A possible "Achilles heel" for chemical weapons has been found.
Drugs to protect against a nerve-gas attack are a distant goal
Scientists have discovered how organophosphate chemicals act on nerves, raising new possibilities for developing antidotes.
The research adds weight to the argument that genetics may play a role in human susceptibility to organophosphates.
The class of chemicals includes household pesticides as well as deadly nerve gases like sarin.
Experiments in mice show organophosphate nerve agents target a key enzyme.
Genetically altered rodents with low levels of the enzyme were more sensitive to the chemicals.
The mice were more likely to die or show symptoms such as hyperactivity when exposed to high doses of organophosphates.
Organophosphates, which are used in sheep dip, have been linked to excessive tiredness, headaches, limb pains, disturbed sleep, poor concentration, mood changes, and suicidal thoughts.
The chemicals are also at the centre of controversy over the mysterious illness suffered by veterans of the 1991 Gulf War.
Commenting on the research, by a team in California, Alison Craig, of the UK campaign group Pesticide Action Network, said: "Some people are more susceptible than others to organophosphates.
"The accepted idea at the moment is about 10 times but it can sometimes be much higher."
The enzyme studied, which is called neuropathy target esterase, is involved in neural development.
It is the target for selected organophosphorus pesticides and chemical warfare agents.
Humans as well as mice have a gene for the enzyme, raising the possibility of developing some sort of treatment for pesticide poisoning or chemical weapon attacks.
The research, carried out at the Salk Institute, La Jolla, is published in the online edition of the journal Nature Genetics.