Background: Trimethylaminuria is a rare disorder characterised by foul odour from bodily fluids and breath. The condition is caused by a homozygous mutation in the FMO3 (flavin monooxygenase 3) gene coding for the enzyme that converts TMA (trimethylamine) to trimethylamine N-oxide. The result is elevated levels of secreted trimethylamine, which has a strong odour. The condition is likely to affect mental, emotional and social health. The diagnosis is reached by testing of free TMA (trimethylamine) and percentage N-oxidation in urine samples or by genetic testing.
Case presentation: A man in his fifties had from childhood occasionally been told that his breath resembled rotten fish. He had searched for a diagnosis on the internet and was referred to testing for trimethylaminuria, and the diagnosis was confirmed.
Interpretation: Urine test samples with high levels of free TMA and subnormal percentage of trimethylamine N-oxide revealed the diagnosis of trimethylaminuria. There is no causal treatment. Patients are advised to avoid choline-rich foods and take hygienic measures.