To establish genetic associations between patients with thiazide-induced hyponatraemia and patients taking a thiazide who did not develop hyponatraemia.

Eligibility criteria

Inclusion criteria:

• Age 18-100 years
• Have the capacity to give informed consent
• Be taking a thiazide or thiazide-related diuretic unless in the non-thiazide control group
• Plasma sodium concentration of less than 130 mM for cases and between 135 mM and 145 mM for controls