Mutations in the SLC26A4 gene have been associated with two autosomal recessive disorders, Pendred syndrome and DFNB4 non-syndromic hearing loss. Pendred syndrome is the most common form of syndromic deafness, accounting for approximately 5-10% of hereditary hearing loss. The Pendred syndrome phenotype includes bilateral sensorineural hearing loss, which is usually severe to profound at birth, temporal bone abnormalities, vestibular abnormalities, and thyroid dysfunction, which usually leads to goiter formation in late childhood to early adulthood. The degree of hearing loss and thyroid disease phenotype is highly variable within families with Pendred syndrome. DFNB4 non-syndromic hearing loss is characterized by enlarged vestibular aqueduct and temporal bone abnormalities, without the thyroid phenotype.