Some evolutionary mutations to human genes have been cause by the ability of ancient retroviruses to insert themselves (randomly) into our genes. One such retrovirus is HK2 – It’s activity was relatively recent (250,000 years) and it is only present in 5 – 10% of humans, inserted into the RASGRF2 gene, which is part of the Dopamine release pathway – the reward feedback circuit.
Two studies communicated today, show that
(a) those who contracted HIV through IV drug use are 2.5 times more likely to have the HK2 mutation than those who contracted HIV through sex.
(b) those who contracted Hepatitis C through IV drug use were 3.6 times more likely to have the HK2 mutation to RASGRF2 than those who contracted Hep C in other ways.
Then, to establish whether the clear implication that addictive behaviour is associated with this HK2 on RASGRF2 mutation, researchers then took normal human brain cells in vitro, and precisely duplicated the mutation. Sure enough the effect was to increase Dopamine expression in the cells, confirming that the reward pathway would be affected by that mutation.