CHARGE syndrome and Usher syndrome are the most commonly associated genetic conditions associated with deaf-blindness. While the prevalence of Down syndrome is higher than CHARGE or Usher combined, not all people with Down syndrome experience a combined vision and hearing loss. There are approximately 70 additional genetic conditions that are associated with combined vision and hearing loss.
CHARGE syndrome is a rare genetic disorder that manifests in a series of birth defects that can include vision and hearing loss. It occurs in approximately 1 out of every 9,000 to 10,000 births. People are typically diagnosed with CHARGE based on the presence of medical features of the syndrome. There is a genetic test to identify the gene associated with the syndrome but the test is not always accurate as 2/3 of people with CHARGE receive a false negative result. Children born with CHARGE syndrome are affected differently. Many experience extensive medical and physical difficulties while others are more mildly impacted. Over the past decade, CHARGE syndrome has been identified as the leading single syndrome associated with deaf-blindness in school age children. CHARGE is an acronym representing the clinical features that were historically used to identify children. Those diagnostics have changed over time but the acronym CHARGE remains. There are several clinical and diagnostic features of CHARGE including:
- Coloboma of eye – A cleft or hole in one of the structures of the eye that may be present in one or both eyes. This may cause vision loss.
- Choanal Atresia or stenosis – bony growth in the nose that causes a narrow or blocked passageway.
- Cranial Nerve Abnormality - Swallowing problems, facial palsy.
- Ear anomalies - Outer ears have a distinctive look including no ear lobes, floppy, typically short and wide. The middle ear may have malformed bones causing a conductive hearing loss. The inner ear may have atypical semicircular canals (causing balance problems) and a malformed cochlea.
- Heart Defects
- Genital abnormalities
- Growth deficiency
- Cleft lip/palate
- TE fistula (an esophageal abnormality)
Usher syndrome is the most common genetic (inherited) cause of deaf-blindness. Recent studies estimate that between 8 and 10% of all individuals who are congenitally deaf or hard of hearing has Usher syndrome. There are three main types of Usher syndrome. All individuals with Usher will have hearing loss and a visual condition called retinitis pigmentosa (RP).
Retinitis pigmentosa is a progressive visual condition. The first symptom may be difficulty seeing at night (night blindness) or in poorly lit or dark environments such as hallways, movie theaters or in any outdoor venue at dusk or during the evening when lighting is poor. The individual with RP is often unaware that they have this condition until their vision loss has progressed significantly. As children or young adults, they may be labeled “clumsy” or “accident prone,” since, due to their night blindness, they bump into people and things in darkened environments. Along with night blindness, RP also causes a loss of peripheral, or side, vision. Whereas individuals with “typical” visual fields can see to their left and right – approximately 180 degrees – individuals with RP gradually lose their side vision. At the later stages of vision loss, their visual fields are such that it is like looking at the world through a tunnel – thus the term “tunnel vision.” This impacts their ability to see people and objects to the far left and right, which may cause them to appear to others as disinterested, absent minded or careless. The slow and progressive nature of the loss of peripheral vision often causes individuals with RP to be unaware of this loss until their visual fields are quite restricted. They may quite naturally and intuitively adapt to this loss of peripheral vision by deliberately scanning their environment before proceeding.
Along with RP, each type of Usher syndrome has an accompanying hearing loss. Those with Usher I are born profoundly deaf and may experience balance problems. Prior to the availability of cochlear implants, many children with Usher I attended schools for the deaf and eventually became part of the Deaf community. American Sign Language was, for many, their primary language. As night blindness and the loss of peripheral vision slowly progressed, their ability to receive signed information was seriously impacted.
Individuals with Usher II are born hard of hearing with RP. As children, they may use hearing aids and lip-reading to assist with oral/aural communication. As their vision loss progresses, they may experience difficulty with lip-reading in darkened environments. Some individuals perceive this as an additional loss of hearing when it is actually the effect of the progressive loss of vision. Usher II does not have balance problems associated with it.
Usher III is quite rare, although there are a few cases diagnosed in the U.S. Hearing loss manifests in the mid-teens or early 20s. This hearing loss is progressive. RP is usually diagnosed in the mid-teens. Progressive balance problems are associated with type III.
Down syndrome is the most common genetic condition in the United States. One in every 691 babies in the U.S. is born with Down syndrome and there are an estimated 400,000 Americans who have Down syndrome.
Down syndrome is associated with a variety of physical, intellectual and health issues including distinctive facial features, heart defects and learning and behavior challenges.
Children with Down syndrome are often born with a combined vision and hearing loss. It is estimated approximately 60-70% of children with Down syndrome have vision impairments. Eye conditions associated with Down syndrome include nystagmus (involuntary eye movement), strabismus (crossed eyes), farsightedness, nearsightedness, congenital cataracts, keratoconus (the cornea becomes cone shaped over time) and conditions like blepharitis (inflammation of the eyelid) and conjunctivitis. All of these conditions can be treated medically, and with education modifications and low vision adaptations can be extremely helpful.
In addition, it is estimated 75% of children with Down syndrome have a hearing loss. Most often the loss is a conductive hearing loss where sound is unable to move through the outer ear into the inner ear due to a blockage most often caused by otitis media (middle ear infection). The effects of persistent or recurrent middle ear infections are noted in hearing loss, speech delays and comprehension. There is also the possibility of sensorineural hearing loss in Down syndrome due to damage to the sensitive hair cells in the cochlea or the auditory nerve. This hearing loss is permanent and cannot be treated.
Neurofibromatosis is a genetic disorder that causes (typically) benign tumors to form on nerve tissue anywhere in the body.
Neurofibromatosis affects each person differently depending where the tumors grow and compress nerves, blood vessels, organs and other body tissue. NF can range from extremely severe causing heart, hearing and vision problems to relatively mild and hardly noticeable.
Treatment for NF is often focused on tumor management. In some cases, surgery or chemotherapy is used to remove or shrink tumors that are causing health problems.
NF has been classified into three distinct types: NF1, NF2 and Schwannomata's.
NF2 is closely linked to hearing loss and in some cases, vision loss. In NF2, benign tumors grow on the eighth nerve that carries sound and balance information to the brain. This can cause progressive hearing loss, balance problems and tinnitus (ringing in the ears). Tumors can also grow on the optic nerve causing vision loss. Hearing and vision in people with neurofibromatosis can fluctuate based on management of the affecting tumors.