Prothrombin mutation G20210A information from Michael Wosnick

A bit that I gleaned about Prothrombin mutation G20210A for those that asked

The Factor II, prothrombin G20210A mutation is a common genetic risk factor for thrombosis and is associated with elevated prothrombin levels. Prothrombin is another of the cascade steps in the blood clotting system. The G20210A mutation causes elevated plasma prothrombin levels, which in turn leads to increased rates of thrombin generation, and an increase in the risk for a thrombotic event due to the potential for excessive growth of fibrin clots.

The Factor II (prothrombin) mutation is in fact the second most common genetic defect for inherited thrombosis, with Factor V Leiden being the most common. It is an autosomal dominant disorder, with heterozygotes being at a 3- to 11-fold greater risk for thrombosis in both men and women and for all age groups. Although homozygosity is rare, inheritance of two 20210A alleles would increase the risk for developing thrombosis.

The 20210A allele of the prothrombin gene is frequently co-inherited in Factor V Leiden carriers. If a patient is heterozygous for both the prothrombin G20210A and the Factor V Leiden mutation, the combined heterozygosity leads to an earlier onset of thrombosis and tends to be more severe than single-gene defects.

Interestingly, the genetic variant (G20210A) is found in what is referred to as the 3' untranslated region of the Factor II (prothrombin) gene. This variant, a G-to-A substitution at nucleotide position 20210 (G20210A) is associated with increased prothrombin levels. This is quite a different type of mutation than I have described previously for FVL. In FVL there is a single point mutation in the DNA which changes an amino acid in the FVL protein itself. This tiny change in the FVL protein makes the FVL protein a bit less susceptible to being cleaved by APC/Protein S and hence leads to APC resistance.

In the case of the Prothrombin G20210A mutation, the single point mutation is not in the so-called "coding" part of the gene at all. There is no change in the amino acid composition of the Prothrombin protein. It is normal. What is changed is the amount of the protein. The mutation is in a part of the gene that may confer some added stability to the gene itself, or otherwise control the rate at which the Prothrombin is made, or in some other way lead to increased amounts of normal Prothrombin protein.

Just one more elegant example of how complicated the system is, and how many opportunities there are for things to go wrong....

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