It may be possible to start treating affected babies during pregnancy
Scientists believe they have made a breakthrough in the treatment of a severe muscle disease that causes floppy baby syndrome.
Most babies born with the rare disorder are severely paralysed and the majority die before the age of one.
The Australian team was able to cure affected mice by replacing a missing muscle protein.
A UK expert said the findings, in the Journal of Cell Biology, could lead to improved movement for affected babies.
The team focussed on proteins called actins. A gene called ACTA1 controls the production of actin in skeletal muscles.
It is key to allowing muscles to contract, but children with this disease have flawed versions of the gene and so the protein is not produced.
However, the scientists had seen that some children with floppy baby syndrome were not totally paralysed at birth.
When these children were studied, it was found that heart actin - another form of the protein - was "switched on" in their skeletal muscles, when that would not normally be the case.
Heart actin is found in skeletal muscles while the baby is developing in the womb, but has almost completely disappeared by birth.
The researchers found it was possible to cure mice genetically engineered to have the recessive form of the muscle disorder by replacing the missing skeletal muscle actin with heart actin.
Dr Kristen Nowak, of the Western Australian Institute for Medical Research, who led the study, said: "The mice with floppy baby syndrome were only expected to live for about nine days, but we managed to cure them so they were born with normal muscle function, allowing them to live naturally and very actively into old age.
"This is an important step towards one day hopefully being able to better the lives of human patients - mice who were cured of the disease lived more than two years, which is very old age for a mouse."
The team now plan to apply their findings to human patients.
They are analysing 1,000 existing medicines to see if any could increase the amount of heart actin in skeletal muscles.
Professor Nigel Laing, head of the research group, said: "Current therapies only target the effects of these conditions, not the condition itself - we hope our approach could lead to a much greater improvement for a range of muscle diseases."
Professor Dame Kay Davies, of the University of Oxford, helped create the mice used in the study. She said the findings were promising.
"What we can't guarantee is if we can find a chemical to increase levels of heart actin enough.
"But we do have an idea of what kind of compounds might work."
Professor Davies added: "If we could then screen every pregnancy, we could start treating this towards the end of foetal life.
"It could go some way past giving just some movement, but it probably wouldn't be possible to enable children to run around.
"However they would be likely to have a good quality of life."
Floppy baby syndrome is distinct from babies who are deemed "floppy" because the development of their gross motor skills such as sitting and crawling is delayed.