"The gene responsible for cystic fibrosis httpshealth.nytimes.comhealthguidesdiseasecysticfibrosisoverview.htmlinlinenytclassifier was discovered in . Now  years later a drug that tries to compensate for the genetic defect might be nearing the market. Vertex Pharmaceuticals https announced Wednesday morning that the drug VX https improved lung function in people with cystic fibrosis in a latestage clinical trial. The drug also reduced the frequency of disease exacerbations that required treatment with antibiotics httpstopics.nytimes.comtopnewshealthdiseasesconditionsandhealthtopicsantibioticsindex.htmlinlinenytclassifier. The caveat is that VX is designed to counter one specific genetic mutation that accounts for about  percent of cases of cystic fibrosis. Vertex is working on another drug for the most common mutation but that one is further behind in development. Still the news is expected to be greeted favorably by doctors and patients and by Wall Street. Ive been doing clinical trials for  years in C.F. and these are amazing results Dr. Bonnie W. Ramsey https_Bonnie.html a lead investigator in the trial said in an interview.  Dr. Ramsey a professor of pediatrics httpstopics.nytimes.comtopnewshealthdiseasesconditionsandhealthtopicspediatricsindex.htmlinlinenytclassifier at the University of Washington httpstopics.nytimes.comtopreferencetimestopicsorganizationsuuniversity_of_washingtonindex.htmlinlinenytorg was briefed on the results by Vertex. The results were announced by a press release httpsinvestors.vrtx.comreleasedetail.cfmReleaseID and have not been peer reviewed by experts. About  Americans and  people worldwide have cystic fibrosis a disease caused by defects in a gene responsible for the transport of chloride ions across cell membranes. People with the disease tend to have very thick mucus in their lungs which leads to infections and lung damage. Many do not live past age . Two inhaled antibiotics and one drug that loosens mucus are approved to treat cystic fibrosis but nothing that directly improves chloride ion transport.  In the trial those who received VX gained . percentage points more on a lung function test after  weeks than those getting a placebo a difference that statistically was highly significant. Patients continued to take either drug or placebo for another  weeks and the improvement was sustained. Lung function the primary endpoint of the trial was measured by how much a person could exhale in one second a standard test. Investors had been expecting around a  percentage point improvement. In a note to clients Tuesday evening before the results were known an analyst at ISI Group Mark Schoenebaum https said that an improvement of  percent would be a home run that could lead to  million in annual sales for the drug. Dr. Ramsey who has received research grants from Vertex said that some patients could perceive a  percentage point change in lung function. She said other results of the trial were encouraging. These included fewer exacerbations of the disease in those who got the drug fewer selfreported respiratory symptoms and a gain in weight which is good for people with cystic fibrosis who often have digestive problems. The saltiness of their sweat  a measure used to diagnose the disease  was markedly reduced suggesting that the drug was having an effect on chloride ion transport. The trial involved  people age  and older all with at least one copy of the particular mutation known as GD. The main side effects Vertex said were headache httpshealth.nytimes.comhealthguidessymptomsheadacheoverview.htmlinlinenytclassifier upper respiratory tract infections nasal congestion httpshealth.nytimes.comhealthguidessymptomsnasalcongestionoverview.htmlinlinenytclassifier rash and dizziness httpshealth.nytimes.comhealthguidessymptomsdizzinessoverview.htmlinlinenytclassifier. Vertex said it hoped to apply in the second half of the year for approval of VX in the United States and Europe. The company is awaiting results of a second trial of the drug this one in younger children. Vertex has not said how much it will charge for VX. But since there are only about  Americans who are candidates for the drug the price is likely to be tens of thousands of dollars a year. Vertex based in Cambridge Mass. was founded in  coincidentally the same year the cystic fibrosis gene was discovered. It has not yet had a big commercial success and had a . billion net loss in the last five years. The company is hoping that by late May it will win approval to sell a new type of drug for hepatitis C httpshealth.nytimes.comhealthguidesdiseasehepatitiscoverview.htmlinlinenytclassifier which analysts expect will be a blockbuster. The long time needed to develop a drug for cystic fibrosis is a lesson for those expecting a quick payout from the sequencing of the human genome which was completed a decade ago. It is not enough to know the gene behind a disease. It can take years of research to determine how a mutation actually causes a disease and then to design a drug that corrects the problem. Vertex received  million in financial support from the Cystic Fibrosis Foundation one of the first nonprofit disease groups to give money to companies. These results are highly encouraging Robert J. Beall president of the foundation said in a statement Wednesday. They provide scientific evidence that support our longstanding belief that targeting the underlying defect of C.F. may have a profound effect on the disease."