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Author: admin | 25.08.2015 | Category: Homeopathic Treatment For Tinnitus

In addition to type, hearing loss can be classified based on degree of severity.  In increasing levels of severity, hearing loss is classified as mild, moderate, moderately severe, severe, or profound.
The other 44 chromosomes that are not sex chromosomes are called autosomes.  A disorder of a gene that is located on an autosome is referred to as autosomal. The Heart of the Matter: What Does America Really Know about Coronary Artery Disease Treatments?
Scientists at the Institut Pasteur, Inserm, the College de France and Pierre & Marie Curie University, working closely with scientists at the University of Auvergne, have recently discovered the function of pejvakin, a molecule that plays a vital role in the hearing system.
The scientists, particularly Sedigheh Delmaghani, studied young mice whose pejvakin gene had been inactivated. The auditory sensory cells in people with impaired pejvakin were observed to be extremely vulnerable to noise.
The scientists will now look into possible techniques to restore the function of pejvakin, particularly using gene therapy, which has already proved successful in conserving hearing in mice lacking in pejvakin, even when they are overexposed to noise. One of the most common birth defects is hearing loss or deafness (congenital), which can affect as many as three of every 1,000 babies born.
The most common and useful distinction in hearing impairment is syndromic versus non-syndromic. Non-syndromic hearing impairment accounts for the vast majority of inherited hearing loss, approximately 70 percent.
Syndromic (sin-DRO-mik) means that the hearing impairment is associated with other clinical abnormalities. Genes are a road map for the synthesis of proteins, which are the building blocks for everything in the body: hair, eyes, ears, heart, lung, etc. Autosomal Dominant Inheritance: For autosomal dominant disorders, the transmission of a rare allele of a gene by a single heterozygous parent is sufficient to generate an affected child.
Autosomal Recessive Inheritance: An autosomal recessive trait is characterized by having parents who are heterozygous carriers for mutant forms of the gene in question but are not affected by the disorder. X-linked Inheritance: A male offspring has an X chromosome and a Y chromosome, while a female has two copies of the X chromosome only. Mitochondrial Inheritance: Mitochondrias, small powerhouses within each cell, also contain their own DNA. In the last decade, advances in molecular biology and genetics have contributed substantially to the understanding of development, function, and pathology of the inner ear. This is why hearing loss should be detected and treated as early as possible.  A hearing loss present at birth should be addressed by no later than 6 months of age.How severe does the hearing loss have to be to affect language development? Other causes of hearing loss, listed above, should be ruled out before investigating genetics causes. The absence of this molecule appears to be responsible for noise-induced hearing loss, one of the most common causes of deafness.

Their observations revealed an astonishing variation in hearing impairments from one mouse to the next, ranging from mild to profound hearing loss. They observed that in mice without pejvakin, the auditory sensory cells are damaged as soon as they are exposed to even seemingly harmless sounds – the equivalent of a minute spent in a nightclub for humans. When a standard hearing test was performed on these hearing-impaired individuals, the responses of their auditory sensory cells and neurons, although normal to begin with, gradually worsened as the test went on as a result of the sounds used.
Urban crowding means that large cities are getting noisier, particularly in developing countries. Please use newer version of your browser or visit Internet Explorer 6 countdown page for more information. Inherited genetic defects play an important role in congenital hearing loss, contributing to about 60 percent of deafness occurring in infants. Autosomal- recessive inheritance is responsible for about 80 percent of cases of non-syndromic hearing impairment, while autosomal-dominant genes cause 20 percent, less than two percent of cases are caused by X-linked and mitochondrial genetic malfunctions. Some aspects may be expressed in a range from mild to severe or different combinations of associated symptoms may be expressed in different individuals carrying the same mutation within a single pedigree. A heterozygous parent has two types of the same gene (in this case, one mutated and the other normal) and can produce two types of gametes (reproductive cells).
Interestingly, the sperm does not have any mitochondria, and consequently, only the mitochondria in the egg from the mother can be passed from one generation to the next.
Researchers have identified several of the various genes responsible for hereditary deafness or hearing loss, most notably the GJB2 gene mutation. The scientists’ discovery, which was published on November 5 in the journal Cell, offers new prospects for the treatment of this condition. Audiometric tests performed on individuals with mutations in this gene subsequently revealed an unusually high level of diversity in hearing impairments, in terms of both severity and characteristics. Young mice are highly vocal for the first three weeks after they are born, particularly when feeding. WHO predicts that by 2030, one billion people will be at risk of noise-induced hearing loss.
Although exact data is not available, it is likely that genetics plays an important role in hearing loss in the elderly.
Over 400 syndromes are known to include hearing impairment and can be classified as: syndromes due to cyotgenetic or chromosomal anomalies, syndromes transmitted in classical monogenic or Mendelian inheritance, or syndromes due to multi-factorial influences, and finally, syndromes due to a combination of genetic and environmental factors. An example of variable expressivity is seen in families transmitting autosomal dominant Waardenburg syndrome. If the inherited genes are defective, a health disorder such as hearing loss or deafness can result. One gamete will carry the mutant form of the gene of interest, and the other the normal form.

This leads to an interesting inheritance pattern where only affected mothers (and not affected fathers as their sperms do not have mitochondria) can pass on a disease from one generation to the next.
As one of the most common genetic causes of hearing loss, GJB2-related hearing loss is considered a recessive genetic disorder because the mutations only cause deafness in individuals who inherit two copies of the mutated gene, one from each parent. This latest study, carried out by scientists from the Institut Pasteur, Inserm, the College de France, Pierre & Marie Curie University and the University of Auvergne, aimed to clarify the reasons for this heterogeneity. Inherited genetic defects are just one factor that can lead to hearing loss and deafness, both of which may occur at any stage of a person’s lifespan. Within the same family, some affected members may have dystopia canthorum (an unusually wide nasal bridge due to sideways displacement of the inner angles of the eyes), white forelock, heterochromia irides (two different-colored irises or two colors in the same iris), and hearing loss, while others with the same mutation may only have dystopia canthorum. Sensitivity to aminoglycoside antibiotics can be inherited through a defect in mitochondrial DNA and is the most common cause of deafness in China! The scientists observed that as the number of mice in the cage increased, so did their hearing threshold – the minimum sound level at which they are able to hear sounds. The scientists also identified the noise-sensitive element in the cell as being the peroxisome, a small organelle involved in detoxification. Other factors may include: medical problems, environmental exposure, trauma, and medications. Thus the chance that the offspring of a parent with an autosomal dominant gene will develop the disorder is 50 percent.
In general, only one of the two X chromosomes carried by a female is active in any one cell while the other is rendered inactive.
Screening tests for the GJB2 gene are available for at risk individuals to help them determine their risk of having a child with hearing problems. Using direct, controlled acoustic stimulation, the scientists were able to prove that the auditory system of mice lacking in pejvakin is affected by their acoustic environment. Overall, offspring of these two parents will face a 25 percent chance of inheriting the disorder. This is why when a female inherits a defective gene on one X chromosome, the normal gene on the other X chromosome can usually compensate. As males only have one copy of the X chromosome, any defective gene is more likely to manifest into a disorder.
However, we don’t yet know what percentage of the population is either lacking in pejvakin or has a less effective form of the protein.

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