Usher syndrome is a frequent cause of deaf-blindness and involves sensorineural hearing loss and retinitis pigmentosa (RP). It occurs in four of every 10,000 births (NIH). The hearing loss is always sensorineural; the vision loss is always progressive; and the etiology of this combination is always genetic, specifically autosomal recessive. Parents are literally "blindsided" by this diagnosis and frequently complain this cannot be genetic because it is "not in their family." Such is the nature of recessive inheritance: both parents are asymptomatic, unknowing carriers of the same gene.

RP is a degenerative retinal disease in which initially sighted individuals gradually lose their vision. Although RP occurs in one of every 4,000 persons in the general population, about 14% of all RP cases are caused by Usher syndrome (Hamel, 2006). The pattern of vision loss is quite predictable: night blindness followed by restricted tunnel vision and later loss of acuity and color perception. The onset and rate of progression of RP are, however, highly variable. The delayed onset of expression presents a challenge to the audiologist in assisting families with the diagnosis of Usher syndrome. Although clinical observation and behavioral measures of visual function are possible in older children, the definitive diagnostic test is objective: an electroretinalgram (ERG). Using electrodes placed on the cornea, an ERG measures the responses of retinal photoreceptor cells to light stimulation.

There are three recognized clinical types of Usher syndrome, labeled simply Type I, Type II, and Type III. While some atypical expressions have been identified, they are beyond the scope of this article (for a review, see Cohen et al., 2007). The three types are distinguished primarily by severity of hearing loss, presence or absence of vestibular function, and onset of vision loss. All these variables are important, as hearing loss alone cannot diagnose Usher syndrome, nor can it differentiate clearly between the subtypes (Wagenaar et al., 1996).

Characteristics

Type I presents with congenital, severe-to-profound sensorineural hearing loss, no vestibular function, and noticeable vision involvement in the preteen years. Due to the severity of the hearing loss, hearing aids are generally ineffective. Individuals with Type I are typically identified as deaf during childhood and, prior to cochlear implantation, placed in educational programs that focus on visual communication. Because of the lack of vestibular function these children demonstrate delays in sitting and walking, with the latter being reported at older than 18 months of age (Moller et al., 1989). Night blindness typically appears by age 10. These children may be afraid of the dark and are often described as clumsy because they bump into or trip over objects in the environment. Significant deterioration of visual field and acuity begins between the second and third decade of life, with cataracts being a common complication (Piazza et al., 1986; Edwards et al., 1998; Sadeghi, 2006).

Most individuals with Type II exhibit a stable, moderate sensorineural hearing loss (Reisser et al., 2002) and often respond well to amplification. The sub-Type IIa, however, may demonstrate progressive hearing loss not found in other Type II expressions (Sadeghi et al., 2004). Balance is unaffected and vision loss is unnoticed until late teens. Although the sequence of RP progression is similar to that of other types of RP (Iannaccone et al., 2004), visual field and acuity impairments are somewhat less severe compared to Type I during the third and fourth decades of life (Piazza et al., 1986; Edwards et al., 1998; Sadeghi, 2006).

Type III has the most variable onset and presentation. Hearing loss is progressive and vestibular function may or may not be affected (Sadeghi et al., 2005). This clinical type, although common in Finland, is rare in the United States and has vision outcomes more similar to Type I (Plantinga, 2006). Type III represents 40% of all cases in Finland but only 2%–4% of all cases in the United States.

The National Center for Hearing Assessment and Management (NCHAM) reports that 95% of infants born in the United States are evaluated prior to discharge by early hearing detection and intervention programs (EHDI), which have lowered the average age of identification of hearing loss from 12–18 months to 6 months or younger (Harrison & Roush, 1996). Sininger and colleagues (2009) demonstrated that newborns screened through EHDI are diagnosed more than 24 months earlier than those babies who were not screened. Despite these achievements, a diagnosis of Usher syndrome, with its devastating vision prognosis, typically lags five or 10 years behind the identification of the hearing loss (Kimberling & Lindenmuth, 2007). Although parents learn of their child's hearing loss relatively early, without a differential diagnosis they make critical decisions related to intervention, communication, and educational options without knowing their child eventually will be blind.

Parents rely upon audiologists for information and support in working with their children who have hearing loss. ASHA's Guidelines for the Audiologic Assessment of Children From Birth to 5 Years of Age recommend that audiologists should "as appropriate, discuss additional specialty evaluations (e.g., genetics, ophthalmology, child development) with parents/caregivers and the infants' primary care provider" (ASHA, 2004, p. 13). This recommendation requires that the audiologist be familiar with genetic epidemiology of hearing loss and resources for referral and information. Once a child is identified, intervention services require a multi-disciplinary team, but audiologists are often the first—and primary—health care provider for individuals with Usher syndrome, and they must recognize and refer for proper and timely diagnosis those individuals who present with clinical signs and symptoms that may suggest the presence of Usher syndrome.