A tiny "genetic patch" can be used to prevent a form of deafness which runs in families, according to animal tests.Patients with Usher syndrome have defective sections of their genetic code which cause problems with hearing, sight and balance.A study, published in the journal Nature Medicine, showed the same defects could be corrected in mice to restore some hearing.Experts said it was an "encouraging" start.There are many types of Usher syndrome tied to different errors in a patient's DNA - the blueprint for building every component of the body.One of those mutations runs in families descended from French settlers in North America.When they try to build a protein called harmonin, which is needed to form the tiny hairs in the ear that detect sound, they do not finish the job.It results in hearing loss at birth and has a similar effect in the eye where it causes a gradual loss of vision.PatchScientists at the Rosalind Franklin University of Medicine and Science, in Chicago in the US, designed a small strip of genetic material which attaches to the mutation and keeps the body's factories building the protein.When mice with Usher syndrome were injected with the "genetic patch" they grew up able to hear and had no balance problems.For the first couple of months their hearing was close to normal in the lower frequencies, but had started to deteriorate by six months.One of the researchers Michelle Hastings, assistant professor at Rosalind Franklin University, told the BBC: "It was a surprising result that we could treat mice right after they are born and have such a profound effect."The treatment had to be given early, within the first 10 to 13 days of life.The researchers do not know if this is because the patch needs to be in place during early development in order to make a difference or if the patch struggles to make it into the inner ear beyond a certain point.This could raise problems in designing a similar treatment in people. Humans spend far longer in the womb than mice meaning any treatment might need to be given before a baby is born.Dr Ralph Holme, head of biomedical research at Action on Hearing Loss, said: "It is encouraging that researchers have been able to rescue hearing using an approach which targeted a specific type of inherited deafness."More research is now needed to understand how this new therapy could be used to treat this particular type of Usher Syndrome in humans and discover whether vision can also be rescued."