Genetic studies in alcohol research

Comparison of the role of dopamine, serotonin, and noradrenaline genes in ADHD, ODD and conduct disorder: multivariate regression analysis of 20 genes

The present study is based on the proposal that complex disorders resulting from the effects of multiple genes are best investigated by simultaneously examining multiple candidate genes in the same group of subjects. We have examined the effect of 20 genes for dopamine, serotonin, and noradrenergic metabolism on a quantitative score for attention deficit hyperactivity disorder (ADHD) in 336 unrelated Caucasian subjects. The genotypes of each gene were assigned a score from 0 to 2, based on results from the literature or studies in an independent set of subjects (literature-based scoring), or results based on analysis of variance for the sample (optimized gene scoring). Multivariate linear regression analysis with backward elimination was used to determine which genes contributed most to the phenotype for both coding methods. For optimized gene scoring, three dopamine genes contributed to 2.3% of the variance, p = 0.052; three serotonin genes contributed to 3%, p = 0.015; and six adrenergic genes contributed to 6.9%, p = 0.0006. For all genes combined, 12 genes contributed to 11.6% of the variance, p = 0.0001. These results indicate that the adrenergic genes play a greater role in ADHD than either the dopaminergic or serotonergic genes combined. The results using literature-based gene scoring were similar. An examination of two additional comorbid phenotypes, conduct disorder and oppositional defiant disorder (ODD), indicated they shared genes with ADHD. For ODD different genotypes of the same genes were often used. These results support the value of the simultaneous examination of multiple candidate genes.

Molecular cloning and characterization of the human CLOCK gene: expression in the suprachiasmatic nuclei

The Clock gene is an essential regulator of circadian rhythms. It encodes a member of the basic helix-loop-helix/PER-ARNT-SIM family of transcription factors known to play a central role in the control of diverse cellular events. Previously we described the functional identification and molecular isolation of the Clock gene in the mouse, its interaction with the BMAL1 protein, and the role of this complex as a transcriptional activator in the circadian pacemaker. Here, we report the cloning, exon organization, chromosomal location, and mRNA expression of the human CLOCK gene. The coding sequence of human CLOCK extends for 2538 bp and is 89% identical to its mouse ortholog; its deduced amino acid sequence is 846 residues long and is 96% identical to mouse CLOCK. Radiation hybrid mapping localized human CLOCK to the long arm of human chromosome 4 (4q12). Direct sequencing of a genomic CLOCK clone indicated that the coding sequence of human CLOCK extends over 20 exons and that its intron/exon organization is identical to that of the mouse ortholog. Northern blot analysis indicated widespread expression of two major transcripts of 8 and 10 kb, and in situ hybridization of human brain tissue revealed elevated expression of CLOCK mRNA in the suprachiasmatic nuclei, the locus of circadian control in mammals, and in the cerebellum. Comparison of cDNA clones revealed two single nucleotide polymorphisms in noncoding sequence flanking the CLOCK open reading frame. The central role of Clock in the organization of circadian rhythms suggests that it will be a useful candidate gene for genetic analyses of disorders associated with dysfunction of the circadian system.

The impact of genomics on mammalian neurobiology

The benefit of genomics lies in the speeding up of research efforts in other fields of biology, including neurobiology. Through accelerated progress in positional cloning and genetic mapping, genomics has forced us to confront at a much faster pace the difficult problem of defining gene function. Elucidation of the function of identified disease genes and other genes expressed in the Central nervous system has to await conceptual developments in other fields.

Genes, free will, and criminal responsibility

Advances in human genetics have raised the possibility that genetic mechanisms can explain various aspects of human behavior. It has been suggested that such genetic explanations would tend to diminish responsibility for one's actions. In this paper I argue that the genetic approach adds little to our understanding of free will, determinism, and responsibility. Even though human beings are material systems obeying the laws of the physical and biological sciences, their behavior may still be unpredictable and essentially undetermined. Moreover, with few exceptions, behavior influenced by genes is no more deterministic than is behavior influenced by the environment. An analysis of the genetic and environmental influences and the complex interactions between them reveals a certain symmetry between genetic and environmental explanations of behavior. Consequently, any argument concerning the relevance of a genetic excuse to a criminal defense will be equally applicable to an environmental excuse.

Genetic regulation of gene-specific mRNA by ethanol in vivo and its possible role in ethanol preference in a cross with RI lines in mice

Relative ethanol preference is a well-recognized phenotype in a number of species, including mice, but the molecular basis for this phenotype remains speculative. We generated novel recombinant inbred (RI) mouse lines from C57BL/6J (ethanol preferring) and BALB/c (ethanol avoiding) strains and evaluated the effect of ethanol feeding on the mRNA levels of three genes (Adh-1, Ahd-2, and Cas-1) of alcohol metabolism. Ethanol feeding affects the mRNA levels of all three genes in both a gene- and a genotype-specific manner. The effect of ethanol feeding on Ahd-2 mRNA, in particular, is highly correlated with the relative ethanol acceptance of the genotypes. DNA sequencing of approximately 500 bp of the 5' upstream region of the Ahd-2 gene has yielded identical sequence for the two strains and the genetically determined associated factors are hypothesized to be regulatory proteins. Quantitative trait locus analysis on the RI lines should lead to the molecular characterization and mapping of such gene-specific regulatory factors.

Polygenic inheritance of Tourette syndrome, stuttering, attention deficit hyperactivity, conduct, and oppositional defiant disorder: the additive and subtractive effect of the three dopaminergic genes--DRD2, D beta H, and DAT1

Polymorphisms of three different dopaminergic genes, dopamine D2 receptor (DRD2), dopamine beta-hydroxylase (D beta H), and dopamine transporter (DAT1), were examined in Tourette syndrome (TS) probands, their relatives, and controls. Each gene individually showed a significant correlation with various behavioral variables in these subjects. The additive and substractive effects of the three genes were examined by genotyping all three genes in the same set of subjects. For 9 of 20 TS associated comorbid behaviors there was a significant linear association between the degree of loading for markers of three genes and the mean behavior scores. The behavior variables showing the significant associations were, in order attention deficit hyperactivity disorder (ADHD), stuttering oppositional defiant, tics, conduct, obsessive-compulsive, mania, alcohol abuse and general anxiety-behaviors that constitute the most overt clinical aspects of TS. For 16 of the 20 behavior scores there was a linear progressive decrease in the mean score with progressively lesser loading for the three gene markers. These results suggest that TS, ADHD, stuttering oppositional defiant and conduct disorder, and other behaviors associated with TS, are polygenic, due in part to these three dopaminergic genes, and that the genetics of other polygenic psychiatric disorders may be deciphered using this technique.

Priorities for neuropsychiatric genetics at the National Institutes of Health

Over the last decade, molecular genetics has become one of the most important technologies in medical research. However, the application of these approaches to neuropsychiatric disorders has been met with both unreasonable expectations, and at times, unreasonable criticism. Molecular genetics has opened a new window into these disorders that has great promise, but is likely to reveal a complex reality. Clearly, the potential exists to actually define some of the disorders that make up the syndromes that we are studying. In doing so, we will not only begin to address the fundamental pathophysiology of these disorders, but also begin to design treatments based on this new understanding. In this report, a series of four papers on the genetics programs of the National Institutes of Health will be introduced.