,13) and international (14) registries must permit sufficient experience to accumulate so that the evolution of these patients may be studied.

REFERENCES

(1) Jardi R, Rodriguez-Frias F, Miravitlles M, et al. Identification and molecular characterization of the new [alpha]-1-antitrypsin deficient allele PI Ybarcelona (Asp256 to Val and Pro391 to His). Mutation in brief no. 174. Hum Mutat 1998; 12:213. Available at: http://interscience.wiley.com. Accessed March 24, 2003

(2) Vidal R, Miravitlles M, Torrella M, et al. Estudio de la frecuencia de los diferentes fenotipos de alfa-1-antitripsina en la poblacion de Barcelona. Med Clin (Bare) 1996; 107:211214

(3) Weidinger S, Jahn W, Cujnik F, et al. [[alpha].sub.1]-Antitrypsin: evidence of fifth PIM subtype and a new deficiency allele P I*Z Augsburg. Hum Genet 1985; 71:27-29

(4) Rodriguez F, Buti M, Jardi R, et al. Hepatitis B virus infection: precore mutants and its relation to viral genotypes and core mutations. Hepatology 1995; 22:1641-1647

(5) Long G, Chandra T, Woo S, et al. Complete sequence of the eDNA for human [alpha]-1-antitrypsin and the gene for S variant. Biochemistry 1984; 23:4828-4837

(6) Pierce JA. Antitrypsin and emphysema: perspective and prospects. JAMA 1988; 259:2890-2895

(7) Crystal RG, Brantly ML, Hubbard RC, et al. The [[alpha].sub.1]-antitrypsin gene and its mutations: clinical consequences and strategies for therapy. Chest 1989; 95:196-208

(8) Jardi R, Rodriguez-Frias F, Casas F, et al. Caracterizacion molecular de 2 variantes deficitarias de la alfa-1-antitripsina: PI Mpalermo y PI Plovel. Med Clin (Barc) 1997; 109:463-466

(9) Dahl M, Tybjarg-Hansen A, Lange P, et al. Change in lung function and morbidity from chronic obstructive pulmonary disease in [alpha]-l-antitrypsin MZ heterozygotes: a longitudinal study of the general population. Ann Intern Med 2002; 136:270-279

(10) Campbell EJ. [[alpha].sub.1]-Antitrypsin deficiency: incidence and detection program. Respir Med 2000; (Suppl C):S18-S21

(11) Rodriguez F, Jardi R, Costa X, et al. Rapid screening for [[alpha].sub.1]-antitrypsin deficiency in patients with chronic obstructive pulmonary disease using dried blood specimens. Am J Respir Crit Care Med 2002; 166:814-817

(12) Miravitlles M, Vidal R, Barros-Tizon JC, et al. Usefulness of a national registry of [[alpha].sub.1]-antitrypsin deficiency: the Spanish experience. Respir Med 1998; 92:1181-1187

(13) Miravitlles M, Vidal R, Barros-Tizon JC, et al. Estado actual del tratamiento sustitutivo en el enfisema congenito por deficit de alfa-l-antitripsina. Arch Bronconeumol 1999; 35: 446-454

(14) Wencker M, for the International Registry of Alpha-1-antitripsin Deficiency. New formation of the International Registry on Alpha-1-Antitrypsin Deficiency as a joint database of multiple national registries [abstract]. Eur Respir J 1998; 12(suppl 28):382s

* From the Department of Pneumology (Drs. Miravitlles, Vila, and de la Roza), Clinical Institute of Pneumology and Thoracic Surgery, Hospital Clinic (IDIBAPS), Barcelona; and Departments of Biochemistry (Drs. Jardi and Rodriguez-Frias) and Pneumology (Dr. Vidal), Hospital Universitari Vail d'Hebron, Barcelona, Spain.

This study was funded in part by the Fundacio La Marato TV3. Dr. Vila received a "Becario SEPAR" 1998-1999 grant from the Sociedad Espanola de Neumologia y de Cirugia toracica, and a grant from the Societat Catalana de Pneumologia 1999.

Manuscript received November 12, 2002; revision accepted January 27, 2003.

Correspondence to: Marc Miravitlles, MD, Department of Pneumology, Hospital Clinic i Provincial, C/Villarroel 170 (esc 2, planta 3), E-08036 Barcelona, Spain; e-mail: marcm@separ.es

COPYRIGHT 2003 American College of Chest Physicians
COPYRIGHT 2003 Gale Group