Pendred syndrome
Overview
Pendred syndrome is a genetic disorder that causes early hearing loss in children. It also can affect the thyroid gland and sometimes may affect a person's balance. The syndrome is named after Vaughan Pendred, the physician who first described individuals with the disorder. Children who are born with Pendred syndrome may begin to lose their hearing at birth or by the time they are three years old. The hearing loss is progressive, which means that a child will have less hearing over time. Some individuals may become totally deaf. The loss of hearing often happens suddenly and in stages. Sometimes, after a sudden decrease in hearing, a person's hearing will nearly return to its previous level. Almost all people with Pendred syndrome have bilateral hearing loss, or hearing loss in both ears. The hearing loss often is greater in one ear than in the other.
Symptoms
The hearing loss of Pendred's syndrome is present from birth, and language acquisition may be a significant problem if this is severe in childhood. Hearing typically worsens over the years, and many proceed to deafness at a later age. In some cases, language development worsens after head injury, suggesting that the inner ear is sensitive to trauma in Pendred syndrome.[3] A goitre is present in 75% of all cases.
Causes
Pendred syndrome can be caused by changes, or mutations, to a gene known as SLC26A4 (also referred to as the PDS gene) on chromosome 7. Because it is a recessive trait, a child needs to inherit two mutated SLC26A4 genes—one from each parent—to have Pendred syndrome. The child's parents do not need to have Pendred syndrome to be a carrier of a mutation in the SLC26A4 gene. Couples who are concerned that they might be able to pass Pendred syndrome on to their children may seek genetic testing. A possible sign that a person may be a carrier of a mutated SLC26A4 gene is a family history of early hearing loss. Another sign is a family member who has both a goiter and hearing loss. A mutation in the SLC26A4 gene can be determined by genetic testing that uses a blood sample. The decision to have a genetic test is complex. Most people receive assistance from a genetic counselor trained to help them weigh the medical, emotional, and ethical considerations. A genetic counselor is a health professional who provides information and support to individuals and families who have a genetic disease or who are at risk for such a disease.
Diagnosis
A physician called an otolaryngologist or a clinical geneticist will consider a person's hearing, inner ear structures, and sometimes the thyroid in diagnosing Pendred syndrome. The specialist will evaluate the timing, amount, and pattern of hearing loss. He or she will ask questions such as "When did the hearing loss start?", "Has it worsened over time?", and "Did it happen suddenly or in stages?" Early hearing loss is one of the most common characteristics of Pendred syndrome; however, this symptom alone does not mean a child has the condition. The specialist uses inner ear imaging techniques known as magnetic resonance imaging (MRI) or computed tomography (CT or CAT) to look for two key characteristics of Pendred syndrome. One characteristic might be a cochlea with too few turns. The cochlea is the spiral-shaped part of the inner ear that converts sound into electrical signals that are sent to the brain. A healthy cochlea has two-and-a-half turns, but the cochlea of a person with Pendred syndrome may have only one-and-a-half turns. A second characteristic of Pendred syndrome is enlarged vestibular aqueducts (see figure). The vestibular aqueduct is a bony canal that runs from the vestibule (a part of the inner ear between the cochlea and the semicircular canals) to the inside of the skull. Inside the vestibular aqueduct is a fluid-filled tube called the endolymphatic duct, which ends at a balloon-shaped endolymphatic sac. When the vestibular aqueduct is enlarged, the endolymphatic duct and sac grow large with excess fluid in comparison to their normal sizes. The function of the vestibular aqueduct is not well understood. When screening for Pendred syndrome, it is not recommended to test the blood for thyroid hormone because the amount usually is the same whether someone has Pendred syndrome or not. Some people may receive a "perchlorate washout test," a test that determines whether the thyroid is functioning properly. Although this test is probably the best test for determining thyroid function in Pendred syndrome, it is not used often and may be replaced by genetic testing. Individuals who have a goiter may be referred to an endocrinologist, a doctor who specializes in glandular disorders, to determine whether the goiter is due to Pendred syndrome or to another cause. Goiter is a common feature of Pendred syndrome, but many individuals who develop a goiter do not have Pendred syndrome. Conversely, many people who have Pendred syndrome never develop a goiter.
Treatment
Treatment options are available for individuals with Pendred syndrome. Because the syndrome is inherited and can involve thyroid and balance problems, many specialists may be involved in treatment. The treatment team may include a primary care physician, an audiologist, an endocrinologist, a clinical geneticist, a genetic counselor, an otolaryngologist, and a speech-language pathologist. To reduce the likelihood of progression of hearing loss, individuals with Pendred syndrome should avoid contact sports that might lead to head injury; wear head protection when engaged in activities that might lead to head injury (such as bicycle riding or skiing); and avoid situations that can lead to barotrauma (extreme, rapid changes in pressure), such as scuba diving or hyperbaric oxygen treatment. Pendred syndrome cannot be cured. However, the medical team can help parents and individuals make informed choices about treatment options. They also can help them prepare for increased hearing loss and other possible long-term consequences of the syndrome. Children with Pendred syndrome should start early treatment to learn skills that will help them communicate, such as learning sign language or cued speech or how to use a hearing aid. Most individuals with Pendred syndrome will have hearing loss significant enough to be considered eligible for a cochlear implant. A cochlear implant is an electronic device that is surgically inserted into the cochlea. A cochlear implant does not restore or create normal hearing. Instead, a cochlear implant helps a person develop a new way of understanding speech. Children over 12 months of age as well as adults are eligible to receive an implant. (For more information, see the National Institute on Deafness and Other Communication Disorders [NIDCD] fact sheet "Cochlear Implants.") Individuals with Pendred syndrome who develop a goiter need to have it checked regularly. The goiter in Pendred syndrome is unusual because the thyroid is making the right amount of thyroid hormone but it is growing in size. Such a goiter often is called a euthyroid goiter. For more information on the treatment of goiters, contact the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) at www.niddk.nih.gov.