Pooling/bootstrap-based GWAS (pbGWAS) identifies new loci modifying the age of onset in PSEN1 p.Glu280Ala Alzheimer's disease.

The literature on GWAS (genome-wide association studies) data suggests that very large sample sizes (for example, 50,000 cases and 50,000 controls) may be required to detect significant associations of genomic regions for complex disorders such as Alzheimer's disease (AD). Because of the challenges of obtaining such large cohorts, we describe here a novel sequential strategy that combines pooling of DNA and bootstrapping (pbGWAS) in order to significantly increase the statistical power and exponentially reduce expenses. We applied this method to a very homogeneous sample of patients belonging to a unique and clinically well-characterized multigenerational pedigree with one of the most severe forms of early onset AD, carrying the PSEN1 p.Glu280Ala mutation (often referred to as E280A mutation), which originated as a consequence of a founder effect. In this cohort, we identified novel loci genome-wide significantly associated as modifiers of the age of onset of AD (CD44, rs187116, P=1.29 × 10⁻¹²; NPHP1, rs10173717, P=1.74 × 10⁻¹²; CADPS2, rs3757536, P=1.54 × 10⁻¹°; GREM2, rs12129547, P=1.69 × 10⁻¹³, among others) as well as other loci known to be associated with AD. Regions identified by pbGWAS were confirmed by subsequent individual genotyping. The pbGWAS methodology and the genes it targeted could provide important insights in determining the genetic causes of AD and other complex conditions.

Motivation deficit in ADHD is associated with dysfunction of the dopamine reward pathway.

Attention-deficit hyperactivity disorder (ADHD) is typically characterized as a disorder of inattention and hyperactivity/impulsivity but there is increasing evidence of deficits in motivation. Using positron emission tomography (PET), we showed decreased function in the brain dopamine reward pathway in adults with ADHD, which, we hypothesized, could underlie the motivation deficits in this disorder. To evaluate this hypothesis, we performed secondary analyses to assess the correlation between the PET measures of dopamine D2/D3 receptor and dopamine transporter availability (obtained with [(11)C]raclopride and [(11)C]cocaine, respectively) in the dopamine reward pathway (midbrain and nucleus accumbens) and a surrogate measure of trait motivation (assessed using the Achievement scale on the Multidimensional Personality Questionnaire or MPQ) in 45 ADHD participants and 41 controls. The Achievement scale was lower in ADHD participants than in controls (11±5 vs 14±3, P<0.001) and was significantly correlated with D2/D3 receptors (accumbens: r=0.39, P<0.008; midbrain: r=0.41, P<0.005) and transporters (accumbens: r=0.35, P<0.02) in ADHD participants, but not in controls. ADHD participants also had lower values in the Constraint factor and higher values in the Negative Emotionality factor of the MPQ but did not differ in the Positive Emotionality factor-and none of these were correlated with the dopamine measures. In ADHD participants, scores in the Achievement scale were also negatively correlated with symptoms of inattention (CAARS A, E and SWAN I). These findings provide evidence that disruption of the dopamine reward pathway is associated with motivation deficits in ADHD adults, which may contribute to attention deficits and supports the use of therapeutic interventions to enhance motivation in ADHD.

Stimulant-related state-dependent learning in hyperactive children.

Hyperactive and nonhyperactive children performed a learning task in two states, while being treated with stimulant medication (methylphenidate) and while taking a placebo, and were tested for retention of each class of learned material in both states. Symmetrical state-dependent learning was demonstrated in the hyperactive group but not in the nonhyperactive group. The state-dependent effect was contingent on the presence of drug-induced facilitation during initial learning. This is apparently the first report on record of state-dependent learning with a drug agent that facilitates rather than impairs performance of human subjects.

Food dyes impair performance of hyperactive children on a laboratory learning test.

Forty children were given a diet free of artificial food dyes and other additives for 5 days. Twenty of the children had been classified as hyperactive by scores on the Conners Rating Scale and were reported to have favorable responses to stimulant medication. A diagnosis of hyperactivity had been rejected in the other 20 children. Oral challenges with large doses (100 or 150 milligrams) of a blend of FD & C approved food dyes or placebo were administered on days 4 and 5 of the experiment. The performance of the hyperactive children on paired-associate learning tests on the day they received the dye blend was impaired relative to their performance after they received the placebo, but the performance of the nonhyperactive group was not affected by the challenge with the food dye blend.

Erythrosin B inhibition of neurotransmitter accumulation by rat brain homogenate.

A mixture of seven food dyes inhibited the accumulation of eight neurotransmitters or neurotransmitter precursors by rat brain homogenate. At a low concentration (1 microgram per milliliter), erythrosin B (FD&C red 3) was the only dye that inhibited dopamine accumulation. Erythrosin also was effective in decreasing the accumulation of all the other transmitter substances, suggesting that the inhibition is nonspecific and probably secondary to general membrane alteration.

A risk calculator to predict adult attention-deficit/hyperactivity disorder: generation and external validation in three birth cohorts and one clinical sample.

AIM: Few personalised medicine investigations have been conducted for mental health. We aimed to generate and validate a risk tool that predicts adult attention-deficit/hyperactivity disorder (ADHD). METHODS: Using logistic regression models, we generated a risk tool in a representative population cohort (ALSPAC - UK, 5113 participants, followed from birth to age 17) using childhood clinical and sociodemographic data with internal validation. Predictors included sex, socioeconomic status, single-parent family, ADHD symptoms, comorbid disruptive disorders, childhood maltreatment, ADHD symptoms, depressive symptoms, mother's depression and intelligence quotient. The outcome was defined as a categorical diagnosis of ADHD in young adulthood without requiring age at onset criteria. We also tested Machine Learning approaches for developing the risk models: Random Forest, Stochastic Gradient Boosting and Artificial Neural Network. The risk tool was externally validated in the E-Risk cohort (UK, 2040 participants, birth to age 18), the 1993 Pelotas Birth Cohort (Brazil, 3911 participants, birth to age 18) and the MTA clinical sample (USA, 476 children with ADHD and 241 controls followed for 16 years from a minimum of 8 and a maximum of 26 years old). RESULTS: The overall prevalence of adult ADHD ranged from 8.1 to 12% in the population-based samples, and was 28.6% in the clinical sample. The internal performance of the model in the generating sample was good, with an area under the curve (AUC) for predicting adult ADHD of 0.82 (95% confidence interval (CI) 0.79-0.83). Calibration plots showed good agreement between predicted and observed event frequencies from 0 to 60% probability. In the UK birth cohort test sample, the AUC was 0.75 (95% CI 0.71-0.78). In the Brazilian birth cohort test sample, the AUC was significantly lower -0.57 (95% CI 0.54-0.60). In the clinical trial test sample, the AUC was 0.76 (95% CI 0.73-0.80). The risk model did not predict adult anxiety or major depressive disorder. Machine Learning approaches did not outperform logistic regression models. An open-source and free risk calculator was generated for clinical use and is available online at https://ufrgs.br/prodah/adhd-calculator/. CONCLUSIONS: The risk tool based on childhood characteristics specifically predicts adult ADHD in European and North-American population-based and clinical samples with comparable discrimination to commonly used clinical tools in internal medicine and higher than most previous attempts for mental and neurological disorders. However, its use in middle-income settings requires caution.

Highly conserved charge-pair networks in the mitochondrial carrier family.

Selection for regain-of-function mutations in the yeast ADP/ATP carrier AAC2 has revealed an unexpected series of charge-pairs. Four of the six amino acids involved are found in the mitochondrial energy transfer motifs used to define this family of proteins. As such, the results found with the ADP/ATP carrier may apply to the family as a whole. Mitochondrial carriers are built from three homologous domains, each with the conserved motif PX(D,E)XX(K,R). Neutralization of the conserved positive charges at K48, R152 or R252 in these motifs results in respiration defective yeast. Neutralization of the negative charges at D149 and D249 also make respiration defective yeast, though E45G or E45Q mutants are able to grow on glycerol. Regain of function occurs when a complementary charge is lost from another site in the molecule. This phenomenon has been observed independently eight times and thus is strong evidence for charge-pairs existing between the affected residues. Five different charge-pairs have been detected in the yeast AAC2 by this method and three more can be predicted based on homology between the domains. The highly conserved charge-pairs occurring within or between the three mitochondrial energy transfer signatures seem to be a critical feature of mitochondrial carrier structure, independent of the substrates transported. Conformational switching between alternative charge-pairs may constitute part of the basis for transport.

National Institute of Mental Health Collaborative Multimodal Treatment Study of Children with ADHD (the MTA). Design challenges and choices.

The Collaborative Multimodal Treatment Study of Children with Attention Deficit Hyperactivity Disorder (ADHD), the MTA, is the first child multisite cooperative agreement treatment study of children conducted by the National Institute of Mental Health, Rockville, Md. It examines the long-term effectiveness of medication vs behavioral treatment vs both for treatment of ADHD and compares state-of-the-art treatment with routine community care. In a parallel-groups design, 576 children (age, 7-9 years) with ADHD (96 at each site) are thoroughly assessed and randomized to 4 conditions: (1) medication alone, (2) psychosocial treatment alone, (3) the combination of both, (4) or community comparison. The first 3 groups are treated for 14 months and all are reassessed periodically for 24 months. Designers met the following challenges: framing clinically relevant primary questions; defining the target population; choice, intensity, and integration and combination of treatments for fair comparisons; combining scientific controls and standardization with clinical flexibility; and implementing a controlled clinical trial in a nonclinical setting (school) controlled by others. Innovative solutions included extensive decision algorithms and manualized adaptations of treatments to specific needs.

Serum and brain concentrations of methylphenidate: implications for use and abuse.

When used to treat children with Attention Deficit Hyperactivity Disorder, methylphenidate (MPH) acts primarily by blocking the dopamine (DA) transporter (DAT) and increasing extracellular DA in the striatum. This is strikingly similar to the mechanism of action of cocaine, a primary stimulant drug of abuse. When administered intravenously, MPH like cocaine has reinforcing effects (euphoria) at doses that exceed a DAT blockade threshold of 60%. When administered orally at clinical doses, the pharmacological effects of MPH also exceed this threshold, but reinforcing effects rarely occur. Here we discuss the pharmacokinetic properties of MPH in serum (and in brain) that differ for oral and intravenous routes of administration and the importance of acute tolerance in determining pharmacodynamic effects in clinical use and illegal abuse. We suggest that intravenous administration of MPH mimics the rapid phasic cell firing of DA neurons, which may be a critical factor associated with reinforcing effects and abuse, while oral administration of MPH mimics the tonic DA cell firing, which may be a critical factor associated with clinical effects.

Dopamine genes and ADHD.

Family, twin, and adoption studies have documented a strong genetic basis for ADHD/HKD, but these studies do not identify specific genes linked to the disorder. Molecular genetic studies can identify allelic variations of specific genes that are functionally associated with ADHD/HKD, and dopamine genes have been the initial candidates based on the site of action of the stimulants drugs, which for a half century have provided the primary pharmacological treatment for ADHD/HKD. Two candidate dopamine genes have been investigated and reported to be associated with ADHD/HKD: the dopamine transporter (DAT1) gene [Cook et al., American Journal of Human Genetics 1995;56:993-998, Gill et al., Molecular Psychiatry 1997;2:311-313] and the dopamine receptor D4 (DRD4) gene [LaHoste et al., Molecular Psychiatry 1996;1:121-124: Smalley et al., 1998;3:427-430; Swanson et al., Molecular Psychiatry 1998;3:38-41]. Speculative hypotheses [Swanson and Castellanos, NIH Consensus Development Conference: Diagnosis and Treatment of Attention Deficit Hyperactivity Disorder, November 1998. p. 37-42] have suggested that specific alleles of these dopamine genes may alter dopamine transmission in the neural networks implicated in ADHD/HKD (e.g. that the 10-repeat allele of the DAT1 gene may be associated with hyperactive re-uptake of dopamine or that the 7-repeat allele of the DRD4 gene may be associated with a subsensitive postsynaptic receptor). These and other variants of the dopamine hypothesis of ADHD will be discussed.

Covert visual spatial attention in boys with attention deficit hyperactivity disorder: lateral effects, methylphenidate response and results for parents.

We report three related studies of covert visual spatial orienting in child attention deficit hyperactivity disorder (ADHD). In Study 1, we examined covert visual spatial orienting in ADHD and comparison boys, Study 2 comprised a dose-response study of methylphenidate for the ADHD group, and Study 3 was an investigation of biological and adoptive parents. In contrast with comparison subjects (n = 17). ADHD boys aged 6-12 (n = 27) showed both slower reaction times overall and within-condition (lateral) asymmetries in reaction times. Specifically, boys with ADHD reacted more slowly to uncued targets in the left visual field than in the right visual field. Responses to stimuli in the two visual fields were differentially affected by methylphenidate for the ADHD group. Medication equalized visual field responses to the uncued targets, resulting in a significant cue x dose x visual field interaction. Further, medication altered the relative cue responsivity in the two visual fields, resulting in a significant dose x visual field interaction for the Validity Effect. Biological parents of ADHD boys (n = 16) also showed slower reaction times to uncued left visual field targets than to right visual field targets; in addition they showed slower response to invalidity cued targets in the right visual field. These literal effects were not observed in adoptive parents of ADHD boys (n = 12) or biological parents of comparison boys (n = 14). Possible abnormal hemispheric asymmetry of attention functions in boys with ADHD and their biological parents is discussed.

Lateralized attentional deficits in drug-free and medicated schizophrenic patients.

Performance on a cued reaction time (RT) task, theoretically linked to posterior and anterior neuroanatomical systems in the brain (Posner, M. I. et al., Science, 1988, 210, 1627-1631; Archives of General Psychiatry, 1988, 15, 811-821), was used to assess sensory orienting and maintenance of attention. In schizophrenic patients, Posner et al. found a lateralized abnormality in RT (longer RTs to uncued targets in the right visual field than in the left visual field), as did Maruff et al. (Neuropsychologia, 1995, 33, 1205-1223), but Strauss et al. (Journal of Psychiatric Research, 1991, 37, 139-146), among others, did not replicate this effect. However, the subjects in these studies differed in the percentage of schizophrenic patients taking neuroleptic medication at the time of testing and in the chronicity of the illness. In the present study, we used two groups of schizophrenic subjects to control for the use of neuroleptic medication. The lateralized abnormality in RT was observed in the drug-free group of schizophrenic subjects, but not in the group of drug-treated schizophrenic subjects.

Lateralized deficits in visual attention in males with developmental dopamine depletion.

Children with early treated phenylketonuria (ETPKU), a disorder associated with developmental dopamine depletion, were tested with a visual orienting paradigm to determine the existence of lateralized deficits in specific attentional operations. Male ETPKU subjects showed a right visual field impairment in disengaging attention, indicating left hemisphere dysfunction, and overall slowed reaction times. Female ETPKU and normal subjects did not differ. The results suggest that for males, dopamine depletion disrupts left hemisphere function. This finding has important implications for disorders with suspected developmental dopamine abnormalities, and may also illustrate how sex differences in functional lateralization develop in the normal brain.

Methylphenidate hydrochloride given with or before breakfast: I. Behavioral, cognitive, and electrophysiologic effects.

Methylphenidate HCl (Ritalin) is usually given for the treatment of hyperactivity or attention deficit disorder (ADD) at 30 minutes to one hour before meals. This schedule is based on the assumption that, when taken with meals, its absorption or metabolism is altered. However, no behavioral or pharmacologic data exist to support this recommendation. Eleven patients with attention deficit disorder were tested to evaluate this hypothesis using a double-blind crossover design (methylphenidate with or before breakfast) with a placebo control condition. Parents' ratings, performance on a paired-associate learning test, and cortical auditory-evoked potentials were measured. All of these measurements showed clear differences between the placebo condition and conditions when medication was given. However, none of the measurements showed a significant difference between the conditions when methylphenidate was given with breakfast and the condition when methylphenidate was given 30 minutes before breakfast.

Methylphenidate hydrochloride given with or before breakfast: II. Effects on plasma concentration of methylphenidate and ritalinic acid.

Methylphenidate HCl (Ritalin) is often prescribed for the treatment of hyperactivity and is usually administered orally 30 minutes to 1 hour before meals, based on an assumption that meals may interfere with the absorption or metabolism of the drug. Seven boys who were taking methylphenidate regularly for the treatment of hyperactivity were hospitalized and given their established dose of the drug intravenously or orally, either with breakfast or in a fasted state. Blood samples were taken to determine the pharmacokinetics of the drug in each condition. Few differences between the "fed" and "fasted" states were noted, but the statistically significant differences indicated that meals accelerate rather than impede the absorption of methylphenidate.

Pemoline pharmacokinetics and long term therapy in children with attention deficit disorder and hyperactivity.

The pharmacokinetic behaviour of pemoline was studied in 28 children, aged 5 to 12 years, diagnosed as having the attention deficit disorder with hyperactivity. The mean elimination half-life of pemoline in these children was approximately 7 hours, which is considerably shorter than the half-life of 11 to 13 hours previously reported in adults. The tendency of the half-life to increase with age may be explained by the statistically significant decrease in total body clearance with age. The increasing half-life of pemoline with age should be considered during long term drug therapy. In this study no tolerance to the beneficial effects of pemoline was observed over 6 months. The apparent therapeutic serum concentration range for these children was attained after doses of 37.5 to 131.25 mg pemoline daily. Since the optimum serum concentration shows wide variation, the dosing regimen must be determined individually. Routine monitoring of the pemoline serum concentrations is not useful because of this apparent variation in optimum serum concentration and because of the linear relationship between dose and concentration.

Visual perception dominance of fallers among community-dwelling older adults.

The authors postulated that older adult fallers show a greater tendency than older adult nonfallers to rely more on visual information sources in maintaining upright posture than on kinesthetic and vestibular cues. This paper presents descriptive statistics on 199 older adults living independently in the community. Their visual perception of the vertical and horizontal was analyzed with respect to age, sex, health status, and severity of injury as a result of a fall. The finding of significant impairments for fallers in visual perceptual abilities confirmed a trend previously established by one of the authors (Tobis). When the visual field entailed only misleading or ambiguous cues in the form of a tilted frame, fallers again showed a larger error than nonfallers in establishing the vertical and horizontal. The authors feel that this relatively greater dependence on visual sources may develop in response to impairment of feedback on posture and gait from the kinesthetic and vestibular systems as a result of age and chronic health problems. Errors in visual perception of the vertical and horizontal intercorrelated with age, sex, and a large number of medical problems. However, visual variables were more important in predicting faller status than physical characteristics.

Pharmacokinetic and pharmacodynamic properties of stimulants: implications for the design of new treatments for ADHD.

In the USA, the stimulant drug methylphenidate (MPH) is used to treat a large number (2 million or more per year) of children with Attention Deficit Hyperactivity Disorder (ADHD). Although the US FDA approved MPH in the 1960s, the pharmacokinetic (PK) properties of serum concentrations of MPH in children with ADHD were not described until the 1980s, and then in only a few cases. Recently, information from drug development programs have increased our knowledge about the serum PK and some pharmacodynamic (PD) characteristics of MPH in ADHD children, and studies based on positron emission tomograpy (PET) in adult volunteers have provided new knowledge about the PK properties of MPH at the primary site of action in the brain. We will review these two topics and use this new information to evaluate the mechanisms of action of MPH.

Genetic latent structure analysis of dysmorphology in attention deficit disorder.

Dysmorphology--in the form of minor physical anomalies--has been frequently reported in children with attention deficit disorder (ADD). The authors report an overrepresentation of minor physical anomalies in both ADD probands and their first-degree relatives. Further, ADD probands who are not dysmorphic have non-ADD relatives who are dysmorphic; this familial pattern suggests that a single underlying factor may influence transmission of both traits. A genetic latent structure model was fit to these data to describe the factor's mode of transmission. In this analysis, an autosomal dominant model emerged. Successfully fitting this model is not equivalent to testing the validity of the model itself. Meaningful tests of the model will require larger samples than available at present, and would benefit from diagnostic refinement of the ADD and dysmorphic phenotypes.