Hearing problems genetic 239

(with or without sedation), earphones and electrodes record activity from the hearing nerve. The test, which measures high-pitched sounds better than low-pitched sounds, is often used by hospitals to test newborns.

As nerve impulses pass through the lower levels of the brain from the auditory nerve on their way to higher brain centers, they make connections in the brain stem near the base of the skull. The auditory brain stem response (ABR) test measures this electrical activity in the brain stem to see how well certain portions of the auditory system in the brain respond to a presented tone or beep. Clicks or tone pips are fed into the ear and a computer then analyzes brain activity to see if the brain waves change. Rather than a true test of the entire process of hearing, the ABR determines whether sound signals are reaching the brain.

By repeating the stimulus up to 100 times and averaging the response by computer, the responses can be enhanced while eliminating random background electrical activity. This way, auditory thresholds can be established that are quite close to those that can be obtained in conventional audiometry.

Otoacoustic emissions This test is a new method of testing hearing that also can be used with a child who cannot respond to behavioral testing. This rapid test can be used for screening in the newborn nursery; it is based on the fact that the ear not only hears noise but also makes noise. By measuring the very faint noises made by the ear, the test estimates how well the ear hears. An ear that does not hear will not make the expected noises. These noises are much too faint to be heard by human ears, but there are machines that can measure the sounds.

Central auditory processing testing A child must be able to speak in full sentences and have reasonably advanced language to take the central auditory processing test, so they must be at least over age five. The test assesses the ability to process the sounds children hear. Some children hear very well but have trouble deciding what to do with the sound once they hear it. These children are typically intelligent but have trouble following directions in school (especially in noisy environments). They may have had many ear infections when they were younger and developed difficulty dealing with sound as a method of communication. (See also hearing problems, genetic.)

hearing problems, genetic Deafness may be caused by a wide variety of inherited abnormalities, most of which are present at birth and do not improve. These genetic types of deafness are responsible for about half of all types of deafness in children. There are about 200 different types of genetic hearing problems ranging in degree from mild to profound. Although some types of hearing loss are associated with other physical characteristics or medical problems (such as changes in the eye or hair color), most types of genetic hearing loss do not involve other types of physical changes. The ability to hear is just one of many different physical traits that are handed down in families.

There are several ways that genes can influence a child's ability to hear. Each child receives half of its genetic material from each parent. There are many different gene locations that affect hearing and many different varieties of genes. Different forms of deafness may involve different gene locations.

Research has found mutations in several genes that are linked to deafness. The gene called Con-nexin 26 may be responsible for as many as 40 percent of cases of inherited hearing loss. Most of these children are born to parents with normal hearing. About 40 percent of children with this genetic mutation will have a profound hearing loss. Another gene (GJB2) mutation is the predominant cause of inherited moderate-to-profound deafness in the Midwest. Although there are many deafness-causing mutations in the GJB2 gene, one mutation causes the most cases of deafness. Couples who have had one child with GJB2-associ-ated deafness have a 17.5 percent chance of having a second deaf child.

Scientists also have found a gene that plays a significant role in the development of cells essential to hearing. The gene (Math 1) sends a signal that triggers certain ear cells to mature into hair cells in the inner ear. Hair cells are responsible for both hearing and balance, and loss of these cells is a common cause of deafness. once these cells have been destroyed, they cannot be re-created.

Genetic Diseases

There are a number of diseases that can be passed down in families that will result in hearing loss in children, including Alport's syndrome, Cogan's syndrome, Penred's syndrome, Refsum's syndrome, and Usher's syndrome.

Alport's disease This genetic condition causes kidney inflammation in childhood, followed by a sensorineural hearing impairment in young adulthood. It is more common among boys than girls. There is no clear relationship between the extent of kidney disease and the onset of deafness. Treatment is supportive, since glucocorticoids and cyto-toxic agents do not help.

Cogan's syndrome This condition involves an inflammation of the cornea that also can damage new bone formation around the round window and destroy the organ of Corti and cochlear nerve cells, leading to vertigo, tinnitus, and severe sen-sorineural hearing loss. Treatment with steroids is often effective in suppressing disease activity; in some patients, drugs may be tapered off and stopped, while others require maintenance-level treatment.

Penred's syndrome An inherited condition that causes deafness usually at birth. Children with the syndrome have different degrees of hearing loss, but it is severe for more than half. The syndrome is probably the most common form of deafness that appears with another condition (in this case, goiter). Research suggests that Penred's syndrome may be related to a gene mutation that produces a defective form of the protein pendrin and associated problems in transporting chloride ions that are normally found in the inner ear. This could lead to abnormal electrolyte concentrations that may make it impossible for the inner ear to properly transfer sound waves to the brain.

Refsum's syndrome A rare, genetic neurological disease of fat metabolism that is associated with hearing loss that begins in childhood and very slowly progresses. In 1997 the gene for the disease was identified on chromosome 10. While the syndrome can be treated with dietary changes, once the deafness appears the damage cannot usually be repaired.

Infantile Refsum's disease An unrelated condition affecting infants that leads to a buildup of phytanic acid in tissue and blood. it causes hearing loss that begins in infancy, and there is no cure. Death usually occurs in the 20s.

Usher's syndrome type II A condition that begins with a profound congenital deafness followed by a gradual loss of vision that often reaches complete blindness. This is one form of retinitis pigmentosa, in which pigment is deposited in and damages the light-sensitive portion of the eye. Originally described in 1959, the syndrome may account for 10 percent of all cases of congenital deafness. Although there is no treatment, regular exams by an ophthalmologist are recommended for all deaf children, as they can help identify Usher's syndrome early (usually before age six). Scientists have identified genes causing all three types of Usher syndrome to five different places on the chromosomes.

Waardenburg's syndrome A rare genetic syndrome. About half of all patients have a nonprogressive sensorineural hearing loss ranging from mild to severe in one or both ears. Only about one out of five patients have a hearing loss severe enough to require some aid to verbal communication. But some with the gene are totally deaf, and others are deaf in one ear yet have completely normal hearing in the other.

heart problems While most people think of heart disease as an adult problem, more than 40,000 American children are born with a heart defect each year, and others develop heart disease in childhood. Congenital heart defects are the most common birth defect and are the number one cause of death from birth defects during the first year of life. Nearly twice as many children die from congenital heart disease in the United States each year as die from all forms of childhood cancers combined. At present at least 35 different heart defects in children have now been identified.

Still, the outlook for children born with heart disease is slowly improving. The risk of dying after congenital heart surgery has declined from 30 percent in the 1970s to 5 percent today.

Congenital Heart Disease Most heart disease in children is congenital, which means that a structural problem with the heart was present at birth. Eight out of 1,000 infants will be

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