Norrie disease is an X-linked recessive disorder that causes a progressive hearing loss, along with blindness and mental retardation. The gene defective in Norrie disease, NDP, has recently been identified by positional cloning by our group at Massachusetts General Hospital, in collaboration with a group in England. The gene codes for norrin, a protein of 15 kDa predicted size, which has partial homology to the mucins, a family of highly g1ycosylated, secreted proteins. Knowledge of the sequence of the defective protein will enable us to determine its normal role in hearing, and how the defect contributes to the etiology of Norrie disease. Preliminary results with an antiserum to norrin suggests that the protein is a constituent of the tectorial membrane, which conveys the acoustic stimulus to the receptor cells, and that mutations might cause a weak or absent tectorial membrane. We propose to define the cellular distribution of norrin in the inner ear, by in situ hybridization to determine the cells that make it and by immunocytochemistry to locate its final position. We will determine its molecular weights vivo by gel electrophoresis of micro-dissected cochlear structures, and we will investigate the extent and nature of its glycosylat n. We will also evaluate the nature of hearing loss in Norrie disease. Norrie disease patients will be given complete audiological testing to understand the exact nature of their hearing deficit, and the mutation they carry will be determined to correlate specific mutations with pathology. We hope to obtain material from aborted fetuses with Norrie disease or autopsy material to study the histological pathology of the inner ear. To create an animal model for further study, we will make a transgenic mouse lacking the norrin gene. These mice will be studied audiologically with evoked potentials and otoacoustic emissions, and their inner ears will be studied histologically. Correlation of the onset of the hearing deficit with changes in morphology will help understand the etiology of the disease. If the tectorial membrane is in fact absent in transgenics, these mice will also be a useful tool to understand generation of otoacoustic emissions. Finally, inherited diseases will ultimately be treated by some form of gene transfer. A mouse model for an inherited deafness will later serve as a basis for designing gene therapy.
Showing the most recent 10 out of 41 publications
