Scientists have identified gene mutations responsible for a psychiatric disorder that causes people to compulsively pull their own hair.
Trichotillomania causes sufferers to pull their hair out
Trichotillomania is often accompanied by other symptoms, such as anxiety, depression, obsessive compulsive disorder or Tourette's syndrome.
People with the disorder may have hair loss or bald patches, but often mask their habit.
The Duke University study appears in the journal Molecular Psychiatry.
The researchers focused on a gene called SLITKR1, as it had previously been linked to Tourette's.
They found two mutant versions of the gene were more common in trichotillomania patients.
The mutations were found to account for only a small percentage of cases. However, the team believe the findings are significant because they suggest the condition can have a biological basis.
Lead researcher Dr Stephan Züchner said "Society still holds negative perceptions about psychiatric conditions such as trichotillomania.
"But, if we can show they have a genetic origin, we can improve diagnosis, develop new therapies and reduce the stereotypes associated with mental illness."
Currently, there is no specific treatment for trichotillomania, although it is sometimes successfully managed with drugs used for depression and anxiety disorders.
The Duke team studied 44 families with one or more members who had trichotillomania.
They found the key mutations were found in individuals with the condition, but not in unaffected family members.
The SLITRK1 gene is involved in forming connections between brain cells.
The researchers suspect the mutant versions cause brain cells to develop faulty connections - and that this faulty "wiring" produces the urge to pull one's hair.
Dr Allison Ashley-Koch, who also worked on the study, said numerous other genes were likely to contribute to the condition.
She said: "The SLITRK1 gene could be among many other genes that are likely interact with each other and environmental factors to trigger trichotillomania and other psychiatric conditions.
"Such discoveries could open the door for genetic testing, which is completely unheard of in the field of psychiatry."
Dr Rob Wilson, of the Priory Hospital, north London, is an expert in Obsessive Compulsive Disorder, to which trichotillomania is closely related.
He said: "Trichotillomania can be a distressing problem, and indeed some people will feel that their feelings of shame will be reduced by the suggestion that it has a genetic component.
"However, most contemporary psychiatrists and psychologists already accept that psychiatric problems have multiple contributing factors.
"We need much more widespread education and normalising of 'psychiatric' problems so that sufferers don't feel blamed or ashamed - even without a genetic explanation."
Dr Wilson said cognitive behaviour therapy had shown promise in treating the condition.
It is thought trichotillomania may affect up to 5% of the population.