Description, Causes and Risk Factors:
Alterative Names: Goiter-deafness syndrome, thyroid hormone organification defect IIB.
Pendred syndrome is a common form of syndromic deafness. At least 5% of the total cases with congenital deafness are PDS. 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.
Pendred syndrome is inherited as an autosomal recessive trait. The only gene known to be associated with PDS is the solute carrier family 26, member 4 gene (SLC26A4), or PDS gene. The normal PDS gene makes a protein (pendrin) that is found at significant levels only in the thyroid. Pendrin transports anions, particularly chloride (Cl-) and iodide (I-), into and out of the cells. This action is important for thyroid function and inner ear development. Alteration in PDS gene will impair the function of pendrin leading to thyroid malfunction and improper development of the ear. Mutations in PDS gene are found in more than 90% of typical cases and they differ according to ethnic group.
Incidence differs according to geographic location with a range between 1/100,000 births and 10/100,000 births. Audio-prosthetic management of deafness can be helpful and if the goiter becomes compressive because of excessive size, a thyroidectomy must be performed.
Typical PDS has the association of congenital bilateral neurosensory deafness, thyroid goiter, cochleovestibular malformation and potential vestibular dysfunction. The severity of the symptoms and the age of onset vary from case to case. Deafness often appears at birth, but it may develop in late infancy or early childhood. Sometimes, deafness is asymmetrical or fluctuant and often it is progressive. Abnormal bones of the inner ear can be observed in PDS. Thyroid status varies from euthyroid (goiter) to hypothyroidism. Goiter is secondary to abnormal iodine transport across the thyrocyte and it develops most commonly during adolescence.
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 doctor will ask about your symptoms and medical history. A physical exam will be done.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.
Genetic Testing: Testing is performed by sequencing all exons and the surrounding intronic regions of the SLC26A4 gene.This assay will detect point mutations, small deletions, and small insertions. It will not detect a partial orwhole gene deletion or duplication.
Molecular testing of the SLC26A4 gene should be considered for individuals with hearing loss and EVA (enlarged vestibular aqueduct).SLC26A4 mutations are identified in 80 to 90% of familial cases of Pendred syndrome, and in about 30%of cases with no family history. Mutations have been identified throughout the SLC26A4 gene andinclude point mutations, small insertions or deletions, and splice site mutations. Deletions of single andmultiple exons have also been reported.
The detection of two pathogenic mutations in SLC26A4 is consistent with a diagnosis of Pendredsyndrome or DFNB4. However, single heterozygous mutations have been identified in SLC26A4 in 20 to30% of individuals who meet criteria for Pendred syndrome or DFNB4. It is hypothesized that a secondunidentified mutation is present in SLC26A4 or in another gene. There is some evidence to suggest thatindividuals with one identified mutation in SLC26A4 are less likely to develop thyroid manifestationsthan individuals with two identified mutations.
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.
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.
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.
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.
NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.
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