What is Factor V Leiden?
Factor V Leiden is an alternative form of Factor V caused by a small mutation in the factor V gene. First, I will take you through some basic genetics to help you understand this. If you have no knowledge of genetics, this may seem complex, but I will explain this as simply as possible.
Genetics of factor V Leiden
- Factor V is a protein
- All proteins are made up of a string of amino acids. Factor V has 2224 amino acids.
- Factor V is made in the liver and released into the blood.
Assembling the protein
How does the liver know to put the amino acids in the correct order when it makes factor V? The information comes from the factor V gene in the DNA in the cell’s nucleus.
DNA carries the blueprint for all the proteins in your body. It comprises millions of structures called bases joined in a long chain. DNA has only four different types of bases: adenine, cytosine, guanine and thymine. They are usually referred to by their first letters, ACGT.
The factor V gene is the piece of DNA that carries the information to make factor V.
If you went to a database to look at the factor V gene, you would see a series of letters.
This is the start of the factor V sequence – ATGTTCCCAGGCTGCCCACGCCTCT
This sequence of DNA looks relatively meaningless, but the cell can interpret this and convert it to a sequence of amino acids.
Each three bases codes for an amino acid. For example, ATG = Methionine, TTC = Phenylalanine, CCA = Proline. The cell assembles the amino acids in the correct order in ribosomes. Finally, the complete protein is released into the circulation.
Factor V Leiden is due to a point mutation
A point mutation occurs when one of the bases in the DNA sequence is altered. In Factor V Leiden, the point mutation occurs at the position of amino acid number 506. The mutation is due to the change in a single base from a G to an A in the DNA sequence. The amino acid at position 506 usually is arginine, but in Factor V Leiden, glutamine replaces the arginine residue.
What does the mutation do?
In my last post, we looked at how activated protein C cut up the factor V molecule and stopped it from working. The scissors chopped factor V at position 506. However, in factor V Leiden, the amino acid at position 506 is now glutamine, and the scissors won’t work at that site. This means that the factor V activity is not switched off as quickly, and clotting can continue for longer than expected.
Factor V Leiden works the same as standard Factor V and accelerates clotting like petrol on the fire but is broken down more slowly, and the fire burns for longer. This delayed inactivation is the reason factor V Leiden increases the risk of clotting.
My next post will discuss how having Factor V Leiden affects you.
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