Fish odour syndrome with features of both primary and secondary trimethylaminuria

We report a patient with the fish odour syndrome who has both primary and secondary trimethylaminuria. The diagnosis was made using biochemical and genetic analysis in the apparent absence of any characteristic smell. Differentiation of primary and secondary trimethylaminuria is usually made on urinary analysis of trimethylamine and its metabolite trimethylamine N-oxide, with different, characteristic patterns of both compounds in primary and secondary trimethylaminuria. Our patient had biochemical analysis consistent with a diagnosis of secondary trimethylaminuria, while analysis of the flavin-containing mono-oxygenase 3 gene, the causative gene in primary trimethylaminuria, demonstrated three sequence polymorphisms, two of which are known to reduce enzyme activity. The patient showed temporary clinical and biochemical response to treatment with metronidazole and neomycin. It is important to be aware of this diagnosis in patients without obvious clinical signs, and of the subjective benefits of treatment.