LVAS/Pendred

Question 1

What causes Pendred syndrome?

Answer 1

Pendred syndrome is an autosomal recessive condition caused by a faulty gene called PDS. PDS codes for a protein called pendrin which is expressed both in the thyroid and the inner ear.

Question 2

Pendred syndrome causes…

Answer 2

Thyroid dysfunction and congenital sensorineural hearing loss.
Mondini malformation may be present
Can also cause enlarged vestibular aqueduct and sac.

Question 3

Hearing loss is…

Answer 3

Generally present at birth but can develop in early childhood.
Hearing loss is most often severe to profound but can vary.
Low frequency air bone gap due to 3rd window
Vestibular symptoms may be present

Question 4

Vestibular acqeduct is…

Answer 4

Narrow bony canal that travel from inner ear endolymphatic space to deep inside skull.

Question 5

Running through the vestibular acqueduct is…

Answer 5

The endolymphatic duct

Question 6

Endolymphatic duct leads to the…

Answer 6

Endolymphatic sac. Contains Endolymph (high K low Na)

Question 7

EVAS causes…

Answer 7

Malformation of the temporal bone associated with syndromic or non syndromic early onset progressive sensorineural and vestibular issues.
No effective treatment.
A marker of congenital problem not just HL

Question 8

EVAS can result from…

Answer 8

abnormal or delayed development, Pendred Syndrome, Brachio-otorenal syndrome, Charge syndrome
Or Congential disroder resulting from faulty embryogenesis of the duct and sac.

Question 9

Theories of hearing loss caused by EVAS

Answer 9

1) Enlarged duct and sac unable to maintain endolymph volume/pressure.
2) Lack of pendrin results in ineffective ionic transport of cochlea fluids affecting the outer hair cells and their amplification function. This leads to hearing dysfunction.
3) Inability to maintain ionic homeostasis leading to degeneration of Stria Vascularis and hair cells.