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Understanding Hereditary Hearing Loss
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Hearing Loss |
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We frequently think of hereditary hearing problem as being congenital; even so, some cases don’t become visible until later in life. Genetic mutations that can result in hearing loss have already been detected in more than 50 different genes; scientists believe they'll identify many more. Although scientists have identified most of the genes related to childhood deafness, those related to hearing loss that spring up later in life aren't as well understood.
Close to 30,000 genes shape our personal characteristics by creating a blueprint for how we function and develop throughout our life. Hereditary hearing loss can be caused by a single pair of genes, interactions among multiple gene pairs, or complications between environmental and genetic factors (for example, prolonged exposure to aminoglycoside antibiotics seems to trigger a specific kind of genetic hearing loss). As a matter of fact, the degree to which contemporary factors such as ototoxic drugs, noise exposure, aging, or some combinations of these factors will affect your hearing ability probably depends on your present genetic make-up. It means that you and your friend could be exposed to similar noises (or similar drugs) for the same period of time, however only one is more susceptible to hearing loss. One of you is more vulnerable to hearing loss than the other, and the difference is probably hereditary.
For the dominantly inherited hearing loss, a gene for normal hearing is dominated by a gene for hearing loss; hearing loss will appear although the instruction from another gene in the pair are for normal and healthy hearing. In many cases, an individual with this category of hearing loss has a family member with a similar hearing problem. In other words, there are no parents or carriers who don’t have hearing problem themselves but pass it on to their descendants. Because the affected parents have one dominant hearing loss gene and another gene for normal hearing, in each conception there’s a fifty percent probability that he or she will have inherited gene for hearing loss. Inherited hearing loss accounts for approximately fifteen to twenty percent of all genetic hearing cases.
Another seventy to eighty percent of genetic hearing problems are inherited recessively. In recessive inheritance, the effect appears only when all genes in a pair deliver the same instructions (for instance, brown eyes and brown eyes). The affected person’s parents usually have normal hearing. Each parent has a gene for hearing loss; however it’s dominated by another gene for normal hearing. Therefore, hearing loss happens only when two carriers meet and each contributes the hearing loss gene for the child. Thus, an individual with recessively inherited hearing problem ends up with a couple of hearing loss genes in a single gene pair. If normally-hearing parents have the same recessive gene, a pregnancy carries a twenty-five percent risk that the infant will inherit a hearing problem (and a fifty percent risk that the infant will be a carrier).
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