Testing and Genetics
Alpha-1 Antitrypsin Deficiency (A1AD) can be detected by a simple blood test that indicates the serum level of Alpha-1 Antitrypsin (AAT). If the serum blood level is low (usually less than 50% of normal), your physician may order other tests that will determine phenotype and / or genotype. Actually, a number of laboratories automatically have further testing done if the blood concentration is below 50% of normal. Specific tests for the various types of Alpha-1 Disease are discussed in the sections on liver, lung and skin disease.
There are two different methods of expressing the blood test results for alpha-1 and this can lead to some confusion among patients. Many of the commercially available standards have an abnormally high normal range (1.5 – 3.0 g/L). Expression as a percent of normal is useful, as this is not dependent upon units and can apply to any normal range. The following is a rough approximation of the ranges / levels and how the two systems of interpretation correlate with each other. To convert from the milligrams per decilitre scale to the grams per litre scale, divide by 100.
|% of Normal||mg/dL||g/L|
80 – 120
106 – 158
1.06 – 1.58
66 – 112
.66 – 1.12
65 – 90
86 – 119
.86 – 1.19
12 – 20
41 – 120
.41 – 1.2
9 – 27
18 – 32
.18 – .32
- Normal average 1.32 grams/litre (g/L) or 25 micro molar (mM).
- Commercial laboratory standards may be inappropriately high (e.g. 1.5-3 g/L)
- mM = micromolar
- mg/dL = milligrams per decilitre
- g/L = grams per litre
Most of the PI variants are associated with a normal concentration of AAT. The normal mean concentration is 1.32 g/L, as determined against purified protein. PI MM individuals usually have plasma concentrations of 80-120% of this mean. Expressed on a molar basis, the normal mean is 25 mM. There is considerable overlap in plasma level between PI types. Generally no further PI typing is carried out when the concentration is above 32 micro molar to ensure identifying any non-MM PI types, as in the Table above. (Some laboratories and institutions have slightly different standards for the various cut-off points.)
PI typing is important because a low level of AAT can also occur for non-genetic reasons, such as in respiratory distress syndrome in newborns, conditions of severe protein loss, liver failure, and during the course of cystic fibrosis Measurement of plasma AAT is not always reliable for the identification of heterozygotes. AAT can show a marked increase (up to four-fold) in a wide range of inflammatory conditions, cancer, and liver disease. Pregnancy and estrogen therapy also produce modest increases.
How to get tested for Alpha-1 Antitrypsin Deficiency in Canada
Testing for Alpha-1 Antitrypsin Deficiency: Measurement of AAT level is the first step.
The diagnosis of A1AD relies on demonstration of low plasma concentration of AAT, followed by (when low) either observation of a deficient variant of the protein AAT by protease inhibitor (PI) typing, genotyping or detection of mutations in both copies of the gene SERPINA1, which encodes AAT. PI*Z is the most common deficiency allele. Ninety-five percent of A1AD results from the presence of two Z alleles (PIZZ).
Phenotyping or genotyping are usually done only when previously measured AAT is 1.5 g/L or less (or below the normal mean for the testing laboratory), OR the patient is a first-degree relative/spouse of a known AAT deficient subject. A request for PI typing when ordered separately should specify the previous result or the subject’s name and relationship for phenotyping to proceed.
Confirmatory Testing for Alpha-1 Antitrypsin Deficiency in Canada
The following information about testing applies in all provinces except Alberta.
Testing serum levels of Alpha-1 Antitrypsin (AAT) continues to be easily available throughout Canada. Following a low serum AAT result, confirmatory testing should be carried out to determine if the low level is the result of a genetic abnormality. In Canada there are six validated laboratories that can carry out the confirmatory testing. They are located at St. Paul’s Hospital in Vancouver, the Royal Victoria Hospital and CHUM – Hôpital Notre-Dame, both in Montreal, and Credit Valley Hospital in Mississauga. Through collaboration, these four laboratories have developed a comprehensive testing algorithm to confirm or rule out the diagnosis of Alpha-1 Antitrypsin deficiency. The AAT serum level threshold for confirmatory testing used by these four laboratories is 1.15 g/L. Individuals with a serum level less than 1.15 g/L would be processed for confirmatory testing. Alberta is the only exception where testing is done in southern Alberta by Calgary Laboratory Services and in northern Alberta at DynaLIFEDx.
Individuals with serum level above this threshold would not normally proceed through the testing algorithm unless there is a strong suspicion of alpha-1 deficiency. This information should be outlined in the requisition form by the physician and provided to the testing laboratories. In a stepwise fashion, the laboratory will run a series of tests to characterize the individual’s Alpha-1 genetics. This includes a genotyping assay to identify the presence of the common deficiency alleles, followed by phenotyping (isoelectric focusing) and finally, if required, full gene sequencing of the individual’s alpha-1 gene.
Currently there is no cost to be tested. The physician simply needs to complete the requisition form for alpha-1 genetic testing, and have one tube of the individual’s blood and one tube of frozen serum shipped to one of the testing labs. Following analysis, a detailed response is provided to the physician within 30 days that outlines the results of the tests.
AlphaKit Blood Drop Cards
Another option is the AlphaKit blood drop cards. Grifols, the makers of Prolastin®-C, have developed and received government approval for an Alpha-1 test kit. Once the physician has determined that the patient’s AAT level is low (1.5 g/L or less, or below the normal mean for the testing laboratory) he or she can call the bilingual call-centre at 1-877-3 ALPHA1 (1-877-325-7421), to order a test kit. Once your doctor receives the kit, three dry blood drop samples are taken then mailed to a testing facility at the University of Florida. Within two to three weeks the physician will receive the results through the mail.
It is important to understand that while the patient’s personal information and test results will only be divulged to their physician, unlike test kits that were available a few years ago, these kits are not anonymous. Since the kits and results can only be sent to your physician, he or she will place your results in your medical file (please see our web page on “Ethical Issues” to learn about the ethical implications of this procedure).
Grifols provides the specimen collection kit (including a postage paid mailer pre-addressed to the testing facility) and the testing services of the University of Florida Alpha1 Lab at no charge. This program is being managed and operated for Grifols by third parties; Grifols will not have access to anyone’s test results.
Early detection of Alpha-1 is critically important. Once a patient knows they have Alpha-1 they can make important lifestyle changes and receive treatment from their physician to slow the progression of the disease. The only way to detect Alpha-1 is through testing. We encourage you to take charge of your healthcare, take advantage of this speedy, easy process and contact your physician with this critical information. Whether you have been diagnosed or are awaiting testing, please keep your physician informed. Print this page and bring it with you to your next doctor’s appointment. And please, inform your close blood relatives that testing and diagnosis is now quick, easy and free.
The gene for Alpha-1 Antitrypsin deficiency (A1AD) resides near the end (teolmere) of chromosome 14. At the genetic level, a grossly simplified explanation of A1AD is that it is similar to a spelling mistake on this strand of the individual’s DNA. This ‘spelling mistake’ can be transmitted from parent to child.
As has already been mentioned, A1AD is a genetically transmitted disorder. It is something one is born with and can do nothing about. However, there are varying degrees of disorder depending on what is passed on from parents to children. The range is from normal to severely deficient. MM is normal, ZZ is severely deficient and the others (MZ, MS, SS, SZ, etc) are intermediate. If a child inherits one normal gene and one defective gene, for example MZ or MS, each gene will express its specific protein that can be identified in the blood (co-dominance). In order to inherit full-blown A1AD (usually ZZ), an individual must inherit two defective ZZ genes, one from each parent.
Each parent has two genes for A1AD but can pass on only one to the child. Thus, out of a possible four genes, the child will receive two, one from the mother and one from the father. If both parents have two M (normal) genes, then all their children must also have two M genes. If both parents have two Z (deficient) genes then all their children are destined to have two Z genes. Similarly if one parent is ZZ and the other parent is MM, they, of necessity, must produce children who are all MZ (intermediate level). There are no other possibilities with these genotypes.
Other variations in genetic make-up come into play when the parents are not homozygotes, that is, not MM nor ZZ. The following can result:
- If both parents are MZ, there is a one in four, or 25%, chance that the child will be ZZ, a one in four chance that the child will be MM, and a one in two chance that the child will be MZ.
- If one parent is MM and the other is MZ there is a 50% chance that the child will be MM and 50% chance that the child will be MZ.
- If one parent is MZ and the other is ZZ there is a 50% chance that the child will be MZ and a 50% chance that the child will be ZZ.
While inheriting two ZZ genes means that a person may be predisposed to develop A1AD, it is not a simple cause and effect equation. People who are diagnosed as ZZ have been known to never develop clinical disease. Individuals who inherit only one defective gene are considered to be at little risk for developing A1AD disease, especially if they do not smoke. Individuals who inherit no defective genes are, of course, at no risk for developing AATD or its associated disease.
Note that there are rare deficiency genes that produce NO Alpha-1 Antitrypsin, and the usual inheritance pattern is altered, so that a parent can appear not to be the ‘true’ parent.
To test or not to test, that is the dilemma. Those in favour of testing suggest that knowledge is power and that, with knowledge, one can make appropriate decisions. Early diagnosis can lead to earlier and better treatment; relieve uncertainty; encourage changes in lifestyle that could minimize or even prevent the onset of disease; and allow for planning for the future. Concerns about testing revolve around issues of privacy and whether the individual will be branded as ‘ill’ and discriminated against in insurance and / or employment.
There are many factors to consider: the age of the individual; the implications for other members of the extended family (since Alpha-1 is a genetic disorder); the right of informed consent prior to testing; and possible psycho-social effects of a positive diagnosis for a disorder for which there is currently no cure. Genetic counseling can help concerned individuals come to a decision that is appropriate for them.
The American Alpha-1 Association’s Genetic Counseling Center provides free genetic counseling for patients, families, caregivers and healthcare professionals, including Canadians. They can be reached at 1-800-785-3177.
Individuals who are diagnosed with Alpha-1 need education and information, but they may also need support in dealing with their feelings or with the other social impacts of a genetic diagnosis. Your doctor and nurse can provide information about your medical condition, but the Counseling Center is there to help you deal with the social issues related to Alpha-1.
Before giving you advice the genetic counselor may first ask you about your personal goals, what resources are available in your area, how many family members are involved, and what kind of economic impact Alpha-1 may have on your life. In this way, the advice and information you are given fits your situation. A particular focus on the family can assist affected individuals; parents and extended family members deal with the issues of Alpha-1. All genetic counselors have special training and expertise in discussing the issues of children.