A syndrome is a disease or disorder that has more than one feature or symptom. Usher syndrome is a rare genetic disorder that primarily causes hearing and vision loss and for some, balance issue is also present. It is the leading genetic cause of deafblindness affecting approx. 1 in 20,000 people worldwide, and there is no treatment or cure at present.
There are three types of Usher syndrome which are clinically based on the characteristics of the hearing loss experienced at birth,
- USH1: Profound at birth
- USH2: Mod-Severe at birth
- USH3: Normal at birth, deterioration starts during childhood
In America, USH1 and USH2 together makes up for 95% of all Usher syndrome cases.
Explaining the vision loss:
Sight loss experienced is due to Retinitis Pigmentosa (RP), an eye disease affecting the photoreceptor cells in the retina of the eyes. For most, it starts with loss of night vision and is usually the first sign of the disease for many. Difficulty with different light settings can be experienced too. Eventually day vision is affected and the peripheral field begins to deteriorate thus decreasing the field of vision leading to limited tunnel vision. A person may at this point become registered as legally blind, despite having good central vision. It also may lead to complete blindness for some.
The severity of RP can vary widely from individual to individual, even for those with the same mutation of Usher syndrome. Some may be legally blind in their teens, while others may not be declared legally blind until in their 30s. Many retain useful central vision into their 60s, while others may be completely blind earlier. There is absolutely no way to predict how RP will progress for each person with Usher, and this is why we strongly believe that more research urgently needs to be done to help provide us with answers on how to better predict the progression rate of RP for individuals with Usher syndrome.
Explaining the hearing loss:
The level of hearing loss can vary widely for people with Usher syndrome, and this in turn leads to different communication methods used by people with Usher syndrome. Hearing loss is due to impaired hair cells in the cochlea impacting how the auditory nerves transmits sounds input to the brain. There are also cases where the vestibular hair cells, (sensory cells that detect gravity and head movement), are also impaired leading to balance issues, typically seen in those with USH1.
These days, the majority of those born with a profound loss, mainly those with USH1, receive cochlear implants, and are oral. For those with a profound loss and who were not implanted with CIs, sign language is used as a communication method. However, as the sight deteriorates, it can become quite difficult for sign language users to see the hand movements. In this case, tactile sign language is used and it involves a person placing their hand over the signer to feel the movements in order to understand what is being said.
Those born with a mod-severe hearing loss tend to wear hearing aids, and most are oral. In very few cases, those with the mod-severe hearing loss at birth, may experience further hearing loss in later life, and some may opt to receive cochlear implants.
How is Usher syndrome confirmed?
A diagnosis of Usher syndrome can only be confirmed through genetic testing, as well as the type and subtype. There are three types of Usher syndrome and, there are a further 10 known subtypes based on the mutated gene.
The list below provides the subtype and the mutated gene.
Usher syndrome 1:
- USH1B, caused by mutations in the MYO7A gene
- USH1C, caused by mutations in the USH1C gene
- USH1D, caused by mutations in the CDH23 gene
- USH1F, caused by mutations in the PCDH15 gene
- USH1G, caused by mutations in the SANS gene
Usher syndrome 2:
- USH2A, caused by mutations in the USH2A gene
- USH2C, caused by mutations in the ADGRV1 gene
- USH2D, caused by mutations in the WHRN gene
Usher syndrome 3:
- USH3A, caused by mutations in the CLRN1 gene
- USH3B, caused by mutations in the HARS gene
How is Usher syndrome inherited?
Usher syndrome is a recessive genetic disease, meaning both parents have to be carrying the same gene for Usher syndrome if their child has the disease. If a person is only a carrier of the Usher syndrome mutation, then they show no symptoms of the disease and for many, they are unaware that they are carriers, unless there is history of Usher syndrome in the family. For the majority though, there is no known history of Usher syndrome in the family and the diagnosis can come as a shock.
When both parents are carriers of the same gene for Usher syndrome, the odds for their child are as follows:
- 1 in four chance, (25%), their child will have Usher syndrome.
- 2 in four chance, (50%), their child will be carriers of Usher syndrome.
- 1 in 4 chances, (25%), their child will not have/be carriers of Usher syndrome.
If one parent has Usher syndrome, and the other parent is neither a carrier nor has the same Usher gene, then all of their children will be carriers of the disease but will not have Usher syndrome themselves. In the very rare cases where the other parent is a carrier of the same Usher gene, there is a 50% chance for their child to either be a carrier/have Usher syndrome.
Find out how joining patient registries can accelerate Usher syndrome research here: