Endocrine Abstracts

A 26 year old lady presented to her general practitioner complaining of fatigue. Investigations showed serum potassium of 2.5 mmol/l, (reference range 3.3–4.7 mmol/l). This was repeated on two more occasions and was 2.6 and 2.8 mmol/l. An ECG showed no features of hypokalaemia. She was seen in Endocrine clinic with serum potassium of 2.5 mmol/l. There was no history of an eating disorder, laxative or diuretic abuse. Her father had type 2 diabetes. Her height was 1.56 m and she weighed 50 kg. Blood pressure was 102/60 mmHg.

Further investigation revealed chloride 97 mmol/l (98–109), magnesium 0.64 mmol/l (0.74–1.03), renin 2.0 pmol/ml/h (0.5–3.1), aldosterone 160 pmol/l (100–800), and urinary calcium 1.1 mmol/24 h (2.5–7.5). The findings of hypokalaemia, hypochloraemia, hypomagnesaemia and hypocalciuria are consistent with a diagnosis of Gitelman’s syndrome (GS). The patient was treated with amiloride.

GS is a hypokalaemic renal tubulopathy characterised by metabolic alkalosis with hypocalcuria and hypomagnesaemia. GS can be distinguished clinically from Bartter’s syndrome because GS is milder and tends to present at a later age. Patients are less likely to be short or to have polyuria and polydipsia. They typically present with fatigue, muscle weakness and symptoms of neuromuscular irritability. GS is also diagnosed in asymptomatic adults who present with unexplained hypokalaemia. Joint pain secondary to chondrocalcinosis has been described in a subset of patients and attributed to hypomagnesaemia.

GS is autosomal recessive, caused by mutations in the SLC12A3 gene, which encodes the thiazide sensitive sodium-chloride co-transporter, located in the distal convoluted tubules of the kidney. Management is directed towards potassium and magnesium replacement and long-term prognosis is excellent. GS should be considered in the differential diagnosis of normotensive or hypotensive adults who present with hypokalaemia.