genetics of usher syndrome
Usher syndrome is a genetic disorder and is inherited in an ‘autosomal recessive’ manner. Basic inheritance genetics tells us that:
- Each person receives 23 chromosomes from each parent: 22 being non-sex (autosome) chromosomes and one sex chromosome to give a total of 46 chromosomes.
- These 46 chromosomes are located in every cell in the human body and contain the approximately 20,000 genes which act as blueprints for how our bodies grow, develop and function.
- Mutations in at least ten different genes are known to cause Usher syndrome, although in each family, only one of the Usher syndrome genes is involved.
- Usher syndrome occurs when a child inherits two faulty copies of an Usher syndrome gene, one from each parent. This is called autosomal recessive inheritance.
- For a couple to have a child with Usher syndrome, the mother and father must both be ‘carriers’ of a fault on the same Usher syndrome gene. Carriers of Usher syndrome also have one functioning copy of the Usher syndrome gene, and therefore are healthy (and do not have Usher syndrome).
- When both parents are carriers of a fault on the same Usher syndrome gene, each child has a 1 in 4 (25%) chance of having Usher syndrome, a 1 in 2 (50%) chance of being a carrier of Usher syndrome (like the parents) and a 1 in 4 (25%) chance of being neither affected by Usher syndrome nor a carrier of Usher syndrome.
A genetic test involves looking at a patient's DNA to see if there are any mutations present. It involves taking either a blood sample or saliva swab from the patient which is then analysed in a laboratory. Genetic tests are important because they allow doctors to predict how severe the condition might become and what other symptoms can be expected. It also enables the research community to better understand the genetics of Usher syndrome, and may be useful in identifying gene-specific treatment options in the future.