Damaged or abnormal stereocilia that are a result of genetic mutations often cause hearing loss and other complications, and can be passed down to children. In a recent study, researchers studied mice that inherited a mutated hair cell gene called whirlin, which leads to shorter and fatter stereocilia that are organized in additional rows and that often die off after birth. No current therapies or reparative measures exist to replace such defective hair cells in humans. In order to correct this mutation, researchers injected a gene therapy containing the corrected gene into the inner ear of mice with the genetic mutation. The therapy restored stereocilia to normal lengths and eliminated the additional rows of stereocilia in newborn whirler mice. Despite the restoration of hair cells, the treated whirler mice exhibited no signs of improved hearing ability following testing after one month and after three months of treatment. Further studies are looking to understand why the restoration of the stereocilia did not improve the hearing ability of the mutated mice.