Usher Syndrome - Genetics

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The four major types of Usher syndrome are split into sub-types based on the gene responsible for causing Usher syndrome. The chart above shows each of the currently known sub-type of Usher syndrome along with their respective USH gene. 

USH type one and two are the most common types of Usher syndrome with USH type three representing only about 2-5% of overall USH cases. In USH type one, USH1B is the most common subtype representing between 33 – 50% of all USH type 1 cases, followed by USH1D. In USH type 2, USH2A is believed to represent up to 85% of all USH type 2 cases. 

Every person has two copies of each gene, one inherited from each parent. Usher syndrome is inherited when both parents have passed the same gene mutation for Usher syndrome to their child. This inheritance pattern is known as autosomal recessive, and the symptoms of this condition are only evident when the person has two copies of the same mutated USH gene. 

As shown in the above diagram, where both parents carry the same USH mutation:

• there is a one-in-four (25%) chance of their child having Usher syndrome
• there is a one-in-four (25%) chance of their child not being affected
• there is a one-in-two (50%) chance of their child being a carrier of Usher syndrome

Where one parent has Usher syndrome, all of their children will be carriers of this condition. However, it is rare for a person with USH to meet a partner that is also carrying the same USH gene thus making it very rare for a person who has USH to have a child with Usher syndrome. 

Please reach out to your genetic counselor who can provide more details to any further questions you may have. 

To avail of genetic testing to confirm a clinical diagnosis of Usher syndrome, please get in touch with your GP. Your GP will take the relevant information from you and will then make a referral to a genetic consultant on your behalf. At your appointment with a genetic consultant, usually a genetic counsellor, you will be asked a series of questions including your family history. A blood sample is then usually taken, and will be screened in a lab to find an USH gene. This process can take some time, at least a few months. When your results have been issued, your genetic consultant will provide this to you as well any advice. It is important to keep a safe copy of any results provided as this may be needed in the future especially for participation in trials and research, and for registering in a patient registry.