All About Hereditary Hearing Loss

Genetics word cloud concept

There are several ways that genetics can play a role in hearing loss.  Hearing loss or deafness can be experienced from birth, genetic mutations can make certain people more susceptible to age and noise-related hearing loss, and someone can inherit a gene mutation that does not manifest with them but may result in hearing loss in their offspring.
Hearing loss present from birth is categorized as either non-syndromic, which means the hearing loss occurs without any other symptoms in the rest of the body, or syndromic, which means that the hearing loss is part of a syndrome which affects other parts of the body.
Non-syndromic hearing loss accounts for 70% of hearing loss present at birth.  The most common cause of non-syndromic hearing loss is gene mutations resulting in damage to the structures of the inner ear.  Mutations in more than 60 genes can cause non-syndromic hearing loss.
Syndromic hearing loss accounts for 30% of hearing loss present at birth.  The most common causes of syndromic hearing loss are:
DiGeorge Syndrome
DiGeorge syndrome or 22q11.2 deletion syndrome is caused by a missing part of chromosome 22.  The missing part results in conditions that may include hearing loss, heart defects, developmental delays and cleft palate.  The types and severity of symptoms vary by case and by which part of the body is affected.  
Treacher-Collins Syndrome
Most cases of Treacher-Collins Syndrome are caused by mutations in the TCOF1 gene.  A very small percentage of cases are caused by mutations in either the POLR1C or POLR1D genes. The gene mutations cause abnormalities in the development of facial bones and tissues, including the ears which may cause hearing loss or deafness.
Otosclerosis is an inherited disease that causes the bones of the ear to fuse together, instead of remaining separate and flexible. The fusion can occur in the inner ear, middle ear, or both and causes hearing difficulties and sometimes complete hearing loss.   With Otosclerosis, hearing loss usually begins around age 10 and hearing loss progression generally stops around age 30.  Depending on the bones affected, treatment may include surgery or hearing aids.
Pendred Syndrome
Pendred Syndrome is a genetic disorder caused by mutations in the SLC26A4 gene.  It causes early hearing loss in children and may also cause balance or thyroid gland issues.  Hearing loss may be present at birth or may begin anytime after birth until the age of three.  Hearing loss caused by Pendred Syndrome often happens suddenly and can sometimes lead to total deafness.
Usher Syndrome
Usher Syndrome is an inherited trait that interferes with the auditory nerve’s ability to transmit data to the brain.  It is a rare disorder and it causes both hearing and vision issues. There are several types of Usher Syndrome which affect hearing, vision, and balance in different ways.    The severity of symptoms, along with the age of onset, helps doctors determine the type.
Recent strides in gene therapy are producing promising results, including advances to stop the progression of hearing loss in Usher Syndrome.  Researchers at Case Western Reserve University School of Medicine were able to curb the hearing loss in mice with a specific type of Usher Syndrome by replacing defective genes with normal genes.  Gene therapy for humans is still years away, but progress against genetic hearing loss continues with several studies being conducted.
If you suspect hearing issues with your child, schedule an appointment with us for an evaluation and speak to your child’s pediatrician.

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