Genetic Causes of Hearing Loss in Newborns

Newborn screening for hearing loss is important because the sooner a hearing loss is detected, the sooner a child can receive early intervention and develop communication skills. About 3/1000 children have hearing loss detected in the newborn period. There are many reasons for hearing loss, including both environmental and genetic causes. Environmental exposures include such things as infections, injury, and premature birth. Currently, it is known that genetic factors account for at least 50% of childhood deafness. Exploring the underlying cause of a child's hearing loss is important so that families and health care providers are able to discuss the child's long term prognosis not only for hearing and communication, but also regarding the possibility of other health or learning problems. This article will examine some of the more common genetic causes for deafness that occur in newborns and children. Genetic causes of hearing loss can be divided into non-syndromic and syndromic categories.

Non-syndromic deafness accounts for about 70% of genetic hearing loss and means that the hearing loss is isolated and affected children do not have other health problems or developmental delays. Most non-syndromic deafness is inherited in an autosomal recessive manner. Autosomal recessive means that both parents must be carriers for the same gene mutation in order for a child to be affected. Two parents who are both carriers for a recessive mutation have a 25% chance in each pregnancy to have a child with hearing loss.

There are two genes that are responsible for at least 50% of autosomal recessive non-syndromic hearing loss. An infant identified by newborn screening to have hearing loss but no other apparent health problems would be a good candidate for genetic testing for these genes, connexin 26 and connexin 30.

Autosomal dominant non-syndromic hearing loss has been seen with various mutations in many different genes. The best way to determine which genetic test is most appropriate is to examine when the hearing loss began (before or after language development) and what decibel level is affected. A person with autosomal dominant non-syndromic hearing loss has a 50% chance in each pregnancy to have a child with hearing loss.

Syndromic hearing loss involves abnormalities of the ear, other birth defects, or problems with other organ systems. Syndromic hearing loss can also be inherited in autosomal recessive and autosomal dominant patterns. Several common syndromes are discussed below.

Waardenburg syndrome is the most common autosomal dominant syndrome with hearing loss. In addition to hearing loss, individuals with Waardenburg syndrome may have abnormalities in the pigment of their skin, hair and eyes. Some individuals have abnormalities of their upper limbs, or an intestinal disorder called Hirschprung disease.

Branchio-oto-renal syndrome (BOR) is the next most common autosomal dominant syndrome with hearing loss. Individuals may have visible external ear abnormalities, branchial cysts, and renal abnormalities.

Stickler syndrome is an autosomal dominant syndrome caused by mutations in genes that code for collagen, one of the connective tissues that hold our bodies together. Collagen is an important component of the eye and the palate as well as hearing.

Usher syndrome is the most common autosomal recessive syndrome with hearing loss. Affected children are born with hearing loss and go on to develop blindness due to retinitis pigmentosa. The vision loss begins in the teens with loss of peripheral vision and night blindness, and gradually progresses to total blindness. Although intelligence is normal, motor milestones may be delayed due to abnormal vestibular function (affecting balance).

Pendred syndrome is the next most common autosomal recessive syndrome with hearing loss. Babies have hearing loss at birth and abnormal thyroid function.

Since there are so many different types of hearing loss and underlying causes for the loss, if your child had an abnormal newborn hearing test or if you have any concerns about your child's hearing, please ask your child's physician for further testing to clarify his/her hearing loss. If the hearing loss is confirmed, or if your child has additional birth defects or developmental delays, request a referral to a local genetics center for a thorough workup. A genetics evaluation involves reviewing a child's medical and family history and any test results with a geneticist and genetic counselor. A geneticist is a physician with special training in diagnosing and managing genetic disorders. A genetic counselor is a medical professional who assists the physician with diagnosis and management as well as coordination of genetic testing and follow up. A genetic counselor also helps to ensure that families understand the information they receive. A genetics evaluation is designed to help families understand why their child has hearing loss, and whether future children or other family members are also at risk. More information about a genetics evaluation can be found at:

http://www.nsgc.org/consumer/faq_consumers.cfm

http://www.genetests.org/servlet/access?id=8888892&key=UcHOirLqIFF4t&fcn=y&fw=5pcq&filename=/concepts/primer/primerwhatiscons.html

The Missouri Newborn Hearing Screening Program (MNHSP) is a part of continuing national efforts to promote the early detection of hearing loss, the tracking of infants/children who are deaf or hard of hearing and the initiation of effective intervention systems for identified children. In Missouri, hearing screening for newborns became mandatory on January 1, 2002. All Missouri birth facilities screen newborns for hearing loss prior to discharge. Screening is quick, simple and safe. Most babies sleep during the process. If a baby does not pass the screening, the birth facility will provide the parent/guardians with a list of audiologists who can provide diagnostic testing. If hearing loss is found, a MNHSP Regional Representative will refer the infant's parents/ guardians to First Steps, administered by the Missouri Department of Elementary and Secondary Education, for appropriate early intervention programs.

To contact the MNHSP, call Cathy Harbison at (573) 751-6266. More information about the MNHSP can be found at: http://www.dhss.mo.gov/NewbornHearing/.