The division into the three clinical types is as follows:
type 1 1: children are born deaf and their organ of balance does not work. The first signs of night-blindness and an ever narrowing field of vision appear during childhood.
type 2 2: children are born hard of hearing and the first signs of deteriorating eyesight show around puberty.
3type 3:children are born with good hearing or hard of hearing, but their hearing and eyesight deteriorate during childhood.
There is still a lot of variation in the seriousness of the disease. This depends on the nature of the individual mutations and the specific combination of the USH mutations with patients. Consequently, it is very well possible to suffer from Usher type 1 and at the same time have the loss of hearing and/or a stage of RP that corresponds with Usher type 2. Or you resemble a patient with Usher type 3, but you have been diagnosed for Usher type 1.
Also, Usher genes are known in which mutations may only lead to loss of hearing. In this case, no retinitis pigmentosa (RP) will be developed. These mutations are particularly found in Usher 1 genes and in the USH 2D gene. This is also called non-syndromic loss of hearing in the Usher gene.
Apart from this, the USH 2A gene also knows mutations that only cause loss of eyesight as a result of retinitis pigmentosa (RP). These patients do not or hardly loose their hearing. This is also called non-syndromic RP in the Usher 2A gene.
At this moment, 10 different Usher Syndrome genes are known, all of which are involved in the production of an Usher protein. The various genes are divided into three clinical types: USH 1, USH 2 and USH 3. The gene involved is indicated by a letter (A, B, C, etc.).
Some genetic disorders occur more frequently with people the ancestors of whom originate from specific geographic areas or ethnic groups.
People diagnosed for Usher 1F or Usher 3A more often are of Ashkenazi Jewish origin.
Usher 1C more often occurs in families with an Acadian French background. Individuals suffering from Usher Syndrome 1C and carriers of the USH 1C gene migrated to Canada and Louisiana, USA. Louisiana has a large USH 1C population in and around the Lafayette area. Some families have known members suffering from Usher Syndrome for several generations.
Usher 3A is very rare in this area. 40% of the people in this group appears to live in Finland.
Usher Syndrome is a rare disease. About 1000 people in the Netherlands suffer from Usher Syndrome (400,000 worldwide).
1 out of 20,000 people becomes both deaf and blind caused by Usher Syndrome.
The spread of the three clinical types is as follows:
80% suffers from USH 2 = 320,000 people, of whom
- 52% has mutations in the USH 2A gene = 208,000 people
- 10% has mutations in the USH 2C gene = 40,000 people
- 3% has mutations in the USH 2D gene = 12,000 people
17% suffers from USH 1 = 68,000 people, of whom
- 14% has mutations in the USH 1B gene = 56,000 people
- 2% has mutations in the USH 1C gene = 8,000 people
- 7.5% has mutations in the USH 1D gene = 30,000 people
- 4.5% has mutations in the USH 1F gene = 18,000 people
- 2% has mutations in the USH 1G gene = 8,000 people
- < 1% has mutations in the USH 1J gene = 400 people
3% suffers from USH 3 = 12,000 people
- 1 out of 75 people carries a mutation in 1 of the 10 Usher genes.
3 to 6% of all children who are hard of hearing or deaf suffers from Usher Syndrome.