They hope the breakthrough can provide better information about which babies are most at risk of cot death.
The discovery resulted from research into genes thought to be responsible for the rare hereditary neurological disorder hyperekplexia, led by Professor Mark Rees.
Also known as the "startle syndrome", the disorder leaves children with an exaggerated startle reflex and prolonged muscle stiffness.
One of the symptoms is that of the child unintentionally holding their breath for prolonged periods, particularly during sleep, leading to brain damage or cot death.
The researchers at the university's School of Medicine became aware of a mutation in the SLC6A5 gene among several children affected by the condition during their first year, despite previous research which linked a different gene to the disorder.
A spokeswoman for Swansea University, said, "The findings provide further insights into other neurological movement disorders, epilepsy and susceptibility to sudden infant death syndrome."
This may mean that adults and children could now be screened for the mutated genes.
Professor Rees said that prompt medical intervention was essential in such cases.
He also said that the research would not be used to screen babies before birth for the defective gene. Instead it will help parents and medical professionals understand the increased risk of cot death should a child be diagnosed with hyperekplexia.
"Hyperekplexia has an obvious clinical presentation at birth with breath holding and muscular stiffness as a reaction to things like loud noises and running bath water," he said.
"There is evidence that hyperekplexia, because of the muscle stiffness and breath-holding, can potentially cause SIDS [sudden infant death syndrome]."
"There are no implications for pre-natal screening, but presentation of the symptoms of hyperekplexia at birth would allow for rapid genetic screening of the newborn child and then all the measures could be taken to prevent cot death."

Every week in the UK around seven babies less than a year old die from cot death.
Joyce Epstein, director of the Foundation for the Study of Infant Deaths (FSID), was unable to comment on the new research until experts had been given a chance to look at the findings in detail.
However, she commented, "Nobody knows what causes SIDS, so research has to look into every area. We're looking at a range of factors, including genetics."
She doubted whether genetics was going to be the entire answer.
Despite the latest discoveries,she stated that until the latest research is evaluated, the existing advice offered to parents continues to hold true.
28 June 2006 |