Alpha-1 antitrypsin deficiency

Alpha-1 antitrypsin deficiency (AATD) is a genetic condition in which low levels of the alpha-1 antitrypsin (A1AT) protein predispose affected individuals to hepatic dysfunction and early-onset lung disease.

AATD can present at any age and should be considered in individuals with:

• hepatic dysfunction:
  • neonatal cholestasis with raised liver enzymes; and
  • cirrhosis in adulthood (more common in men);
• lung disease:
  • emphysema (in individuals above 30 years old);
  • bronchiectasis;
  • childhood-onset lung disease (though this is extremely rare); and
  • individuals who smoke or who are exposed to occupational dust; and
• panniculitis (though this is uncommon).

AATD is caused by pathogenic variants in the SERPINA1 gene. SERPINA1 encodes A1AT, a protease inhibitor that protects the lungs from the elastase released by neutrophils.

AATD is inherited in an autosomal codominant manner with three common SERPINA1 alleles:

• M: the most common ‘wild type’ allele, which produces normal levels of A1AT;
• S: produces moderately low levels of A1AT; and
• Z: produces very little A1AT.

The most common genotypes are MM, MS, MZ, SS, SZ and ZZ, with MM being unaffected and ZZ being the most severe. The age of onset and symptoms are highly variable and are dependent on the genotype. The genotype-to-phenotype correlation of AATD is shown below.

• MM: Associated with a normal serum concentration of A1AT and no increased risk of liver or lung disease.
• MS: Not usually associated with an increased risk of disease. May be associated with an offspring risk, depending on the partner’s genotype.
• MZ: Not usually associated with an increased risk of disease. May be associated with an offspring risk, depending on the partner’s genotype.
• SS: Not usually associated with an increased risk of disease. May be associated with an offspring risk, depending on the partner’s genotype.
• SZ: Serum A1AT levels are usually below the protective threshold value, which means that these individuals are at increased risk of developing emphysema and chronic bronchitis, especially if they are smokers. May be associated with an offspring risk, depending on the partner’s genotype.
• ZZ: Individuals with this genotype have serum A1AT levels that are approximately 10%–20% below the norm and are at high risk of developing both lung and liver disease. This genotype is present in 95% of individuals with clinical manifestations of AATD.

AATD is inherited in an autosomal codominant manner, which is similar to autosomal recessive inheritance. It is important to note that 10% of the European population are carriers for the S or Z variant. The parents of most affected individuals are carriers for the condition and therefore have a 25% chance of having another affected child.

Management of individuals with AATD depends on the clinical manifestations that present (such as emphysema or liver cirrhosis). Individuals may require referral to specialist services (respiratory, liver, gastroenterology), depending on the severity of their manifestations.

All patients should be strongly advised to avoid smoking, which greatly accelerates lung disease and significantly reduces life expectancy.

Patients should also be advised against excessive alcohol consumption, which can not only accelerate liver disease, but has been associated with the exacerbation of chronic obstructive pulmonary disease in individuals with AATD.

For clinicians

• GeneReviews: Alpha-1 antitrypsin deficiency
• MedlinePlus: Alpha-1 antitrypsin deficiency
• NHS England: National Genomic Test Directory
• North Bristol NHS Trust: Alpha-1 antitrypsin fact sheet for primary care (PDF, three pages)

References:

• McElvaney GN, Sandhaus RA, Miravitlles M and others. ‘Clinical considerations in individuals with α1-antitrypsin PI*SZ genotype’. European Respiratory Journal 2020: volume 55, issue 6. DOI: 1183/13993003.02410-2019
• Sandford, AJ, Weir TD, Spinelli JJ and others. ‘Z and S mutations of the α1-antitrypsin gene and the risk of chronic obstructive pulmonary disease’. American Journal of Respiratory Cell and Molecular Biology 1999: volume 20, issue 2, pages 287–291. DOI: 1165/ajrcmb.20.2.3177

For patients

• Alpha-1 Foundation
• Asthma + Lung UK: Alpha-1-antitrypsin deficiency