The effect of two different 18-week walking programmes on aerobic fitness, selected blood lipids and factor XIIa

Forty-nine previously sedentary or low active individuals aged 40-71 years were allocated to three groups. The long walking group participated in an 18-week walking programme which consisted of walks lasting 20-40 min; the repetitive short walking group completed walks of between 10 and 15 min, up to three times a day, with no less than 120 min between each walk; and the control group maintained their low level of activity. Both walking programmes began at a prescribed 60 min x week(-1), which increased steadily up to 200 min x week(-1) by week 12. During the study, the long walking group walked for an estimated 2514 min (139 min x week(-1)), expending an estimated 67.5 MJ (3.72 MJ x week(-1)) at an estimated 73% of their age-predicted maximum heart rate and 68% of their estimated VO2max. The repetitive short walking group walked for an estimated 2476 min (135 min x week(-1)), expending an estimated 58.5 MJ (3.17 MJ x week(-1)) at an estimated 71% of their age-predicted maximum heart rate and 65% of their estimated VO2max. The results showed a statistically significant reduction in heart rate during a standardized step test (pre- vs post-intervention) in both walking groups, indicating an improvement in aerobic fitness, although the control group showed a higher average heart rate during the post-intervention test, indicating reduced fitness. When compared with the male subjects pre-intervention, the females possessed more favourable levels of high-density lipoprotein (HDL) cholesterol (P< 0.001), apolipoprotein (apo) AI (P < 0.001) and ratios of total cholesterol:HDL cholesterol (P< 0.02) and low-density lipoprotein (LDL) cholesterol: HDL cholesterol (P< 0.02). Compared with the controls post-intervention, the walking groups showed no statistically significant changes in total cholesterol, LDL cholesterol, HDL cholesterol, apo AI, apo AII, apo B, or the ratios of total cholesterol: HDL cholesterol, LDL cholesterol: HDL cholesterol, apo AI: apo B or apo AI: apo AII (P > 0.05). Relative to the walking groups, factor XIIa increased in the control group (P < 0.05). We conclude that, although both walking programmes appeared to improve aerobic fitness, there was no evidence of improvements in the blood lipids or associated apolipoproteins of the walking groups. Further analysis indicated that this apparent lack of change may have been related to the subjects' relatively good pre-intervention blood lipid profiles, which restricted the potential for change. The implications of the observed changes in the coagulation/fibrinolytic factors remain unclear.

Reduced central serotonin transporters in alcoholism

OBJECTIVE

Dysfunction of monoamine uptake mechanisms has been implicated in the pathogenesis of alcohol dependence. The authors explored whether serotonergic dysfunction is associated with anxiety and depression, which increase the risk of relapse in alcoholics.

METHOD

The availability of serotonin and dopamine transporters in 22 male alcoholics and 13 healthy male volunteers was measured with the use of [123I] beta-CIT and single photon emission computed tomography, and psychopathological correlates were assessed.

RESULTS

A significant reduction (a mean of about 30%) in the availability of brainstem serotonin transporters was found in the alcoholics, which was significantly correlated with lifetime alcohol consumption and with ratings of depression and anxiety during withdrawal.

CONCLUSIONS

The findings support the hypothesis of serotonergic dysfunction in alcoholism and in withdrawal-emergent depressive symptoms.

The evaluation of resin composite consistency

OBJECTIVE

To evaluate a method for the assessment of the consistency of unset resin composite.

METHODS

Fourteen commercial resin composites were selected, which had a range of consistencies as assessed subjectively. The material was placed in a cylindrical mold with 8 mm diameter and 8 mm depth, and a glass rod with 4.37 mm diameter driven into the composite at 24.4 mm min-1 for 6 s, i.e., to a depth of 2.44 mm. The maximum force reached during the 6 s period was recorded, and used as a measure of consistency.

RESULTS

Consistency values ranged from 0.33 N to 31.3 N, with the highest values being found for some of the recently introduced 'packable' materials. The reliability of the test was high.

SIGNIFICANCE

The test may be useful as a standard method of assessing resin composite consistency.

Tourette's syndrome: [I-123]beta-CIT SPECT correlates of vocal tic severity

OBJECTIVE

To examine in vivo the density of brain monoaminergic transporters in Tourette's syndrome (TS).

BACKGROUND

TS is a heritable neuropsychiatric disorder characterized by chronic vocal and motor tics and is often associated with obsessive-compulsive symptoms. Hyperstimulation of dopamine receptors and dysfunction of serotonergic transmission have been implicated in its pathogenesis, but direct evidence of involvement of these neurochemical systems has been limited.

METHODS

Symptom severity and the availability of presynaptic monoaminergic transporters in the basal ganglia, midbrain, and thalamus were measured using SPECT and the radioligand [I-123]2beta-carbomethoxy-3beta-(4-iodophenyl)tropane ([I-123]beta-CIT) in 10 patients with TS and in 10 age- and sex-matched normal volunteers.

RESULTS

A significant negative correlation was found between a measure of overall tic severity and beta-CIT binding in the midbrain (r = -0.73, p = 0.02) and the thalamus (r = -0.82, p < 0.01). When examined post hoc, these correlations were determined largely by vocal tic severity. No other significant correlations were found between symptom severity and beta-CIT binding in the striatum or cortex.

CONCLUSIONS

These findings indicate that serotonergic neurotransmission in the midbrain and serotonergic or noradrenergic neurotransmission in the thalamus may be important factors in the expression of TS and may suggest novel targets for treatment.

In vivo association between alcohol intoxication, aggression, and serotonin transporter availability in nonhuman primates

OBJECTIVE

Studies on brain serotonin metabolism in human and nonhuman primates have indicated that dysfunction of serotonin transmission may play a role in the biological vulnerability to dependence on alcohol. Among young men, low sensitivity to alcohol intoxication predicts subsequent alcohol abuse and dependence.

METHOD

The authors used single photon emission computed tomography and the radioligand [(I)123]beta-CIT ([(I)123]methyl 3beta-(4-iodophenyl) tropane-2-carboxylate) to measure the availability of serotonin transporters in 11 male rhesus monkeys, and the monkeys were genotyped for a functional polymorphism of the serotonin transporter gene. The 11 monkeys had experienced parental separation after birth; their behavior and 5-hydroxyindoleacetic acid (5-HIAA) concentrations in CSF had been assessed regularly.

RESULTS

In the 5-year-old monkeys, there was a significant negative correlation between beta-CIT binding to serotonin transporters in the brainstem and 5-HIAA concentrations in CSF. Animals with greater beta-CIT binding and low CSF 5-HIAA concentrations displayed greater aggressiveness and were less sensitive to alcohol-induced intoxication. The genetic constitution of the serotonin transporter promoter gene did not significantly contribute to the availability of brainstem serotonin transporters as measured by beta-CIT binding.

CONCLUSIONS

In adult nonhuman primates who underwent early developmental stress, variables indicating a low serotonin turnover rate were associated with behavior patterns similar to those predisposing to early-onset alcoholism among humans.

A Canadian perspective on the dental amalgam issue

This article provides a view of government reaction in Canada to public concern over the use of dental amalgam. It also addresses the basis of the irrational fears the general public may have regarding the impact of external factors on their health.

Psychomotor slowing, negative symptoms and dopamine receptor availability--an IBZM SPECT study in neuroleptic-treated and drug-free schizophrenic patients

Anhedonia and psychomotor slowing in schizophrenia have been attributed to a dysfunction of dopaminergic neurotransmission. To differentiate between disease and drug-induced negative symptoms, we examined eight drug-free and eight neuroleptic-treated schizophrenic patients. Positive and negative symptoms and extrapyramidal side effects were assessed using standardized rating scales (PSAS, AMDP, SANS). 'Reaction time' and 'motor speed' were measured using a computer-aided system and striatal dopamine D2/D3 receptor availability was assessed using [I-123]IBZM SPECT. Psychomotor reaction time, parkinsonism, affective flattening and avolition were increased in treated patients relative to the untreated cohort and were negatively correlated with dopamine D2/D3 receptor availability. Significant positive correlations were found between parkinsonism and affective flattening and between psychomotor slowing and avolition. Positive symptoms were not significantly associated with striatal IBZM binding. These findings support the hypothesis that neuroleptic-induced dopamine D2/D3 blockade in the striatum can mimic certain negative symptoms, such as affective flattening and avolition, and indicates that psychomotor testing may be helpful in differentiating between disease and drug-induced negative symptoms.

An automated chromogenic peptide substrate assay for coagulation factor XII

We have developed an automated chromogenic peptide substrate assay for factor XII (FXIIcs) on a Cobas Mira S Plus clinical chemistry analyser using a new commercially available kit. This was used to determine factor XII (FXII) levels in plasma samples from 320 blood donors, 206 patients with a history of venous thrombosis and 74 lupus anticoagulant positive (LA+) patients. Results were compared with those obtained in a clotting assay for FXII (FXIIct) and an immunochemical assay (FXIIag). A satisfactory correlation coefficient of 0.92 and a regression line equation of y = 7.898 + 0.871x was obtained between FXIIcs and FXIIct in the 320 blood donors. Levels of FXII below the calculated normal range were found in nine blood donors (2.8%) and 16 venous thrombosis patients (7.8%). The blood donors and patients with venous thrombosis with low FXIIcs values had FXII levels below our lower limits of normal for both FXIIct and FXIIag; all were lupus anticoagulant negative. When FXII levels were determined in the 74 LA+ patients, 27 (36.5%) gave markedly lower FXII values in the FXIIct when compared with the FXIIcs. FXIIag levels corresponded with FXIIcs. The automated FXIIcs assay is therefore lupus anticoagulant insensitive and allows us to measure FXII levels accurately and routinely in large numbers of patient samples.

Factor XII determinations in the presence and absence of phospholipid antibodies

Factor XII (FXII) levels were determined in plasma samples from 29 normal donors, 10 patients with inherited FXII deficiency (all lupus anticoagulant [LA] negative) and 67 LA positive patients, using clotting (FXIIct), chromogenic substrate (FXIIcs) and immunochemical (FXIIag) assays. Excellent correlations were obtained in the three FXII assays with the LA negative samples and between the FXIIcs and FXIIag assays in the LA positive samples. Correlations between both the FXIIcs and FXIIag with FXIIct in the LA positive patients were poor. Of 67 LA positive samples studied, 25 (37.3%) showed lower values in the FXIIct assay; 13 (19.4%) of these patients were pseudo FXII deficient with values of FXII below the lower limit of normal. These results indicate that a diagnosis of FXII deficiency can be made inappropriately in the presence of phospholipid antibodies and that such a diagnosis should not be made by FXIIct assay alone.

Joint position sense and rehabilitation in the anterior cruciate ligament deficient knee

BACKGROUND

Impaired joint position sense (JPS) has been shown in anterior cruciate ligament (ACL) deficient and osteoarthritic knees. The relation between JPS and function is uncertain. The aim of this study was to determine further if ACL deficient knees show abnormal JPS and the effect of exercise therapy on JPS, and also to assess the relation between JPS, functional stability, and strength.

METHODS

Fifty patients (46 men and four women, mean age 26.3 years) with unilateral ACL deficient knees were assessed on admission and after rehabilitation (5 hours a day for four weeks). JPS was assessed by reproduction of passive positioning using a visual analogue incorporating a goniometer. Knee stability was analysed by self report questionnaire (score 0-280) and functional activity test (single leg hop and figure of eight run). Isokinetic dynamometry was performed to evaluate quadriceps and hamstring peak torque strength. Controls were either age and sex matched individuals or the contralateral knee. Statistical analysis was by Wilcoxon signed rank test and Spearman rank order correlation coefficient.

RESULTS

JPS was impaired in ACL deficient knees. The mean (SD) errors in reproducing angles were 9.4 (3.1) degrees and 7.1 (2.3) degrees for the ACL deficient knee and control knee respectively (P < 0.0005). There was no improvement in JPS after rehabilitation (9.4 (3.1) degrees and 8.5 (3.2) degrees before and after rehabilitation respectively, P = 0.14). There was improvement as ascertained from the questionnaire (on admission 202 (32.1), after rehabilitation 243 (25.4), P < 0.0001) and functional activity testing (hop: on admission 148.7 (37.3) cm, after rehabilitation 169.8 (31.1) cm, P < 0.0005; figure of eight: on admission 48.4 (16.6) seconds, after rehabilitation 41.6 (3.4) seconds, P < 0.0001). Quadriceps strength improved (peak torque on admission 198.5 (58.9) Nm, after rehabilitation 210.5 (54.2) Nm, P < 0.05), but not hamstring strength (peak torque on admission 130.6 (28.1) Nm, after rehabilitation 135.5 (27.7) Nm, P = 0.24). JPS did not correlate with the functional activity tests (hop and figure of eight run), the responses to the questionnaire, or strength. There was no correlation between the responses to the questionnaire and functional activity tests or muscle strength.

CONCLUSIONS

JPS was impaired in ACL deficient knees. Although knee stability improved with exercise therapy, there was no improvement in JPS. The role of JPS in the stability of ACL deficient knees remains unclear.

Cortical abnormality in schizophrenia: an in vivo application of the gyrification index

To investigate the hypothesis that patients with schizophrenia exhibit gross cortical abnormalities of developmental origin, we utilized the gyrification index (GI) (ratio of inner to outer cortical contours), a measure of overall cortical folding, in an in vivo magnetic resonance imaging study of young, strongly right-handed male patients and controls. The two groups did not differ with respect to whole-brain volume, age, or handedness. In an examination confined to the left hemisphere, mean GI values were significantly reduced in the patient group in both anterior and posterior regions. Neither age nor length of illness were found to be significant predictors of GI variance in the patients group, suggesting that GI reductions do not result from an ongoing atrophic process. Rather, these results are consistent with the hypothesis of neurodevelopmental abnormalities in schizophrenia that result in an overall reduction in cortical folding.

Analysis of the metabolites of [I-123] beta-CIT in plasma of human and nonhuman primates

[I-123] beta-CIT is a single photon emission computed tomography (SPECT) radioligand that has been used for in vivo studies of the dopamine and serotonin transporters. Two metabolite peaks of beta-CIT have been observed by high performance liquid chromatography (HPLC), but neither has been chemically identified. One major metabolite is clearly hydrophilic. Previous reports have not agreed on the amount of the second metabolite and the extent to which it may cross the blood-brain barrier. To clarify this controversy, we have studied beta-CIT metabolites using a protein precipitation method and an organic extraction method followed by HPLC separation. Plasma from both human and nonhuman (rhesus) primates was analyzed. Concentrations of the second metabolite were substantially lower in rhesus than in human for nearly equal parent concentrations. Furthermore, in rhesus the second metabolite is partially soluble in the organic solvent ethyl acetate, whereas in human it is essentially insoluble. These observations account for the contradictions in the literature. The hydrophilic nature of the human metabolite renders it unlikely that it crosses the blood-brain barrier in sufficient quantities to interfere with the quantitative assessment of dopamine transporter densities.

Pennsylvania hospital continues to reduce seclusion and restraints

Haverford State Hospital in Haverford, Penn, was one of three hospitals profiled in case studies of organizations that have made efforts to reduce their use of seclusion and restraints in the January/February 1996 issue of Perspectives. As a result of this article, the hospital received numerous requests for assistance and information about its practices from other health care organizations. Haverford State Hospital is a 300-bed inpatient care facility for the seriously and persistently mentally ill. During 1996, it continued its efforts to reduce the use of seclusion and restraints. In this On Site column, David W.P.Jones, assistant superintendent for quality assurance and risk management at Haverford State Hospital, shares information on the hospital's progress and provides some additional data.

Genetic variability of human brain size and cortical gyral patterns

The development of the primate brain is determined by an interaction of genetic programmes and environmental events. We examined quantitatively the contribution of each of these factors to adult human brain hemisphere volume and global cortical gyral patterns by comparing 3-D MRI renderings of brains of 10 pairs of monozygotic (MZ) and nine pairs of same-sex dizygotic (DZ) twins. Brain volume was highly correlated in MZ pairs [unbiased intraclass correlation coefficient, ICC(U) = 0.95, P < 0.00001], but not in DZ pairs [ICC(U) = 0.35, P = 0.09]. Structural equation modelling indicated a 94% heritability of brain volume. Gyral patterns appeared visually more similar in MZ than in DZ pairs. This was confirmed statistically by a cross-correlation analysis of rendered images of lateral and mesial cortical surfaces. MZ twins exhibited significantly greater similarity than did DZ twins in comparisons of gyral patterns; DZ twins were not more alike than unrelated pairings. Ipsilateral hemispheres were significantly more alike than contralateral hemispheres within MZ pairs, but not within DZ pairs. Contralateral hemispheres within an individual were more alike than contralateral hemispheres between twins in the DZ pairs, but not in the MZ pairs. Heritability for gyral-sulcal patterns, as reflected in the cross-correlation data, was low and ill defined. These results indicate that human cerebral size is determined almost entirely by genetic factors and that overall cortical gyral patterns, though significantly affected by genes, are determined primarily by nongenetic factors.

Efficacy of nonpharmacologic interventions in adults with high-normal blood pressure: results from phase 1 of the Trials of Hypertension Prevention. Trials of Hypertension Prevention Collaborative Research Group

Phase 1 of the Trials of Hypertension Prevention was conducted in 2182 adults, aged 35-54 y, with diastolic blood pressure of 80-89 mm Hg to test the feasibility and blood pressure-lowering effects of seven nonpharmacologic interventions (weight loss, sodium reduction, stress management, and supplementation with calcium, magnesium, potassium, and fish oil). At 6 and 18 mo, weight loss and sodium reduction were well-tolerated and produced significant declines in systolic and diastolic blood pressures (-2.9/-2.4 and -2.1/-1.2 mm Hg for weight loss and sodium reduction, respectively, at 18 mo). None of the other interventions lowered blood pressure significantly at either the 6- or 18-mo follow-up visits. These results suggest that both weight loss and sodium reduction provide an effective means to prevent hypertension. The long-term effects of both of these interventions are being tested in phase 2 of the trial.

Variations in circadian rhythms of activity, sleep, and light exposure related to dementia in nursing-home patients

We measured 24-hour circadian-rhythm patterns of activity and sleep/wake activity in a group of nursing-home patients (58 women and 19 men with a mean age of 85.7 years). Severely demented patients were contrasted with a composite group of moderate y, mild, or not-demented patients. Sleep/wake activity and light exposure were recorded with the Actillume recorder. Cosinor analyses were computed to determine the mesor, amplitude, acrophase, and circadian quotient of the activity rhythms. The diagnosis of dementia was based on the Mini Mental Examination and on examination of medical records. Sleep was extremely fragmented in both groups of nursing-home patients. Severely demented patients slept more both at night and during the day, but there were no significant differences in the number of awakenings during the night or in the number of naps during the day when compared to the composite group of moderate, mild, or no-dementia patients. The severely demented group had lower activity mesor, more blunted amplitude, and were more phase delayed (i.e. had later acrophases) than the other group. In addition, the severely demented patients spent less time exposed to bright light. These results confirm that circadian rhythms in nursing-home patients are disturbed with more disturbance in the severely demented. Much of the disturbance may be related not just to age but to mental status.

An improved method for rapid and efficient radioiodination of iodine-123-IQNB

The SPECT radioligand, 3-quinuclidinyl-4-[123I]iodobenzilate ([123I]IQNB), binds to muscarinic receptors and has generated interest as a potential agent for clinical SPECT. Unfortunately, cumbersome and inefficient radioiodination procedures have limited the practicality of [123I]IQNB SPECT imaging.

METHODS

We report a rapid (5 min) and simple radioiodination procedure for preparing [123I]IQNB from a tri-n-butylstannyl precursor in a no-carrier-added reaction that yields high specific activity with radiochemical yield exceeding 60%. The radiochemical purity of the final product exceeds 95%.

RESULTS

We have used this procedure to radioiodinate the four stereoisomers of [123I]IQNB. The procedure is highly reliable and reproducible. SPECT studies on a healthy human volunteer at 1, 2, 6 and 24 hr after injection of each of the four stereoisomers reveal expected differences in the kinetic and binding characteristics of the four stereoisomers. (R,S)-[123I]IQNB appears to be the SPECT agent of choice.

CONCLUSION

Radioiodination of [123I]IQNB from our tri-n-butylstannyl precursor is simpler, more efficient and less expensive than previous techniques. The potential exists for a "kit" which would be practical in a typical clinical setting.

Cortical gyral anatomy and gross brain dimensions in monozygotic twins discordant for schizophrenia

BACKGROUND

This study combines recent advances in three-dimensional neuroimaging technology and the genetic constraints inherent in monozygotic (MZ) twins to examine surface gyral anatomy and gross brain dimensions in monozygotic twin pairs discordant for schizophrenia. Results are presented and evaluated with respect to prior observations of cortical anomalies in schizophrenia and the hypothesis that schizophrenia involves cortical maldevelopment.

DESIGN

Three-dimensional renderings from volumetric magnetic resonance imaging (MRI) data of 13 MZ twin pairs discordant for schizophrenia and nine normal MZ pairs were studied. Qualitative assessments of left and right hemisphere surfaces were made by raters blind to diagnosis in an effect to identify developmental gyral abnormalities such as vertical temporal gyri or microgyria. Measurement of brain hemisphere length, area, and volume were also determined. These data were compared within discordant MZ schizophrenia pairs, within normal MZ pairs, and between matched unaffected discordant and normal MZ groups.

RESULTS

Raters did not identify qualitatively abnormal gyri in the schizophrenia subjects to enable distinction from their unaffected co-twins or from normal controls. Brain hemisphere volumes in the affected DS were significantly smaller bilaterally by about 3% compared with their unaffected DS co-twins, who did not differ from normals on this measure.

CONCLUSIONS

We were unable to confirm previous reports of vertical gyri or localized gyral thinning as being characteristic of the cortical anatomy of schizophrenia. If cortical maldevelopment is associated with schizophrenia it does not appear to disrupt gross gyral pattern formation in these ways. The quantitative results of diminished hemisphere volume and length in the twins with schizophrenia are consistent with previous reports of smaller brain size in schizophrenia. Our results suggest that this is a bilateral phenomenon that may be dependent, at least in part, on environmental factors.

Crystallization of experimental bioactive glass compositions

Crystallization kinetics studies for six experimental glass formulations in the system Na2O-CaO-SiO2-P2O5 synthesized by wet chemistry were conducted by means of differential thermal analysis. These glasses had CaO/P2O5 and SiO2/ (CaO + Na2O) ratios ranging from 8.74-3.38 and 0.92-3.03, respectively. Samples of each glass (n = 30 were heated from 23 to 1250 degrees C under N2 atmosphere at heating rates ranging from 10 to 50 degrees C/min. Glass-ceramics were obtained after heat treating the initial glasses at temperatures determined from their DTA exotherms. The activation energy of crystallization for each glass composition was calculated from an expression-relating log-heating rate and the reciprocal of the exothermic peak temperature. The compositions of the six glasses were significantly different (p = 0.05). The activation energy of crystallization (Q) values ranged from 196 to 782 kJ/mole. A correlation was obtained between Q and CaO/P2O5 and between Q and the Young's modulus (P < 0.001). Two of the six glasses exhibited bulk crystallization. X-ray diffraction studies showed that four of the six glasses exhibited different proportions of crystalline phases following heat treatment. These phases were wollastonite (CaSiO3), Na2CaSi3O9, combeite [Na4Ca3SI6O16(OH)2], and some unidentifiable phases. Two of the six bioceramic materials had a mixture of unknown crystalline phases.

Hypertension awareness, treatment and control rates for an Asian population: results from a national survey in Korea

OBJECTIVE

This observational study was performed in order to determine the hypertension awareness, treatment, and control rates for the country of Korea.

METHODS

Rates were determined in conjunction with a national blood pressure survey in Korea in 1990. Through cluster sampling, individuals aged > 30 in 190/146,944 districts were selected for study. Among 25,567 eligible individuals, 21,242 had measurement of blood pressure (BP) and answered a standard questionnaire. BP was recorded as the mean of two measurements with a standard mercury manometer. Hypertension was defined either as BP > or = 160/95 mm Hg or on treatment (n = 2628), or as BP > or = 140/90 mm Hg or on treatment (n = 4219). Treatment was defined as any method of BP treatment, including dietary, traditional, or medication.

RESULTS

Rates for BP > or = 160/95 mm Hg or on treatment: aware 1057 (40%), treated 696 (27%), controlled 367 (14%). Rates for BP > or = 140/90 mm Hg or on treatment: aware 1069 (25%), treated 696 (16%), controlled 221 (5%).

CONCLUSIONS

Hypertension awareness, treatment, and control rates are relatively low in Korea. Blood-pressure control programs, including detection strategies, are needed here and worldwide.

Tourette syndrome: prediction of phenotypic variation in monozygotic twins by caudate nucleus D2 receptor binding

Tourette syndrome, a chronic tic disorder with autosomal dominant inheritance, exhibits considerable phenotypic variability even within monozygotic twin pairs. The origins of this variability remain unclear. Recent findings have implicated the caudate nucleus as a locus of pathology, and pharmacological evidence supports dopaminergic involvement. Within monozygotic twins discordant for Tourette syndrome severity, differences in D2 dopamine receptor binding in the head of the caudate nucleus predicted differences in phenotypic severity (r = 0.99); this relation was not observed in putamen. These data may link Tourette syndrome with a spectrum of neuropsychiatric disorders that involve associative striatal circuitry.