USH type 1 (USH1) is the most severe subtype and is characterized by a severe to profound prelingual SNHL, early RP onset and vestibular alterations. Even though a recent report has cast doubts about the vestibular phenotypic differences among the USH subtypes, this disease is traditionally classified into three different subtypes depending on the age of onset, severity and progression of the symptoms, and the presence or absence of vestibular dysfunction. USH is considered a rare disease, because it has a low prevalence, which ranges from 3 to 6.2 per 100,000 people. This disorder is characterized by the combination of a degenerative vision loss condition known as retinitis pigmentosa (RP), sensorineural hearing loss (SNHL) and, sometimes, vestibular dysfunction. Usher syndrome (USH) is the most common cause of genetic deafblindness and follows an autosomal recessive inheritance. The aim is to identify possible mutation associations with the disease and provide an updated genotype–phenotype correlation. In this paper, we review the genetics of Usher syndrome and the spectrum of mutations in USH genes. Moreover, expression of some USH genes has been detected in other tissues, which could explain their involvement in additional mild comorbidities. Even though some genes are clearly involved in the syndrome, others are controversial. In the retina, the USH protein network is principally located in the periciliary region of the photoreceptors, and plays an important role in the maintenance of the periciliary structure and the trafficking of molecules between the inner and the outer segments of photoreceptors. In the organ of Corti, the USH proteins are essential for the correct development and maintenance of the structure and cohesion of the stereocilia. These genes encode proteins of a diverse nature, which interact and form a dynamic protein network called the “Usher interactome”. There are three clinical types depending on the severity and age of onset of the symptoms in addition, ten genes are reported to be causative of USH, and six more related to the disease.
Usher syndrome (USH) is an autosomal recessive syndromic ciliopathy characterized by sensorineural hearing loss, retinitis pigmentosa and, sometimes, vestibular dysfunction.
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