It is essential that the diagnosis of Usher syndrome is made as early as possible to allow the parents and child to begin special educational programs to help them manage as the disease progresses.
There are three characteristic signs of the condition, which are loss of vision, hearing and balance. At present, the is no cure and affected children will, therefore, benefit from an early diagnosis in order to begin learning to cope with related changes as soon as possible.
Diagnosis usually consists of several tests designed to measure the vision, hearing and balance abilities of the child. In some cases, genetic testing may also be required in the diagnostic procedure.
A disturbance in night vision is the first sign of Usher syndrome for many children that are affected by the syndrome, which may present in childhood or adolescence, depending on the type.
A physical examination is usually conducted to detect any change in the blood vessels in the eye, leading to a waxy appearance of the retina and clumps of dead cells on the surface.
A visual field test can also be used to measure the peripheral vision of the child. An electroretinogram (ERG) measures the response of the retina cells to light and is commonly utilized in the diagnosis of Usher syndrome.
It is a widespread practice for babies born in developed nations to undergo hearing tests at birth. Any children that exhibit abnormalities should be tested for any genetic reason that may suggest they have Usher syndrome.
An audiological test is used to measure how loud sounds at several different frequencies need to be in order to become audible for the patient. This helps to give an indication as to the hearing ability of the individual and any abnormalities that may be present.
A problem in balance is the third distinctive sign of Usher syndrome and can be evaluated with an electronystagmogram (ENG). This works by detecting involuntary eye moments that may indicate problems with balance.
There are three different types of Usher syndrome, each of which is associated with certain gene mutations and onset of symptoms.
To date, nine genetic mutations have been identified to cause the syndrome including:
- MY07A (Type 1)
- USH1C (Type 1)
- CDH23 (Type 1)
- PDCH15 (Type 1)
- SANS (Type 1)
- USH2A (Type 2)
- VLGR1 (Type 2)
- WHRN (Type 2)
- USH3A (Type 3)
As there are a large number of possible genes that may be responsible for causing Usher syndrome, genetic tests are not routinely conducted to screen for the disease. Rather, when it is suspected that an individual may be affected due to the presence of characteristic symptoms and results from other tests, genetic tests may be utilized to confirm the diagnosis.
However, this is not always necessary and genetic testing is not required for diagnosis to be made.
It is very rare for deafness and retinitis pigmentosa to occur together and most patients that present with both signs are likely to have Usher syndrome.
Many individuals in the early stages of progression may be mistaken to have an auditory problem without the involvement of vision abnormalities. For this reason, the presence of retinitis pigmentosa should be sought out to identify eye involvement.
Congenital rubella is another major cause of deafness and blindness that may occasionally be mistaken for Usher syndrome. This is caused by a rubella infection of the fetus, however, and is not a genetic disease.