A frequent polymorphism in the coding exon of the human cannabinoid receptor (CNR1) gene

The central cannabinoid receptor (CB1) mediates the pharmacological activities of cannabis, the endogenous agonist anandamide and several synthetic agonists. The cloning of the human cannabinoid receptor (CNR1) gene facilitates molecular genetic studies in disorders like Gilles de la Tourette syndrome (GTS), obsessive compulsive disorder (OCD), Parkinsons disease, Alzheimers disease or other neuro psychiatric or neurological diseases, which may be predisposed or influenced by mutations or variants in the CNR1 gene. We detected a frequent silent mutation (1359G-->A) in codon 453 (Thr) of the CNR1 gene that turned out to be a common polymorphism in the German population. Allele frequencies of this polymorphism are 0.76 and 0.24, respectively. We developed a simple and rapid polymerase chain reaction (PCR)-based assay by artificial creation of a Msp I restriction site in amplified wild-type DNA (G-allele), which is destroyed by the silent mutation (A-allele). The intragenic CNR1 polymorphism 1359(G/A) should be useful for association studies in neuro psychiatric disorders which may be related to anandamide metabolism disturbances.

[Tic disease. Current genetic and neurochemical factors]

We review historical, conceptual, clinical and diagnostic criteria as well as present genetic and neurochemical factors of tic disorders. Epidemiologic data suggest that tic is an organic disease with autosomal dominant transmission. We emphasize immunohistochemical studies particularly related to the dopaminergic, noradrenergic and serotonergic systems. These modulate the activity of the cortico-striato-thalamocortical circuits implicated in both Tourette's syndrome and obsessive-compulsive disorder.

Association of the androgen receptor gene (AR) with ADHD and conduct disorder

The male predominance of externalizing behaviors suggests that the X-linked androgen gene might be involved. Since the shorter alleles of the CAG and GGC polymorphisms of the AR gene are associated with increased gene expression we sought to determine whether they were also associated with externalizing behaviors. We examined 302 subjects consisting of Tourette syndrome probands and controls. ANOVA showed a significant association between the AR haplotypes and ADHD (p < 0.0001), conduct disorder (CD; p < 0.017), and oppositional defiant disorder (ODD; p < 0.004) with the lowest scores in those with the longer alleles at both polymorphisms. These results suggest that genetic variation at the human AR gene plays a role in human externalizing disorders.

Tourette syndrome and the norepinephrine transporter gene: results of a systematic mutation screening

Tourette syndrome (TS) is a complex inherited neuropsychiatric disorder characterized by multiple motor and phonic tics. Involvement of central norepinephrine mechanisms is suggested by central norepinephrinic hyperactivity in patients with TS and by the therapeutic effects of the presynaptic alpha2-adrenergic agonist clonidine. The norepinephrine transporter gene (NET) was systematically screened by single-strand conformation analysis for genetic variants, including the whole coding region and adjacent exon-intron boundaries in 43 patients with TS and 46 healthy controls. We detected 12 DNA sequence variants, among them four missense mutations (Val69Ile, Thr99Ile, Va1245Ile, and Gly478Ser). The observed missense mutations may alter conformational rearrangements during gating of the transporter, assembly of subunits, and norepinephrine-specific uptake affinity. Allele frequency and genotype distribution of the genetic variants showed no differences between TS patients and controls. No mutation of likely functional significance was found that distinguished TS patients from healthy controls, indicating that genetic variants of the NET gene are not causally related to Tourette syndrome.

[Tic disorders in children and adolescents. Clinical and genetic features, comorbidity]

Tic disorders in children and adolescents. Clinical and genetic features, comorbidity.

BACKGROUND

Aim of the study is to evaluate the clinical and genetic characteristics of tic disorders, in view of individuating similarities or differences relevant to the prognosis among different nosological groups.

METHODS

A retrospective study of 79 children and adolescents (average age 9.3 yrs) was performed. The cases were diagnosed according to DSM-IV as: transitory tics (TT) 13 cases; chronic tics (CT) 50 cases; Tourette disease (TD) 16 cases. They were compared to a control group of 18 school age children without any neurological or psychiatric disturbance. The study included: semi-structured interviews focused on natural history of the disturbances, familiarity, presence of perinatal pathology, comorbidity; neurological examination, EEG, psychodiagnostic tests and investigation.

RESULTS

Mean age of onset and type of first symptoms are the same in the three groups. Compared to the control group there is a significant increase in: familiarity for tics disturbances in TD; presence of perinatal pathological factors in the three groups of patients; comorbidity for obsessive-compulsive disorder (OCD) in CT and TD, comorbidity with ADHD in CT group. Three clinical cases are reported to exemplify the mixed features in the families and the different responsivity to the pharmacological treatment.

Additive effect of three noradrenergic genes (ADRA2a, ADRA2C, DBH) on attention-deficit hyperactivity disorder and learning disabilities in Tourette syndrome subjects

Halperin et al. (Halperin JM. Newcorn JH, Koda VH, Pick L, McKay KE, Knott P. Noradrenergic mechanisms in ADHD children with and without reading disabilities: a replication and extension. J Am Acad Child Adolesc Psychiatry 1997: 36: 1688 1696) reported a significant increase in plasma norepinephrine (NE) in attention-deficit hyperactivity disorder (ADHD) children with reading and other cognitive disabilities compared to ADHD children without learning disabilities (LD). We examined the hypothesis that ADHD + LD was associated with NE dysfunction at a molecular genetic level by testing for associations and additive effects between polymorphisms at three noradrenergic genes the adrenergic alpha2A receptor (ADRA2A), adrenergic alpha2C receptor (ADRA2C), and dopamine beta-hydroxylase (DBH) genes. A total of 336 subjects consisting of 274 individuals with Tourette syndrome (TS) and 62 normal controls were genotyped. Regression analysis showed a significant correlation between scores for ADHD, a history of LD, and poor grade-school academic performance that was greatest for the additive effect of all three genes. Combined, these three genes accounted for 3.5% of the variance of the ADHD score (p = 0.0005). There was a significant increase in the number of variant NE genes progressing from subjects without ADHD (A-) or learning disorders (LD-) to A + LD - to A - LD + to A + LD + (p = 0.0017), but no comparable effect for dopamine genes. These data support an association between NE genes and ADHD, especially in ADHD + LD subjects.

Genetic susceptibility to neurodevelopmental disorders

A large body of evidence suggests that genetic factors influence liability to many common neurodevelopmental disorders. Examples include Tourette syndrome, attention-deficit hyperactivity disorder, autism, and dyslexia. Characterization of the genetic component of susceptibility to these conditions at a molecular level should improve classification, elucidate fundamental neurobiologic mechanisms of disease, and suggest novel approaches to treatment. Susceptibility loci for complex traits could be identified by detecting linkage to a well-mapped genetic marker or by detecting association with a putative high-risk allele at a candidate locus. This article reviews the principles underlying these complementary approaches, and notes recent progress in specific conditions. As the molecular epidemiology of susceptibility to common neurodevelopmental disorders emerges, it might be increasingly possible to identify "high-risk" and "low-risk" genotypes. Clinicians should understand the nature of this kind of information in order to appreciate its power as well as its limitations.

Complex segregation analysis for obsessive compulsive disorder and related disorders

Complex segregation analysis was applied to a sample of 107 Italian families with probands with obsessive compulsive disorder (OCD), using regressive logistic models to test for possible models of genetic transmission. We used two different phenotypic definitions of affection: 1) OCD; and 2) OCD plus Tourette's syndrome/chronic motor tics (CMT). Because of the potential relationship between OCD, Tourette's syndrome (TS), and other tic disorders, we considered these diagnoses to be determined by the same liability in subsequent steps of the analysis. For the 107 OCD families, the best fit was a dominant model of transmission (with a higher penetrance for females). When the phenotype boundaries were widened (OCD + CMT + TS), an unrestricted model of transmission became the best fit. We concluded that additional data are needed to support the hypothesis that Tourette's syndrome and OCD share a common etiology: on the basis of clinical and epidemiological considerations, the OCD phenotype probably presents a higher level of heterogeneity than the TS phenotype, and it could be regulated through different etiologic pathways.

Influence of family history on clinical expression of Tourette's syndrome

OBJECTIVE

To determine the influence of family history on clinical expression of Tourette's syndrome (TS).

BACKGROUND

Recent studies have suggested that clinical expression of TS is similar among sporadic (SP) and familial patients but may be influenced by bilineal (BIL) transmission of tics or obsessive-compulsive behavior (OCB) in high-density pedigrees.

METHODS

The authors used family history methodology, supported by direct examination of affected relatives in 73% of familial patients, to determine the frequency of SP TS, and of unilineal (UNL) and BIL transmission of tics or OCB in 111 consecutively ascertained juvenile TS patients. For individuals in each group, severity of tics, attention deficit hyperactivity disorder (ADHD), and OCB were assessed at presentation and after a mean follow-up interval of 2.6 years, using the Tourette's Syndrome Global Scale and the Clinical Global Impression scales. The phenomenology of OCB was evaluated using the symptom checklist of the Children's Yale-Brown Obsessive Compulsive Scale.

RESULTS

The authors documented BIL transmission of tics in seven patients (6%). Patient age and sex were similar for the SP (n = 21; 19%), UNL (n = 66; 59%), and BIL (n = 24; 22%) groups, as was ADHD and tic severity at presentation and follow-up. Severity of OCB differed significantly between groups, with moderate to severe OCB affecting 5% of SP, 12% of UNL, and 37% of BIL patients at presentation (p = 0.007), and 5% of SP, 17% of UNL, and 54% of BIL patients at follow-up (p = 0.0001). Relative to UNL or SP patients, BIL patients were more likely to exhibit self-injurious behaviors (p = 0.0005).

CONCLUSIONS

OCB is less prominent in SP than in familial TS, perhaps reflecting a more restricted pathophysiology in this subgroup. Although BIL transmission of tics is relatively infrequent in consecutive TS pedigrees, cotransmission of OCB from an otherwise unaffected parent is common and significantly influences development of OCB and self-injurious behaviors, but not tics, in offspring. Genetic heterogeneity, epigenetic factors, and gene-environment interactions may play a more important role than genetic dosage effects in determining tic severity in TS.

Genetics and child psychiatry: II Empirical research findings

Key substantive findings from quantitative and molecular genetic research are reviewed in relation to affective disorder, schizophrenia, autism, hyperkinetic/attention deficit disorder, oppositional and conduct disorders, drug/alcohol problems, and Tourette's syndrome/chronic tics.

Clinical differences between subjects with familial and non-familial Tourette's syndrome: a case series

OBJECTIVE

As many as 35 percent of Tourette's Syndrome patients do not acquire this disorder genetically. Since there has been little research conducted in this area, the purpose of this study was to compare the clinical differences between two groups of patients with Tourette's Syndrome (TS), one with family history of TS and one without.

METHOD

Using data of eight previously diagnosed TS patients, the authors made comparisons of clinical and sociodemographic variables between a group of three patients with family history of TS and five with no family history.

RESULTS

There were no differences in clinical presentation, current age, age at diagnosis, gender, and socioeconomic status. There were differences in birth history, developmental milestones, I.Q., and neurological findings between patients with family history and no family history of TS.

CONCLUSIONS

Our findings support the need for testing the hypothesis of a multidetermined origin of TS, a disorder in which hereditary, neuropsychological, and environmental factors play a role.

Dopamine uptake by platelet storage granules in first-degree relatives of Tourette's syndrome patients

BACKGROUND

Considering that platelets have been established to be good peripheral markers for the study of catecholaminergic neurons, we have applied an assay to measure the uptake of (3H)-dopamine (DA) into platelet storage granules (PSG). Recently, we reported that Tourette's syndrome (TS) patients (pts) show decreased DA uptake into PSG.

METHODS

In the present study, 28 first-degree relatives (3 with chronic motor tics, 3 with transient tics, 6 with obsessive-compulsive behavior, and 16 without symptomatology) belonging to the families of 13 patients, and 14 unrelated healthy controls were studied.

RESULTS

Double reciprocal plots were constructed for each subject, and the apparent maximum velocity (Vmax) and Michaelis constant (K(m)) were determined by linear regression analysis (Lineaweaver-Burke plots). The uptake of DA (0.5-5 mumol/L) (mean +/- SEM) by PSG from relatives with symptomatology was similar to the TS patients (symptomatic relatives Vmax 181 +/- 22.2 fmol/mg protein, K(m) (mumol/L) 6.42 +/- 0.29; TS pts Vmax 108 +/- 6.9, K(m) 7.79 +/- 0.64). Relatives without symptomatology on the contrary showed DA affinity characteristics similar to the controls (t test, paired t test, multivariate analysis of variance, and log transformation).

CONCLUSIONS

The data presented suggest that TS is hereditary, but they do not distinguish between an autosomal dominant inheritance and a mixed or polygenic model.

Identification of genetic markers associated with Gilles de la Tourette syndrome in an Afrikaner population

Because gene-mapping efforts, using large kindreds and parametric methods of analysis, for the neurologic disorder Tourette syndrome have failed, efforts are being redirected toward association studies in young, genetically isolated populations. The availability of dense marker maps makes it feasible to search for association throughout the entire genome. We report the results of such a genome scan using DNA samples from Tourette patients and unaffected control subjects from the South African Afrikaner population. To optimize mapping efficiency, we chose a two-step strategy. First, we screened pools of DNA samples from both affected and control individuals, using a dense collection of 1,167 short tandem-repeat polymorphisms distributed throughout the genome. Second, we typed those markers displaying evidence of allele frequency-distribution shifts, along with additional tightly linked markers, using DNA from each affected and unaffected individual. To reduce false positives, we tested two independent groups of case and control subjects. Strongest evidence for association (P values 10-2 to 10-5) were obtained for markers within chromosomal regions encompassing D2S1790 near the chromosome 2 centromere, D6S477 on distal 6p, D8S257 on 8q, D11S933 on 11q, D14S1003 on proximal 14q, D20S1085 on distal 20q, and D21S1252 on 21q.

Volumetric neuroimaging in children with neurodevelopmental disorders--mapping the brain and behavior

The recent volumetric neuroimaging studies in children with fragile X syndrome, Down syndrome (DS), Rett syndrome (RS), and Tourette syndrome (TS) were reviewed. Neuroimaging studies and cognitive and behavioral phenotypes pertinent to each disorder were reviewed within the context of current knowledge of their neurobiological mechanisms. The mainly involved brain regions in fragile X syndrome are the cerebellar vermis, temporal areas, and the caudate nucleus which may be related to autistic tendency, problems of memory and language and deficits in executive function, respectively. The preferential involvement of frontal lobe, cerebellum and mesial temporal areas may correspond to the selective language and speech deficits in DS children. There was significantly generalized cerebral volume reduction with greater loss of gray matter in comparison to white matter, consistent with the extensive clinical features of RS. Right side predominance of basal ganglia supported the suggestion that the basal ganglia is related to pathogenesis of TS, which may also be related to the impaired executive function and the absence of functional asymmetry. Further prospectives for integrating neuroanatomic findings and neurobehavioral studies also were discussed.

Abnormal cerebral activation associated with a motor task in Tourette syndrome

BACKGROUND AND PURPOSE

In Gilles de la Tourette syndrome, PET scanning and EEG suggest an abnormal organization of the sensorimotor cortex and basal ganglia. The purpose of this study was to use functional MR imaging to study activation in the sensorimotor cortex in patients with Tourette syndrome.

METHODS

From echo-planar images acquired during intermittent performance of a finger-tapping task, the location of activated pixels was determined by means of conventional signal processing methods. In five patients with Tourette syndrome and five healthy volunteers, the number of activated pixels in the sensorimotor cortices and supplementary motor areas were counted. The area over which the activation was distributed was calculated.

RESULTS

In the five patients, the average number of pixels activated during the finger-tapping task in the sensorimoter cortices and supplementary motor area (69.4 pixels) exceeded that in the volunteers (49.2 pixels). The difference was significant. The area over which the pixels was distributed was significantly larger (25.4 vs 13.8 cm2).

CONCLUSION

Motor function is organized differently in patients with Tourette syndrome than in healthy subjects.

The Bal I and Msp I polymorphisms in the dopamine D3 receptor gene display, linkage disequilibrium with each other but no association with Tourette syndrome

The D3-dopamine receptor gene, DRD3, has been considered as a candidate gene in several disorders in which the dopaminergic system has been implicated including Tourette syndrome and schizophrenia. The DRD3 studies to date have all used as the gene marker a Bal I polymerase chain reaction restriction fragment length polymorphism (PCR RFLP). There have been recent reports on a second marker, an Msp I PCR RFLP, that lies 40 kb downstream. We have typed a sample of 16 Tourette syndrome families with both markers and observed significant linkage disequilibrium between the two markers but no apparent association of either marker with Tourette syndrome.

Mutation screening of the dopamine D1 receptor gene in Tourette's syndrome and alcohol dependent patients

We report a single stranded conformational polymorphism (SSCP) analysis of the coding region of the dopamine D1 receptor (DRD1) in Tourette's syndrome (n = 50) and control (n = 50) subjects. Tourette's syndrome populations with comorbidity for attention deficit-hyperactivity disorder (AD-HD) (n = 35) and obsessive compulsive disorder (OCD) (n = 30) were also screened. As a related study, we also screened patients diagnosed with alcohol dependence (n = 72). The present study discovered no DRD1 coding region mutations in any of the Tourette's syndrome or alcohol dependent patients. One silent mutation, a C for a T at Ile49, was discovered in one control subject. The non-polymorphic structure of the DRD1 gene among the Tourette's syndrome, Tourette's syndrome comorbid with AD-HD and OCD and the alcohol dependent populations screened by SSCP suggests that coding region mutations of the DRD1 gene are unlikely to contribute to the inheritance of these disorders.

The relation of the dopamine transporter gene (DAT1) to symptoms of internalizing disorders in children

The relation of the dopamine transporter gene (DAT1) to symptoms of internalizing disorders, Tourette's disorder, and obsessive-compulsive disorder was examined using both within- and between-family tests of association. The sample consisted of clinic-referred children and their siblings and controls and their siblings. Between-family association was examined via the association of DAT1 genotypes with disorder symptoms in the population. Symptoms of all eight disorders increased with a greater number of 10-repeat DAT1 alleles. Using a quantitative transmission disequilibrium test (QTDT), linkage and within-family association was indicated by increased symptoms in children who received 10 repeat alleles from heterozygous parents relative to children who received 9 repeat alleles. Four disorders were associated with DAT1 using the QTDT: generalized anxiety, social phobia, obsessive-compulsive, and Tourette's. The effects of comorbidity were investigated by repeating the same between- and within-family analyses on residual scores, with any effects of attention deficit hyperactivity disorder symptoms removed. Although the residuals were associated less strongly with DAT1 than were the original scores, three disorders continued to show association both between and within families: generalized anxiety, Tourette's, and social phobia.

Current status of genetic studies of Gilles de la Tourette syndrome

Gilles de la Tourette syndrome (TS) is a familial, neuropsychiatric disorder characterized by chronic, intermittent motor and vocal tics. Despite strong evidence for a genetic basis of this disorder from family, twin, and adoption studies, no convincing evidence for genetic linkage has been reported. Numerous groups world-wide have searched for genetic susceptibility factors for TS, testing specific candidate genes in neurotransmitter systems as well as DNA markers with known locations. Several factors may complicate the search for genes for this disorder, including diagnostic uncertainties, definition of the TS phenotypic spectrum as it relates to genetic susceptibility, assortative mating, genetic heterogeneity, and unclear mode of inheritance. In this article, we review the evidence for the genetic basis of TS and the current status of genetic studies.

Neuropsychiatric disorders

Neuropsychiatric disorders of childhood include autism spectrum disorders, disorders comprising attention deficits (attention-deficit-hyperactivity disorder and deficits in attention, motor control and perception), tics (motor or vocal, or both), and obsessions and compulsions (obsessive-compulsive disorder). They affect a small proportion of the child population. They can now reliably be diagnosed, and are valid and clinically meaningful conditions. Effective interventions are available for most of these disorders.

Clinical characteristics of Tourette syndrome

The aim of the present study was to examine the clinical characteristics of Tourette syndrome (TS) in terms of symptomatology, outcome and organic and genetic factors, and to compare these with results of previous studies on TS in Western countries and in Japan, on the basis of precise information taken from a large number of TS patients under psychiatric treatment in Japan. There was a total of 64 TS patients (55 males and nine females) selected from those who visited our outpatient clinic from 1974 to 1993 and were found to meet the criteria for Tourette's disorder of DSM-III-R. The mean patient age at entry to the present study was 17.4 years (SD: 7.2). All data were collected through a systematic chart review of subjects, including data on tic symptoms and the course of their development; complications and developmental histories; family histories; medical and psychological examinations; treatment; severity and outcome. A check of the data showed that the mean age at onset was 6.9 years (SD: 2.7). An analysis of the progression of the symptoms revealed that 'generalized tics' afflicting the entire body were found in 64.1% of subjects and coprolalia was found in 50%. The main complications were obsessive-compulsive symptoms (OCS) in 62.5% of patients and attention deficit hyperactivity disorder (ADHD) in 17.2%. Of their parents, 7.0% had tic disorders except TS and 1.6% had TS. Contrary to results from previous studies of TS, our study revealed that at least the incidence of coprolalia in TS patients in Japan is not lower than in Western countries. However, the frequency of familial cases seemed to be lower than previously reported for Western patients. Outcome was fairly related with 'generalized tics,' OCS, aggressiveness and ADHD.

Correlation of length of VNTR alleles at the X-linked MAOA gene and phenotypic effect in Tourette syndrome and drug abuse

Abnormalities in monoamine oxidase (MAO) levels have been implicated in a wide range of psychiatric disorders. We have examined a VNTR polymorphism at the X-linked MAOA gene to test two hypotheses: (1) Do variants of the MAOA gene play a role in any of the behavioral disorders associated with Tourette syndrome or drug abuse? (2) If so, is there any correlation between the length of the alleles and the phenotypic effect? We examined two independent groups: 375 TS patients, relatives and controls, and 280 substance abusers and controls. The alleles were divided into four groups of increasing size. There was a significant association between the MAOA gene and behavioral phenotypes in both groups, and in both the longest alleles were associated with the greatest phenotypic effect. The strongest effect was for the diagnosis of drug dependence (P=0.00003). The VNTR allele groups were in significant linkage disequilibrium with the Fnu4H1 polymorphism previously shown to be associated with MAO-A activity. While these results are consistent with the possibility that different-sized alleles of the short-repeat polymorphisms themselves may play a role in gene regulation, further studies directly linking these alleles with enzyme levels need to be done.