Causes of Deafblindness

 

Acquired or congenital

When someone is born with combined sight and hearing difficulties this is called congenital deafblindness. Conditions that cause congenital deafblindness include Rubella and CHARGE.

If the combined sight and hearing loss occurs later in life, this is called acquired deafblindness. This may be due to an accident, illness or as a result of aging.

In some cases, people may be born with a genetic condition such as Usher syndrome, which may mean that they progressively lose their sight.


Causes of Congenital Deafblindness

Rubella
CHARGE Syndrome
Fetal Alcohol Syndrome
Encephalitis
Premature birth
Other

 

Causes of Acquired Deafblindness

Usher Syndrome
Age related
Trauma related

 

Rubella

When the CDBA was formed in 1978, the main cause for congenital deafblindness in Canada was Rubella during pregnancy. Due to Canada’s comprehensive vaccination program, this is no longer the case.

Rubella, commonly known as German Measles, is an infection that affects primarily the skin and lymph nodes. It is caused by the rubella virus, which is transmitted by secretions from the nose and throat or through a pregnant woman’s bloodstream to infect her unborn child. The infection of a pregnant woman may cause Congenital Rubella Syndrome (CRS) in her unborn child.

Consequences of CRS include any combination of:

  • Blindness
  • Deafness
  • Heart defects
  • Brain damage
  • Low birth rate
  • Epilepsy

Before a vaccine against rubella became available in 1969, epidemics occurred every six to nine years.

 

CHARGE Syndrome

Individuals with CHARGE Syndrome are afflicted with a specific set of birth defects. The cause of CHARGE is unknown at present, but research into specific genes is ongoing. The problems seen in an individual with CHARGE would indicate that an issue in development occurred between 35 to 45 days after conception. "CHARGE" originally came from the first letter of some of the most common features seen in this condition.

C Coloboma (eye defects)
H Heart defects
A Choanal Atresia (nasal blockage)
R Retardation of growth and developmental delay
G Genitalia (small penis, undescended testicles)
E Ear anomalies

CHARGE is almost always a sporadic occurrence. This means that there is no family history of CHARGE and there is a very low chance that any one else in the family will have the same problems. The recurrence risk (chance of another child having CHARGE) is 1-2%, which also means there is a 98-99% chance that it will not happen again. However, an individual with CHARGE may have a higher risk of having affected children.

 

Fetal Alcohol Syndrome

Fetal alcohol syndrome (FAS) is a set of physical and mental birth defects that can result when a woman drinks alcohol during her pregnancy.

FAS is characterized by brain damage, facial deformities, and growth deficits. Heart, liver, and kidney defects also are common, as well as vision and hearing problems. Individuals with FAS have difficulties with learning, attention, memory, and problem solving.

Fetal Alcohol Spectrum Disorders (FASD) is an umbrella term describing the range of effects that can occur in an individual whose mother drank alcohol during pregnancy. These effects may include physical, mental, behavioural, and/or learning disabilities with possible lifelong implications. The term FASD is not intended for use as a clinical diagnosis.

 

Encephalitis

Encephalitis means inflammation of the brain. It can occur at any age and is usually the result of a viral infection. 

Encephalitis is different from meningitis, which is an inflammation of the layers that cover the brain (the meninges) and may be the result of a bacterial or viral infection.

 Types of Encephalitis include:

 

Other

There are over 90 identified causes of congenital deafblindness. Sense, the United Kingdom’s largest organization dedicated to adults and children with deafblindness has compiled a detailed list. To access the list, click here.

 

Causes of Acquired Deafblindness

Usher Syndrome

Usher syndrome is the most common cause for acquired deafblindness. The major symptoms of Usher syndrome are hearing impairment and retinitis pigmentosa, an eye disorder that causes a person's vision to worsen over time. Some people with Usher syndrome also have balance problems. There are three general types of Usher syndrome. Although the syndrome was first described by Albrecht Von Graefe in 1858, it was named for Charles Usher, a British eye doctor, who believed that the condition was inherited or passed from parents to their children.

Usher syndrome accounts for approximately three percent of individuals who are congenitally deaf (born deaf) and over 50 percent of the deafblind community.

 

 

Who is affected by Usher syndrome?


Approximately 3-6 percent of all deaf children and perhaps another 3-6 percent of hard-of-hearing children have Usher syndrome. In developed countries such as the Canada, about 4 babies in every 100,000 births have Usher syndrome.

What causes Usher syndrome?
Usher syndrome is inherited or passed from parents to their children genetically. Genes for Usher syndrome are autosomal recessive, a term meaning that 1) Usher genes are located on chromosomes other than the sex chromosomes, and 2) both parents must contribute the mutated gene to the child before the disorder is seen. Usually, parents are unaware that they have an Usher gene because they would need two of the mutated genes in order to show signs of Usher syndrome. A number of different genes have been found to cause the various types of Usher syndrome.  

 

 

What are the types of Usher syndrome?


The three types of Usher syndrome are Usher syndrome type 1 (USH1), Usher syndrome type 2 (USH2), and Usher syndrome type 3 (USH3). USH1 and USH2 are the most common types. Together, they account for approximately 90-95 percent of all cases of children who have Usher syndrome.

What are the characteristics of the three types of Usher syndrome?


Type 1
Individuals with Usher syndrome type I are often born profoundly deaf or severely hearing impaired. Consequently, there may be speech abnormalities. Special testing will show abnormalities with their balance (vestibular) system, although this may not be particularly noticeable to either the patient or a doctor performing an examination. Researchers believe these symptoms are caused by a malfunctioning of the nerve cells in the cochlea in the inner ear. The symptoms of retinitis pigmentosa often begin in childhood or adolescence.

 

Type 2
Individuals with Usher syndrome type 2 are born having mild to moderate hearing impairment. The symptoms of retinitis pigmentosa often are evident by late adolescence. The degree of hearing loss usually remains stable, and there are no problems with the vestibular (balance) system.

 

Type 3
Children born with User syndrome type 3 have normal hearing and normal to near-normal balance. Hearing worsens over time. However, the rate at which hearing and sight are lost can vary between affected individuals, even within the same family. Children develop noticeable hearing problems by their teenage years and usually become deaf by mid- to late adulthood. Night blindness usually begins sometime during puberty. Blind spots appear by the late teenage years to early adulthood. By mid-adulthood, the individual is usually blind.

 

How is Usher syndrome diagnosed?
Hearing loss and retinitis pigmentosa are rarely found in combination. Therefore, most people who have retinitis pigmentosa and hearing loss probably have Usher syndrome. Special tests such as electronystagmography (ENG) to detect balance problems and electroretinography (ERG) to detect retinitis pigmentosa help doctors to detect Usher syndrome early. Early diagnosis is important in order to begin special educational training programs to help the individual manage the combined hearing and vision difficulties.

 

How is Usher syndrome treated?
Presently, there is no cure for Usher syndrome. The best treatment involves early identification in order to begin educational programs. The exact nature of these educational programs will depend on the severity of the hearing and vision impairments as well as the age and abilities of the individual. Typically, individuals will benefit from adjustment and career counseling; access to technology such as hearing aids, assistive listening devices, or cochlear implants; orientation and mobility training; and communication services and independent-living training that may include braille instruction, low-vision services, or auditory training. Researchers are hard at work finding the genes that contribute to Usher syndrome and it is hoped that this knowledge will provide the basis for treatments and cures.