Atypical Usher Syndrome and Usher Syndrome type 4: Do they really exist?

Margaret Kenna, MD, MPH: Usher syndrome is the most common form of genetic deaf-blindness, often presenting soon after birth with hearing loss and later developing retinal and variable vestibular dysfunction. At least three clinical subtypes and nine genes have been clearly recognized. However, over the last few years, there has been discussion about “atypical” Usher syndrome or “type 4” Usher syndrome, but it is unclear whether these are actually separate entities or rather an expansion of the already identified phenotype-genotype relationships. Additionally, new genes may be defined. In the emerging era of gene therapy, getting both the genetic and clinical diagnosis correct is extremely important for candidacy for, and outcomes of, clinical trials. This presentation will discuss and update the phenotype-genotype presentation for patients with Usher syndrome and will specifically address atypical and Type 4 Usher syndrome. Genes that have been potentially identified as additional Usher Genes will also be presented, as well as some discussion about genes that clinically present with deaf-blindness but do not meet the clinical definition of Usher syndrome.