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Hearing Journal:
doi: 10.1097/01.HJ.0000444138.01516.32
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Genetics Evaluation in Children with Hearing Loss: Knowledge Is Power

McCreery, Ryan PhD

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Dr. McCreery is associate director of audiology and staff scientist at Boys Town National Research Hospital in Omaha, NE.

When hearing loss is first identified in a child, information overload can follow for all those involved in the child's care. Determining the type, degree, and configuration of hearing loss; figuring out amplification options; referring the child to early intervention; and providing informational and support counseling to families are crucial components of an ongoing process.

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As hearing healthcare professionals know, the Joint Committee on Infant Hearing recommends screening by one month of age, diagnostic assessment by three months, and early intervention by six months. When the dust settles, many families are left with questions about the cause of their child's hearing loss.

Medical genetics evaluation can help answer these questions, as well as shed light on the likelihood of there being an underlying medical condition related to the hearing loss.

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MAKING THE TEAM

The Centers for Disease Control and Prevention (CDC) estimates that 50 percent to 60 percent of congenital hearing loss cases have a genetic cause and, of these, 70 percent are not associated with a syndrome.

Figure. Ryan McCreer...
Figure. Ryan McCreer...
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More than 90 percent of children with hearing loss are born to parents who have normal hearing (Sign Lang Stud 2004;4[2]:138-163 http://research.gallaudet.edu/Demographics/SLS_Paper.pdf), and many families are interested in determining whether a genetic cause is likely or if future children may have the same condition.

Children with obvious physical or medical complications related to a syndrome may be more likely to receive a medical genetics assessment than those who only appear to have hearing loss.

In either instance, however, families and caregivers should be informed about the availability of genetics assessment, and hearing healthcare professionals should be resources for the clinics in their region that provide such evaluations.

Ideally, genetics assessment is completed by a team of professionals that includes, at a minimum, an audiologist, a pediatric otolaryngologist, the child's primary care provider, a pediatric geneticist, and a genetic counselor.

Although the audiological and medical aspects are essential, gathering information about other developmental and sensory systems can contribute valuable information as well. Therefore, other professionals who may be involved are psychologists, speech–language pathologists, physical and occupational therapists, and ophthalmologists.

The obvious disadvantage of this approach is that the critical mass of specialists required is often only available at large children's hospitals or medical centers.

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SUBSTANTIAL BENEFITS

The potential benefits of medical genetics assessment for children with hearing loss are substantial. One of the most significant is the identification of underlying medical conditions or, on the other hand, the determination that the genetic cause of hearing loss is not often associated with other medical problems.

About 50 percent of nonsyndromic hearing loss cases are related to a single recessive mutation known as DFNB1, or connexin 26 deafness (JAMA 1999;281[23]:2211-2216 http://jama.jamanetwork.com/article.aspx?articleid=190417). Children with DFNB1 typically do not have other medical problems associated with their hearing loss.

In Jervell and Lange–Nielsen Syndrome, however, hearing loss comes with a heart defect that can result in arrhythmia and sudden death without treatment. Although this condition is rare, the opportunity to educate the family about underlying medical conditions is a major benefit of genetics assessment.

Another significant advantage is the chance to provide information about the likelihood of future children having the same condition. In my experience, this knowledge does not affect decisions about whether or not to have additional children, but it allows the family to anticipate needs and make informed choices about family planning.

Genetics assessment also can help guide treatment and intervention. For example, one type of auditory neuropathy is caused by a mutation in the gene that encodes the protein otoferlin, which is important for the functioning of inner hair cells in the cochlea. The mutation often results in profound hearing loss.

Cochlear implants have been reported to be successful in children with this type of auditory neuropathy (Int J Pediatr Otorhinolaryngol 2006;70[4]:689-696 http://www.sciencedirect.com/science/article/pii/S0165587605004295), primarily because the auditory nerve is not affected by otoferlin.

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OVERCOMING THE CHALLENGES

Medical genetics evaluation has inherent challenges that professionals should discuss with families. In many cases, the assessment does not identify a definitive genetic cause, which can be frustrating for families.

With over 100 genes now known to be associated with hearing loss and new genes added to the list all the time, most medical genetics teams focus on the likeliest underlying conditions given the child's audiological and medical history, or the diseases that would most affect the child's health.

However, the development of tools that use a single blood sample to test for multiple genetic conditions associated with hearing loss can help simplify the assessment process for professionals and families.

For example, the Otoscope genetic test developed at the University of Iowa evaluates the potential for 66 types of nonsyndromic hearing loss in a single test (Proc Natl Acad Sci U S A 2010;107[49]:21104-21109 http://www.pnas.org/content/107/49/21104.full).

Families may experience complex feelings about participating in genetics evaluation, such as fear and guilt. These emotions may be unavoidable, but an experienced genetic counselor can help families cope with them as they arise and understand the implications of the assessment.

While some families may decide not to pursue genetics evaluation, professionals working with children who have hearing loss should outline the options, including the benefits and limitations. Having knowledge about their child's condition can help parents make informed decisions and plan for the future.

Read past Building Blocks columns in a special collection on the HJ website:

bit.ly/HJBuildingBlocksbit.ly/HJBuildingBlocks.

© 2014 by Lippincott Williams & Wilkins, Inc.

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