Men who are a flop in bed can now blame their genes, new research suggests.
For the first time, scientists have discovered a confirmed genetic link to erectile dysfunction.
Researchers pinpointed a stretch of DNA where variations made it more difficult for men to perform as expected.
The finger of suspicion points to a gene called SIM1 which could be a target for new impotence treatments.
Lead researcher Dr Eric Jorgenson, from US health service providers Kaiser Permanente, said: "Identifying this SIM1 locus as a risk factor for erectile dysfunction is a big deal because it provides the long sought-after proof that there is a genetic component to the disease.
"Identifying the first genetic risk factor for erectile dysfunction is an exciting discovery because it opens the door for investigations into new, genetic-based therapies."
Besides having a potential influence on men's erections, SIM1 is thought to play a role in brain development.
The scientists carried out the study by analysing the complete genomes, or genetic codes, of more than 36,000 American and 222,000 British men.
A search was made for genetic differences that occurred more often in men with a history of erectile dysfunction.
Variations in the SIM1 locus, the region of DNA containing the SIM1 gene, was associated with a 26 per cent increased risk of impotence.
Erectile dysfunction has a number of known physical causes including hormonal deficiencies and nerve and artery damage.
But despite the effectiveness of treatments such as Viagra, many men cannot be helped.
The scientists believe a genetic "promoter" that turns SIM1 on and off may explain their findings rather than the gene itself.
The research is reported in the journal Proceedings of the National Academy of Sciences.
