Scientists are a step closer to more effective migraine treatments after finding a genetic fault that causes the crippling headaches.
A team of researchers - including one who suffered from migraines when she was younger - made the breakthrough during a study of two families of sufferers.
They found a common genetic mutation which, when tested on mice, lowered pain thresholds significantly.
It is hoped the findings will lead to a better understanding of what causes migraines, which affect one in four women and one in 12 men in the UK.
"It's our initial glimpse into a black box that we don't yet understand," said Louis Ptacek, lead researcher and professor of neurology at the University of California.
"The need for better treatments is huge," he said. "(This research) put us one step closer to understanding the molecular pathway to pain in migraine.
"As we come to a clearer understanding, we can start thinking about better therapies. Certain molecules might be targets for new drugs."
In the study, scientists found the mutation affects the production of an enzyme that carries out vital functions in the brain and body.
As well as the resulting lower pain threshold, the mutant mice were more susceptible to cortical spreading depression.
This "wave of silence" in the brain is thought to cause the visual sensations that sometimes come before a migraine, such as flickering lights and jagged lines.
Mr Ptacek said that although several drugs can ease the pain felt by sufferers, "they only help some of the patients, some of the time".
"The need for better treatments is huge," he added.
Migraines usually begin in young adults, with 90% of sufferers experiencing the condition before their 40th birthday.
They cause a pulsating or throbbing pain on one side of the head that can last for up to three days, and can also lead to nausea, vomiting and extreme sensitivity to bright light and loud sounds.