Social functioning and personality of subjects at familial risk for affective disorder

BACKGROUND

Particular patterns of personality (e.g., neuroticism, obsessionality) and difficulties in various social roles have been found to be associated with unipolar depression. Interpersonal and instrumental difficulties of depressives can be understood either as a risk factor, or as a consequence caused by the disorder itself. Concerning patients with bipolar disorder, there is some evidence that their premorbid level of occupational and educational achievement is often superior when compared to the premorbid functioning of patients with unipolar depression.

METHODS

Personality features and the level of social functioning of 114 high-risk subjects (healthy first-degree relatives of patients suffering from an affective disorder) have been investigated using self- and expert-ratings. Sixty-three subjects without a personal and family history of psychiatric disorder served as the reference group.

RESULTS

Relatives of melancholic depressives described themselves as more neurotic than controls but proved to be inconspicuous regarding their role functioning. Relatives of bipolar I patients were more strongly oriented toward social norms, and their instrumental role functioning was superior to that of controls. Neuroticism was strongly associated with depressive symptoms.

LIMITATION

The statistical power of our data is sufficient to detect medium effect sizes but is insufficient for identifying small group differences.

CONCLUSION

Whether these discriminating personality features and other variables (not characterising the high-risk group (HRG) as a whole) act as true vulnerability factor have to be clarified by a follow-up investigation.

HTR2A: association and expression studies in neuropsychiatric genetics

Over the last decade the gene encoding 5-hydroxytryptamine (serotonin) receptor 2A (HTR2A) has been implicated as a functional candidate in many neuropsychiatric phenotypes including: schizophrenia, attention deficit hyperactivity disorder (ADHD), affective disorders, eating disorders, anxiety disorders, obsessive-compulsive disorder, suicide and Alzheimer's disease (AD). Different studies have tested for genetic association (case-control and family-based studies), protein expression (receptor binding assays), transcriptional expression (mRNA assays) and allelic expression. In this review we examine and summarize these findings in various neuropsychiatric phenotypes.

Listening to mutant mice: a spotlight on the role of CRF/CRF receptor systems in affective disorders

Genetically engineered mice were originally generated to delineate the role of a specific gene product in behavioral or neuroendocrine phenotypes, rather than to produce classic animal models of depression. To learn more about the neurobiological mechanisms underlying a clinical condition such as depression, it has proven worthwhile to investigate changes in behaviors characteristic of depressed humans, such as anxiety, regardless of whether or not these alterations may also occur in other disorders besides depression. The majority of patients with mood and anxiety disorders have measurable shifts in their stress hormone regulation as reflected by elevated secretion of central and peripheral stress hormones or by altered hormonal responses to neuroendocrine challenge tests. In recent years, these alterations have been increasingly translated into testable hypotheses addressing the pathogenesis of illness. Refined molecular technologies and the creation of genetically engineered mice have allowed to specifically target individual genes involved in regulation of corticotropin releasing factor (CRF) system elements (e.g. CRF and CRF-related peptides, their receptors, binding protein). Studies performed in such mice have complemented and extended our knowledge. The cumulative evidence makes a strong case implicating dysfunction of these systems in the pathogenesis of depression and leads us beyond the monoaminergic synapse in search of eagerly anticipated strategies to discover and develop better therapies for depression.

Attention and memory biases in the offspring of parents with bipolar disorder: indications from a pilot study

BACKGROUND

Although children of bipolar parents are at heightened risk for developing emotional disorders, the processes underlying this vulnerability are not well understood. This study examined biases in the processing of emotional stimuli as a potential vulnerability marker of bipolar disorder.

METHODS

Sixteen children of bipolar parents who did not show any indication of having an emotional disorder at the time of testing and ten children of never-disordered control parents underwent a negative mood induction designed to activate cognitive schemas and were then administered an emotion Stroop task and a self-referent encoding task.

RESULTS

Children of bipolar parents were found to exhibit an attentional bias towards social-threat and manic-irritable words. Furthermore, although high- and low-risk children did not differ in their endorsement of positive and negative words as self-descriptive, the high-risk children demonstrated better recall of negative words than did the low-risk children.

CONCLUSIONS

Thus, children without a mood disorder who are at high risk for developing a mood disorder were found to exhibit biases in attention and memory that are similar to those found for bipolar and unipolar depressed adults, suggesting that children at increased risk for affective disorder are characterized by potentially pathogenic cognitive structures that can be activated by sad mood. These findings offer insights into mechanisms of cognitive vulnerability for bipolar disorders.

The Munich vulnerability study on affective disorders: premorbid neuroendocrine profile of affected high-risk probands

One of the most characteristic alterations in depression is a disturbed regulation of the hypothalamic-pituitary-adrenocortical (HPA) system. A function test combining the pre-treatment of 1.5 mg dexamethasone (DEX) with a challenge of 100 microg corticotropin-releasing hormone (CRH) reveals a pathological increase in the adrenocorticotropin and cortisol release in patients with major depression. These changes partially persist after successful treatment with remission and therefore, might represent trait or vulnerability markers. To further address this question, we were investigating the premorbid neuroendocrine profile of 74 healthy high-risk probands (HRPs) with a positive family history for affective disorders. The aim was to identify premorbid vulnerability factors. During the observation period, 19 HRPs developed an affective disorder. Their premorbid DEX/CRH test results were compared with 19 age- and sex matched controls. No significant differences could be observed between these two groups. Our results suggest that a dysregulated HPA system indicated by this function test can rather be regarded as a neurobiological scar developing during the course of affective disorders.

No association of clock gene T3111C polymorphism and affective disorders

CLOCK was hypothesised to be related to susceptibility of affective disorders. To test subsamples of affectively disordered patients, we examined age of onset (AoO), numbers of episodes and melancholic type of clinical manifestation. Using PCR and RFLP, we investigated in patients with unipolar depression and bipolar disorder (BP) whether the CLOCK T3111C SNP is associated with affective disorders (n=102) compared to healthy controls (n=103). No differences were found either in genotype or allele frequency distributions of T3111C polymorphism between patients compared to healthy controls (p>0.2). No deviations from Hardy-Weinberg Equilibrium (HWE) were detected either in patients, or healthy controls. Results suggest that there is no association between the T3111C SNP and affective disorders in general. Data of our sample replicate prior findings of Desan et al. [Am. J. Med. Genet. 12 (2000) 418]. Subsamples of patients with high numbers of affective episodes did show some deviations in genotypes (p=0.0585).

YB-1 and CTCF differentially regulate the 5-HTT polymorphic intron 2 enhancer which predisposes to a variety of neurological disorders

The serotonin transporter (5-HTT) gene contains a variable number tandem repeat (VNTR) domain within intron 2 that is often associated with a number of neurological conditions, including affective disorders. The implications of this polymorphism are not yet understood, however, we have previously demonstrated that the 5-HTT VNTR is a transcriptional regulatory domain, and the allelic variation supports differential reporter gene expression in vivo and in vitro. The aim of this study was to identify transcription factors responsible for the regulation of this VNTR. Using a yeast one-hybrid screen, we found the transcription factor Y box binding protein 1 (YB-1) interacts with the 5-HTT VNTR. Consistent with this, we demonstrate in a reporter gene assay that the polymorphic VNTR domains differentially respond to exogenous YB-1 and that YB-1 will bind to the VNTR in vitro in a sequence-specific manner. Interestingly, the transcription factor CCTC-binding factor (CTCF), previously shown to interact with YB-1, interferes with the ability of the VNTR to support YB-1-directed reporter gene expression. In addition, CTCF blocks the binding of YB-1 to its DNA recognition sequences in vitro, thus providing a possible mechanism of regulation of YB-1 activation of the VNTR by CTCF. Therefore, we have identified YB-1 and CTCF as transcription factors responsible, at least in part, for modulation of VNTR function as a transcriptional regulatory domain. Our data suggest a novel mechanism that explains, in part, the ability of the distinct VNTR copy numbers to support differential reporter gene expression based on YB-1 binding sites.

Neural network analysis in pharmacogenetics of mood disorders

Background

The increasing number of available genotypes for genetic studies in humans requires more advanced techniques of analysis. We previously reported significant univariate associations between gene polymorphisms and antidepressant response in mood disorders. However the combined analysis of multiple gene polymorphisms and clinical variables requires the use of non linear methods.

Methods

In the present study we tested a neural network strategy for a combined analysis of two gene polymorphisms. A Multi Layer Perceptron model showed the best performance and was therefore selected over the other networks. One hundred and twenty one depressed inpatients treated with fluvoxamine in the context of previously reported pharmacogenetic studies were included. The polymorphism in the transcriptional control region upstream of the 5HTT coding sequence (SERTPR) and in the Tryptophan Hydroxylase (TPH) gene were analysed simultaneously.

Results

A multi layer perceptron network composed by 1 hidden layer with 7 nodes was chosen. 77.5 % of responders and 51.2% of non responders were correctly classified (ROC area = 0.731 – empirical p value = 0.0082). Finally, we performed a comparison with traditional techniques. A discriminant function analysis correctly classified 34.1 % of responders and 68.1 % of non responders (F = 8.16 p = 0.0005).

Conclusions

Overall, our findings suggest that neural networks may be a valid technique for the analysis of gene polymorphisms in pharmacogenetic studies. The complex interactions modelled through NN may be eventually applied at the clinical level for the individualized therapy.

Exploring the relationship between serotonin and brain-derived neurotrophic factor: analysis of BDNF protein and extraneuronal 5-HT in mice with reduced serotonin transporter or BDNF expression

Serotonin (5-HT) has been proposed to promote neuronal plasticity during the treatment of mood and anxiety disorders and following neurodegenerative insult by altering the expression of critical genes including brain-derived neurotrophic factor (BDNF). In this study, mice with constitutive reductions in the serotonin transporter (SERT) or BDNF were investigated to further assess the functional relationship between serotonin neurotransmission and BDNF expression. Using a modified extraction procedure and a commercial enzyme-linked immunosorbant assay, 50% decreases in BDNF protein in hippocampus, frontal cortex and brain stem were confirmed in 4-month-old mice lacking one copy of the BDNF gene (BDNF(+/-)). By contrast, 4-month-old male and female mice with partial (SERT(+/-)) or complete (SERT(-/-)) reductions in SERT expression showed no differences in BDNF protein levels compared to SERT(+/+) mice, although male SERT knockout mice of all genotypes had higher BDNF levels in hippocampus, frontal cortex, and brain stem than female animals. Microdialysis also was performed in BDNF(+/-) mice. In addition to other phenotypic aspects suggestive of altered serotonin neurotransmission, BDNF(+/-) mice show accelerated age-related degeneration of 5-HT forebrain innervation. Nevertheless, extracellular 5-HT levels determined by zero net flux microdialysis were similar between BDNF(+/+) and BDNF(+/-) mice in striatum and frontal cortex at 8-12 months of age. These data illustrate that a 50% decrease in BDNF does not appear to be sufficient to cause measurable changes in basal extracellular 5-HT concentrations and, furthermore, that constitutive reductions in SERT expression are not associated with altered BDNF protein levels at the ages and in the brain regions examined in this study.

Family study of fibromyalgia and affective spectrum disorder

BACKGROUND

Fibromyalgia is one member of a proposed group of psychiatric and medical disorders, collectively termed affective spectrum disorder (ASD), hypothesized to share possibly heritable pathophysiologic features. Two predictions of the ASD hypothesis were tested: ASD, taken as a single entity, aggregates in families; and fibromyalgia coaggregates with other forms of ASD in families.

METHODS

Probands with and without fibromyalgia, together with their first-degree relatives, were administered structured diagnostic interviews. Noninterviewed relatives were diagnosed according to information provided by interviewed relatives. Aggregation and coaggregation of disorders were analyzed with proband predictive logistic and linear regression models.

RESULTS

In 533 relatives of 78 probands with fibromyalgia and 272 relatives of 40 probands without fibromyalgia, the estimated odds ratio (OR) (95% confidence interval) for the familial aggregation of ASD was 1.8 (.97, 3.2), p = .065, and the increase in number of forms of ASD in a relative for each additional form of ASD in a proband was .076 (.027, .1240), p = .002. The OR for the coaggregation of fibromyalgia with other forms of ASD was 2.0 (1.2, 3.2), p = .004; this remained significant even after excluding all mood-disorder diagnoses: 1.8 (1.1, 3.0), p = .012.

CONCLUSIONS

These findings support familial aggregation of ASD collectively and familial coaggregation of fibromyalgia with other forms of ASD.

The epidemiology of mood disorders

This review provides an overview of the epidemiology, risk factors, and genetic epidemiology of mood disorders in adults and children. The magnitude and impact of mood disorders in the community outweighs that of most other chronic diseases. Although there is substantial knowledge regarding the sociodemographic risk factors for mood disorders, our understanding of the pathogenesis and classification still is evolving. Comorbidity of mood disorders with anxiety disorders and substance abuse has been documented widely. Whereas substance abuse and mood disorders seem to be independent etiologically, anxiety and mood disorders result from partially common etiologic factors. The results of family, twin, and adoption studies reveal that a positive family history is the most potent risk factor for mood disorders, particularly bipolar disorder. However, the specific factors that are transmitted in families still are unknown. The two areas that will inform future genetic research include phenomenologic studies that refine the validity of the current phenotypic classification of mood disorders, and application of study designs to elucidate specific factors that may explain the familial transmission of these disorders.

Human 5-HT1A receptor C(-1019)G polymorphism and psychopathology

Dysfunction of the serotonin (5-HT1A) receptor (5-HTR1A) has been implicated in mood disorders, anxiety disorders, psychosis and the action of antidepressants. A common C(-1018)G [C(-1019)G] functional polymorphism in the promoter region of the human 5-HT1A receptor gene has been reported, which may be useful in identifying psychopathology associated with altered function of the human 5-HT1A receptor. We studied the relationship of this polymorphism to psychopathology and 5-HT1A binding in prefrontal cortex. The 5-HT1A receptor genotype for the C(-1019)G polymorphism was typed in 696 unrelated psychiatric subjects, 107 unrelated healthy volunteers, and in post-mortem brain samples from 241 cases. 5-HT1A receptor binding was assayed in post-mortem prefrontal cortex using [3H]8-OH-DPAT, and specific binding determined by 1 microM 5-HT. An association of genotype distribution and allele frequency of the 5-HTR1A C(-1019)G locus was observed in schizophrenia (chi2=9.51, d.f.=2, p=0.009; chi2=9.52, d.f.=1, p=0.002; Armitage's trend test: chi2=9.07, d.f.=1, p=0.003), in substance use disorder (chi2=8.41, d.f.=2, p=0.015; chi2=8.35, d.f.=1, p=0.004; Armitage's trend test: chi2=6.27, d.f.=1, p=0.0012), and in panic attack (chi2=6.31, d.f.=2, p=0.043; chi2=6.14, d.f.=1, p=0.013; Armitage's trend test: chi2=6.27, d.f.=1, p=0.012). An association of the 5-HTR1A C(-1019)G locus with schizophrenia, substance use disorder, and panic attack was suggested by our results. In post-mortem brain samples, 5-HT1A receptor binding in prefrontal cortex and suicide were not associated with genotype. The relationship does not appear to be explained by binding differences, although we cannot rule out altered receptor affinity and transduction.

The C(-1019)G polymorphism of the 5-HT1A gene promoter and antidepressant response in mood disorders: preliminary findings

Several studies have demonstrated the involvement of 5-HT1A receptors in the pathogenesis of depression and in the antidepressant response to SSRIs. A functional new variant in the promoter region of the 5-HT1A gene was recently reported (-1019 C>G). The aim of this study is to investigate a possible association between this 5-HT1A receptor variant and antidepressant response to fluvoxamine in a sample of 262 mood-disorder subjects (151 major depressed and 111 bipolars) treated with fluvoxamine for 6 wk. The severity of depressive symptoms was assessed weekly with the Hamilton Rating Scale for Depression (HAMD). 5-HT1A variants did not influence antidepressant response in the whole sample and in unipolar subjects. In bipolars, 5-HT1A*C/C genotype carriers showed a better response to fluvoxamine (p=0.036), independently from clinical variables. The 5-HT1A polymorphism effect on antidepressant response was independent from the previously reported effect of the 5-HTTLPR polymorphism. In conclusion, 5-HT1A variants could influence the antidepressant efficacy in bipolar subjects, even if results must be verified on larger samples.

Association study of brain-derived neurotrophic factor in adults with a history of childhood onset mood disorder

Brain-derived neurotrophic factor (BDNF) is a nerve growth factor that has antidepressant-like effects in animals. BDNF gene polymorphisms have been associated with bipolar disorder. We tested two genetic polymorphisms of BDNF for their association with childhood-onset mood disorders (COMD) within the context of a case-control design. Two BDNF polymorphisms, a dinucleotide repeat (GT)(n), and a single nucleotide polymorphism (SNP) in the coding region, val66met, were genotyped in 99 adults with a history of COMD and matched psychiatrically healthy controls. A genomic control (GC) method was used to evaluate population substructure. Alleles at (GT)(n) were highly associated with COMD in this sample (chi(2) = 17.8; d.f. = 5; P = 0.0032). The odds of carrying the 168 bp allele were 3.94 times greater for cases than controls (CI = 1.72-9.04). Alleles of val66met were not significantly associated with COMD. GC analysis suggested population substructure was not a confounder of association. Analysis of haplotypes, in which (GT)(n) was treated as a binary variable (long vs. short alleles), provided significant evidence that the haplotype val/short contributes to liability to COMD. The BDNF (GT)(n) marker and the val/short haplotype are associated with COMD in this sample, in accordance with the previously described neurotrophic hypothesis of depression and some previous studies of association for bipolar disorder and neuroticism.

Serotonin transporter 5HTTLPR polymorphism and affective disorders: no evidence of association in a large European multicenter study

The available data from preclinical and pharmacological studies on the role of the serotonin transporter (5-HTT) support the hypothesis that a dysfunction in brain serotonergic system activity contributes to the vulnerability to affective disorders (AD). 5-HTT is the major site of serotonin reuptake into the presynaptic neuron, and it has been shown that the polymorphic repeat polymorphism in the 5-HTT promotor region (5-HTTLPR) may affect gene-transcription activity. 5-HTT maps to chromosome 17 at position 17q11.17-q12, and the 5-HTTLPR polymorphisms have been extensively investigated in AD with conflicting results. The present study tested the genetic contribution of the 5-HTTLPR polymorphism in a large European multicenter case-control sample, including 539 unipolar (UPAD), 572 bipolar patients (BPAD), and 821 controls (C). Our European collaboration has led to efforts to optimize a methodology that attenuates some of the major limitations of the case-control association approach. No association was found with primary psychiatric diagnosis (UPAD and BPAD) and with phenotypic traits (family history of AD, suicidal attempt, and presence of psychotic features). Our negative findings are not attributable to the lack of statistical power, and may contribute to clarify the role of 5-HTTLPR polymorphism in AD.

Genetic association studies in mood disorders: issues and promise

Genetic association is a powerful method for identifying genetic variants that contribute to the molecular basis of complex diseases. There is now a wealth of informative, validated and densely-spaced single nucleotide polymorphism (SNP) markers for use in association studies, and the delineation of the genome-wide haplotype architecture will greatly enhance our ability to conduct whole genome association screens, fine mapping of linkage regions, and systematic screening of functional candidate genes. Single nucleotide polymorphism-based genotyping technology has progressed dramatically to the point of high-throughput methods that can assay up to thousands of SNPs on many samples in one experiment. Genotyping cost remains a limiting factor in complex disease studies, where numerous SNPs and large sample sets are needed to maximize statistical power. Strategies designed to reduce cost include DNA pooling and analysis with tagSNPs. As larger clinical samples become available, it will be increasingly important to test for hidden stratification in case-control studies, as well as transmission distortion in family-based studies, either of which can lead to spurious association findings. As yet, there is no widely-accepted genetic association finding in mood disorders, but functional candidate genes, such as the serotonin transporter, and positional candidates, such as G72/G30 on chromosome 13q, are beginning to be identified in several studies. Relating associated variants to the phenotype represents the next critical step toward establishing the pathogenic role of gene variants in mood disorders.

Preschool-onset mania: incidence, phenomenology and family history

OBJECTIVE

To ascertain the incidence of mania among preschool children presenting in a community mental health clinic over a 24-month period, to describe the signs and symptoms of the children meeting criteria for mania and present their family histories based on systematic diagnostic interview.

METHODS

Forty children less than the age of 5 years presented between October 2001 and September 2003. Signs of mania were determined using a structured interview. Family history was determined via live, structured interview of parents. Those meeting the criteria for major depressive disorder (MDD) or bipolar disorder (BP) were classified as having mood disorder.

RESULTS

Eleven of the 40 children (27.5%) met the criteria for mania, of which only 3 (27.3%) were mixed manic. Symptoms often included "classic" mania features (i.e. euphoric, elated mood), despite co-existing features of attention-deficit hyperactivity disorder (ADHD)--such as incessant, chaotic, even frenetic motor activation--in all of them. Seven of the 11 (63.6%) had at least one parent with BP and a total of 8 (72.7%) had a parental history of affective illness when parents with MDD were counted. One child without a first-degree relative with BP had a second degree relative with this illness. Thus, 8 of 11 (72.7%) had a relative with BP, and 9 (81.8%) a family history of mood disorder (counting both MDD and BP).

LIMITATION

Open case series.

CONCLUSION

There was a surprisingly high incidence of mania with classical features in this population. The family history data strongly support the view that these children have BP. Preschool mania appears to be strongly linked to the presence of familial affective illness. Admittedly, preschool mania is a controversial topic, and data from other centers is needed to further characterize its clinical and familial features.

Reduced spinophilin but not microtubule-associated protein 2 expression in the hippocampal formation in schizophrenia and mood disorders: molecular evidence for a pathology of dendritic spines

OBJECTIVE

Aberrant synaptic connectivity may underlie the involvement of the hippocampus in schizophrenia. There is reasonable neuropathological evidence for a presynaptic pathology but few studies of the postsynaptic component. This study tested the hypothesis that hippocampal dendritic pathology is also present in schizophrenia.

METHOD

Using in situ hybridization in sections of hippocampal formation from 10 patients with schizophrenia, 10 patients with mood disorders (three with bipolar disorder and seven with major depression), and 10 healthy comparison subjects, the authors examined the expression of two important dendritic genes: spinophilin, which serves as a marker of dendritic spines, and microtubule-associated protein 2 (MAP2), an overall dendritic marker.

RESULTS

The patients with schizophrenia had lower levels of spinophilin mRNA in CA4 (hilus), CA3, the subiculum, and the entorhinal cortex than did the normal comparison subjects. The mood disorder group showed similar differences from the comparison group. MAP2 and cyclophilin mRNA did not differ between the groups in any subfield.

CONCLUSIONS

Decreased spinophilin but unchanged MAP2 expression provides molecular evidence for a hippocampal dendritic pathology in schizophrenia that preferentially affects the spines. As spines are the target of most glutamatergic synapses, the data extend the evidence that excitatory synapses are particularly affected. Similar dendritic spine pathology may also occur in mood disorders.

Familial transmission of mood disorders: convergence and divergence with transmission of suicidal behavior

OBJECTIVE

Both mood disorder and suicidal behavior are familial. In this study, the authors examine the factors associated with the familial transmission of these two related conditions to learn which are shared or unique risk factors for familial transmission.

METHOD

The 285 offspring of 141 probands with mood disorder were studied. Proband and offspring characteristics associated with offspring mood disorder were examined by univariate statistics, logistic and Cox regression, and path analysis.

RESULTS

Parental history of sexual abuse was associated with an increased risk of offspring mood disorder. The relationship between parent sexual abuse and offspring mood disorder was mediated by offspring impulsive aggression, sexual abuse, and anxiety disorder. In offspring, higher levels of impulsive aggression were associated with earlier age at onset of mood disorder. Offspring suicide attempt was mainly related to offspring mood disorder, with additional contributions from offspring sexual abuse and impulsive aggression.

CONCLUSIONS

The pathways associated with the familial transmission of mood disorder and of suicide attempt are similar but not identical. Prevention of early-onset mood disorder by targeting high- risk families may help to prevent the transmission of suicidal behavior. Because these data are cross-sectional, these results must be confirmed by prospective follow-up.

Autism and familial major mood disorder: are they related?

Family history studies of autism consistently reveal a large subgroup with a high incidence of major mood disorder in family members, suggesting the two entities are related clinically and genetically. This review examines this concept, comparing current clinlical and biological knowledge of autism and major mood disorder, and advances the hypothesis that this subgroup of autism represents an early-life phenotype of major mood disorder. If confirmed, this hypothesis would suggest that the basic biological defects determining major mood disorders may have prominent neurodevelopmental and cognitive dimensions. Testing of the hypothesis will depend on genetic studies.

Power calculations for familial aggregation studies

Family studies are frequently undertaken as the first step in the search for genetic determinants of disease. Significant familial aggregation of disease is suggestive of a genetic etiology for the disease, and may lead to more focused genetic analyses. Many methods have been proposed in the literature for the analysis of family studies. One model that is appealing for its simplicity of computation and the conditional interpretation of its parameters is the quadratic exponential model (e.g., Zhao and Prentice [1990] Biometrika 77:642-648; Betensky and Whittemore [1996] Appl. Stat. 45:422-429; Hudson et al. [2001a] Am. J. Epidemiol. 153:500-514). However, a limiting factor in its application, as well as that of the other proposed methods, is that power and sample size calculations have not been derived. These calculations are essential for investigators who are designing family studies. Here we derive analytic approximations for power for testing for familial aggregation, for both randomly sampled and nonrandomly sampled families. We also present simulation studies of power for both single- and two-disease cases, both under random and nonrandom sampling.