UK Malodour Research Projects

Date - 2019

The genetic and biochemical basis of trimethylaminuria

Principal Investigator - S Doyle 

Lead Research Investigator - Sheffield Diagnostic Genetics Service, Sheffield Children's NHS Trust Sheffield UK.



Inherited trimethylaminuria (TMAU), a rare genetic disorder of hepatic metabolism of trimethylamine (TMA) causing excessive accumulation of malodorous trimethylamine (TMA), is a socially distressing disorder. Diagnosis is made by biochemical analysis of urine, with the calculation of flavin monooxygenase trimethylamine conversion capacity. Genetic testing, sequencing the entire coding region of the FMO3 gene has been recommended for affected individuals who convert less than 90% of the total TMA load to TMAO.


Genetic analysis was undertaken for 13 Irish patients with TMAU of varying phenotypic severity (three severe, six moderate, and four mild).


A genetic diagnosis was made for seven patients, including for five of the nine moderate to severely affected cases. We noted the c.913G>T;p.(Glu305*) and c.458C>T;p.(Pro153Leu) mutations in this Irish population with severe TMAU which is consistent with our earlier findings in Australian and North American families of Irish and British descent.Three individuals were noted to be homozygous for the common variant haplotype c.472G>A;923A>G;p.(Glu158Lys);(Glu308Gly). We also identified three novel variants in this population, which are likely to be pathogenic: c.682G>A;p(Gly228Ser), c.694G>T:p(Asp232Tyr), and c.989G>A;p.(Gly330Glu).


Urinary biochemical analysis probably remains the first line diagnostic approach to classify the various types of TMAU. FMO3 gene analysis is likely only to be informative for certain presentations of TMAU.

Date - 2019 

Diagnosis and phenotypic assessment of trimethylaminuria, and its treatment with riboflavin: 1H NMR spectroscopy and genetic testing.



Trimethylaminuria (TMAU) is a metabolic disorder characterized by the excessive excretion of the malodorous compound trimethylamine (TMA). The diagnosis of TMAU is challenging because this disorder is situated at the boundary between biochemistry and psychiatry. Here, we used nuclear magnetic resonance spectroscopy to assess TMAU in 13 patients. We also sequenced the FMO3 gene in 11 of these patients. Treatment with vitamin B2 was prescribed.


Two patients (aged 3 and 9 years at the initial consultation) had a particularly unpleasant body odor, as assessed by their parents and the attending physicians. The presence of high urine TMA levels confirmed the presence of a metabolic disorder. The two (unrelated) children carried compound heterozygous variants in the FMO3 gene. In both cases, vitamin B2 administration decreased TMA excretion and reduced body odour. The 11 adults complained of an unpleasant body odor, but the physicians did not confirm this. In all adult patients, the urine TMA level was within the normal range reported for control (non-affected) subjects, although two of the patients displayed an abnormally high proportion of oxidized TMA. Seven of the 9 tested adult patients had a hypomorphic variant of the FMO3 gene; the variant was found in the homozygous state, in the heterozygous state or combined with another hypomorphic variant. All 11 adults presented a particular psychological or psychiatric phenotype, with a subjective perception of unpleasant odor.


The results present the clinical and biochemical data of patients complaining of unpleasant body odor. Contrary to adult patients, the two children exhibited all criteria of recessively inherited trimethylaminuria, suspected by parents in infancy. B2 vitamin treatment dramatically improved the unpleasant body odour and the ratio of TMA/Cr vs TMAO/Cr in the urine in the children. Other patients presented a particular psychological or psychiatric phenotype.

Date - 2019

Development and feasibility of the use of an assessment tool measuring treatment efficacy in patients with trimethylaminuria: A mixed methods study.

Principal Investigator - K Rutkowski 

Lead Research Investigator - NIHR, Clinical Research Facility, Guy's & St Thomas' Hospital NHS Foundation Trust, London, UK.

Trimethylaminuria (TMAU) is a rare metabolic condition characterised by an unpleasant smell resembling rotting fish. Currently, the only measure of treatment efficacy is urine trimethylamine levels which do not always reflect the patient's experience of symptoms. A literature review did not find a specific tool to assess treatment efficacy from the patient's perspective. The aim of this study was to develop an assessment tool to provide a quantitative measure of treatment efficacy in patients diagnosed with TMAU before and after treatment and assess its acceptability (feasibility of use and face and content validity) to people living with TMAU. Mixed methods; a modified, four-round Delphi by email and semi-structured interviews conducted after clinical appointments. Delphi; Eight individuals living with TMAU from the TMAU forum, six medical consultants, and four dieticians in Metabolic Medicine in four National Health Service hospitals in England. Semi-structured interviews; three patients with TMAU in two National Health Service hospitals, United Kingdom. The assessment tool contains 27 items distributed across four domains; Odour characteristics with 6 items, mental well-being with 13 items, social well-being with 5 items, and healthcare professionals support with 3 items. Semi-structured interviews; views on the content and design of the tool. The co-produced tool was successfully developed and considered acceptable to people living with TMAU. While further testing is needed to evaluate the validity and reliability of the assessment tool, the tool may serve as a prompt for questioning for clinicians diagnosing and treating TMAU.

Date - 2017

Trimethylamine - The Extracorporeal Envoy

Principal Investigator : Dr Steve Mitchell 

Lead Research Organisation : University College London 

Date - 2017 

Trimethylamine and Trimethylamine N-Oxide, a Flavin-Containing Monooxygenase 3 (FMO3)-Mediated Host-Microbiome Metabolic Axis Implicated in Health and Disease.

Principle Investigator - Prof Elizabeth Shepherd 

Lead Research Organisation - Institute of Structural and Molecular Biology, University College London (D.F., I.R.P., E.A.S.), and School of Biological and Chemical Sciences, Queen Mary University of London (I.R.P.), London, United Kingdom.


Flavin-containing monooxygenase 3 (FMO3) is known primarily as an enzyme involved in the metabolism of therapeutic drugs. On a daily basis, however, we are exposed to one of the most abundant substrates of the enzyme trimethylamine (TMA), which is released from various dietary components by the action of gut bacteria. FMO3 converts the odorous TMA to nonodorous TMA N-oxide (TMAO), which is excreted in urine. Impaired FMO3 activity gives rise to the inherited disorder primary trimethylaminuria (TMAU). Affected individuals cannot produce TMAO and, consequently, excrete large amounts of TMA. A dysbiosis in gut bacteria can give rise to secondary TMAU. Recently, there has been much interest in FMO3 and its catalytic product, TMAO, because TMAO has been implicated in various conditions affecting health, including cardiovascular disease, reverse cholesterol transport, and glucose and lipid homeostasis. In this review, we consider the dietary components that can give rise to TMA, the gut bacteria involved in the production of TMA from dietary precursors, the metabolic reactions by which bacteria produce and use TMA, and the enzymes that catalyze the reactions. Also included is information on bacteria that produce TMA in the oral cavity and vagina, two key microbiome niches that can influence health. Finally, we discuss the importance of the TMA/TMAO microbiome-host axis in health and disease, considering factors that affect bacterial production and host metabolism of TMA, the involvement of TMAO and FMO3 in disease, and the implications of the host-microbiome axis for management of TMAU.

Date - 2013 - 2016 

Status - Completed 

MICA: Therapy for the body and breath malodour disorder Trimethylaminuria (TMAU

Lead Research Organisation: University College London

Department Name: Structural Molecular Biology

Funded Value : £360,683

Funder : MRC

Principal Investigator : Elizabeth Ann Shepherd 


Trimethylaminuria (TMAU) is a disorder in which affected people suffer from severe body odour often accompanied by severe bad breath. The disorder arises because of mutations in a gene called FMO3 and not because of poor hygiene. Why do changes in the FMO3 gene cause body and breath odour? When we eat food that contains choline (which many foods do, e.g. red meat, seafood, some vegetables, soya, eggs and chocolate) then the bacteria that live in our gut cause the problem. The bacteria break choline down to produce a small molecule called trimethylamine. This chemical is the one to which the human nose is most sensitive and which is also the chemical that gives rotting fish its characteristic smell. In people with a normal FMO3 gene there is no odour problem because the FMO3 enzyme we have in our liver changes trimethylamine into a chemical that does not smell. BUT, if the FMO3 enzyme cannot do this, then the trimethylamine is not changed and is excreted in urine, sweat and breath. Social isolation, ridicule and limited employment prospects are experienced by those with TMAU, this usually means a low quality of life; high levels of depression, suicide and divorce occur in this population. Our study will test a therapy for TMAU that will reduce the amount of urinary trimethylamine excreted. Our pre-clinical findings will prepare the way for clinical studies in humans in the future. A reduction in body and breath odour will contribute greatly to an improved quality of life for those with TMAU.


Technical Summary

Trimethylaminuria (TMAU) is an inherited disorder caused by mutations in the FMO3 gene. A lack of active FM03 means affected individuals cannot convert odorous trimethylamine (TMA), produced from breakdown of dietary choline by gut bacteria, to the non-odorous N-oxide. TMAU individuals excrete large amounts of TMA in all bodily excretions, including breath. Social isolation, ridicule and limited employment prospects are experienced by those with TMAU, which translates to a low quality of life; high levels of depression, suicide and divorce occur in this population. We will carry out preclinical animal studies to test a therapeutic for TMAU. We have established very promising early proof of concept data in a rodent model indicating that this therapeutic approach is both realistic and potentially of great use to humans suffering from this condition. The end point measurements of efficacy of the treatment are the amounts of TMA and TMA N-oxide excreted in urine, which are a measure of the severity of TMAU in humans. Affected individuals with TMAU excrete greater than 10 uM TMA /mmol creatinine (> 10% of total TMA excreted as unmetabolised TMA, calculated as a ratio of TMA/TMAO). Severity of TMAU correlates with levels of urinary TMA, this will be our main endpoint indicator in the proposed preclinical studies. Male mice, >6-weeks of age, are natural knockouts for FMO3 and excrete large amounts of urinary TMA. Female mice will be subjected to a choline challenge. Mice will be dosed i.v. or s.c. with the therapeutic. Initially, we will assess route of delivery; therapeutic window of dosage; half-life of therapeutic; pharmacokinetics. A longer-term study, using GLP therapeutic, prepared to the standard for human clinical studies, will determine bioavailability, biodistribution, toxicity and pathology.


Planned Impact

The major beneficiaries of the therapy will be those who suffer from TMAU and their families and friends. Through her communications with patients, the PI is aware of the stigma, ridicule and other difficulties the patients face in their daily lives. The results from our pre-clinical study will provide a much-needed boost for those with TMAU. It will represent a pathway to a future therapy in humans. A therapy that can abolish body and breath odour will have a major impact on the quality of life of TMAU individuals, improving self-confidence and esteem, relationships and employment. A barrier to a normal life will be removed. The preclinical study runs for two years. With orphan drug designation and if fast track status is approved we anticipate a therapy to the clinic within five years.

At present clinicians are limited in their help for those with TMAU. Offering antidepressant or antipsychotic drugs is not helpful (as several of these are substrates for FMO3 and thus make the condition of TMAU worse). Therefore, key beneficiaries, when the therapeutic is made available, will be the clinicians treating those with TMAU and the prospect of a therapy that can prove beneficial for their patient. Health providers will be positioned to target the disorder instead of treating the symptoms of despair associated with the difficulties of living with TMAU.

Other beneficiaries include pharmaceutical companies with an interest in both primary TMAU (inherited form and basis of this project) and the treatment of secondary TMAU (acquired form through e.g. gut bacterial overgrowth; bowel surgery; liver dysfunction). Our proposal is focused on primary TMAU but secondary TMAU results from an impairment in, or overload of, FMO3. Results generated from our studies will therefore impact also on a therapy for acquired TMAU. This industry would benefit from development of the therapeutic for clinic and subsequent sales of the product - this would be within 2 to 5 years of the pre-clinical study end.

Researchers interested in the approach we have selected to develop the therapy, will benefit from our findings and be able to use our knowledge in future projects that target metabolic disorders. Anticipated publication of results is during and within one year of the project end.