Current updates on genetic spectrum of usher syndrome.

Usher syndrome (USH) is a genetic disorder that is characterized by sensorineural hearing loss (HL) and visual abnormality, i.e., loss of night vision and side (peripheral) vision. Usher syndrome is categorized into four subtypes (USH1, USH2, USH3, USH4) on the basis of phenotypic spectrum. Profound hearing loss (HL), vestibular are flexia and language disturbance are typically associated with Usher type 1, while USH2 is linked with moderate to severe level of congenital HL. USH3 has late onset of deafness in life (referred to as "postlingual"), inconstant vestibular abnormality and onset of retinitis pigmentosa (RP) typically in 2nd decade of life. Patients with USH4 have no vestibular impairment and have late onset of retinitis pigmentosa (RP) and sensorineural hearing loss. Until now, 15 genetic loci have been reported to be linked with all types of USH. Among reported USH loci, nine are related to be involved in USH1, three in USH2, two in USH3 and one locus in USH4, respectively. Current review has described different types of Usher syndrome and their molecular genetics, and role of usher proteins in sensory organs. Moreover, we also suggested certain candidate genes for uncharacterized loci that may help the molecular geneticist to reach their target easily. Conclusion: The current catalogue of USH genetic data may assist in genetic counseling, genetic diagnosis, and genotype-phenotype correlation.