INTRODUCTION: Pendred syndrome, a combination of sensorineural deafness, 
impaired organification of iodide in the thyroid and goitre, results from 
biallelic defects in pendrin (encoded by SLC26A4), which transports chloride and 
iodide in the inner ear and thyroid respectively. Recently, pendrin has also 
been identified in the kidneys, where it is found in the apical plasma membrane 
of non-α-type intercalated cells of the cortical collecting duct. Here, it 
functions as a chloride-bicarbonate exchanger, capable of secreting bicarbonate 
into the urine. Despite this function, patients with Pendred syndrome have not 
been reported to develop any significant acid-base disturbances, except a single 
previous reported case of metabolic alkalosis in the context of Pendred syndrome 
in a child started on a diuretic.
CASE REPORT: We describe a 46-year-old female with sensorineural deafness and 
hypothyroidism, who presented with severe hypokalaemic metabolic alkalosis 
during inter-current illnesses on two occasions, and who was found to be 
homozygous for a loss-of-function mutation (V138F) in SLC26A4. Her acid-base 
status and electrolytes were unremarkable when she was well.
CONCLUSION: This case illustrates that, although pendrin is not usually required 
to maintain acid-base homeostasis under ambient condition, loss of renal 
bicarbonate excretion by pendrin during a metabolic alkalotic challenge may 
contribute to life-threatening acid-base disturbances in patients with Pendred 
syndrome.