Molecular genetic studies of complex disorders require a number of parallel strategies. Many of the more familial psychiatric syndromes are highly prevalent and may represent a collection of a number of distinct genetic subtypes and possibly a number of nongenetic subtypes. A nongenetic form of illness may appear clinically indistinguishable from a genetic form. These nongenetic subtypes of a syndrome would be considered phenocopies. In this and the subsequent issue of CNS Spectrums, a number of papers are presented that review the current state of psychiatric genetics of major disorders. Clinical strategies to narrow phenotypes and better define study populations are paired with laboratory and statistical strategies to optimize both candidate gene and genome scanning methods.

In this issue, Kennedy and colleagues focus on a review of the genetics of schizophrenia, highlighting genome scans already completed and studies on special populations. Schindler and colleagues present a unique and efficient method for defining the homogeneity of a study population, surname analysis, and the importance of population selection in the design of genetic studies. Macedo and colleagues demonstrate the study of anticipation in bipolar mood disorder. Genetic anticipation is the observation of an earlier age of onset and greater disease severity in younger generations. This pattern has been associated with dynamic repeat expansions in the DNA in several neuropsychiatric disorders, and represents a good example of a unique genetic mechanism causing a unique phenotypic pattern. Nicolini and colleagues present work done to date on obsessive-compulsive disorder.

In this study, we attempt to demonstrate an association between low platelet monoamine oxidase (MAO) activity, as assessed by isotopic methods, and the stable behavioral pattern of sensation- and risk-seeking of professional bull-fighters. Sixteen professional bullfighters were studied and compared with a control group of 46 healthy control subjects who did not engage in risky jobs or activities. The group of bullfighters had significantly reduced platelet MAO activity compared with the control group (P<0.05). Bullfighters were shown to be significantly more extroverted and sensation-seeking than controls on various temperament scales. A predisposition to engage in risky activities (eg, bullfighting) and sensation-seeking could be partly conditioned by the presence of biological components of personality manifested by a significantly decreased platelet MAO activity.

Two symptom clusters within the obsessive-compulsive (OC) spectrum—the impulsive cluster and the schizo-obsessive cluster—are discussed in this paper. Disorders characterized by impulsivity include disorders of impulse control (eg, intermittent explosive disorder, pyromania, kleptomania, pathologic gambling, trichotillomania); paraphilias, sexual impulsions, and sexual addictions; and impulsive aggression personality disorders (eg, borderline, antisocial, histrionic, and narcissistic personality disorders). The schizo-obsessive cluster includes comorbid symptoms of obsessive-compulsive disorder (OCD) and schizophrenia. Both clusters of disorders have a substantial impact on individuals and society. This article examines the overlap of symptoms between OCD and OC spectrum disorders, along with possible treatment options. Studies on the effectiveness of serotonin reuptake inhibitors in treating pathologic gambling, compulsive buying, and comorbid OCD and schizophrenia are presented. The need for additional large scale, adequately-controlled studies is discussed.

A growing number of anatomic and physiologic studies have shown that parallel sensory and motor information processing occurs in multiple cortical areas. These findings challenge the traditional model of brain processing, which states that the brain is a collection of physically discrete processing modules that pass information to each other by neuronal impulses in a stepwise manner. New concepts based on neural network models suggest that the brain is a dynamically shifting collection of interpenetrating, distributed, and transient neural networks. Neither of these models is necessarily mutually exclusive, but each gives different perspectives on the brain that might be complementary. Each model has its own research methodology, with functional magnetic resonance imaging supporting notions of modular processing, and electrophysiology (eg, electroencephalography) emphasizing the network model. These two technologies might be combined fruitfully in the near future to provide us with a better understanding of the brain. However, this common enterprise can succeed only when the inherent limitations and advantages of both models and technologies are known. After a general introduction about electrophysiology as a research tool and its relation to the network model, several practical examples are given on the generation of pathophysiologic models and disease classification, intermediate phenotyping for genetic investigations, and pharmacodynamic modeling. Finally, proposals are made about how to integrate electrophysiology and neuroimaging methods.

Previous reports concerning the cerebrospinal fluid (CSF) of pathologic gamblers have described disturbed norepinephrine and dopamine (but not serotonin) functioning in the central nervous system. We analyzed neurotransmitter metabolites in two consecutive 6-mL samples of CSF obtained from 10 pathologic male gamblers punctured at the L4-5 level following 8 hours of fasting along with strict bed rest. Data were compared with those for healthy male controls. In conformity with findings in healthy male controls, we found gradients in CSF 5-hydroxyindoleacetic acid (5-HIAA) and homovanillic acid (HVA), but not 4-hydroxy-3-methoxyphenyl glycol (HMPG). Expressing the CSF concentrations as nmol x L-1 x min-1 of tapping time (an estimate of the mass flow through the needle), the levels of 5-HIAA and HMPG (but not HVA) were found to be significantly lower in gamblers. Levels of 5-HIAA and HVA showed a significant correlation in gamblers but not in healthy controls. Taking tapping time into account, the CSF levels of HMPG and 5-HIAA were significantly lower in gamblers. We concluded that, in light of previous CSF findings of disturbed norepinephrine and dopamine function, altered indolamine function cannot be fully ruled out.

The “Genetics of Obsessive-Compulsive Disorder” session at the Third International Obsessive-Compulsive Disorder Conference focused on the strong evidence of familial transmission of obsessive-compulsive disorder (OCD) and the new strategies available for molecular genetic research in this area. The opportunity to create a truly collaborative approach to the genetic study of OCD with standard methodology and large-scale cooperation among groups was emphasized. The importance of phenotype definition, including systematic subtyping, was discussed in the context of reducing heterogeneity and false-positive results.

The genetics of schizophrenia are characterized by a set of complex questions, with few answers forthcoming. However, molecular genetic approaches remain the most promising avenue to the understanding of etiologic mechanisms. Powerful discoveries may arise in the near future from candidate gene studies that are benefiting from the extensive neurobiology research in schizophrenia over the past decades. Furthermore, there are promising new divisions of the phenotype into more manageable subtypes that may make both candidate gene and genome scan studies more revealing. The following review discusses selected highlights of the epidemiology, molecular genetic strategies, candidate genes, and genome scan investigations in schizophrenia.