Trimethylaminuria: the detection of carriers using a trimethylamine load test

Balancing the Equation: A Natural History of Trimethylamine and Trimethylamine-N-oxide

Trimethylamine (TMA) and its N-oxide (TMAO) are ubiquitous in prokaryote and eukaryote organisms as well as in the environment, reflecting their fundamental importance in evolutionary biology, and their diverse biochemical functions. Both metabolites have multiple biological roles including cell-signaling. Much attention has focused on the significance of serum and urinary TMAO in cardiovascular disease risk, yet this is only one of the many facets of a deeper TMA-TMAO partnership that reflects the significance of these metabolites in multiple biological processes spanning animals, plants, bacteria, and fungi. We report on analytical methods for measuring TMA and TMAO and attempt to critically synthesize and map the global functions of TMA and TMAO in a systems biology framework.

Simultaneous Measurement of Urinary Trimethylamine (TMA) and Trimethylamine N-Oxide (TMAO) by Liquid Chromatography-Mass Spectrometry

Trimethylamine (TMA) is a gut microbial metabolite—rendered by the enzymatic cleavage of nutrients containing a TMA moiety in their chemical structure. TMA can be oxidized as trimethylamine N-oxide (TMAO) catalyzed by hepatic flavin monooxygenases. Circulating TMAO has been demonstrated to portend a pro-inflammatory state, contributing to chronic diseases such as cardiovascular disease and chronic kidney disease. Consequently, TMAO serves as an excellent candidate biomarker for a variety of chronic inflammatory disorders. The highly positive correlation between plasma TMAO and urine TMAO suggests that urine TMAO has the potential to serve as a less invasive biomarker for chronic disease compared to plasma TMAO. In this study, we validated a method to simultaneously measure urine TMA and TMAO concentrations by liquid chromatography–mass spectrometry (LC/MS). Urine TMA and TMAO can be extracted by hexane/butanol under alkaline pH and transferred to the aqueous phase following acidification for LC/MS quantitation. Importantly, during sample processing, none of the nutrients with a chemical structure containing a TMA moiety were spontaneously cleaved to yield TMA. Moreover, we demonstrated that the acidification of urine prevents an increase of TMA after prolonged storage as was observed in non-acidified urine. Finally, here we demonstrated that TMAO can spontaneously degrade to TMA at a very slow rate.

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

Background

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.

Results

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 odor. 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.

Conclusions

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 odor and the ratio of TMA/Cr vs TMAO/Cr in the urine in the children. Other patients presented a particular psychological or psychiatric phenotype.

Effect of Flavin-Containing Monooxygenase Genotype, Mouse Strain, and Gender on Trimethylamine N-oxide Production, Plasma Cholesterol Concentration, and an Index of Atherosclerosis

The objectives of the study were to determine the contribution, in mice, of members of the flavin-containing monooxygenase (FMO) family to the production of trimethylamine (TMA) N-oxide (TMAO), a potential proatherogenic molecule, and whether under normal dietary conditions differences in TMAO production were associated with changes in plasma cholesterol concentration or with an index of atherosclerosis (Als). Concentrations of urinary TMA and TMAO and plasma cholesterol were measured in 10-week-old male and female C57BL/6J and CD-1 mice and in mouse lines deficient in various Fmo genes (Fmo1^−/−, 2^−/−, 4^−/−, and Fmo5^−/−). In female mice most TMA N-oxygenation was catalyzed by FMO3, but in both genders 11%–12% of TMA was converted to TMAO by FMO1. Gender-, Fmo genotype-, and strain-related differences in TMAO production were accompanied by opposite effects on plasma cholesterol concentration. Plasma cholesterol was negatively, but weakly, correlated with TMAO production and urinary TMAO concentration. Fmo genotype had no effect on Als. There was no correlation between Als and either TMAO production or urinary TMAO concentration. Our results indicate that under normal dietary conditions TMAO does not increase plasma cholesterol or act as a proatherogenic molecule.

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

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.

[Primary trimethylaminuria: the fish odor syndrome]

Primary trimethylaminuria, or fish odor syndrome, is a congenital metabolic disorder characterized by a failure in the hepatic trimethylamine (TMA) oxidation route to trimethylamine N-oxide (TMANO). TMA is mostly derived from dietary precursors such as choline, carnitine and TMANO. The presence of abnormal amounts of TMA in the urine, sweat, exhaled air and other body secretions confers a very unpleasant body odor resembling that of decaying fish. As a consequence, patients can suffer from serious psychosocial sequelae. We present a case of primary trimethylaminuria with the aim of raising awareness about this condition.

Choline- and betaine-defined diets for use in clinical research and for the management of trimethylaminuria

This article describes the development of a series of choline- and betaine-controlled diets that were served to research subjects as part of an ongoing study of diet requirements in humans. These diets were developed based on the analysis of choline and betaine in individual foods. The calculated diets were compared with analyses of all foods combined into a single sample for each day. The laboratory analyses of choline and betaine in the whole-diet aliquots matched the estimated amounts in the diets that were calculated from the analyses of individual foods. These diets were adjusted for several levels of choline and betaine and were well accepted by research subjects who consumed them for a time period of up to 2 months. This article describes applications of this diet for use in clinical research on methyl-group requirements in humans and for use in clinical practice for counseling the client who requires a choline-controlled diet.

Development of analytical technology in pharmacogenetic research

Methods used to determine phenotype and genotype for pharmacogenetic polymorphisms are discussed. Phenotyping is mainly applicable to polymorphisms affecting drug disposition rather than drug response and can involve either direct measurement of enzyme activity or administration of a probe drug followed by measurement of drug and/or metabolite levels. Genotyping is now more widely used than phenotyping and can be used to determine genotype for polymorphisms affecting either drug disposition (for example those in the cytochromes P450 or N-acetyltransferases) or drug response (for example those in drug receptors). Most genotyping for known polymorphisms involves use of the polymerase chain reaction and the wide variety of methods based on this technique that are now used for routine genotyping are discussed in detail. In addition, a range of methods that can be used to detect novel polymorphisms, thereby further increasing understanding of interindividual variability in drug disposition and response, is described.

Trimethylaminuria and a human FMO3 mutation database

Trimethylaminuria (TMAuria), or fish-odor syndrome, is due to defective flavin-containing monooxygenase 3 (FMO3). In the liver, this protein catalyzes the NADPH-dependent oxidative metabolism of odorous trimethylamine (TMA), derived in the gut from dietary sources, to nonodorous trimethylamine N-oxide (TMA N-oxide). Affected individuals are unable to carry out this reaction and consequently exude a fishy body odor, due to the secretion of TMA in their breath and sweat and its excretion in their urine. This leads to a variety of psychosocial problems, including disruption of schooling, clinical depression, and attempted suicide. Twelve missense, three nonsense, and one gross deletion mutation are known to cause TMAuria. FMO3 is also a drug-metabolizing enzyme and compromised activity is expected to have implications for the efficacy of drug treatment and the possibility of adverse drug reactions both in TMAuric patients and in the general population. To date eight polymorphic variants, not associated with TMAuria, have been reported. A human FMO3 mutation database was created using MuStar, a locus-specific database system for maintaining data about allelic variants and distributing these via the World Wide Web. The database currently contains 24 entries and is accessible on the World Wide Web via the URL http://human-fmo3.biochem.ucl.ac.uk/Human_FMO3. Additional entries can be submitted via the curator of the database or via a web-based form.

Concentrations of choline-containing compounds and betaine in common foods

Choline is important for normal membrane function, acetylcholine synthesis and methyl group metabolism; the choline requirement for humans is 550 mg/d for men (Adequate Intake). Betaine, a choline derivative, is important because of its role in the donation of methyl groups to homocysteine to form methionine. In tissues and foods, there are multiple choline compounds that contribute to total choline concentration (choline, glycerophosphocholine, phosphocholine, phosphatidylcholine and sphingomyelin). In this study, we collected representative food samples and analyzed the choline concentration of 145 common foods using liquid chromatography-mass spectrometry. Foods with the highest total choline concentration (mg/100 g) were: beef liver (418), chicken liver (290), eggs (251), wheat germ (152), bacon (125), dried soybeans (116) and pork (103). The foods with the highest betaine concentration (mg/100 g) were: wheat bran (1339), wheat germ (1241), spinach (645), pretzels (237), shrimp (218) and wheat bread (201). A number of epidemiologic studies have examined the relationship between dietary folic acid and cancer or heart disease. It may be helpful to also consider choline intake as a confounding factor because folate and choline methyl donation can be interchangeable.

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.

[Primary trimethylaminuria or fish odor syndrome. A novel mutation in the first documented case in Spain]

BACKGROUND AND OBJECTIVE

Trimethylaminuria or fish odor syndrome is a metabolic disorder characterized by a failure in the oxidation route from trimethylamine (TMA) to trimethylamineN-oxide (TMA-O). Primary trimethylaminuria is an inherited autosomic recessive disease due to mutations in the human FMO3 gene. High levels of free TMA in urine and other body fluids confer an unpleasant body odor resembling that of fish. Here we report a case of primary trimethylaminuria in a 4-year-old girl.

PATIENT AND METHOD

A 4-year-old girl who presented with a strong corporal scent resembling that of fish from the age of 9 months agreeing with the introduction of fish in the diet. The patient did not have other relevant personal history and had a correct psychomotor and growing development. Liver function, urea and creatinine levels were normal. The biochemical diagnosis was done by spectrometry, measuring the amount of TMA and TMA-O prior to and after fish intake.

RESULTS

Genetic analysis evinced that the patient was homozygous for a novel mutation in exon 3, R51G (c. 151A > G). Both parents were heterozygous.

CONCLUSIONS

R51G (c. 151 A > G) mutation had not been found in other patients with trimethylaminuria.

A Mutation in the Flavin-containing Monooxygenase 3 Gene and its Effects on Catalytic Activity for N-oxidation of Trimethylamine In Vitro

To clarify the mutation of the flavin-containing monooxygenase (FMO) 3 gene causing fish-odor syndrome, we analyzed the FMO3 gene of a Thai subject who possibly suffered from fish-odor syndrome. A novel mutation, a single-base substitution from G to A at the position of 265 (G265A), was identified in exon 3. The mutation caused an amino acid substitution from valine to isoleucine at residue 58 (V58I). The mutated FMO3 protein with V58I exhibited the reduced trimethylamine N-oxidase activity when it was expressed in E. coli. The V(max)/K(m) value for the activity of the mutant-type FMO3 was about 5 times lower than that for the wild-type FMO3.

Measurement of trimethylamine and trimethylamine N-oxide independently in urine by fast atom bombardment mass spectrometry

We report a method based upon fast atom bombardment mass spectrometry (FAB-MS) and stable isotope dilution techniques for the measurement of urinary trimethylamine (TMA) and trimethylamine N-oxide (TMAOx). TMA is extracted from urine that was spiked with (15)N-labeled TMA. The extracted TMA isotopomers are quaternized with trideuteromethyl iodide and analyzed in FAB-MS with hexaethylene glycol as matrix. TMAOx is measured by evaporation of another sample of the urine spiked with (15)N-labeled TMAOx on the FAB probe and analyzed as for the TMA. The method allows the ready and simple distinguishing of controls and patients with TMAuria, and is useful in monitoring patients with the disorder. We give examples of its use in determining normal control ranges for these metabolites and in evaluating patients.

Mild trimethylaminuria caused by common variants in FMO3 gene

Mild to transient trimethylaminuria is caused by common variants in the FMO3 gene leading to greatly reduced enzyme activity in vivo. FMO3 deficiency may have clinical relevance well beyond unpleasant body odour.

Quantitative determination of trimethylamine in urine by solid-phase microextraction and gas chromatography-mass spectrometry

Trimethylaminuria (fish odour syndrome) is diagnosed from an increase in urinary excretion of trimethylamine with decreased trimethylamine oxide. We report a new quantitative stable isotope dilution gas chromatography-mass spectrometry procedure for the analysis of these metabolites using solid-phase microextraction (SPME). Both polydimethylsiloxane and mixed Carboxen-polydimethylsiloxane SPME fibres were found to be suitable for the headspace extraction of TMA. This new sampling technique could have wide application for the analysis of volatile and semi-volatile compounds by metabolic screening laboratories.

Human flavin-containing monooxygenase form 3: cDNA expression of the enzymes containing amino acid substitutions observed in individuals with trimethylaminuria

Trimethylaminuria is an autosomal recessive human disorder affecting a small part of the population as an inherited polymorphism. Individuals diagnosed with trimethylaminuria excrete relatively large amounts of trimethylamine in their urine, sweat, and breath, and this results in a fishy odor characteristic of trimethylamine. Activity of the human flavin-containing monooxygenase (FMO) has been proposed to be deficient in trimethylaminuria patients causing a decrease in the metabolism of trimethylamine that results in a fishy body odor. Cohorts of Australian, American, and British individuals suffering from trimethylaminuria have been identified. The human FMO3 cDNA was amplified from lymphocytes of affected patients. We report preliminary evidence of substitutions detected by screening of the cDNA and genomic DNA. The variant human FMO3 cDNA was constructed from wild type human FMO3 cDNA by site-directed mutagenesis as maltose-binding protein fusions. Five distinct human FMO3 mutants were expressed as fusion proteins in Escherichia coli and compared with wild type human FMO3 maltose-binding proteins (FMO3-MBP) for the N-oxygenation of 10-[(N,N-dimethylamino)pentyl]-2-(trifluoromethyl)phenothiazine, tyramine, and trimethylamine. Human Lys158 FMO3-MBP and, to a greater extent, human Glu158 FMO3-MBP efficiently N-oxygenated the three amine substrates. Human Lys158 Ile66 FMO3-MBP, Glu158 Ile66 FMO3-MBP, Lys158 Leu153 FMO3-MBP, and Glu158 Leu153 FMO3-MBP were all constructed as mutants identified as possible FMO3 variants responsible for trimethylaminuria and were found to be inactive as N-oxygenases. The results suggest that mutations at codons 66 and 153 of FMO3 can cause trimethylaminuria in humans. We observed a common polymorphism of Lys to Glu at codon 158 of FMO3 that segregated with almost equal allele frequencies in a number of control Australian and North American samples studied. The Lys158 to Glu158 human FMO3 polymorphism does not decrease trimethylamine N-oxygenation for the cDNA-expressed enzyme and thus does not appear to be causative of trimethyaminuria. The data show that the functional activity of human FMO3 can be significantly altered by amino acid changes that have been observed in individuals with clinically diagnosed trimethylaminuria.

Discontinuous distribution of N-oxidation of dietary-derived trimethylamine in a British population

1. Whilst the majority of individuals within a British white population are able to convert > 90% of their dietary-derived trimethylamine to its N-oxide, outliers exist who show varying degrees of decreased metabolism. Such individuals, excrete unoxidized trimethylamine in their urine and, if N-oxidation is sufficiently low, may experience malodour problems (Fish-Odour syndrome). 2. Such observations have now been extended to a much larger group (n = 421; 221 males) of British white volunteers recruited from staff and students of Imperial College Medical School at St. Mary's, London. Each subject collected a 0-24-h urine sample, which was subsequently analysed for total trimethylamine and trimethylamine N-oxide content. 3. Sixteen subjects (3.8% population; seven male, nine female) excreted < 90% of their total trimethylamine output as N-oxide. All six subjects who excreted < 80% as N-oxide (indicative of potential heterozygous status for deficient N-oxidation-fish odour syndrome) were female.

Effect of dietary intake of trimethylamine on human metabolism of the industrial catalyst dimethylethylamine

OBJECTIVES

The aim was to study the effect of trimethylamine (TMA) on the metabolism of the industrial catalyst dimethylethylamine (DMEA) to ascertain whether biological monitoring of industrial exposure to DMEA is compromised and excretion of the malodorous DMEA in sweat and urine is increased by dietary intake of TMA.

METHODS

DMEA (0/25 mg) and TMA (0/300/600 mg) were given simultaneously once weekly for six weeks to five healthy volunteers. Plasma was collected before and one hour after the doses, and urine 0-2, 2-4, 4-6, 6-8, and 8-24 hours after the doses. Specimens were analysed by gas chromatography with a nitrogen sensitive detector.

RESULTS

Both amines were readily absorbed from the gastrointestinal tract and excreted in urine within 24 hours (DMEA 80%; TMA 86%). Oral intake of TMA increased the DMEA content of plasma and urine dose dependently, although there were large individual differences. Plasma and urinary TMA concentrations also increased, but not dose dependently. Moreover, the findings suggested the formation of endogenous TMA, little dealkylation of DMEA and TMA, and considerable first-pass metabolism.

CONCLUSIONS

Although intake of TMA reduced N-oxygenation of DMEA and TMA, total urinary DMEA values (aggregate of DMEA and its oxide DMEAO excretion) were unaffected. Thus, monitoring occupational exposure to DMEA by analysis of biological specimens is not confounded by dietary intake of TMA, provided that total urinary DMEA is monitored. Although the increased urinary and hidrotic excretion of DMEA may contribute to body odour problems, they were primarily due to TMA excretion, which is much the greater.

The N-oxidation of trimethylamine in a Jordanian population

The ability to oxidise trimethylamine (TMA) to trimethylamine N-oxide (TMAO) is distributed polymorphically within a British white population with the majority of individuals excreting greater than 90% of total urinary TMA as TMAO. The opposite extreme is characterised by a rare inborn error of TMA N-oxidation known as the fish-odour syndrome. However there is a lack of information regarding inter-individual variability in the N-oxidation of TMA in other ethnic groups. In this study the urinary excretion of TMA and TMAO was determined over a period of 24 h in 82 Jordanian subjects. A frequency distribution histogram of % of total urinary TMA excreted as TMAO revealed that the majority of subjects excreted greater than 80% of the total urinary TMA as TMAO, however eight subjects (9.7%) excreted less than 80% of the total TMA as TMAO. In a previous study of 169 white British subjects only one (0.6%) excreted less than 80% of the total TMA as TMAO. The results suggest that the prevalence of compromised ability to N-oxidise TMA may be higher in a Jordanian population than in a British population.

Fish odour syndrome: verification of carrier detection test

An oral trimethylamine challenge test has been used to confirm the heterozygous status of patients with 'fish-odour syndrome'. By measuring the percentage of total urinary trimethylamine-related material excreted as the N-oxide, no discrimination could be made between obligate heterozygotes (parents of 'fish-odour syndrome' patients) (n = 15; 96 +/- 2%, range 92-98%) and control individuals (parents of unaffected children) (n = 16; 96 +/- 2%, range 93-99%) on a normal diet. However, after ingesting a trimethylamine load (600 mg base) the obligate heterozygotes were clearly distinguishable (76 +/- 3%, range 71-79%) from controls (95 +/- 2%, range 91-99%) (t-test; p <0.001). One of a hundred apparently normal volunteers who were subsequently challenged with trimethylamine had a N-oxidation capacity which fell within the range found among the obligate heterozygotes.

Fate of dimethylamine in man

1. The fate of [14C]-dimethylamine was investigated following oral administration to four male volunteers. 2. The major route of excretion was urine, with 94% of the administered radioactivity being voided over 3 days (87% during the first 24 h). Small amounts (1-3%) of radioactivity were found in the faeces and expired air. 3. Metabolism was limited with only 5% being demethylated to methylamine. The remainder of the dose was excreted unchanged. 4. Pharmacokinetic studies indicated rapid (t1/2ab = 8 min) and extensive absorption (bioavailability = 82%) from the gastrointestinal tract followed by widespread distribution and a fairly prompt excretion (t1/2el = 6-7 h) with a plasma clearance of 190 ml/min.

Urinary excretion of methylamines in men with varying intake of fish from the Baltic Sea

Fish contain methylamines, especially trimethylamine N-oxide (TMAO), trimethylamine (TMA), and dimethylamine (DMA). Further, DMA may be formed TMA and TMAO. DMA is a precursor of nitrosodimethylamine (NDMA), which is a potent carcinogen. Levels of DMA, TMA, and TMAO in urine were used as indicators of the dietary exposure and in vivo formation of these amines in 44 men, representing 3 groups with different fish consumption habits. The levels of TMA (median 0.24 mmol/mol creatinine; range 0-2.7) and TMAO (median 38 mmol/mol creatinine; range 8-290) were significantly associated with the weekly intake of fish (r = .47, p = .001, and r = .53, p = .0002, respectively), while no such relation was found for DMA (median 24 mmol/mol creatinine; range 5-46). Further, urinary levels of TMA and TMAO were dependent on recent intake of fish.

The fish odour syndrome: biochemical, familial, and clinical aspects

OBJECTIVES

To study the biochemical, familial, and clinical features of the fish odour syndrome among subjects with suspected body malodour.

DESIGN

Subjects who responded to a newspaper article were screened for the fish odour syndrome by interview and biochemical tests. Families of subjects with the syndrome were tested if possible.

SETTING

St Mary's Hospital, London, and some interviews at subjects' homes.

SUBJECTS

187 subjects (28 males) with suspected body malodour, of whom 156 (19 males) underwent biochemical tests. Five families of six of the subjects with the fish odour syndrome agreed to further tests.

MAIN OUTCOME MEASURES

Amounts of trimethylamine and trimethylamine N-oxide in urine collected over 24 hours under normal dietary conditions and for eight hours after oral challenge with 600 mg trimethylamine.

RESULTS

The fish odour syndrome was diagnosed in 11 subjects: the percentage of total trimethylamine excreted in their urine samples that was oxidised to trimethylamine N-oxide was < 55% under normal dietary conditions and < 25% after oral challenge with trimethylamine (in normal subjects > 80% of trimethylamine was N-oxidised). Parents of six of the subjects with the syndrome were tested: all showed impaired N-oxidation of excreted trimethylamine (< 80%) after oral challenge, indicating that they were heterozygous carriers of the allele for the syndrome. The syndrome was associated with various psychosocial reactions including clinical depression.

CONCLUSIONS

The fish odour syndrome can be inherited in an autosomal recessive fashion. It should be considered as a possible causative factor in patients complaining of body malodour.

Metabolic polymorphisms

Polymorphisms have been detected in a variety of xenobiotic-metabolizing enzymes at both the phenotypic and genotypic level. In the case of four enzymes, the cytochrome P450 CYP2D6, glutathione S-transferase mu, N-acetyltransferase 2 and serum cholinesterase, the majority of mutations which give rise to a defective phenotype have now been identified. Another group of enzymes show definite polymorphism at the phenotypic level but the exact genetic mechanisms responsible are not yet clear. These enzymes include the cytochromes P450 CYP1A1, CYP1A2 and a CYP2C form which metabolizes mephenytoin, a flavin-linked monooxygenase (fish-odour syndrome), paraoxonase, UDP-glucuronosyltransferase (Gilbert's syndrome) and thiopurine S-methyltransferase. In the case of a further group of enzymes, there is some evidence for polymorphism at either the phenotypic or genotypic level but this has not been unambiguously demonstrated. Examples of this class include the cytochrome P450 enzymes CYP2A6, CYP2E1, CYP2C9 and CYP3A4, xanthine oxidase, an S-oxidase which metabolizes carbocysteine, epoxide hydrolase, two forms of sulphotransferase and several methyltransferases. The nature of all these polymorphisms and possible polymorphisms is discussed in detail, with particular reference to the effects of this variation on drug metabolism and susceptibility to chemically-induced diseases.

Trimethylaminuria in a girl with Prader-Willi syndrome and del(15)(q11q13)

We report on an individual with trimethylaminuria, Prader-Willi syndrome, and del(15) (q11q13). To our knowledge, such an association has never been reported. Skin sores secondary to choline-rich foods and amenable to dietary control have not been described in trimethylaminuria, although they are seen in some patients with Prader-Willi syndrome. Pathogenesis, clinical diagnosis, and management of reported cases with trimethylaminuria are reviewed. Serious social and behavioral problems may result from strong body odor. Amelioration of the "fish odor" by dietary choline restriction makes trimethylaminuria detection important. Association of trimethylaminuria with Prader-Willi syndrome and del(15) (q11q13) in this patient is of particular interest. It may represent a contiguous gene syndrome, or deletion of the normal allele leading to expression of a single recessive trimethylaminuria gene, or an unrelated association, such as in Noonan syndrome. However, recent development of mapping of flavin-containing monooxygenase 2 (FMO2), the likely enzyme that is defective in fish odor syndrome, to chromosome 1q probably excludes pathogenetic association of fish odor syndrome with the Prader-Willi syndrome.

Metabolism of verapamil in a family pedigree with deficient N-oxidation of trimethylamine

The oxidative N-dealkylation of verapamil has been studied in a family of five members with two propositi with an inherited deficiency of trimethylamine N-oxidation (fish-odour syndrome). The results were assessed for possible co-segregation of the trimethylamine N-oxidation phenotype and any observed deficiency in oxidative N-dealkylation. The general pattern of metabolism of verapamil in the five subjects studied was similar to that reported in earlier investigations. Moreover, there were no differences between the two affected subjects and other family members with respect to the metabolic pattern. It is concluded that there is no functional segregation with respect to the mechanisms controlling trimethylamine N-oxidation and verapamil N-dealkylation.