Variants of SERPINA1 and the increasing complexity of testing for alpha-1 antitrypsin deficiency

Abstract

Alpha-1 antitrypsin deficiency (AATD) is caused by mutations in the SERPINA1 gene, which encodes the alpha-1 antitrypsin (AAT) protein. Currently, over 200 SERPINA1 variants have been identified, many of which cause the quantitative and/or qualitative changes in AAT responsible for AATD-associated lung and liver disease. The types of these pathogenic mutations are varied, often resulting in misfolding, or truncating of the AAT amino acid sequence, and improvements in sequencing technology are helping to identify known and novel genetic variants. However, due to the diversity and novelty of rare variants, the clinical significance of many is largely unknown. There is, therefore, a lack of guidance on how patients should be monitored and treated when the clinical significance of their variant combination is unclear or variable. Nevertheless, it is important that physicians understand the advantages and disadvantages of the different testing methodologies available to diagnose AATD. Owing to the autosomal inheritance of the genetic mutations responsible for AATD, genetic testing should be offered not only to patients at increased AATD risk (e.g. patients with chronic obstructive pulmonary disease), but also to relatives of those with an abnormal result. Genetic counseling may help patients and family members understand the possible outcomes of testing and the implications for the family. While stress/anxiety can arise from genetic diagnosis or confirmation of carrier status, there can be positive consequences to genetic testing, including improved lifestyle choices, directed medical care, and empowered family planning. As genetic testing technology grows and becomes more popular, testing without physician referral is becoming more prevalent, irrespective of the availability of genetic counseling. Therefore, the Alpha-1 Foundation offers genetic counseling, as well as other support and educational material, for patients with AATD, as well as their families and physicians, to help improve the understanding of potential benefits and consequences of genetic testing.

Keywords: SERPINA1; alpha-1 antitrypsin; alpha-1 antitrypsin deficiency; genetic counseling; rare variants; testing.

Figure 1.

SERPINA1 gene.

Figure 2.

Autosomal inheritance of SERPINA1 alleles. Autosomal inheritance of SERPINA1 alleles if parents are: ‘normal’ and heterozygous (a), ‘normal’ and homozygous (b), both heterozygous (c), and heterozygous and homozygous (d). Only eventualities c and d confer risk of the offspring being severely deficient in AAT (25% and 50% chance, respectively). Estimated worldwide prevalence: MZ, 42,564,136; ZZ, 181,894.