The patient is a one-year-old boy residing in Portugal.
A striking and potent symptom emerged in a 10-month-old child: a noxious odor of rotting fish emanating from his body, particularly concentrated around his head and hands. This concerning phenomenon first manifested shortly after the infant, who had transitioned to solid foods at seven months following exclusive breastfeeding, consumed various types of fish. In an investigative effort, his mother temporarily removed fish from his diet. However, two months later, upon reintroducing fish to his meals, the distinctive and powerful odor promptly returned, firmly linking the consumption of fish to the unusual bodily emanation.
During the subsequent medical evaluation, physicians detected no trace of a fishy odor. This observation was consistent with reports that the child had not consumed fish prior to his medical appointment, according to the case study. Significantly, doctors identified no abnormalities in the boy’s neurodevelopment or growth. Comprehensive laboratory tests further confirmed that his kidneys, liver, and thyroid were functioning optimally.
Following a medical assessment, doctors suspected the child had developed trimethylaminuria, an uncommon metabolic condition often referred to as “fish odor syndrome.” This disorder is characterized by a distinctive and potent smell, where an individual’s breath, saliva, sweat, and urine exude the aroma of decaying fish.
The source of this foul scent is trimethylamine, a molecule the human body produces from nitrogen-rich foods, including fish. Typically, an enzyme known as flavin-containing monooxygenase 3 (FMO3) plays a crucial role in breaking down trimethylamine, converting it into an odorless compound called trimethylamine N-oxide. However, when the FMO3 enzyme is dysfunctional or impaired, trimethylamine accumulates within the body, leading to the emission of the characteristic and unpleasant rotting-fish odor.
A metabolic pediatrician conducted a detailed molecular analysis, uncovering a series of genetic variants within a child’s FMO3 gene. This gene is vital for producing the FMO3 enzyme, and the identified variations were deemed capable of disrupting its normal production. This disruption, the pediatrician suggested, could be the underlying reason for a mild or temporary case of trimethylaminuria.
Medical professionals outlined a treatment strategy focused on the gradual reintroduction of fish into the child’s diet. Simultaneously, parents were advised to manage any lingering body odor by employing a low-pH soap, recognized for its odor-reducing properties.
This phased approach proved effective. Over time, the “rotten smell” experienced after fish meals progressively weakened. By the age of 19 months, the child was consuming fish five to six times per week without any subsequent malodorous symptoms. This positive outcome was sustained, with no return of symptoms reported by the time the child reached three years old.
This case presents a notable deviation from the typical course of trimethylaminuria. While the condition generally lacks a cure or effective treatment, is primarily genetic in origin, and frequently becomes a chronic ailment for adults, the child’s bout was temporary. Physicians involved in the case reported that this transient manifestation was likely shaped by a combination of factors, including specific inherited variants of the FMO3 gene and the natural immaturity of his metabolic system.
A recent report indicates that as a boy’s metabolic system matured, his FMO3 enzyme grew more effective at breaking down trimethylamine. This particular case, alongside similar observations, suggests a more nuanced understanding of trimethylaminuria’s underlying causes and a broader spectrum of its severity than previously thought.
Trimethylaminuria is an uncommon condition, with only a few hundred cases officially documented in medical literature. However, the true prevalence may be significantly higher, as individuals affected often misattribute their symptoms—specifically, a distinct body odor—to issues with personal hygiene rather than a medical disorder, leading them to forgo professional medical evaluation.
