Trimethylaminuria (fish-odor syndrome) is a rare metabolic disorder characterized by a body malodor similar to that of decaying fish. The condition results from mutations affecting the flavincontaining monooxygenase 3 (FMO3) gene. Affected individuals may exhibit a variety of psychosocial phenomena. A high index of suspicion for this disorder needs to be maintained when treating individuals presenting with a history of real or perceived body odor. Observation: We evaluated a 41-year-old man who

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... presented with a long medical history of a fishy body odor. Results from biochemical investigations confirmed a diagnosis of primary trimethylaminuria, and results of molecular genetic studies revealed homozygosity for a mu-tation on exon 4 of the FMO3 gene, FMO3/P153L (c.458C→T). The patient found that information he subsequently obtained about his condition on the Internet and discussion with friends and family members to be the most useful therapeutic approach. Conclusions: Trimethylaminuria is a rare metabolic disorder. Psychological accompaniments are recognized as major sources of distress to affected individuals. We discuss the features of this syndrome and highlight the importance of counseling and support in the treatment of such patients.