MYO7A-Related Disorders (Usher Syndrome Type 1B and Non-Syndromic Hearing Loss)
MYO7A-related disorders are a group of conditions linked to hearing loss, with or without vision loss. These disorders don’t affect intelligence or cause other health issues.
Usher Syndrome Type 1B: Usher syndrome has three types, and Type 1 is the most severe. MYO7A mutations cause Type 1B (USH1B). Babies with USH1B are profoundly deaf from birth and may struggle with balance due to inner ear issues. They might sit and walk later than usual and have difficulty sensing changes in speed or direction. In childhood, they develop retinitis pigmentosa, leading to night blindness and gradual peripheral vision loss, often resulting in “tunnel vision.” Some may also develop cataracts.
DFNB2: Certain MYO7A mutations lead to nonsyndromic hearing loss (hearing loss without vision loss), known as DFNB2. Individuals with DFNB2 experience profound hearing loss from birth to adolescence, with some facing balance problems. Unlike Usher syndrome, vision loss progression is not expected, but retinitis pigmentosa symptoms may appear later in life.
DFNA11: In rare cases, MYO7A mutations cause dominant nonsyndromic hearing loss (DFNA11). Individuals with DFNA11 have moderate to severe progressive hearing loss after learning to talk. While they may have mild nystagmus or balance issues, they don’t experience the vision loss seen in Usher syndrome. This condition seems to be the mildest associated with MYO7A.
There’s no cure for MYO7A-related disorders, but early treatment is crucial for developing communication skills. Cochlear implants may help regain some hearing, and sign language is a good communication option. Visual aids and specialized instruction assist those with vision loss. Sports participation, well-supervised for safety, can help compensate for balance issues. UV-blocking sunglasses and other optical aids enhance eye comfort, and vitamin A palmitate therapy may slow retinal degeneration for some. Family involvement in instruction is beneficial.
This group of conditions is caused by pathogenic (disease-causing) variants in the MYO7A gene and exhibits autosomal recessive inheritance. This means that both parents must be carriers to have a 25% chance to have a child with the condition. The risk of being a carrier is based on a person’s ancestry or ethnic background. For the autosomal dominant form, carriers have a 50% chance of having children with hearing loss.
As noted above, carriers for certain MYO7A mutations may already having hearing loss.