Usher Syndrome Type I

Alternative Names

  • USH1
  • Retinitis Pigmentosa and Congenital Deafness
  • Usher Syndrome, Type IB
  • USH1B
  • Usher Syndrome, Type IA
  • USH1A
  • Usher Syndrome, Type I, French Variety

Associated Genes

Myosin VIIA
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WHO-ICD-10 version:2010

Diseases of the ear and mastoid process

Other disorders of ear

OMIM Number

276900

Mode of Inheritance

Autosomal recessive

Gene Map Locus

11q13.5

Description

Usher syndrome is the most common genetic form of deaf-blindness. This disorder is characterized by congenital sensorineural hearing loss associated with defects in the inner ear, and vision loss associated with retinitis pigmentosa. In most cases, the rod cells are affected first, followed by the cone cells. In some cases, the foveal vision is spared, resulting in a 'doughnut vision'. According to the severity of the condition, three distinct types of Usher syndromes are recognized. Usher syndrome type 1 is the most severe of these different types. Patients affected with this type are born profoundly deaf, and start to lose their vision within the first decade of their life. In addition, problems in the vestibular system are also seen, resulting in patients exhibiting difficulties in maintaining their balance and a significant delay in walking as infants. Approximately, 5% of children born deaf are actually affected by Usher syndrome type 1. Overall, the incidence of this severe type is about 4 per 100,000, although it is more common in certain populations, such as Ashkenazi Jews and the Acadian population in Louisiana.

Since the vision loss does not occur until much later, a diagnosis of Usher syndrome can be missed out in the face of deafness as the only symptom in infancy. Molecular diagnostic testing has the potential to provide an early diagnosis. The condition, however, cannot be cured. Management strategies include cochlear implant, and preparing for blindness before it manifests itself.

Molecular Genetics

Usher syndrome type 1 is further divided into seven different subtypes, depending on the genetic locus involved. Most of these genes code for proteins that play important roles in normal hearing, vision, and maintenance of balance. These include CDH23, MYO7A, PCDH15, USH1C, and USH1G genes. The condition is transmitted in an autosomal recessive manner.

Usher syndrome type 1B is caused by mutations in the MYO7A gene. This gene codes for the Myosin VIIA protein, an unconventional myosin. In the inner ear, this protein plays a role in the differentiation and morphogenesis of the stereocilia, the hair-like projections that function as acoustic sensors. Within the retina, this protein plays an important role in the distribution and migration of retinal pigment epithelial melanosomes and phagosomes, and in the regulation of opsin transport in retinal photoreceptors.

Epidemiology in the Arab World

View Map
Subject IDCountrySexFamily HistoryParental ConsanguinityHPO TermsVariantZygosityMode of InheritanceReferenceRemarks
276900.1Saudi ArabiaUnknownNoYes Visual impairment; Sensorineural hearin...NM_000260.4:c.487G>AHomozygousAutosomal, RecessivePatel et al, 2018
276900.2EgyptMaleYesYes Progressive visual loss; Bilateral senso...NM_000260.4:c.2863G>AHomozygousAutosomal, RecessiveReddy et al. 2014 The patient had 2 si...
276900.3JordanFemaleYesYes Progressive visual loss; Bilateral senso...NM_000260.3:c.462C>AHomozygousAutosomal, RecessiveReddy et al. 2014 The patient had a si...
276900.4LebanonFemaleNoYes Progressive visual loss; Bilateral senso...NM_000260.3:c.834C>AHomozygousAutosomal, RecessiveReddy et al. 2014

Other Reports

Iraq

In a study comprising 50 children with congenital sensorineural hearing loss (SNHL) attending the Ear, Nose, and Throat Department of Al-Ramadi Teaching Hospital in Al-Ramadi city (December 2007 to October 2008), Al-Ani et al. (2009) diagnosed two children with profound bilateral SNHL.  Upon ophtalmological examination, the children were found to have hearing loss and retinitis pigmentosa and were diagnosed as having Usher syndrome.

Kuwait

Shuja-ud-din et al. (2002) reported the case of a 50-year old Kuwaiti woman as the first case to be diagnosed with Usher syndrome Kuwait. Usher syndrome in this patient was also found to have an unusual comorbid association with hypothyroidism due to autoimmune thyroid disease.

[Shuja-ud-din, Al Adsani A, Baidas G. Autoimmune thyroid disease in a patient with Usher's syndrome: case report. Kuwait Med J. 2002; 34(2):150-2.]

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