Alpha-1 Antitrypsin Phenotype

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Your phenotype or genotype are basically the letters given to the two alleles that make up your Alpha-1 gene. Your phenotype or genotype (e.g. ZZ, MZ, MS, etc.) is important because it can give you a general idea of how at risk you are.

Phenotypes and genotypes of Alpha-1 are reported as letters of the alphabet. These letter assignments were first made when starch gel electrophoresis was the common technique used for testing phenotypes. In this system, the phenotype was determined by how fast the AAT protein moved in a gel. The system was designed so the normal protein moved about halfway up the gel and, therefore, the normal protein was assigned a letter from the middle of the alphabet: M. The most common deficient AAT protein moved hardly at all and was assigned the letter Z.

As more and more individuals have been tested, more and more types of AAT have been found. Each of these types is called an allele. With more than 100 different alleles identified, scientists long ago ran out of letters of the alphabet and resorted to naming them based on the city in which the discovery was made. Thus, for example, one rare deficient gene has been labeled MPittsburgh. There are also at least four variations of the normal AAT gene labeled M1, M2, M3, and M4. Not all alleles result in disease or in deficiency. In fact, most non-M alleles cause no problems whatsoever. Many, however, do cause lower than normal levels of AAT in the blood and put people at increased risk of Alpha-1 related disease.

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