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This entry was posted on 10th October 2012 by Gary.
Hearing loss is mainly a result of aging, continuous noise exposure, medications, underlying conditions, or traumas. However, it can also be acquired at birth or hereditary. Congenital hearing loss is a very common condition and affects about 3 in every 1000 babies. There are many genetic causes that can lead to hearing impairment both mild and severe. The problematic genes can be passed to the children from one or both parents, who may or may not have hearing impairment, and manifest actively or the child may only be a carrier and thus hearing loss may occur in the next generation. About 60% of deafness in newborns is due to inherited genetic issues.
Chromosomes are the parts of cells that carry hereditary information and genes that are defective may be passed on from generation to generation. Hearing loss whose origin comes from such defective genes, can be syndromic or non-syndromic. Depending on the specific type, genetic hearing loss can be classified in 4 groups of hearing impairment - autosomal dominant (usually one parent has hearing loss and passes the gene to the child), autosomal recessive (both parents have normal hearing but carry a recessive gene), X-linked and mitochondrial.
Syndromic hearing loss
Up to 30% of all hereditary hearing impairment is syndromic. This type of hearing loss occurs with additional genetic problems represented in many different medical conditions. There are about 400 known syndromes that include hearing difficulties as part of all genetic abnormalities that occur. One such condition is the Waardenburg syndrome, which represents with a sensorineural hearing loss as well as an abnormal pigmentation of the eyes, hair and skin. Other common syndromes with the participation of autosomal dominant hearing loss are the Branchiootorenal syndrome, the Stickler syndrome and Neurofibromatosis 2 .
In the group of autosomal recessive hearing impairment falls the Usher syndrome, which comprises hearing, visual and vestibular problems. Other common autosomal recessive syndromes are the Pendred syndrome, Jervell and Lange-Nielsen syndrome, Biotinidase deficiency and Refsum disease.
X-linked hearing loss usually affects males and the defective gene is carried by the mother. Syndromes that are connected to this type of abnormality are the Alport syndrome and the Mohr-Tranebjaerg syndrome.
Non-syndromic hearing loss
About 70% of inherited hearing impairment is non-syndromic and hearing loss is the only trait that characterizes it. The greatest portion, around 80%, is due to autosomal recessive inheritance. The two main non-syndromic conditions that cause hearing loss are otosclerosis and DPHL (dominant progressive hearing loss). Otosclerosis usually occurs when the person is between 20 and 50 years of age. It manifests with a growth in the middle ear leading to a progressive conductive hearing loss. The DPHL and prebycusis (hearing loss connected to aging) are the most widespread forms of sensorineural progressive hearing loss. While prebycusis is common for adults over 60 and is a cumulative result of lifestyle, exposure to noise and natural aging, the dominant progressive hearing loss usually occurs early in childhood and may cause balance problems as the organ affected in the condition is the inner ear, host to the vestibular apparatus.
This entry was posted in Hearing Information on 10th October 2012 by Gary.
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