Background: Trimethylaminuria (TMUA) is a rare metabolic genetic disorder caused by a deficiency of flavin-containing monooxygenase 3 (FMO3). The disorder is clinically characterized by a distinctive odor known as fish-odor syndrome. Trimethylaminuria follows an autosomal recessive inheritance pattern. It is caused by homozygous or compound heterozygous mutations in the flavin-containing dimethylaniline monooxygenase 3 (FMO3) gene, located on chromosome 1q24. Here, we present the case of a girl who suffers from an unpleasant odor, which has an embarrassing effect on her social activities.

Materials and Methods: We report a female child of Saudi origin, the product of a consanguineous marriage, who presented with a clinical picture of fish odor syndrome. The diagnosis was confirmed by detecting a mutation in the FMO3 gene through whole exome sequencing (WES).

Result: The constellation of clinical presentation, biochemical, and molecular genetics investigations showed a homozygous pathogenic variant in the FMO3 gene (OMIM: 136132), which is consistent with trimethylaminuria.