More than 400.000 people are affected by this genetic disorder worldwide. Usher syndrome impacts three major senses:
- Hearing: The hearing loss is caused by a profound or moderate to severe sensorineural loss. It’s estimated that upward of 10 percent of people with congenital bilateral, sensorineural hearing loss have Usher syndrome.
- Vision: Caused by a progressive vision disorder known as Retinitis pigmentosa (RP). RP causes the light-sensing cells in the retina to gradually deteriorate, initially resulting in night blindness, followed by a narrowing of the visual field (loss of peripheral vision), commonly known as tunnel vision. People may have additional eye conditions, such as cataracts and macular oedema.
- Balance: People with Usher syndrome may experience severe balance issues due to vestibular dysfunction.
Three clinical types:
- Type 1: Usher syndrome presents with congenital, profound sensorineural loss and no vestibular function. Due to the severity of the hearing loss they are typically identified as deaf during childhood. Individuals demonstrate developmental delays in sitting and walking. Night blindness is typically apparent by age 10. Significant deterioration of visual field and acuity begins between the late teens, early 20s.
- Type 2: Usher syndrome exhibits moderate-to-severe sensorineural hearing loss. Vestibular function is normal, and visual difficulties may not be apparent until their 20-30s.
- Type 3: Usher syndrome presents much like type II but with progressive hearing loss and variable vestibular function. The hearing and sight loss is moderate, becoming more profound. The degree of loss varies from person to person.