Associations of psychotic symptom dimensions with clinical and developmental variables in twin and general clinical samples.

BACKGROUND: Positive, negative and disorganised psychotic symptom dimensions are associated with clinical and developmental variables, but differing definitions complicate interpretation. Additionally, some variables have had little investigation. AIMS: To investigate associations of psychotic symptom dimensions with clinical and developmental variables, and familial aggregation of symptom dimensions, in multiple samples employing the same definitions. METHOD: We investigated associations between lifetime symptom dimensions and clinical and developmental variables in two twin and two general psychosis samples. Dimension symptom scores and most other variables were from the Operational Criteria Checklist. We used logistic regression in generalised linear mixed models for combined sample analysis (n = 875 probands). We also investigated correlations of dimensions within monozygotic (MZ) twin pairs concordant for psychosis (n = 96 pairs). RESULTS: Higher symptom scores on all three dimensions were associated with poor premorbid social adjustment, never marrying/cohabiting and earlier age at onset, and with a chronic course, most strongly for the negative dimension. The positive dimension was also associated with Black and minority ethnicity and lifetime cannabis use; the negative dimension with male gender; and the disorganised dimension with gradual onset, lower premorbid IQ and substantial within twin-pair correlation. In secondary analysis, disorganised symptoms in MZ twin probands were associated with lower premorbid IQ in their co-twins. CONCLUSIONS: These results confirm associations that dimensions share in common and strengthen the evidence for distinct associations of co-occurring positive symptoms with ethnic minority status, negative symptoms with male gender and disorganised symptoms with substantial familial influences, which may overlap with influences on premorbid IQ.

Seasonal changes in gene expression represent cell-type composition in whole blood.

Seasonal patterns in behavior and biological parameters are widespread. Here, we examined seasonal changes in whole blood gene expression profiles of 233 healthy subjects. Using weighted gene co-expression network analysis, we identified three co-expression modules showing circannual patterns. Enrichment analysis suggested that this signal stems primarily from red blood cells and blood platelets. Indeed, a large clinical database with 51 142 observations of blood cell counts over 3 years confirmed a corresponding seasonal pattern of counts of red blood cells, reticulocytes and platelets. We found no direct evidence that these changes are linked to genes known to be key players in regulating immune function or circadian rhythm. It is likely, however, that these seasonal changes in cell counts and gene expression profiles in whole blood represent biological and clinical relevant phenomena. Moreover, our findings highlight possible confounding factors relevant to the study of gene expression profiles in subjects collected at geographical locations with disparaging seasonality patterns.

A genome-wide association study identifies a functional ERAP2 haplotype associated with birdshot chorioretinopathy.

Birdshot chorioretinopathy (BSCR) is a rare form of autoimmune uveitis that can lead to severe visual impairment. Intriguingly, >95% of cases carry the HLA-A29 allele, which defines the strongest documented HLA association for a human disease. We have conducted a genome-wide association study in 96 Dutch and 27 Spanish cases, and 398 unrelated Dutch and 380 Spanish controls. Fine-mapping the primary MHC association through high-resolution imputation at classical HLA loci, identified HLA-A*29:02 as the principal MHC association (odds ratio (OR) = 157.5, 95% CI 91.6-272.6, P = 6.6 × 10(-74)). We also identified two novel susceptibility loci at 5q15 near ERAP2 (rs7705093; OR = 2.3, 95% CI 1.7-3.1, for the T allele, P = 8.6 × 10(-8)) and at 14q32.31 in the TECPR2 gene (rs150571175; OR = 6.1, 95% CI 3.2-11.7, for the A allele, P = 3.2 × 10(-8)). The association near ERAP2 was confirmed in an independent British case-control samples (combined meta-analysis P = 1.7 × 10(-9)). Functional analyses revealed that the risk allele of the polymorphism near ERAP2 is strongly associated with high mRNA and protein expression of ERAP2 in B cells. This study further defined an extremely strong MHC risk component in BSCR, and detected evidence for a novel disease mechanism that affects peptide processing in the endoplasmic reticulum.

Effects of brain-derived neurotrophic factor Val66Met polymorphism on hippocampal volume change in schizophrenia.

A functional polymorphism of the brain-derived neurotrophic factor (BDNF) gene (Val66Met) has been associated with the risk for schizophrenia and volume differences in the hippocampus. However, little is known about the association between progressive brain volume change in schizophrenia and BDNF genotype. The aim of this study was to investigate the relationship between hippocampal volume change in patients with schizophrenia and healthy control subjects and BDNF genotype. Two structural magnetic resonance imaging brain scans were acquired of 68 patients with schizophrenia and 83 healthy subjects with an interval of approximately 5 yrs. Hippocampal volume change was measured and related to BDNF genotype in patients and healthy controls. BDNF genotype was not associated with hippocampal volume change over time in patients or healthy controls, nor could we replicate earlier findings on smaller hippocampal volume in Met-carriers. However, we did find a genotype-by-diagnosis interaction at baseline demonstrating smaller hippocampal volumes in patients homozygous for the Val-allele relative to healthy Val-homozygotes. In addition, irrespective of genotype, patients showed smaller hippocampal volumes compared with healthy controls at baseline. In summary, our results suggest that the BDNF Val66Met polymorphism is not associated with hippocampal volume change over time. Nevertheless, our findings may support the possibility that BDNF affects brain morphology differently in schizophrenia patients and healthy subjects.

Association study of NRG1, DTNBP1, RGS4, G72/G30, and PIP5K2A with schizophrenia and symptom severity in a Hungarian sample.

Genetic association studies have yielded extensive but frequently inconclusive data about genetic risk factors for schizophrenia. Clinical and genetic heterogeneity are possible factors explaining the inconsistent findings. The objective of this study was to test the association of commonly incriminated candidate genes with two clinically divergent subgroups, non-deficit (SZ-ND) and deficit-schizophrenia (SZ-D), and symptom severity, in order to test for replication of previously reported results. A homogeneous sample of 280 schizophrenia patients and 230 healthy controls of Hungarian, Caucasian descent were genotyped for polymorphisms in schizophrenia candidate genes NRG1, DTNBP1, RGS4, G72/G30, and PIP5K2A. Patients were divided into the diagnostic subgroups of SZ-ND and SZ-D using the Schedule for Deficit Syndrome (SDS), and assessed clinically by the Positive and Negative Symptom Scale (PANSS). SNP8NRG241930 in NRG1 and rs1011313 in DTNBP1 were associated with SZ-ND (P = 0.04 and 0.03, respectively). Polymorphisms in RGS4, G72/G30, and PIP5K2A were neither associated with SZ-ND nor with SZ-D. SNP8NRG241930 showed association with the PANSS cognitive and hostility/excitability factors, rs1011313 with the negative factor and SDS total score, and rs10917670 in RGS4 was associated with the depression factor. Although these results replicate earlier findings about the genetic background of SZ-ND and SZ-D only partially, our data seem to confirm previously reported association of NRG1 with schizophrenia without prominent negative symptoms. It was possible to detect associations of small-to-medium effect size between the investigated candidate genes and symptom severity. Such studies have the potential to unravel the possible connection between genetic and clinical heterogeneity in schizophrenia.

Serotonin transporter promoter region (5-HTTLPR) polymorphism is associated with the intravaginal ejaculation latency time in Dutch men with lifelong premature ejaculation.

INTRODUCTION: Lifelong premature ejaculation (LPE) is characterized by persistent intravaginal ejaculation latency times (IELTs) of less than 1 minute, and has been postulated as a neurobiological dysfunction with genetic vulnerability for the short IELTs, related to disturbances of central serotonin (5-hydroxytryptamine [5-HT]) neurotransmission and 5-HT receptor functioning. AIM: To investigate the relationship between 5-HT transporter gene-linked polymorphism (5-HTTLPR) and short IELTs in men with lifelong PE. METHODS: A prospective study was conducted in 89 Dutch Caucasian men with lifelong PE. IELT during coitus was assessed by stopwatch over a 1-month period. Controls consisted of 92 Dutch Caucasian men. All men with LPE were genotyped for a 5-HTT-promoter polymorphism. Allele frequencies and genotypes of short (S) and long (L) variants of 5-HTTLPR polymorphism were compared between patients and controls. Association between LL, SL, and SS genotypes, and the natural logarithm of the IELT in men with LPE was investigated. MAIN OUTCOME MEASURES: IELT measured by stopwatch, 5-HTTLPR polymorphism. RESULTS: In men with lifelong PE, the geometric mean, median, and natural mean IELTs were 21, 26, and 32 seconds, respectively. There were no significant differences in the 5-HTT polymorphism alleles and genotypes between 89 Dutch Caucasian men with LPE (S 47%, L 53%/LL 29%, SL 48%, SS 22%) and 92 Dutch Caucasian controls (S 48%, L 52%/LL 29%, SL 45%, SS 26%). In men with lifelong PE there was a statistically significant difference between LL, SL, and SS genotypes in their geometric mean IELT (P < or = 0.027); the LL genotypes had significantly shorter IELTs than the SS and SL genotypes. CONCLUSIONS: The 5-HTTLPR polymorphism is associated with significant effects on the latency to ejaculate in men with lifelong PE. Men with SS and SL genotypes have 100% and 90% longer ejaculation time, respectively than men with LL genotypes.

Genes and structural brain imaging in schizophrenia.

PURPOSE OF REVIEW: Schizophrenia is a complex genetic disorder, caused by multiple genetic and environmental factors. Recently, studies have focused on testing specific genetic markers in a known candidate gene for association with endophenotypes. These are measurable characteristics of a disorder that are assumed to be closer to the action of the gene, resulting in higher genetic signal-to-noise ratios. Structural brain parameters have been shown to be useful endophenotypes for studies in psychiatric illnesses. RECENT FINDINGS: After reviewing the available studies on the influence of genotype on brain volume in schizophrenia, it is evident that the BDNF and COMT genes are clearly favourites for genetic imaging studies. Results from these studies seem to be quite consistent, with the same associated alleles and direction of brain volume changes. The most frequently investigated polymorphisms suggest that sample sizes of approximately 50-100 patients are sufficient to report consistent findings. Considering the ongoing discussion about the sample size necessary to detect significant associations, however, larger sample sizes are needed. SUMMARY: There is sufficient evidence to defend the use of structural neuroimaging as an endophenotype to investigate a complex phenotype such as schizophrenia despite the notion that, so far, no single causal pathway emerges from these studies. Replication studies and larger numbers of patients are essential in this respect.

Is MYO9B the missing link between schizophrenia and celiac disease?

There has long been discussion on the correlation between schizophrenia and autoimmune diseases (especially celiac disease), which makes the recently discovered celiac disease risk factor, MYO9B, an attractive functional and positional candidate gene for schizophrenia. To test this hypothesis we compared allele frequencies of three MYO9B tag SNPs in 315 schizophrenia cases and 1,624 healthy controls in a genetic association study. Highly significant differences in allele frequencies between schizophrenia cases and healthy controls were observed for SNP rs2305767 in intron 14 of MYO9B (P = 1.16 x 10(-4); OR 1.41, 95% CI 1.18-1.67). We demonstrate significant association of allelic variants in MYO9B with schizophrenia. To our knowledge, this is the first molecular genetic evidence for a correlation between autoimmune diseases and the risk of developing schizophrenia.

Do mood symptoms subdivide the schizophrenia phenotype? Association of the GMP6A gene with a depression subgroup.

Genetic studies of clinically defined subgroups of schizophrenia patients may reduce the phenotypic heterogeneity of schizophrenia and thus facilitate the identification of genes that confer risk to this disorder. Several latent class analyses have provided subgroups of psychotic disorders that show considerable consistency over these studies. The presence or absence of mood symptoms was found to contribute most to the delineations of these subgroups. In this study we used six previously published subtypes of psychosis derived from latent class analysis of a large sample of psychosis patients. In 280 schizophrenia patients and 525 healthy controls we investigated the associations of these subgroups with myelin related genes. After bonferroni correction we found an association of the glycoprotein M6A gene (GPM6A) with the subgroup of schizophrenia patients with high levels of depression (P-corrected = 0.006). Borderline association of the microtubulin associated protein tau (MAPT) with a primarily non-affective group of schizophrenia patients (P-corrected = 0.052) was also observed. GPM6A modulates the influence of stress on the hippocampus in animals. Thus our findings could suggest that GMP6A plays a role in the stress-induced hippocampal alterations that are found in psychiatric disorders in general and schizophrenia in particular. Overall, these finding suggests that investigating subgroups of schizophrenia based symptoms profile and particularly mood symptoms can facilitate genetic studies of schizophrenia.

Meta-analysis of genome-wide linkage scans of attention deficit hyperactivity disorder.

Genetic contribution to the development of attention deficit hyperactivity disorder (ADHD) is well established. Seven independent genome-wide linkage scans have been performed to map loci that increase the risk for ADHD. Although significant linkage signals were identified in some of the studies, there has been limited replications between the various independent datasets. The current study gathered the results from all seven of the ADHD linkage scans and performed a Genome Scan Meta Analysis (GSMA) to identify the genomic region with most consistent linkage evidence across the studies. Genome-wide significant linkage (P(SR) = 0.00034, P(OR) = 0.04) was identified on chromosome 16 between 64 and 83 Mb. In addition there are nine other genomic regions from the GSMA showing nominal or suggestive evidence of linkage. All these linkage results may be informative and focus the search for novel ADHD susceptibility genes.

Accurate determination of microsatellite allele frequencies in pooled DNA samples.

Pooling of DNA samples instead of individual genotyping can speed up genetic association studies. However, for microsatellite markers, the electrophoretic pattern of DNA pools can be complex, and procedures for deriving allele frequencies are often confounded by PCR-induced stutter artefacts. We have developed a mathematical procedure to remove stutter noise and accurately determine allele frequencies in pools. A stutter correction model can be reliably derived from one standard 'training set' of the same 10 individual DNA samples for each marker, which can also include heterozygous patterns with partially overlapping peaks. Compared with earlier methods, this reduces the number of genotypes needed in the training set considerably, and allows standardization of analyses for different markers. Moreover, the use of a procedure that fits all data simultaneously makes the method less sensitive to aberrant data. The model was tested with 34 markers, 18 of which were newly defined from human sequence data. Allele frequencies derived from stutter-corrected DNA pool patterns were compared with the summed individual genotyping results of all the individuals in the pools (n = 109 and n = 64). We show that the model is robust and accurately extracts allele frequencies from pooled DNA samples for 32 of the 34 microsatellite markers tested. Finally, we performed a case-control study in celiac disease and found that weakly associated disease alleles, identified by individual genotyping, were only detectable in pools after stutter correction. This efficient method for correcting stutter artefacts in microsatellite markers enables large-scale genetic association studies using DNA pools to be performed.

Vitamin B-6 vitamers in human plasma and cerebrospinal fluid.

BACKGROUND: Vitamin B-6 comprises a group of 6 interrelated vitamers and is essential for numerous physiologic processes, including brain functioning. Genetic disorders disrupting vitamin B-6 metabolism have severe clinical consequences. OBJECTIVE: To adequately diagnose known and novel disorders in vitamin B-6 metabolism, a reference set is required containing information on all vitamin B-6 vitamers in plasma and cerebrospinal fluid (CSF). DESIGN: Concentrations of vitamin B-6 vitamers in the plasma and CSF of 533 adult subjects were measured by ultra high-performance liquid chromatography-tandem mass spectrometry. RESULTS: The relative vitamin B-6 vitamer composition of plasma [pyridoxal phosphate (PLP) > pyridoxic acid (PA) > pyridoxal] differed from that of CSF (pyridoxal > PLP > PA > pyridoxamine). Sex influenced vitamin B-6 vitamer concentrations in plasma and CSF and should therefore be taken into account when interpreting vitamin B-6 vitamer concentrations. The strict ratios and strong correlations between vitamin B-6 vitamers point to a tight regulation of vitamin B-6 vitamer concentrations in blood and CSF. Given the unique design of this study, with simultaneously withdrawn blood and CSF from a large number of subjects, reliable CSF:plasma ratios and correlations of vitamin B-6 vitamers could be established. CONCLUSIONS: We provide an extensive reference set of vitamin B-6 vitamer concentrations in plasma and CSF. In addition to providing insight on the regulation of individual vitamers and their intercompartmental distribution, we anticipate that these data will prove to be a valuable reference set for the diagnosis and treatment of conditions associated with altered vitamin B-6 metabolism.

Fibroblast growth factors in neurodevelopment and psychopathology.

In psychiatric disorders, the effect of genetic and environmental factors may converge on molecular pathways and brain circuits related to growth factor functioning. In this review, we describe how disturbances in fibroblast growth factors (FGFs) and their receptors influence behavior by affecting brain development. Recently, several studies reported associations of members of the FGF family with psychiatric disorders. FGFs are key candidates to modulate the impact of environmental factors, such as stress. Mutant mice for FGF receptor 1 show schizophrenia-like behaviors that are related to general loss of neurons and postnatal glia dysfunction. Mice lacking FGF2, a FGFR1 ligand, show similar reductions in brain volume and hyperactivity, as well as increased anxiety behaviors. FGFR2 and FGF17 are involved in the development of frontal brain regions and impairments in cognitive and social behaviors, respectively. Moreover, treatment with FGF2 was beneficial for depressive and cognitive measures in several animal studies and one human study. These findings indicate the importance of the FGF system with respect to developing novel etiology-directed treatments for psychopathology.

NMDA-receptor coagonists in serum, plasma, and cerebrospinal fluid of schizophrenia patients: a meta-analysis of case-control studies.

Serine and other amino acids that function as coagonists at the N-methyl-d-aspartate receptor (NMDAR) have been extensively investigated in schizophrenia (SCZ). However, studies comparing amino acid levels in body fluids of SCZ patients with healthy controls have yielded inconsistent results. We therefore conducted a meta-analysis (search: May 9, 2013) of serine, l-serine, d-serine, glycine, alanine, proline, and aspartate levels in blood and cerebrospinal fluid (CSF) obtained from adult SCZ patients and healthy controls. Standardized differences of means (SDMs) were computed, and heterogeneity, subgroup, sensitivity, and publication bias analyses were conducted. Blood serine levels were found to be significantly higher in SCZ patients compared to healthy controls (SDM=0.280 (0.021-0.540), p=0.034; N=1671 subjects), whereas CSF serine, l-serine, d-serine, glycine, alanine, proline, and aspartate levels did not differ. Stratification by sex suggested that the case-control difference in blood serine levels particularly applies to male subjects. These results provide support for blood serine level aberrations in SCZ patients and warrant further research to disentangle the involvement of serine with SCZ in both sexes.

Genetic schizophrenia risk variants jointly modulate total brain and white matter volume.

BACKGROUND: Thousands of common single nucleotide polymorphisms (SNPs) are weakly associated with schizophrenia. It is likely that subsets of disease-associated SNPs are associated with distinct heritable disease-associated phenotypes. Therefore, we examined the shared genetic susceptibility modulating schizophrenia and brain volume. METHODS: Odds ratios for genome-wide SNP data were calculated in the sample collected by the Psychiatric Genome-wide Association Study Consortium (8690 schizophrenia patients and 11,831 control subjects, excluding subjects from the present study). These were used to calculate individual polygenic schizophrenia (risk) scores in an independent sample of 152 schizophrenia patients and 142 healthy control subjects with available structural magnetic resonance imaging scans. RESULTS: In the entire group, the polygenic schizophrenia score was significantly associated with total brain volume (R2 = .048, p = 1.6 × 10(-4)) and white matter volume (R2 = .051, p = 8.6 × 10(-5)) equally in patients and control subjects. The number of (independent) SNPs that substantially influenced both disease risk and white matter (n = 2020) was much smaller than the entire set of SNPs that modulated disease status (n = 14,751). From the set of 2020 SNPs, a group of 186 SNPs showed most evidence for association with white matter volume and an explorative functional analysis showed that these SNPs were located in genes with neuronal functions. CONCLUSIONS: These results indicate that a relatively small subset of schizophrenia genetic risk variants is related to the (normal) development of white matter. This, in turn, suggests that disruptions in white matter growth increase the susceptibility to develop schizophrenia.

D-amino acid aberrations in cerebrospinal fluid and plasma of smokers.

The glutamatergic neurotransmission system and the N-methyl-D-aspartate receptor (NMDAR) have been implicated in smoking and alcohol consumption behavior. Preclinical studies have demonstrated that nicotine and ethanol influence NMDAR functionality, which may have a role in tendencies to consume these substances. Nonetheless, little is known about concentrations of NMDAR coagonists in the cerebrospinal fluid (CSF) and plasma of individuals who smoke or consume alcohol. Glycine and L- and D-stereoisomers of alanine, serine, and proline were therefore measured using ultra-high-performance liquid chromatography-tandem mass spectrometry in 403 healthy subjects. Nicotine and alcohol consumption were quantified using questionnaires. Possible differences in NMDAR coagonist concentrations in plasma and CSF were investigated using ANCOVA with age, body mass index, and storage duration as covariates. The significance threshold was Bonferroni corrected (α=0.00625). Compared with non-smokers, smokers displayed lower levels of D-proline in plasma (p=0.0027, Cohen's d=-0.41) and D-proline in CSF (p=0.0026, Cohen's d=-0.43). D-Serine in CSF was higher in smokers than in non-smokers (p=0.0052, Cohen's d=0.41). After subdividing participants based on smoking quantity, dose-dependent decreases were demonstrated in smokers for D-proline in plasma (F=5.65, p=0.0039) and D-proline in CSF (F=5.20, p=0.0060). No differences in NMDAR coagonist levels between alcohol consumption groups were detected. To our knowledge, this is the first report to implicate D-amino acids in smoking behavior of humans. Whether such concentration differences lie at the root of or result from smoking habits may be addressed in prospective studies.

The association of the alpha-5 subunit of the nicotinic acetylcholine receptor gene and the brain-derived neurotrophic factor gene with different aspects of smoking behavior.

Recent studies show that different aspects of smoking behavior are associated with the α-5 subunit of the nicotinic acetylcholine receptor (CHRNA5) gene and the gene coding for brain-derived neurotrophic factor (BDNF). This raises the question whether the amount of cigarettes smoked per day has a different genetic background than smoking initiation and what other smoking phenotypes may be relevant. The aim of this study was to replicate these associations in a large population-based sample. We investigated the association with smoking initiation and the number of cigarettes used per day and additional smoking phenotypes in a population-based sample of 2166 participants of Dutch origin. Rs6265 in BDNF was not associated with smoking initiation. This single nucleotide polymorphism was associated with smoking cessation. Rs16969968 in CHRNA5 was associated with the amount of nicotine used and in particular smoking 25 cigarettes or more per day. Overall, the results confirm the involvement of the CHRNA5 gene in the amount of nicotine use and further suggest involvement of the BDNF gene in smoking behavior.

A common variant in ERBB4 regulates GABA concentrations in human cerebrospinal fluid.

The neuregulin 1 (NRG1) receptor ErbB4 is involved in the development of cortical inhibitory GABAergic circuits and NRG1-ErbB4 signaling has been implicated in schizophrenia (SCZ). A magnetic resonance spectroscopy ((1)H-MRS) study has demonstrated that a single-nucleotide polymorphism in ERBB4, rs7598440, influences human cortical GABA concentrations. Other work has highlighted the significant impact of this genetic variant on expression of ERBB4 in the hippocampus and dorsolateral prefrontal cortex in human post mortem tissue. Our aim was to examine the association of rs7598440 with cerebrospinal fluid (CSF) GABA levels in healthy volunteers (n=155). We detected a significant dose-dependent association of the rs7598440 genotype with CSF GABA levels (G-allele standardized ß=-0.23; 95% CIs: -0.39 to -0.07; P=0.0066). GABA concentrations were highest in A homozygous, intermediate in heterozygous, and lowest in G homozygous subjects. When excluding subjects on psychotropic medication (three subjects using antidepressants), the results did not change (G-allele standardized ß=-0.23; 95% CIs: -0.40 to -0.07; P=0.0051). The explained variance in CSF GABA by rs7598440 in our model is 5.2% (P=0.004). The directionality of our findings agrees with the aforementioned (1)H-MRS and gene expression studies. Our observation therefore strengthens the evidence that the A-allele of rs7598440 in ERBB4 is associated with increased GABA concentrations in the human central nervous system (CNS). To our knowledge, our finding constitutes the first confirmation that CSF can be used to study genotype-phenotype correlations of GABA levels in the CNS. Such quantitative genetic analyses may be extrapolated to other CSF constituents relevant to SCZ in future studies.

Season of sampling and season of birth influence serotonin metabolite levels in human cerebrospinal fluid.

BACKGROUND: Animal studies have revealed seasonal patterns in cerebrospinal fluid (CSF) monoamine (MA) turnover. In humans, no study had systematically assessed seasonal patterns in CSF MA turnover in a large set of healthy adults. METHODOLOGY/PRINCIPAL FINDINGS: Standardized amounts of CSF were prospectively collected from 223 healthy individuals undergoing spinal anesthesia for minor surgical procedures. The metabolites of serotonin (5-hydroxyindoleacetic acid, 5-HIAA), dopamine (homovanillic acid, HVA) and norepinephrine (3-methoxy-4-hydroxyphenylglycol, MPHG) were measured using high performance liquid chromatography (HPLC). Concentration measurements by sampling and birth dates were modeled using a non-linear quantile cosine function and locally weighted scatterplot smoothing (LOESS, span = 0.75). The cosine model showed a unimodal season of sampling 5-HIAA zenith in April and a nadir in October (p-value of the amplitude of the cosine = 0.00050), with predicted maximum (PC(max)) and minimum (PC(min)) concentrations of 173 and 108 nmol/L, respectively, implying a 60% increase from trough to peak. Season of birth showed a unimodal 5-HIAA zenith in May and a nadir in November (p = 0.00339; PC(max) = 172 and PC(min) = 126). The non-parametric LOESS showed a similar pattern to the cosine in both season of sampling and season of birth models, validating the cosine model. A final model including both sampling and birth months demonstrated that both sampling and birth seasons were independent predictors of 5-HIAA concentrations. CONCLUSION: In subjects without mental illness, 5-HT turnover shows circannual variation by season of sampling as well as season of birth, with peaks in spring and troughs in fall.