Alpha-1-Antitrypsin Deficiency

A recent terrific review on Alpha-1-Antitrypsin (A1AT) Deficiency: P Strnad et al. NEJM 2020; 382: 1443-55

Background:

  • 95% of A1AT deficiency is due to homozygosity for the Z allele; prevalence of 1 in 2000 in those of European descent.
  • A1AT protects the lung tissue against attack by the enzyme neutrophil elastase.
  • The presence of A1AT genetic variants suggests that these mutations may confer a selective advantage, perhaps by amplifying the inflammatory response to invasive respiratory/gastrointestinal infections.

Pathophysiology/Clinical Features:

  • Table 1 lists the key alleles/mutations associated with A1AT deficiency -17 deficiency/null listed including: F, I, Iners, King’s, M-malton, M-procida, Pittsburgh, Queen’s, S, S-iyama, Z, QO-bellingham, QO-granitefalls, QO-hongkong
  • S allele deficiency often results in disease (emphysema, cirrhosis) in the setting of SZ heterozygotes.  The disease is typically less severe than in ZZ disease.  This allele is the most common deficiency variant (1 in 5 in Southern Europe, 1 in 30 in U.S.)
  • Z allele deficiency is the most common severe deficiency variant.  Carrier frequency: 1 in 27 persons in Northern Europe, 1 in 83 in the U.S. It is NOT seen in China, Japan, Korea, Malaysia, or Northern and Western Africa.

PI ZZ Genotype:

  • 73% of infants with PI ZZ genotype had elevated ALT level in the 1st 12 months of life
  • Cholestatic jaundice noted in 10% of infant; 15% of these infants progress to juvenile cirrhosis
  • Only 15% with abnormal ALT values by 12 years of age
  • 35% of adults with ZZ genotype show clinically-significant liver fibrosis. Risk factors for advanced fibrosis: male gender, metabolic syndrome/obesity, and alcohol consumption.

Lung Disease Due to A1AT Deficiency:

  • The clinical features of lung disease due to A1AT deficiency are “mainly indistinguishable from those of nonhereditary emphysema…this is partly why severe A1AT deficiency remains undiagnosed in approximately 90% of case, with an interval of 5 to 7 years from the onset of symptoms to diagnosis.”  When the diagnosis is late, lung disease has become irreversible.
  • Early diagnosis allows lifestyle changes (eg. smoking cessation), reduction in occupational risks, and access to therapies.

MZ Phenotype:

PI MZ genotype is more susceptible to multiple disorders, including a predisposition to COPD (at least among smokers) with odds ratio of 1.4.  Other conditions with increased risk: NAFLD-related cirrhosis (OR 3-7), Alcoholic cirrhosis, and CF-associated liver disease

Treatment:

  • Smoking cessation
  • Plasma-purified A1AT infusions.  “Randomized, controlled trials have focused on decreased loss of lung density as the primary efficacy outcome;” however, augmentation therapy has not been to shown to effect other measures, “such as FEV1, quality of life, or exacerbation of COPD.”

Related blog posts:

Also, this study was previously alluded to by this blog, but now is in print:

Briefly noted: X Lu et al. SARS-CoV-2 Infection in Children (NEJM 2020; 382: 1663-5). In 171 Chinese children with confirmed SARS-CoV-2 infection, 41.5% had fever during illness; 27 (15.8%) had no symptoms of infection or radiographic findings. Three required ICU/ventilator support; all had coexisting conditions.  One 10 month old child with intussusception died.

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