Genetics and Deafness -
About 3-6 percent of all deaf children and perhaps an equal number of hard-of-hearing children have Usher syndrome, which itself is more than one genetic condition. On the basis of clinical findings, at least three types exist (Table 1). Gene localization studies show that each clinical type is due to several different genes located on different chromosomes. The most important clinical distinctions are based on the differences in hearing and balance. The retinitis pigmentosa (RP) may look the same even to an experienced eye doctor except that the symptoms seem to begin earlier in Type I. Usher syndrome is one of several conditions in which both hearing loss and RP are present. In this article, the symptoms of RP and the various forms of Usher syndrome will be discussed. Suggestions will be given on where to go for further diagnosis and information.
Table 1: Types of Usher Syndrome
|Vision Loss from RP
|Gene located on which chromosome
|Genes Identified (Protein)
|Born deaf with profound hearing loss
|Absent inner ear balance
|Night blindness in infancy or early childhood. Tunnel vision by age 16, usually
(most of Acadian descent from Louisiana)
(Myosin VII A)
|Born hard of hearing with a sloping sensorineural loss from mild loss in low frequencies to severe-profound loss in high frequencies.
|Normal inner ear balance
|Night blindness begins in the teens. Tunnel vision in the late teens to early 20s.
|Born with good hearing or mild hearing loss which gets worse over a decade or more. Looks like Type II in teenagers and young adults; looks like Type I in older people.
|Progressive balance disturbance
|Night blindness in childhood or teens. Tunnel vision becomes pronounced in the 20s.