Family based association analysis of statistically derived quantitative traits for drug use in ADHD and the dopamine transporter gene

In Memoriam: Professor Joseph Biederman's Contributions to Child and Adolescent Psychiatry

OBJECTIVE

To provide an overview of Joe Biederman's contributions to child and adolescent psychiatry.

METHOD

Nine colleagues described his contributions to: psychopharmacology, comorbidity and genetics, pediatric bipolar disorder, autism spectrum disorders, Tourette's and tic disorders, clinical and neuro biomarkers for pediatric mood disorders, executive functioning, and adult ADHD.

RESULTS

Joe Biederman left us with many concrete indicators of his contributions to child and adolescent psychiatry. He set up the world's first pediatric psychopharmacology clinic and clinical research program in child adolescent psychiatry. As a young faculty member he began a research program that led to many awards and eventual promotion to full professor at Harvard Medical School. He was for many years the most highly cited researcher in ADHD. He achieved this while maintaining a full clinical load and was widely respected for his clinical acumen.

CONCLUSION

The world is a better place because Joe Biederman was here.

Fungal exposure modulates the effect of polymorphisms of chitinases on emergency department visits and hospitalizations

RATIONALE

Chitinases are enzymes that cleave chitin, which is present in fungal cells. Two types of human chitinases, chitotriosidase and acidic mammalian chitinase, and the chitinase-like protein, YKL-40, seem to play an important role in asthma. We hypothesized that exposure to environmental fungi may modulate the effect of chitinases in individuals with asthma.

OBJECTIVES

To explore whether interactions between high fungal exposure and common genetic variants in the two chitinases in humans, CHIT1 and CHIA, and the chitinase 3-like 1 gene, CHI3L1, are associated with severe asthma exacerbations and other asthma-related outcomes.

METHODS

Forty-eight single nucleotide polymorphisms (SNPs) in CHIT1, CHIA, and CHI3L1 and one CHIT1 duplication were genotyped in 395 subjects and their parents as part of the Childhood Asthma Management Program. Household levels of mold (an index of fungal exposure) were determined on house dust samples. We conducted family-based association tests with gene-environment interactions. Our outcome was severe exacerbation, defined as emergency department visits and hospitalizations from asthma over a 4-year period, and our secondary outcomes included indices of lung function and allergy-related phenotypes.

MEASUREMENTS AND MAIN RESULTS

Of the 395 subjects who had mold levels at randomization, 24% (95 subjects) had levels that were greater than 25,000 units per gram of house dust (high mold exposure). High mold exposure significantly modified the relation between three SNPs in CHIT1 (rs2486953, rs4950936, and rs1417149) and severe exacerbations (P for interaction 0.0010 for rs2486953, 0.0008 for rs4950936, and 0.0005 for rs1417149). High mold exposure did not significantly modify the relationship between any of the other variants and outcomes.

CONCLUSIONS

Environmental exposure to fungi, modifies the effect of CHIT1 SNPs on severe asthma exacerbations.

Polymorphisms of chitinases are not associated with asthma

Despite the potential role of chitinases and chitinase-like proteins in the pathogenesis of asthma, variants in their respective genes are not associated with asthma, changes in lung physiology or allergy-related phenotypes in Caucasian children.

Polymorphisms in dopamine transporter (SLC6A3) are associated with stimulant effects of D-amphetamine: an exploratory pharmacogenetic study using healthy volunteers

Individuals vary in their subjective responses to stimulant drugs, and these differences are believed to be partially genetic in origin. We evaluated associations between mood, cognitive and cardiovascular responses to d-amphetamine and four polymorphisms in the dopamine transporter (SLC6A3): rs460000, rs3756450, rs37022 and rs6869645. Healthy Caucasian male and female volunteers (N = 152) participated in a double-blind, crossover design study in which they received placebo, 10 and 20 mg of d-amphetamine. We measured self-reported rating of mood, performance on the Digit Symbol Substitution Task, blood pressure and heart rate. Individuals with the C/C genotype at rs460000 (N = 83) reported approximately twofold higher ratings of stimulation and euphoria relative to the A/A+A/C (N = 69) genotype group, at both the 10 and 20 mg doses. No other responses or SNPs showed significant effects. rs460000 is in perfect LD with rs463379 (CEU: D' = 1; r (2) = 1), which was not studied here, but has been associated with etiology of Attention Deficit Hyperactivity Disorder (ADHD). These findings suggest a pleiotropic effect of this polymorphic locus on both ADHD and sensitivity to the subjective effects of amphetamine.

Correlates of co-occurring ADHD in drug-dependent subjects: prevalence and features of substance dependence and psychiatric disorders

We examined the prevalence and course of psychiatric and substance dependence (SD) disorders in subjects with SD and attention deficit hyperactivity disorder (ADHD).

METHOD

We interviewed 1761 adults with a lifetime diagnosis of cocaine and/or opioid dependence using the Semi-Structured Assessment for Drug Dependence and Alcoholism. Generalized linear regression with generalized estimating equation analysis was used to examine the associations between a lifetime diagnosis of ADHD and indicators of clinical course, and to identify unique correlates of ADHD.

RESULTS

Lifetime ADHD prevalence in the SD sample was 5.22% (vs. 0.85% in a group of individuals without SD). ADHD was associated with an earlier age of first substance use, more SD and psychiatric diagnoses, a greater likelihood of attempted suicide, and more hospitalizations. After controlling for conduct disorder, there were unique effects of ADHD on age of first substance use and number of SD diagnoses.

CONCLUSION

In subjects with cocaine or opioid dependence, ADHD is associated with greater SD and psychiatric comorbidity and a more severe course of illness.

Vestibular Stimulation for ADHD: randomized controlled trial of Comprehensive Motion Apparatus

OBJECTIVE

This research evaluates effects of vestibular stimulation by Comprehensive Motion Apparatus (CMA) in ADHD.

METHOD

Children ages 6 to 12 (48 boys, 5 girls) with ADHD were randomized to thrice-weekly 30-min treatments for 12 weeks with CMA, stimulating otoliths and semicircular canals, or a single-blind control of equal duration and intensity, each treatment followed by a 20-min typing tutorial.

RESULTS

In intent-to-treat analysis (n = 50), primary outcome improved significantly in both groups (p = .0001, d = 1.09 to 1.30), but treatment difference not significant (p = .7). Control children regressed by follow-up (difference p = .034, d = 0.65), but overall difference was not significant (p = .13, d = .47). No measure showed significant treatment differences at treatment end, but one did at follow-up. Children with IQ-achievement discrepancy > or = 1 SD showed significantly more CMA advantage on three measures.

CONCLUSION

This study illustrates the importance of a credible control condition of equal duration and intensity in trials of novel treatments. CMA treatment cannot be recommended for combined-type ADHD without learning disorder.

Association and linkage of allelic variants of the dopamine transporter gene in ADHD

Previously, we had reported a genome-wide scan for attention-deficit/hyperactivity disorder (ADHD) in 102 families with affected sibs of German ancestry; the highest multipoint LOD score of 4.75 was obtained on chromosome 5p13 (parametric HLOD analysis under a dominant model) near the dopamine transporter gene (DAT1). We genotyped 30 single nucleotide polymorphisms (SNPs) in this candidate gene and its 5' region in 329 families (including the 102 initial families) with 523 affected offspring. We found that (1) SNP rs463379 was significantly associated with ADHD upon correction for multiple testing (P=0.0046); (2) the global P-value for association of haplotypes was significant for block two upon correction for all (n=3) tested blocks (P=0.0048); (3) within block two we detected a nominal P=0.000034 for one specific marker combination. This CGC haplotype showed relative risks of 1.95 and 2.43 for heterozygous and homozygous carriers, respectively; and (4) finally, our linkage data and the genotype-IBD sharing test (GIST) suggest that genetic variation at the DAT1 locus explains our linkage peak and that rs463379 (P<0.05) is the only SNP of the above haplotype that contributed to the linkage signal. In sum, we have accumulated evidence that genetic variation at the DAT1 locus underlies our ADHD linkage peak on chromosome 5; additionally solid association for a single SNP and a haplotype were shown. Future studies are required to assess if variation at this locus also explains other positive linkage results obtained for chromosome 5p.