Usher syndrome, types and inheritance

Introduction 

Usher syndrome is a rare inherited genetic disorder that leads to combined visual and hearing impairment/deafblindness. Usher syndrome is the most common single cause of deafblindness in people under the age of 65. 50% of all deafblind people under the age of 65 have Usher syndrome. Usher syndrome is not linked to other neurological conditions, only visual and hearing impairment.

Based on clinical observations, Usher syndrome is divided into three types, Usher 1, 2 and 3.

Usher syndrome type 1 (35-40%)

Usher syndrome type 1 is characterised by congenital deafness or congenital severe neurogenic hearing loss. The eye disease Retinitis Pigmentosa starts early in life. Varying degrees of balance problems, from normal to absent balance function. 

Usher syndrome type 2 (60-65%)

Usher syndrome type 2 is characterised by congenital or early acquired moderate to severe stable neurogenic hearing loss. The eye disease Retinitis Pigmentosa usually begins in young adulthood. Normal balance function. 

Usher syndrome type 3 (0-5%)

Usher syndrome type 3 is characterised by moderate to severe hearing loss with varying onset times. Hearing loss can be rapidly progressive. The eye disease Retinitis Pigmentosa has varying onset times, often in young adulthood. Varying degrees of balance problems. 

Inheritance and Usher syndrome

All identified Usher genes follow autosomal recessive inheritance. 

To get Usher syndrome, you must have two alleles with the same genetic defect. In other words, you must inherit the gene defect from both father and mother. 

You have two variants of the same gene. One is inherited from the father and one from the mother. If you have two healthy genes, you are healthy. If you have one Usher gene, you are a carrier of the syndrome, but you do not get Usher yourself. If you have two Usher genes, you get Usher syndrome. 

Examples: 

• If a person with Usher syndrome has a child with a person who does not have Usher syndrome and is not a carrier of the syndrome, none of the children will have Usher. All the children will be healthy carriers.
• If two healthy carriers have a child, there is a 25% chance that the child will have Usher syndrome, a 25% chance that the child will have two healthy genes, and a 50% chance that the child will be a healthy carrier.

Source

Information is taken from the article titled Usher written by Castligone & Muller, 2021 and can be read in full here: Audiology Research | Free Full-Text | Usher Syndrome (mdpi.com)

Other useful resources:

Usher syndrome and unreported cases in Norway - Eikholt

Deafblindness, Nordic definition revised

Deafblindness - Eikholt

HDo you have questions about combined visual and hearing impairment?

Contact us - Eikholt

This article was written on 22 June 2023