Pendred syndrome is a clinically variable-genetic disorder characterized by bilateral sensorineural hearing loss and euthyroid goiter. It has an autosomal recessive inheritance pattern and is one of the most frequent forms of syndromic genetic deafness. Although the prevalence is unknown, Pendred syndrome can account for up to 7,5% of cases of congenital hearing loss.
It has been found considerable phenotypic variability even within the affected families. The main clinical symptom of presentation is the pre-lingual sensorineural hearing loss, although sometimes hearing loss develops later in childhood. The degree of hearing loss is variable. The appearance and presentation of euthyroid goiter (75%) is highly variable within and between families, with an enlarged thyroid usual that develops in late childhood and early adulthood. The thyromegaly reflects a defect in the transport of iodine from the colloid thyrocyte although organification itself is unaffected. If intake of iodine in the diet is low, the affected person can develop hypothyroidism.
The diagnosis is based on the presence of a hearing impairment, abnormalities of the temporal bone of the inner ear and abnormal test result perchlorate discharge or goiter. Inner ear anomalies range from dilated vestibular aqueduct to the cochlear hypoplasia. These abnormalities can be diagnosed by CT or MRI. The diagnosis is confirmed by molecular genetic test.
If images of the temporal bone have been obtained to evaluate the fluctuating hearing loss and EVA or cochlear hypoplasia have been observed, the differential diagnosis includes congenital cytomegalovirus infections, BOR syndrome and deafness at the DFNX2 locus (POU3F4).
It is possible to perform prenatal diagnosis in pregnancies at risk when mutations in the family are known.
Patients with Pendred syndrome may develop progressive hearing loss, producing this especially in patients with more severe abnormalities of the inner ear. The approach includes conducting annual audiogram and using headphones with proper amplification as soon as the hearing impairment is diagnosed. Abnormal thyroid function should be treated with standard therapy.