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Usher syndrome and unreported cases in Norway
Prevalence of Usher syndrome
Usher syndrome is the most common syndrome leading to deafblindness, and 50% of all deafblind people under the age of 65 have Usher syndrome (Castiglione & Möller, 2022, p. 42). The diagnosis of Usher syndrome can be made on the basis of clinical findings or a genetic test.
Internationally, the prevalence of Usher syndrome is estimated to be 1 to 4 per 25,000 people (Jouret et al., 2018, pp. 121-122). There are approximately 5,300,000 inhabitants in Norway (ssb.no, 2021). This means that there are between 212 and 848 people in Norway who have Usher syndrome. In 2021, approximately 53,000 children were born in Norway (ssb.no, 2022). Between 2.1 and 8.5 of these children probably have Usher syndrome.
Genetic diseases have different prevalence in different places. Therefore, the prevalence measured in one country or area will not necessarily be representative elsewhere. According to an Usher register in Sweden, the prevalence of Usher syndrome is 10 out of 100,000 (Castiglione & Möller, 2022, p. 54). In Norway, this would mean that there are 530 people with Usher syndrome, and 5.3 children born with Usher syndrome each year.
Usher syndrome in people with congenital hearing loss
Usher syndrome is the second most common cause of syndromic hearing loss, after Pendred syndrome (Castiglione & Möller, 2022, p. 54). In a large French study from 2018, 2,476 people with hearing loss underwent genetic testing. 7.5% had Usher syndrome (Jouret et al., 2018, p. 121). In Nebraska, USA, 72 students between the ages of 14 and 21 at a school for the deaf and hard of hearing were genetically tested. 8 of them had Usher syndrome, and only one already knew this. The study also examines other populations and concludes that 9.2% of children with congenital hearing loss have Usher syndrome (Kimberling et al., 2010, p. 512). Both articles believe that there is a basis for recommending early genetic testing of Usher syndrome for all children born with hearing loss or deafness. This is in line with Norwegian recommendations in "National professional guidance for hearing in young children 0-3 years" chapter 5.
Usher syndrome on Eikholt
In Eikholt's annual report from 2021, 130 people with Usher syndrome are registered (47 Usher 1, 65 Usher 2, 2 Usher 3, 16 unknown type). 130 people gives a prevalence of 0.61 out of 25,000. This is a prevalence relatively far below the lowest estimate. Based on Castiglione & Möller's figures from Sweden, there should be 530 people with Usher syndrome in Norway, which means that there are 400 people with Usher syndrome in Norway that Eikholt does not know about.
Possible reasons for the underreporting
There may be several reasons why the probable unreported figures in Norway are so high. The prevalence from Sweden may be incorrect for Norwegian conditions. It is possible that Norway has more or less Usher syndrome than Sweden. People with certain types of Usher gene defects may develop RP late in life or to a small extent (Jouret et al., 2018, p. 514). Another reason may be that healthcare professionals are unaware of the increased risk of Usher syndrome among people with hearing impairment and therefore do not recognise the visual impairment in their patients. Yet another theory is that people with hearing impairment, deafness and deafblindness avoid contact with healthcare professionals due to communication challenges (Jouret et al., 2018, p. 514).
This only says something about the unreported figures for the diagnosis of Usher syndrome. It is highly likely that there are unreported figures for all the other diagnoses that lead to deafblindness in addition to these figures.
Source
Castiglione, A., & Möller, C. (2022). Usher Syndrome. Audiology research, 12(1), 42-65. https://doi.org/10.3390/audiolres12010005
Eikholt (2021) Annual report 2021 for Eikholt.
Norwegian Directorate of Health (2017). National professional guideline for hearing in young children 0-3 years. Helsedirekotratet. Retrieved from: Hearing in young children 0-3 years - Helsedirektoratet
Jouret, G., Poirsier, C., Spodenkiewicz, M., Jaquin, C., Gouy, E., Arndt, C., Labrousse, M., Gaillard, D., Doco-Fenzy, M., & Lebre, A. S. (2019). Genetics of Usher Syndrome: New Insights From a Meta-analysis. Otology & neurotology : official publication of the American Otological Society, American Neurotology Society [and] European Academy of Otology and Neurotology, 40(1), 121-129. https://doi.org/10.1097/MAO.0000000000002054
Kimberling, W. J., Hildebrand, M. S., Shearer, A. E., Jensen, M. L., Halder, J. A., Trzupek, K., Cohn, E. S., Weleber, R. G., Stone, E. M., & Smith, R. J. (2010). Frequency of Usher syndrome in two paediatric populations: Implications for genetic screening of deaf and hard of hearing children. Genetics in medicine : official journal of the American College of Medical Genetics, 12(8), 512-516. https://doi.org/10.1097/GIM.0b013e3181e5afb8
Statistics Norway (2021). Born. Retrieved from: Births (ssb.no)
Other useful resources:
Usher syndrome, types and inheritance - Eikholt
Deafblindness, Nordic definition revised