In developed countries approximately 80% of congenital hearing loss is due to genetic causes and the remainder to environmental acquired causes. Herein, we describe stateoftheart research on genetic hearing loss treatment through gene therapy and discuss the obstacles to overcome in curative treatments. About 1 in 500 infants is born with or develops hearing loss. Usher syndrome is a condition characterized by partial or total hearing loss and vision loss that worsens over time. Hearing loss gene tests partners personalized medicine. Occasionally, loci merge when multiple independently linked loci overlap and it is discovered that the same underlying gene causes hl. Later in life, the person develops a condition called retinitis pigmentosa. 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. Genetic tests can therefore be helpful even if there is only one person in the family with hearing loss. Mutations in any of those genes may cause hearing loss. Both are genetic and cause hearing loss at different rates and at different ages, although always during childhood. For many babies, the cause of hearing loss is unknown. The study, published in the journal nature, focused on a mutation in a gene called tmc1, a single wrong letter in the genetic code, that causes the loss of the inner ears hair cells over time. Finally, some bacterial and viral infections during pregnancy or shortly after birth can result in the presence of hearing loss at birth 1.
With our expanded tier i and otoseq tests, we have simplified genetic testing for patients with sensorineural hearing loss snhl. Back at home, she secured funding from the pakistani government and then was the first scientist in pakistan to obtain an r01 research grant from the nih a fogarty global research initiative program award. Genetic hearing loss crosses almost all the categories of hearing loss which includes the following. Genetic testing for hearing loss page 3 of 6 enttoday. This enabled her to hunt for genetic mutations involved in moderatetosevere hearing loss. For example, scientists have identified the dfna10 gene, which causes progressive hearing loss later in adulthood 3. The most common cause of genetic hearing loss, accounting for 20 percent of cases, is a recessive connexin 26 mutation on the gbj2 gene. Recent advances and future prospects 1anita jeyakumar, 2jennifer lentz abstract hearing loss hl is a common and complex condition that can occur at any age, be inherited or acquired, and is associated with a wide number of etiologies. Mutations in these genes have been discovered for patients with different modes of inheritance and types of hearing loss, ranging from syndromic to nonsyndromic and mild to profound. Breakthrough for genetic hearing loss as gene editing. For more than half of all deaf and hard of hearing children, a genetic cause can be identified. Knowing the genetic basis of hearing loss provides a framework for medical. Handbook of genetic counselinghearing loss unknown cause. Although generally thought of as a childhood condition, genetic hearing loss can result in adultonset hearing loss.
Genetic factors play a role in up to two thirds of all childhood hearing impairment. Genetic testing for hearing loss blueprint genetics. Agerelated hearing loss first affects the ability to hear highfrequency sounds, such as speech. Understanding the genetics of deafness projects at harvard. Genetic forms of hearing loss must be distinguished from acquired nongenetic causes of hearing loss. It can begin as early as a persons thirties or forties and worsens gradually over time. Shl is a form of hl accompanied by additional clinical features. The chances of developing deafness caused by a mutated gene depend on whether the mutation is dominant or recessive. Two genetic disorders that can cause hearing loss in. Breakthrough for genetic hearing loss as gene editing prevents deafness in mice, reports the guardian after researchers used a technique to snip away a gene mutation that leads to progressive deafness.
It is believed that there are over 400 forms of genetic hearing loss. The laboratory for molecular medicine at partners healthcare personalized medicine offers genetic testing for syndromic and nonsyndromic forms of hearing loss. Genetic sensorineural hearing loss clinical presentation. Advances in genetic diagnosis and treatment of hearing loss a. Can be syndromic or non syndromic need for knowing a new era in audiology b knowledge about etiology of hl. Gene editing shows promise for alleviating hearing loss. Genetic factors make some people more susceptible to hearing loss than others. While many people assume hearing loss is something mainly associated with ageing, many cases are in fact hereditary. The comprehensive genetic testing offered at one of these labs has dramatically improved the diagnostic rate of hearing loss, said dr. Associate director, harvard medical school center for hereditary deafness.
Potential treatments for genetic hearing loss in humans nature. While the majority of hereditary hearing loss is not associated with a specific syndrome, many genetic syndromes possibly more than 300 are associated with congenital hearing loss, including. Agerelated hearing loss genetics home reference nih. The heritability ranges from low to high 6 78910, suggesting that multiple genetic modiiers and environmental factors contribute to the onset and severity of hearing loss. Genetic hearing loss is differentiated from acquired hearing loss with identification of a perinatal infection, such as toxoplasmosis, rubella, cytomegalovirus and herpes torch, or another source such as trauma or noise. A genetic hearing loss may be inherited in an autosomal dominant, autosomal. A combination of genetic and nongenetic factors also can cause hearing loss. Years of exposure to damaging volumes, beginning at a young age with earbuds blasting loud music to occupationally hazardous sounds, whether you are a dentist or a construction worker, to the decline of hearing that. Research in pakistan yields findings on hereditary hearing. A recessive disease mutation requires a copy of the. Agerelated hearing loss also known as presbycusis is a decrease in hearing ability that happens with age.
The genetics of hearing loss clinical education center. The hearing loss is classified as sensorineural, which means that it is caused by abnormalities of the inner ear. Although available for years, gene testing has only recently has become a feasible tool in the clinical setting. Ushers syndrome is a disease that affects both hearing and sight. The genetic forms of hearing loss are diagnosed by otologic, audiologic, and physical examination, family history, ancillary testing e. This booklet is designed to help explain the role of genetics in hearing loss, how genetic testing is done, what the results of genetic tests mean, and what options. Clinical aspects of hereditary hearing loss genetics in medicine. Genes critical for hearing identified sciencedaily. Genetic hearing loss hereditary hearing loss causes. About comprehensive hearing loss and deafness hearing loss is a genetically very heterogenous group of phenotypes varying in severity and causes.
A research advance may stop the progression of hearing loss and lead to significant preservation of hearing in people with usher syndrome type. Dominant hearing loss can be caused by only one copy of a mutated gene dominant hearing loss is seen in every generation if a parent has a dominant mutation, each child has a 50 % chance of inheriting it. Genetic hearing losses are due to single or multiple. Another possibility is that the hearing loss is genetic. A large scale hearing loss screen reveals an extensive unexplored genetic landscape for auditory dysfunction. Sometimes, knowledge of these causes can help to treat the hearing loss or stop it from getting worse. Autosomal dominant hearing loss can run throu gh families from generation to generation or it can occur in a family for the first time as the result of a new gene change. The genetics of hearing loss can be complicated and difficult to understand. Males and females have the same 50% chance of having hearing loss.
A person who is suffering from ushers syndrome is born with a certain degree of hearing loss which may vary from person to person. Their genes make them more predisposed to hearing loss due to ageing or induced by noise, drugs or infections. Hearing loss hl is the most common sensory defect in human beings, affecting 1. Introduction deafness, hearing impairment, or hearing loss is a partial or total inability to hear. Gene mutations can cause hearing loss in several ways. A guide for patients and families harvard university. The other 70% of genetic hearing loss is called non syndromic hearing loss. The loss of vision is caused by an eye disease called retinitis pigmentosa rp, which affects the layer of lightsensitive tissue at the back of the eye the retina. Gene editing prevents inherited deafness in mice nhs. Nonsyndromic sensorineural hearing loss is a partial or total loss of hearing that occurs without other associated clinical findings. Age of onset prelingual hl hl occurs before language acquisition. Shl consists of hl that presents with anomalies of the eye, kidney, the musculoskeletal and the nervous systems, as well as pigmentary disorders and others 15 figure 1.
Molecular genetic testing assists otologists by providing insight into the etiology of hearing impairment in children. Inherited genetic defects play an important role in congenital hearing loss, contributing to about 60% of deafness occurring in infants. Early diagnosis and testing can lead to early support for children. This means that it is carried down through a family. Approximately 30% of the genetic cases of hl are considered to be syndromic 11. A vast number of these hearing loss types can be separated through the audiological characteristics, which means the type of hearing loss, the degree of severity of hearing loss or the progression of hearing loss, or. Hearing loss is the most common sensory defect in humans, affecting normal communication in 10 percent of people aged 65 years or older. The genetic heterogeneity of hereditary hearing loss is thus far represented by hundreds of genes encoding a large variety of proteins. While genetic causes account for 5060%, environmental causes account for more than 25% of hearing loss among infants. Not all congenital hearing loss is genetic, and not all genetically related hearing loss is present at birth. One of the major cause of hearing loss is gene mutations.
In most cases, hearing loss is a multifactorial disorder cau. This booklet answers many of the questions that families have about the causes of hearing loss, including genetic causes. Hl is the most common sensory deficit in newborn children. It is estimated that between 50 and 100 genes are involved in the functioning of the ear. The genetic forms of hearing loss are diagnosed by otologic, audiologic, and physical. Smith recently, he and his colleagues published a study looking at the most current evidence on the use of comprehensive genetic testing. Testing begins with the costeffective tier i test, which includes the most common genes associated with sensorineural hearing loss. Genetic testing may determine whether your childs hearing loss is due to nongenetic causes or due to changes on a gene resulting in hearing loss. The syndromes may also adversely impact balance, vision and the thyroid. Early diagnosis and testing can lead to early support for children and the teaching of communication strategies. Genetic testing for hearing loss page 5 of 6 enttoday. Genetic testing is a powerful tool that can augment more traditional diagnostic methods in identifying and diagnosing the etiology of hearing loss. There are also a number of things in the environment that can cause hearing loss. It is estimated that the causes of agerelated hearing loss are 3555% genetic.
For recessive hearing loss, both copies of a gene must be mutated to get hearing loss. Connexin test gjb2 sequencing and gjb6ds1830 deletion otogenome test for hearing loss and related syndromes 110 genes. Although exact data is not available, it is likely that genetics plays an important role in hearing. From this information, professionals can calculate the likelihood that other children in your family may also have a hearing loss due to the same cause. The auditory system exhibits senescent changes with the past time which could trigger to acquire sensorineural hearing loss. A carrier is a person who carries one copy of a recessive mutation, but does not have hearing loss. Genetic testing for hearing loss cincinnati childrens. Common causes of genetic hearing loss syndromic hearing loss accounts for 30% prelingual deafness autosomal recessive usher syndrome congenital sensorineural hearing loss.