NEW ORLEANS -- In a promising step against a genetic disease that causes deafness and gradual vision loss, scientists have partly restored hearing with a single injection to young mice.Experts praised the study on Usher syndrome, published online recently by the journal Nature Medicine, but the results are a long way from preventing the disease.Children with Usher -- an estimated 1 in 6,000 to 7,500 babies worldwide -- are born deaf.The visual component, called retinitis pigmentosa, often starts in childhood. About half of adults with Usher can still read a newspaper into their 50s.Some groups, such as Louisiana's Cajuns and Canada's Acadians, have an unusually high prevalence of the disease.In the study, Michelle Hastings of Chicago Medical School and Jennifer Lentz of the Louisiana State University Health Science Center found that one injection allowed affected mice to hear for months.The injection, or patch, is a laboratory-created fragment of RNA, which is a chemical cousin of DNA. The patch was designed to interfere with the effects of a faulty gene."It's a very promising and striking finding," said Dr. Henry Paulson, a University of Michigan specialist in neurodegenerative diseases.At least 13 genes are known to cause Usher syndrome. One gene causes all cases in Acadians and Cajuns. Another is common in Finland and a third in Ashkenazi Jewish populations, said Mark Dunning, director of the Coalition for Usher Syndrome Research.