Researchers from Washington University School of Medicine in St Louis, US, are the first to discover a gene linked to itching. The findings, published in the journal Nature last week, may lead to a targeted drug treatment for people affected by chronic itching; a symptom associated with skin disorders such as eczema and kidney or liver diseases, as well as a common side-effect of drugs such as morphine.
The discovery was made by chance when the researchers, who were principally studying genes linked to pain, discovered that mice bred to lack the so-called gasterin-releasing peptide receptor (GRPR) gene, scratched less than normal mice when exposed to 'itchy stimuli'.
'The research was a little disappointing at first', admits Dr Zhou-Feng Chen, who lead the research, 'the knockout mice seemed to have the same reactions to painful stimuli as normal mice', he said.
Traditionally researchers have believed that itching was just a milder version of pain, but the finding that mice lacking GRPR itch less, yet have normal reactions to pain, indicates that itching may be regulated by a completely separate set of genes.
This finding is fundamental to the development of targeted drugs for itch relief, says Chen: 'It suggests that drugs can be used to suppress the itch sensation without affecting the pain sensation', he told the BBC, adding that 'pain can be an important protective cue that warns of danger'.
To further test the theory that GRPR is linked to itching, the researchers injected the GRPR lacking mice with a substance which stimulated the gene, to see if they began scratching. Consistent with the theory, 'the mice started scratching themselves as if they had a bad itch', said the researchers.
A closer look at the itching behaviour in a group of normal mice versus a group of GRPR lacking mice revealed that the GRPR lacking mice were not completely immune to all itching stimuli. This suggests that GRPR may not be the only 'itching gene'. 'The fact that the knockout mice still scratched a little suggests that there are additional itch receptors', Chen explained.
Previous research linking the GRPR gene to tumour growth has resulted in the development of a number of agents aimed at blocking tumour activity. 'Now researchers can study the effect of these agents on the itch sensation and possibly move that research to clinical applications fairly soon' Chen concluded.