An association study between 5-HTTLPR polymorphism, COMT polymorphism, and Tourette's syndrome

Boosted dopamine and blunted serotonin in Tourette syndrome - evidence from in vivo imaging studies

The precise cortical and subcortical mechanisms of Tourette syndrome (TS) are still not fully understood. In the present retrospective analysis, adolescent and adult medication-naïve patients showed increased DA transporter (DAT) binding in nucleus caudate (CAUD), putamen (PUT) and/or whole neostriatum (NSTR). D₂ receptor (R) binding and DA release were not different from controls throughout the nigrostriatal and mesolimbocortical system. When patients were medication-free (either medication-naïve or under withdrawal), DAT was still increased in PUT, but not different from controls in CAUD, NSTR and ventral striatum (VSTR). SERT was unaltered in midbrain/pons (MP), but decreased in PUT, thalamus (THAL) and hypothalamus. D₂R was unaltered throughout the nigrostriatal and mesolimbocortical system, while DA release was not different from controls in PUT, CAUD and NSTR, but elevated in VSTR. 5-HT_2AR binding was unaltered in neocortex and cingulate. In acutely medicated adults, DAT was unaltered in PUT, but still increased in CAUD, whereas DA release remained unaltered throughout the nigrostriatal and mesolimbocortical system. When part of the patients was acutely medicated, vesicular monoamine transporter (VMAT2), DAT, SERT and DA synthesis were not different from controls in striatal regions, whereas D₂R was decreased in NSTR, THAL, frontal cortex and limbic regions. Conversely, 5-HT_2AR binding was unaltered in striatal regions and THAL, but increased in neocortical and limbic areas. It may be hypothesized that both the DA surplus and the 5-HT shortage in key regions of the nigrostriatal and mesolimbic system are relevant for the bouts of motor activity and the deficiencies in inpulse control.

Candidate Genes and Pathways Associated with Gilles de la Tourette Syndrome-Where Are We?

Gilles de la Tourette syndrome (GTS) is a childhood-onset neurodevelopmental and -psychiatric tic-disorder of complex etiology which is often comorbid with obsessive-compulsive disorder (OCD) and/or attention deficit hyperactivity disorder (ADHD). Twin and family studies of GTS individuals have shown a high level of heritability suggesting, that genetic risk factors play an important role in disease etiology. However, the identification of major GTS susceptibility genes has been challenging, presumably due to the complex interplay between several genetic factors and environmental influences, low penetrance of each individual factor, genetic diversity in populations, and the presence of comorbid disorders. To understand the genetic components of GTS etiopathology, we conducted an extensive review of the literature, compiling the candidate susceptibility genes identified through various genetic approaches. Even though several strong candidate genes have hitherto been identified, none of these have turned out to be major susceptibility genes yet.

Elevated Expression of SLC6A4 Encoding the Serotonin Transporter (SERT) in Gilles de la Tourette Syndrome

Gilles de la Tourette syndrome (GTS) is a complex neurodevelopmental disorder characterized by motor and vocal tics. Most of the GTS individuals have comorbid diagnoses, of which obsessive-compulsive disorder (OCD) and attention deficit-hyperactivity disorder (ADHD) are the most common. Several neurotransmitter systems have been implicated in disease pathogenesis, and amongst these, the dopaminergic and the serotonergic pathways are the most widely studied. In this study, we aimed to investigate whether the serotonin transporter (SERT) gene (SLC6A4) was differentially expressed among GTS individuals compared to healthy controls, and whether DNA variants (the SERT-linked polymorphic region 5-HTTLPR, together with the associated rs25531 and rs25532 variants, and the rare Ile425Val variant) or promoter methylation of SLC6A4 were associated with gene expression levels or with the presence of OCD as comorbidity. We observed that SLC6A4 expression is upregulated in GTS individuals compared to controls. Although no specific genotype, allele or haplotype was overrepresented in GTS individuals compared to controls, we observed that the LAC/LAC genotype of the 5-HTTLPR/rs25531/rs25532 three-locus haplotype was associated with higher SLC6A4 mRNA expression levels in GTS individuals, but not in the control group.

Systematic review of co-occurring OCD and TD: Evidence for a tic-related OCD subtype?

OBJECTIVE

The aim of this review is to summarize the current knowledge of associated features of co-occurring obsessive-compulsive disorder (OCD) and tic disorders (TD) and to critically evaluate hypotheses regarding the nature of their comorbidity.

METHOD

We conducted a systematic review following PRISMA guidelines. To this aim, the PubMed, PsychInfo and ISI Web of Knowledge databases were searched up to August 30, 2018. For gender and age-of-onset we additionally conducted meta-analyses.

RESULTS

One hundred eighty-nine studies met inclusion criteria. We substantiate some acknowledged features and report evidence for differential biological mechanisms and treatment response. In general, studies were of limited methodological quality.

CONCLUSIONS

Several specific features are reliable associated with co-occurring OCD + TD. The field lacks methodological sound studies. The review found evidence against and in favor for different hypotheses regarding the nature of comorbidity of OCD and TD. This could indicate the existence of a stepwise model of co-morbidity, or could be an artefact of the low methodological quality of studies.

Progress in Genetic Studies of Tourette's Syndrome

Tourette's Syndrome (TS) is a complex disorder characterized by repetitive, sudden, and involuntary movements or vocalizations, called tics. Tics usually appear in childhood, and their severity varies over time. In addition to frequent tics, people with TS are at risk for associated problems including attention deficit hyperactivity disorder (ADHD), obsessive-compulsive disorder (OCD), anxiety, depression, and problems with sleep. TS occurs in most populations and ethnic groups worldwide, and it is more common in males than in females. Previous family and twin studies have shown that the majority of cases of TS are inherited. TS was previously thought to have an autosomal dominant pattern of inheritance. However, several decades of research have shown that this is unlikely the case. Instead TS most likely results from a variety of genetic and environmental factors, not changes in a single gene. In the past decade, there has been a rapid development of innovative genetic technologies and methodologies, as well as significant progresses in genetic studies of psychiatric disorders. In this review, we will briefly summarize previous genetic epidemiological studies of TS and related disorders. We will also review previous genetic studies based on genome-wide linkage analyses and candidate gene association studies to comment on problems of previous methodological and strategic issues. Our main purpose for this review will be to summarize the new genetic discoveries of TS based on novel genetic methods and strategies, such as genome-wide association studies (GWASs), whole exome sequencing (WES) and whole genome sequencing (WGS). We will also compare the new genetic discoveries of TS with other major psychiatric disorders in order to understand the current status of TS genetics and its relationship with other psychiatric disorders.

Tourette Syndrome: Bridging the Gap between Genetics and Biology

Tourette syndrome is a childhood neuropsychiatric disorder, which presents with disruptive motor and vocal tics. The disease also has a high comorbidity with obsessive-compulsive disorder and attention deficit hyperactivity disorder, which may further increase the distress experienced by patients. Current treatments act with varying efficacies in alleviating symptoms, as the underlying biology of the disease is not fully understood to provide precise therapeutic targets. Moreover, the genetic complexity of the disorder presents a substantial challenge to the identification of genetic alterations that contribute to the Tourette's phenotype. Nevertheless, genetic studies have suggested involvement of dopaminergic, serotonergic, glutamatergic, and histaminergic pathways in the pathophysiology of at least some cases. In addition, genetic overlaps with other neuropsychiatric disorders may point toward a shared biology. The findings that are emerging from genetic studies will allow researchers to piece together the underlying components of the disease, in the hopes that a deeper understanding of Tourette's can lead to improved treatments for those affected by it.

Tics and shorter stature: should we be looking for an association?

Background

Tic disorders have commonly occurring and well recognized comorbidities including obsessive-compulsive disorder (OCD) and attention deficit hyperactivity disorder (ADHD). Shorter stature is not generally appreciated as an associated feature.

Methods

Case reports and a literature review.

Results

We describe four recently encountered patients with tics and shorter stature. The literature suggests that in addition to OCD and ADHD, shorter stature may also commonly accompany tic disorders. A variety of neuroendocrine mechanisms have been proposed.

Discussion

The potential associations between shorter stature and tic disorders and the common comorbidities OCD and ADHD deserve more attention. More research is needed to establish the strength of these associations and the underlying neurobiological mechanisms.

Association of the catechol-O-methyltransferase val158met polymorphism and anxiety-related traits: a meta-analysis

OBJECTIVES

The aims of this study were (i) to examine genotypic association of the catechol-O-methyltransferase (COMT) val158met polymorphism with anxiety-related traits with a meta-analysis; (ii) to examine sex and ethnicity as moderators of the association; and (iii) to evaluate whether the association differed by particular anxiety traits.

METHODS

Association studies of the COMT val158met polymorphism and anxiety traits were identified from the PubMed or PsycInfo databases, conference abstracts, and listserv postings. Exclusion criteria were (a) pediatric samples, (b) exclusively clinical samples, and (c) samples selected for a nonanxiety phenotype. Standardized mean differences in anxiety between genotypes were aggregated to produce mean effect sizes across all available samples, and for subgroups stratified by sex and ethnicity (Whites vs. Asians). Construct-specific analysis was conducted to evaluate the association of COMT with neuroticism, harm avoidance, and behavioral inhibition.

RESULTS

Twenty-seven eligible studies (N=15 979) with available data were identified. Overall findings indicate sex-specific and ethnic-specific effects: valine homozygotes had higher neuroticism than methionine homozygotes in studies of White males [mean effect size(Equation is included in full-text article.)=0.13; 95% CI 0.02, 0.25; P=0.03], and higher harm avoidance in studies of Asian males ((Equation is included in full-text article.)=0.43; 95% CI 0.14, 0.72; P=0.004). No significant associations were found in women and effect sizes were diminished when studies were aggregated across ethnicity or anxiety traits.

CONCLUSION

This meta-analysis provides evidence for sex and ethnic differences in the association of the COMT val158met polymorphism with anxiety traits. Our findings contribute to current knowledge on the relation between prefrontal dopaminergic transmission and anxiety.

Common and rare alleles of the serotonin transporter gene, SLC6A4, associated with Tourette's disorder

To evaluate the hypothesis that functionally over-expressing alleles of the serotonin transporter (SERT) gene (solute carrier family 6, member 4, SLC6A4) are present in Tourette's disorder (TD), just as we previously observed in obsessive compulsive disorder (OCD), we evaluated TD probands (N = 151) and controls (N = 858). We genotyped the refined SERT-linked polymorphic region 5-HTTLPR/rs25531 and the associated rs25532 variant in the SLC6A4 promoter plus the rare coding variant SERT isoleucine-to-valine at position 425 (I425V). The higher expressing 5-HTTLPR/rs25531 LA allele was more prevalent in TD probands than in controls (χ(2)  = 5.75; P = 0.017; odds ratio [OR], 1.35); and, in a secondary analysis, surprisingly, it was significantly more frequent in probands who had TD alone than in those who had TD plus OCD (Fisher's exact test; P = 0.0006; OR, 2.29). Likewise, the higher expressing LAC haplotype (5-HTTLPR/rs25531/rs25532) was more frequent in TD probands than in controls (P = 0.024; OR, 1.33) and also in the TD alone group versus the TD plus OCD group (P = 0.0013; OR, 2.14). Furthermore, the rare gain-of-function SERT I425V variant was observed in 3 male siblings with TD and/or OCD and in their father. Thus, the cumulative count of SERT I425V becomes 1.57% in OCD/TD spectrum conditions versus 0.15% in controls, with a recalculated, family-adjusted significance of χ(2) = 15.03 (P < 0.0001; OR, 9.0; total worldwide genotyped, 2914). This report provides a unique combination of common and rare variants in one gene in TD, all of which are associated with SERT gain of function. Thus, altered SERT activity represents a potential contributor to serotonergic abnormalities in TD. The present results call for replication in a similarly intensively evaluated sample. © 2013 Movement Disorder Society.

Genetic susceptibility and neurotransmitters in Tourette syndrome

Family studies have consistently shown that Tourette syndrome (TS) is a familial disorder and twin studies have clearly indicated a genetic contribution in the etiology of TS. Whereas early segregation studies of TS suggested a single-gene autosomal dominant disorder, later studies have pointed to more complex models including additive and multifactorial inheritance and likely interaction with genetic factors. While the exact cellular and molecular base of TS is as yet elusive, neuroanatomical and neurophysiological studies have pointed to the involvement of cortico-striato-thalamocortical circuits and abnormalities in dopamine, glutamate, gamma-aminobutyric acid, and serotonin neurotransmitter systems, with the most consistent evidence being available for involvement of dopamine-related abnormalities, that is, a reduction in tonic extracellular dopamine levels along with hyperresponsive spike-dependent dopamine release, following stimulation. Genetic and gene expression findings are very much supportive of involvement of these neurotransmitter systems. Moreover, intriguingly, genetic work on a two-generation pedigree has opened new research pointing to a role for histamine, a so far rather neglected neurotransmitter, with the potential of the development of new treatment options. Future studies should be aimed at directly linking neurotransmitter-related genetic and gene expression findings to imaging studies (imaging genetics), which enables a better understanding of the pathways and mechanisms through which the dynamic interplay of genes, brain, and environment shapes the TS phenotype.

No significant association between Catechol-O-methyl transferase (COMT) -287A/G gene polymorphism and Tourette's syndrome in family-based association study in Chinese Han population

To identify the association of Catechol-O-methyl transferase (COMT) -287A/G polymorphism with susceptibility to TS in Chinese Han population. We evaluated the genetic contribution of the COMT -287A/G polymorphism in 108 TS patients including all their parents in Chinese Han population using transmission disequilibrium test and haplotype relative risk design. Our results revealed that no significant association was found in COMT -287A/G genotypic and allelic frequencies with TS. Our results also suggested that there may be a lack of association between the TS and -287A/G polymorphism of COMT in Chinese Han population.

Allele and genotype frequencies of serotonin and dopamine transporter and receptor polymorphisms in a Norwegian population

Polymorphisms in genes coding for dopaminergic and serotonergic receptors and transporters have been associated with the clinical effects and adverse drug reactions of antipsychotic and antidepressant drugs. The objective of this study was to investigate the frequency and combinations of common polymorphisms in the dopamine transporter (DAT1), dopamine D(2) receptor (DRD2), dopamine D(3) receptor (DRD3), serotonin transporter (5HTT), and serotonin 2A receptor (5HTR2A) genes in a Norwegian population. To determine the background frequency in the population, 250 blood samples were consecutively collected from healthy Norwegian blood donors (125 men and 125 women; mean age: 48±11 years). Samples were tested for DAT1 VNTR, DRD2 Taq1A, DRD3 Ser9Gly, 5HTTLPR, and four polymorphisms (102 T>C, His452Tyr, 516 C>T, and Thr25Asn) in the 5HTR2A, using polymerase chain reaction and real-time polymerase chain reaction. We observed the frequency of the nine-repeat allele of DAT1 VNTR polymorphism as 20% (95% confidence interval [CI]: 0.18-0.23), the A1 allele of DRD2 Taq1A polymorphism as 21% (95% CI: 0.19-0.23), the A1 allele of DRD3 Ser9Gly polymorphism as 68% (95% CI: 0.66-0.70), the short allele of 5HTTLPR as 38% (95% CI: 0.36-0.40), and the T allele of 5HTR2A 102 T>C polymorphism as 41% (95% CI: 0.39-0.41), and the frequencies of 5HTR2A His452Tyr and 5HTR2A Thr25Asn were 93% and 95%, respectively. The tested polymorphisms showed differences compared with other European populations. Further studies are necessary to better understand the effect of these alleles and their combinations on personality, mental disorders, drug response, and adverse reactions of psychotropic drugs.

Tourette syndrome: gene expression as a tool to discover drug targets

Gene expression microarrays are a high-throughput, cost-effective method for measuring the expression of all genes in a sample. By comparing the expression patterns of healthy controls to diseased subjects, the genetic regulatory pathways underlying and affected by the disease can be elucidated. Furthermore, dysregulated genes are possible candidates for pharmaceutical therapy. Here, we consider the possibility of applying this approach to Tourette syndrome. We also review current theories of Tourette syndrome etiology and pharmacology.

The genetics of Tourette syndrome: a review

OBJECTIVES

This article summarizes and evaluates recent advances in the genetics of Gilles de la Tourette syndrome (GTS).

METHODS

This is a review of recent literature focusing on (1) the genetic etiology of GTS; (2) common genetic components of GTS, attention deficit hyperactivity disorder (ADHD), and obsessive compulsive disorder (OCD); (3) recent linkage studies of GTS; (4) chromosomal translocations in GTS; and (5) candidate gene studies.

RESULTS

Family, twin, and segregation studies provide strong evidence for the genetic nature of GTS. GTS is a heterogeneous disorder with complex inheritance patterns and phenotypic manifestations. Family studies of GTS and OCD indicate that an early-onset form of OCD is likely to share common genetic factors with GTS. While there apparently is an etiological relationship between GTS and ADHD, it appears that the common form of ADHD does not share genetic factors with GTS. The largest genome wide linkage study to date observed evidence for linkage on chromosome 2p23.2 (P=3.8x10(-5)). No causative candidate genes have been identified, and recent studies suggest that the newly identified candidate gene SLITRK1 is not a significant risk gene for the majority of individuals with GTS.

CONCLUSION

The genetics of GTS are complex and not well understood. The Genome Wide Association Study (GWAS) design can hopefully overcome the limitations of linkage and candidate gene studies. However, large-scale collaborations are needed to provide enough power to utilize the GWAS design for discovery of causative mutations. Knowledge of susceptibility mutations and biological pathways involved should eventually lead to new treatment paradigms for GTS.

Dopaminergic candidate genes in Tourette syndrome: association between tic severity and 3' UTR polymorphism of the dopamine transporter gene

Multiple evidence suggests an involvement of the dopamine neurotransmitter system in Tourette syndrome (TS). Therefore, dopaminergic candidate genes are in the center of genetic association analyses of TS. In this study, 103 TS patients and their parents have been characterized for different dopamine-related polymorphisms including the 48 bp variable number of tandem repeats (VNTR) of the dopamine D4 receptor (DRD4) gene, the 40 bp VNTR of the dopamine transporter (DAT1, SLC6A3) gene and the Val158Met polymorphism of the catechol-O-methyltransferase (COMT) gene. In addition, the 120 bp duplication and three single nucleotide polymorphisms (SNPs) were assessed in the promoter region of the DRD4 gene. The -616G allele and the 2-G-A-C haplotype (i.e., the 2-repeat form of the 120 bp sequence approximately -616G approximately -615A approximately -521C combination) were preferentially transmitted, however, these results did not remain significant after correction for multiple testing. Case-control analyses have also been carried out, resulting in negative findings. On the other hand, using a dimensional approach, the DAT1 40 bp VNTR showed an association with the peak tic-severity as measured by the Yale Global Tic Severity Scale. Patients with at least one copy of the 9-repeat allele had significantly more severe symptoms than individuals with the homozygous 10/10 genotype (P = 0.002). In summary, allele frequencies did not differ between cases and controls, but DAT1 genotype accounted for variations of tic severity within the TS group.

Obsessive-compulsive spectrum disorders: cross-national and ethnic issues

Epidemiological and clinical data from a variety of cultural and geographic settings on obsessive-compulsive disorder (OCD), and many of the obsessive-compulsive spectrum disorders, suggest that this is a group of disorders with a good degree of transcultural homogeneity. However, the content and themes that predominate in patients with these disorders, and the course of illness, can be shaped by cultural, ethnic, and religious experiences. Across cultures, OCD is commonly comorbid with mood, anxiety, and impulse-control disorders. However, little is known about the mechanisms by which culture and ethnicity may affect the expression of OCD and related disorders. Cross-national comparative studies exploring culturally influenced differences in clinical course, treatment outcome, including ethnogenetic differences in drug response, and prognosis are needed.

Tic disorders and obsessive compulsive disorder: where is the link?

Over the last years evidence on the overlap between tic-disorders (TD) and obsessive compulsive behavior/disorder (OCB/OCD) has increased. The main focus of research have been the phenomenological and epidemiological similarities and differences in samples of different age, primary diagnosis (TD vs. OCD) including the co-occurrence of both. Unfortunately, only a minority of studies included all three groups (TD, TD + OCD, OCD). Nevertheless, new insight concerning possible subtypes for both TD and OCD has been gained. While some authors concentrated on OCD with/without tics we will summarize the field of TD and OCB/OCD from the viewpoint of tics, since OCB plays an important role in patients with TD. Thereby we will not only sharpen the clinicans' awareness of known differences in phenomenology, epidemiology, genetics and neurobiology, aimed to improve their diagnoses and treatment but also highlight the gaps of knowledge and discuss possibilities for further research in this field.

Risk factors for extrapyramidal symptoms during treatment with selective serotonin reuptake inhibitors, including cytochrome P-450 enzyme, and serotonin and dopamine transporter and receptor polymorphisms

INTRODUCTION

Extrapyramidal symptoms (EPS) are rare adverse drug reactions to selective serotonin reuptake inhibitors (SSRIs). This study aimed to investigate the potential risk factors for EPS associated with SSRIs including polymorphisms of cytochrome P-450 isoenzymes, and serotonin and dopamine transporters and receptors.

METHODS

All spontaneous adverse drug reaction reports received by the Swedish Medical Products Agency until December 1999 that were coded with EPS and judged to be at least possibly related to SSRI treatment were included in the study. Reporting physicians received a form for collection of relevant information including current and previous use of SSRIs and antipsychotics, alcohol or substance abuse, central nervous system damage, a history of epilepsy or EPS, and a family history of Parkinson disease. A blood sample was also requested for genotyping of selected cytochrome P-450, and serotonin and dopamine transporter and receptor mutations.

RESULTS

A total of 64 cases of EPS were reported. Twenty-eight forms (46%) were returned, and 20 blood samples were obtained. Identified potential risk factors included age of 65 years or older and the presence of the A1 allele of the D2 dopamine receptor gene (DRD2) Taq1A polymorphism (relative risk, 2.4; 95% confidence interval, 1.2-4.5 vs literature controls). No relationship was apparent for sex, drug dose, or other genetic polymorphisms. At least 1 additional potential risk factor for EPS, such as a history of central nervous system damage, alcohol or substance abuse, epilepsy, Parkinson disease, previous or current exposure to antipsychotic drugs, concomitant treatment with other antidopaminergic or serotonergic agents, or a history of EPS, was found in 93% of the cases.

CONCLUSION

The risk of EPS with SSRIs seems to increase with advanced age and with the presence of the A1 allele of DRD2 Taq1A polymorphism. Because of the small sample size of our study and the use of historical controls rather than patients who did not experience EPS during SSRIs treatment, the DRD2 finding is preliminary and needs to be replicated in other studies before firm conclusions can be drawn. At least 1 additional potential risk factor was found in almost all cases.

The catechol-O-methyltransferase polymorphism: relations to the tonic-phasic dopamine hypothesis and neuropsychiatric phenotypes

Diverse phenotypic associations with the catechol-O-methyltransferase (COMT) Val158Met polymorphism have been reported. We suggest that some of the complex effects of this polymorphism be understood from the perspective of the tonic-phasic dopamine (DA) hypothesis. We hypothesize that the COMT Met allele (associated with low enzyme activity) results in increased levels of tonic DA and reciprocal reductions in phasic DA in subcortical regions and increased D1 transmission cortically. This pattern of effects is hypothesized to yield increased stability but decreased flexibility of neural network activation states that underlie important aspects of working memory and executive functions; these effects may be beneficial or detrimental depending on the phenotype, a range of endogenous factors, and environmental exigencies. The literature on phenotypic associations of the COMT Val158Met polymorphism is reviewed, highlighting areas where this hypothesis may have explanatory value, and pointing to possible directions for refinement of relevant phenotypes and experimental evaluation of this hypothesis.

Lack of association of catechol-O-methyltransferase gene polymorphism in obsessive-compulsive disorder

The COMT gene has been implicated to be involved in the pathogenesis of obsessive-compulsive disorder (OCD) and various other psychiatric disorders. COMT enzyme activity is governed by a common genetic polymorphism at codon 158 that results in substantial 3- to 4-fold variation in enzymatic activity [a high-activity COMT variant (H) and a low activity variant (L)]. This study evaluates the association between OCD and the COMT gene polymorphism. Fifty-nine OCD patients that were diagnosed according to DSM-IV criteria and 114 healthy control subjects were included in the study. PCR technique was used for molecular analysis. The genotypic pattern of distribution of the COMT gene (H/H, H/L, and L/L genotypes) was not different between the OCD patients and controls. There were no significant differences among the patients with positive family history for OCD, those with negative family history for OCD, and the controls with respect to allele frequencies of the COMT gene polymorphisms. Patients that were homozygous or heterozygous for the L allele had significantly higher insight scores (i.e., poorer insight) on Y-BOCS compared to those homozygous for the H allele. We did not find an association between OCD, family history for OCD, and the COMT gene polymorphism. This study suggests that the COMT gene polymorphism is not directly associated with OCD in our patient group.

Meta-analysis of the association between the catecholamine-O-methyl-transferase gene and obsessive-compulsive disorder

Obsessive-compulsive disorder (OCD) is a chronic, severely debilitating mental illness that affects approximately 1-2% of the population. Data from twin and family studies have shown that genetic factors contribute to the expression of the disease. The dopaminergic system has been implicated in the pathogenesis of OCD, and catecholamine-O-methyl-transferase (COMT) is a key modulator of dopaminergic and noradrenergic neurotransmission. The gene for COMT has a common polymorphism that has been shown to be correlated with a three- to fourfold change in enzymatic activity. Several groups have searched for an association between the COMT gene polymorphism and the presence or absence of OCD, with contrasting results. We conducted a systematic review and meta-analysis of both the published literature and unpublished data. Available data were stratified according to the original study design as either case-control or family-based, and two separate meta-analyses were conducted, using both fixed-effects and random-effects models. These analyses showed insufficient evidence to support an association between the COMT gene polymorphism and OCD. Subgroup stratification based on gender generated no statistically significant associations. These results should be considered in any future work correlating the COMT gene with OCD.

An update on the genetics of Gilles de la Tourette syndrome

OBJECTIVES

To summarize the current data suggesting that Gilles de la Tourette syndrome (GTS) is inherited and genetic.

METHODS

The extant literature on family studies, segregation analyses, candidate genes studies and linkage studies of GTS was reviewed and summarized.

RESULTS AND CONCLUSIONS

There is considerable data that suggests that: (1). genetic factors play an important role in the manifestation of GTS; (2). several genes are important with some possibly having major effect; and (3). several regions of the genome have been identified as potential locations of these susceptibility genes.

Anticipation of age at onset of obsessive-compulsive spectrum disorders in patients with obsessive-compulsive disorder

Anticipation of age at onset has been observed in several neuropsychiatric disorders. Recent studies have associated anticipation with the presence of unstable DNA and have suggested that trinucleotide repeats may be the main cause in some of these diseases. However, several selection biases may mimic the presence of such an effect. In this study we evaluated the presence of this effect in 40 families of probands with obsessive-compulsive disorder (OCD) compared with affected subjects in the parental generation. We controlled for ascertainment biases by taking into account the age at interview of probands. Using a different recruitment strategy, we controlled for anticipation in a sub-sample of offspring of 13 OCD patients, affected with OC spectrum disorders. While the younger generation showed a significantly earlier age at onset than the parental generation, no effect of age at interview was observed. Drawing on the results, we hypothesised that the presence of anticipation in OCD and OC spectrum disorders could be due to a specific genetic effect (unstable DNA), as it has been hypothesised for other disorders showing this effect.

Genetic modelling of the estrogen metabolism as a risk factor of hormone-dependent disorders

Estradiol is a pleiotropic hormone, involved in the etiology of a wide variety of diseases. Over the last decade individual genetic variability of the estradiol metabolism has been described as a significant contributor to disease susceptibility with variations depending on ethnic background. Among others, genetic variations of genes encoding cytochrome P450 (CYP) enzymes play an important role in this regard. Mutant alleles of the CYP 1A1 gene are major modulators of lung cancer risk among smokers, mediate gender differences in lung cancer susceptibility, and have been associated with an elevated risk for developing breast, prostate, colorectal, and oral squamous cell cancer. Variants of the CYP 1B1 gene modulate the risk for developing prostate, ovarian, lung, and breast cancer. Also, mutations in the CYP 1B1 gene are the major genetic determinant of congenital glaucoma. Mutant CYP 17 alleles are associated with serum and plasma levels of steroid hormones, use of hormone replacement therapy, and the development of endometrial, prostate, and breast cancer. Available data indicate that the protective effect against breast cancer of a later age at menarche is limited to wild-type CYP 17 allele carriers. Among women with the polycystic ovary syndrome, carriage of mutant CYP 17 alleles is sufficient to aggravate the clinical presentation of the disease. Molecular variants of the CYP 19 gene are associated with an increased risk for developing breast cancer, advanced breast cancer stages, and tumor aromatase production. Carriage of a mutant catechol-O-methyltransferase allele is associated with breast cancer, neurologic disorders such as Parkinson's disease, and modulates behavior among patients with schizophrenia, alcoholics and the general population. In summary, the available evidence points to genes that encode estrogen-metabolizing enzymes as strong hereditary determinants of the susceptibility to benign as well as malignant conditions.

Genetic modeling of estrogen metabolism as a risk factor of hormone-dependent disorders

Estradiol is a pleiotropic hormone, involved in the etiology of a wide variety of diseases. Over the last decade individual genetic variability of the estradiol metabolism has been described as a significant contributor to disease susceptibility with variations depending on ethnic background. Among others, genetic variations of genes encoding cytochrome P450 (CYP) enzymes play an important role in this regard. Mutant alleles of the CYP 1A1 gene are major modulators of lung cancer risk among smokers, mediate gender differences in lung cancer susceptibility, and have been associated with an elevated risk for breast, prostate, colorectal, and oral squamous cell cancer. Variants of the CYP 1B1 gene modulate the risk for prostate, ovarian, lung, and breast cancer. Also, mutations in the CYP 1B1 gene are the major genetic determinant of congenital glaucoma. Mutant CYP 17 alleles are associated with serum and plasma levels of steroid hormones, use of hormone replacement therapy, and endometrial, prostate, and breast cancer. Available data indicate that the protective effect of a later age at menarche is limited to mutant CYP 17 allele carriers. Among women with the Polycystic Ovary (PCO) syndrome, mutant CYP 17 alleles are sufficient to aggravate the clinical presentation of the disease. Molecular variants of the CYP 19 gene are associated with an increased risk for breast cancer, advanced disease stage, and tumor aromatase production. Carriage of a mutant catechol-O-methyltransferase (COMT) allele is associated with breast cancer, neurologic disorders such as Parkinson's disease, and modulates behavior among patients with schizophrenia, alcoholics and the general population. In summary, the available evidence points to estrogen metabolising genes as strong hereditary determinants of the susceptibility to benign and malignant conditions.

Exploratory factor analysis of obsessive-compulsive patients and association with 5-HTTLPR polymorphism

The determination of a genetic basis for obsessive-compulsive disorder (OCD) depends on how phenotypic boundaries are defined. Although a hypothesis for serotonin dysfunction in OCD has been advanced, no genes specifically responsible for serotonin regulation have as yet been definitively related to the etiology of OCD. The phenotypic variability of OCD could be at the basis of the failure of molecular biology investigations to find any genes involved in the liability to the disorder. Obsessive and compulsive contents can aggregate in OCD patients differently; multifactorial description may therefore be able to account for OCD phenotypic variance. Using principal component analysis, we derived five factors from 13 main contents of the Yale-Brown Obsessive-Compulsive Scale (YBOCS), and considered them as quantitative phenotypes to evaluate their possible association with an insertion/deletion polymorphism in the promoter region of the serotonin transporter gene (5-HTTLPR). A trend toward positive association between the fifth factor, including counting and repeating rituals, and 5-HTTLPR was found. However, only considering the subgroup of patients with tic codiagnosis, we found a significantly higher score for the fifth factor for patients with L/L genotype with respect to L/S and S/S genotypes.