Endocrine Abstracts

A 22-year old lady was referred with a history of fatigue, generalised aches and pains. Investigations revealed persistently low potassium on few occasions. There was no history of diarrhoea or vomiting. No laxative, diuretic or liquorice abuse. PMH: treated hypothyroidism and Idiopathic thrombocytopenic purpura. She weighed 46 kg and her BP was 115/63. Further investigations: sodium 140 mmol/l, potassium 2.6 mmol/l (3.5–5.0), bicarbonate 28 mmol/l (22–28), magnesium 0.45 mmol/l (0.7–1.00). 24 hr Urinary Calcium excretion1.2 mmol/24 h (2.5–7.5); 24 hr Urinary Magnesium output 3.8 mmol/ 24 h (0.5–4.0); 24 hr Urinary Potassium output 91 mmol/ 24 h; 24 hr Urinary Sodium output 161 mmol/24 h;urinary Na 64 mmol/l (50–125); urinary K+36 mmol/l (20–60). No evidence of diuretics or laxative found in urine. Plasma renin activity (Supine) 8.9 (pmol/ml/hr), after mobilisation 10.4 (pmol/ml/hr). Plasma Aldosterone supine 320 pmol/l & after mobilisation 1755 pmol/l. The findings of hypokalaemia, hypomagnesaemia and hypocalciuria were consistent with a diagnosis of Gitelman’s syndrome. Patient was treated with Spironolactone and slow k tablets. Serum potassium level gradually normalised.

Gitelman’s syndrome is a variant of Bartter’s syndrome and is characterised by hyperreninaemic hyperaldosteronism, hypokalaemic metabolic alkalosis, hypomagnesaemia and hypocalciuria. An autosomal recessive condition and caused by mutations in the SLC12A3 gene, associated with a putative loss of function of the thiazide sensitive sodium-chloride transporter (NCCT) at distal convoluted tubule. Loss of function of sodium-chloride transporter causes defective reabsorption of sodium chloride in the distal convoluted tubule consequent mild volume contraction and aldosterone-stimulated secretion of potassium resulting in mild hypokalaemic metabolic alkalosis. The volume contraction, the stimulation of vasopressin and the renin- angiotensin-aldosterone axis, and the potassium depletion are less marked than in Bartter’s syndrome.

Management is directed to replacement of potassium and magnesium. Long-term prognosis is very good.