Pendred syndrome was first described in 1896 by Vaughen Pendred.
This syndrome is characterized by:
1. Severe degree of sensori neural hearing loss
This condition is characterized by abnormal PS gene in the long arm of chromosome 7. This PS gene is responsible for secretion of a protein called Pendrin.
Pendrin is an anionic exchanger which can cause exchange of chloride, bicarbonate and formate across membranes. Pendrin has been found to be active in thryoid follicular cells. They play a role in transportation of iodide from the cell to the colloid space. This accounts for the presence of goitre in the absence / abnormality of pendrin in these patients.
These patients may manifest with euthyroid state / mild hypothyroid state. Thyroid picture may be highly variable in these patients.
Inner ear findings:
Inner ear shows Mondini type deformity. These patients also show enlarged endolymphatic duct and sac.
In normal conditions, pendrin maintains the ionic exchanges between perilymph and endolymph in the membranous labyrinth which is contained in the bony structure named vestibular aqueduct. If pendrin function is lost, the endolymph volume increases resulting in the enlargement of the membranous labyrinth and of the surrounding bony structures, such as the vestibular aqueduct and the cochlea.
Diagram showing the effects of altered Pendrin in endolymphatic duct / sac.
Vestibular disorder is very rare in this syndrome.
In the absence of inner ear malformations the diagnosis of Pendred syndrome should never be made.
Pendred syndrome should be differentiated from Pendred syndrome like disorders i.e. pseudo pendred syndrome.
Pendrin also play a vital role in the bicarbonate transport in renal tubules. Hence it plays a vital role in the finer electrolyte hemostasis of renal tubules.It also decreases urine chloride excretion. Many of these patients do not manifest with renal problems.