Genetic Testing for Alpha-1 Antitrypsin Deficiency
DESCRIPTIONAlpha-1 antitrypsin deficiency (AATD) is an autosomal recessive genetic disorder that results in decreased production of the alpha-1 antitrypsin (AAT) protein, or production of abnormal types of the protein that are functionally deficient. Individuals with AATD, especially smokers, have an increased risk of lung and liver disease. Tests are available to measure serum AAT levels and for AAT protein variant phenotyping. Genetic testing is also available to detect the most common mutations associated with AATD.
Alpha-1 antitrypsin deficiency (AATD) is an autosomal recessive genetic disorder that results in decreased production of the alpha-1 antitrypsin (AAT) protein, or production of abnormal types of the protein that are functionally deficient. Data from screening studies have found the prevalence of AATD in the United States to be between 1 in 2,857 and 1 in 5,097 individuals respectively.
AAT is an acute phase glycoprotein, synthesized primarily in the liver and secreted into the bloodstream. One of the primary functions of the AAT protein is to protect the lungs from damage by the enzyme elastase. Elastase, part of the normal response to injury and inflammation, breaks down proteins and can damage lung tissue if its action is not regulated by AAT. Individuals with AAT deficiency thus have an increased risk of lung disease.
Respiratory disease tends to be more severe and occur sooner (i.e., between age 40 and 50) in individuals with AAT deficiency who smoke cigarettes and/or are exposed to occupational dust or fumes. In non-smokers and individuals without environmental exposure, onset of respiratory disease occurs more commonly in the sixth decade. Childhood-onset lung disease is rare with AATD. AATD is also associated with an increased risk of liver disease, thought to occur due to aggregation of damaged AAT in the liver cells, where the protein is produced. The most common manifestation of liver disease in childhood is jaundice. Adults with AATD-associated liver disease generally present with cirrhosis and fibrosis. Panniculitis is a rare, but well-recognized complication of AAT deficiency. This dermatologic condition is characterized by inflammatory and necrotizing lesions of the skin and subcutaneous tissue.
The primary interventions to prevent or treat symptoms in individuals with AATD involve behavioral change, especially avoiding or quitting cigarette smoking. Smoking is the most important risk factor for the development of emphysema in AATD in individuals who are homozygous for the most severe AAT mutations. In addition, individuals with AATD are advised to avoid other substances that can irritate the lungs e.g., cigarette smoke, dust and workplace chemicals, as well as substances such as alcohol that can cause liver damage. There are also general recommendations to exercise, avoid stress and have a nutritious diet. Furthermore, patients with AATD may be recommended to have earlier or more aggressive treatments for conditions such as asthma outbreaks or acute exacerbations of chronic obstructive pulmonary disease (COPD). One treatment option that is specific to AATD is alpha-1 antitrypsin augmentation. There are commercially available intravenous AAT augmentation products; patients generally receive injections of plasma every 3 to 4 weeks for life. Inhaled AAT augmentation therapy is under development. There is a lack of consensus about the efficacy of augmentation treatment.
Diagnostic Testing for AAT
Several types of tests are available for patients who are suspected of having AATD. A blood test is available that quantifies the total amount of alpha-1 antitrypsin in the blood, detecting decreases in AAT protein levels, but not distinguishing among abnormal protein types. AAT is an acute phase reactant, and levels will be elevated in acute and chronic inflammatory conditions, infections and some cancers, which may cause levels to appear normal in individuals with mild to moderate AAT deficiency. In general, a serum concentration of AAT less than 15-20% of the normal value is highly suggestive of a homozygous alpha-1 antitrypsin mutation.
The alpha-1 phenotype test identifies the type of circulating AAT protein in the blood by isoelectric focusing of the various AAT protein types. Patterns of protein migration in an electric field are evaluated and compared to normal patterns to determine if and what type of abnormal AAT protein may be present.
Genetic testing is also available. Production of AAT is encoded by the SERPINA1 gene which is co-dominant (each gene copy is responsible for producing half of the AAT). Although there are more than 75 sequence variants of the SERPINA1 gene (i.e., 75 possible alleles), only several are common in North America. Approximately 95% of individuals have 2 copies of the normal M allele sequence (MM) and have mean serum concentrations of AAT ranging from 20-53 umol/L. The most common abnormal forms are the Z allele and the S allele. Individuals with 2 copies of the Z allele (ZZ) tend to be most severely affected, with mean serum concentrations of AAT of 2.5 to 7 umol/L and a high risk of COPD. Individuals with genotype SS and heterozygous individuals with genotype MZ have low risk of COPD and moderately lower levels of AAT. Individuals with rarer mutations of the SERPINA1 gene or null alleles may not produce any AAT and are also at high risk.
Genetic testing for AATD can be done with the alpha-1 genotype test. This test uses Polymerase chain reaction (PCR) analysis, or some other type of nucleic acid-based analysis, to identify abnormal alleles of AAT DNA. Currently, genotype tests are only designed to detect the most common mutations i.e. the S and Z alleles.
A common approach to testing for AATD is to initially perform serum quantitation. If the AAT level is found to be low, a follow-up phenotype or genotype test is ordered. Another approach, as exemplified by the Mayo clinic, is to perform serum protein quantification, followed by genotype testing in subjects with clinical suspicion of AATD. If these tests are discordant, phenotype testing is then performed.
An example of a U.S. Food and Drug Administration (FDA)-cleared phenotyping test is the Hydragel 18 alpha-1 antitrypsin isofocusing kit (Sebia Inc., GA). In 2007, this test was cleared for marketing through the 510(k) process. The test is designed for the qualitative detection and identification of the phenotypes of AAT protein.
No FDA-cleared genotyping tests were found. Thus, genotyping is offered as a laboratory-developed test. Clinical laboratories may develop and validate tests in-house (“home-brew”) and market them as a laboratory service; such tests must meet the general regulatory standards of the Clinical Laboratory Improvement Act (CLIA). The laboratory offering the service must be licensed by CLIA for high-complexity testing.
POLICYGenetic testing for alpha-1 antitrypsin deficiency may be considered medically necessary when both of the following conditions are met:
Genetic testing for alpha-1 antitrypsin deficiency is considered investigational in all other situations.
POLICY GUIDELINESAccording to the 2003 joint statement on diagnosis and management of alpha-1 antitrypsin deficiency by the American Thoracic Society/European Respiratory Society, the following features should prompt suspicion by physicians that their patient may be more likely to have AAT deficiency:
AAT deficiency occurs largely in Caucasians. For example, the prevalence in Sweden is approximately 1 in 1,575 and the estimated prevalence in the United States is between 1 in 2,857 and 1 in 5,097.
The following table shows the range of serum levels of alpha-1 antitrypsin by common phenotypes according to the commercial standard milligram per deciliter (mg/dL) and the purified standard micromole (uM). A level of less than 11 uM is generally considered to be associated with an increased risk of clinical disease, but this cut-off may vary according to the specific test used:
Investigative service is defined as the use of any treatment procedure, facility, equipment, drug, device, or supply not yet recognized by certifying boards and/or approving or licensing agencies or published peer review criteria as standard, effective medical practice for the treatment of the condition being treated and as such therefore is not considered medically necessary.
The coverage guidelines outlined in the Medical Policy Manual should not be used in lieu of the Member's specific benefit plan language.
POLICY HISTORY07/19/2012: Approved by Medical Policy Advisory Committee.
08/07/2013: Policy reviewed; no changes.
07/03/2014: Policy reviewed; descripton updated. Policy statement unchanged.
SOURCE(S)Blue Cross Blue Shield Association policy # 2.04.79
CODE REFERENCEThis may not be a comprehensive list of procedure codes applicable to this policy.
The code(s) listed below are ONLY medically necessary if the procedure is performed according to the "Policy" section of this document.