The gene causing the boy's problem can be traced back to our invertebrate ancestors
A critically ill Turkish boy has had his life saved after scientists were able to read his genome quickly and work out that he had a wrong diagnosis.
The scientists writing in the journal, Proceedings of the National Academy of Sciences, say they completed the analysis of his blood in just 10 days.
They were able to see that he had a mutation on a gene that coded for a gut disease and tell his doctors.
Clinical tests proved that the boy had the disease and he is now recovering.
Richard Lifton, of Yale University Medical School who co-ordinated the research with teams in Beirut and Turkey, said: "The boy's physicians sent a blood sample - they only had a very broad diagnosis of what was happening to this five-month-old child and were suspicious that he had a genetic disorder affecting his kidneys.
"Rather than looking one gene at a time hoping to guess which was the right gene causing the problems, we used a new method were we could look at all the genes in the genome simultaneously.
"We identified a particular gene which had mutations on both copies and which causes a fundamental problem meaning that the child could not absorb water or electrolytes through his gastrointestinal tract.
"We went back to the physicians in Turkey and said we think this is the problem and they confirmed it and are now able to give him better treatment."
The boy has congenital chloride diarrhoea which affects one in 50,000 people.
The main clinical symptom is continual watery diarrhoea which causes dehydration and other metabolic disorders.
If untreated, sufferers can go on to develop kidney disease, inflammatory bowel disease and may have fertility problems.
The scientists then looked at 39 patients who had the same condition the boy was originally thought to have and found that five them had the same genetic mutation.
All five patients were followed up and found to have clinical symptoms for congenital chloride diarrhoea.
Chris Ponting, Professor of Genomics at the Medical Research Council's Functional Genomics Unit said: "This study shows how we've arrived at a turning point in the genetics of disease.
"Previously, finding DNA changes was painstakingly slow.
"Now, with new DNA sequencing technologies, a trickle of newly identified disease genes will soon become a flood.
"This will be helped by knowing the genomes of many people who are not known to have particular diseases because then we can separate DNA changes that cause disease from those that do not."
Professor Mike McCarthy, a geneticist at Oxford University, said: "This is an interesting study - lots of groups are now using the power of new methods for sequencing the human genome to find DNA changes that underlie rare diseases (and increasingly for common diseases too).
"For practical reasons, many groups are concentrating at first on the 1% of the genome which codes for proteins which is what they have done here."