Selection of controls for family studies. Biases and implications

Designing case-control studies: decisions about the controls

The authors quantified, first, the effect of misclassified controls (i.e., individuals who are affected with the disease under study but who are classified as controls) on the ability of a case-control study to detect an association between a disease and a genetic marker, and second, the effect of leaving misclassified controls in the study, as opposed to removing them (thus decreasing sample size). The authors developed an informativeness measure of a study's ability to identify real differences between cases and controls. They then examined this measure's behavior when there are no misclassified controls, when there are misclassified controls, and when there were misclassified controls but they have been removed from the study. The results show that if, for example, 10% of controls are misclassified, the study's informativeness is reduced to approximately 81% of what it would have been in a sample with no misclassified controls, whereas if these misclassified controls are removed from the study, the informativeness is only reduced to about 90%, despite the reduced sample size. If 25% are misclassified, those figures become approximately 56% and 75%, respectively. Thus, leaving the misclassified controls in the control sample is worse than removing them altogether. Finally, the authors illustrate how insufficient power is not necessarily circumvented by having an unlimited number of controls. The formulas provided by the authors enable investigators to make rational decisions about removing misclassified controls or leaving them in.

Association between affective temperaments and bipolar spectrum disorders: preliminary perspectives from a controlled family study

BACKGROUND

The study aimed at determining the temperamental underpinnings of bipolar spectrum disorders (BSD) in the first-degree relatives (FDR) of patients with bipolar I disorder in comparison with control subjects.

SAMPLING AND METHODS

The sample consisted of 198 subjects: 33 bipolar I probands and their 33 FDR in the experimental group, 33 schizophrenia probands and their 33 FDR in the patient control group, and 33 normal healthy controls and their 33 FDR. The affective temperament and the BSD were assessed using the Temperament Evaluation of the Memphis, Pisa, Paris, and San Diego Autoquestionnaire and the criteria of Ghaemi et al. [Can J Psychiatry 2002;47:125-134], respectively.

RESULTS

Among the FDR of bipolar I probands, 27.3% satisfied the diagnosis of BSD, which was significantly higher than in the other groups (relative risk = 6, 95% CI = 1.74-20.69). Bipolar probands were significantly more hyperthymic as compared to controls (relative risk = 2, 95% CI = 1.34-2.98), and both the FDR of the bipolar and the FDR of the patient control groups were significantly more hyperthymic as compared to the FDR of the normal controls (relative risk = 1.52, 95% CI = 0.93-2.51). FDR (of bipolar patients) with BSD had a significantly higher total irritable temperament score as compared to FDR (of bipolar patients) without BSD (mean difference = 2.07, 95% CI = 0.64-3.50).

CONCLUSIONS

Our findings support the fact that the whole spectrum of bipolarity is transmitted in susceptible families. The graded distribution of hyperthymia suggests it to be a milder expression of bipolarity in the FDR of bipolar patients. The irritable temperament appears to be a specific vulnerability marker for the development of BSD.

Childhood antecedent disorders to bipolar disorder in adults: a controlled study

OBJECTIVE

The aim of the study was to examine antecedent childhood psychiatric disorders in adult patients with bipolar disorder.

METHOD

Using structured diagnostic interviews, childhood psychiatric diagnoses of 83 referred patients with diagnosed DSM-IV bipolar disorder were compared to those of 308 adults without mood disorders.

RESULTS

Patients with bipolar disorder had significantly higher rates of childhood disruptive behavior disorders (ADHD, oppositional-defiant disorder, and conduct disorder), childhood anxiety disorders (separation anxiety and overanxious disorder), and enuresis, compared to patients without mood disorders. The presence of these childhood disorders was associated with an earlier age of onset of bipolar illness.

LIMITATIONS

The retrospective nature of the study may have affected both the rates of disorders recalled, as well as the ages of onset of disorders. Different referral sources for bipolar and comparison participants may have also impacted findings.

CONCLUSIONS

Bipolar disorder in adults is frequently preceded by childhood disruptive behavior and anxiety disorders. These childhood disorders may be important markers of risk for adult bipolar disorder.

Cognitive deficits in unaffected first-degree relatives of schizophrenia patients: a meta-analytic review of putative endophenotypes

Cognitive deficits may index genetic liability for schizophrenia and are candidate endophenotypes for the illness. In order to compare the degree of sensitivity among cognitive tasks to group differences between healthy relatives and controls and the influence of moderator variables, this review reports mean effect sizes for 43 cognitive test scores from 58 studies of cognitive performance in the unaffected adult relatives of schizophrenia patients. Results indicate reliable relative-control differences, in the small to medium effect size range, over a diverse array of tasks, with the largest effect sizes seen in complex versions of continuous performance tasks, auditory verbal learning, design copy tests, and category fluency. Three study design features were found to have significant effects on overall effect size magnitude: groups unmatched on education, groups unmatched on age, and asymmetric psychiatric exclusion criteria. After excluding studies with the latter 2 design features, reliable performance differences were still observed over a smaller subset of cognitive test variables, with the largest effect sizes seen in Trails B (d = 0.50) and performance measures from both simple (d = 0.56) and complex (d = 0.60-0.66) versions of continuous performance tasks. Four of the 6 largest effect sizes reflect tasks with high executive control demands in common, such as working memory demands, set shifting, and inhibition of prepotent responses. Cognitive deficits, particularly those tapping such executive control functions, should continue to prove valuable as endophenotypes of interest in the search for specific genetic factors related to schizophrenia.

Psychopathology in the offspring of parents with bipolar disorder: a controlled study

BACKGROUND

To examine the risk for psychopathology in offspring at risk for bipolar disorder and the course of psychiatric disorders in these youth.

METHODS

Using structured diagnostic interviews (Structured Clinical Interview for DSM-IV [SCID] and Kiddie Schedule for Affective Disorders and Schizophrenia [K-SADS]), psychiatric diagnoses of 117 nonreferred offspring of parents with diagnosed bipolar disorder were compared with those of 171 age- and gender-matched offspring of parents without bipolar disorder or major depression.

RESULTS

Compared with offspring of parents without mood disorders, high-risk youth had elevated rates of major depression and bipolar disorder, anxiety, and disruptive behavior disorders. High-risk offspring also had significantly more impaired Global Assessment of Functioning (GAF) scores, higher rates of psychiatric treatment, and higher rates of placement in special education classes. Disruptive behavior disorders, separation anxiety disorder, generalized anxiety disorder (GAD), social phobia, and depression tended to have their onset in early or middle childhood, whereas bipolar disorder, obsessive-compulsive disorder (OCD), panic disorder, and substance use disorder had onset most frequently in adolescence.

CONCLUSIONS

These findings support the hypothesis that offspring of parents with bipolar disorder are at significantly increased risk for developing a wide range of severe psychiatric disorders and accompanying dysfunction. Early disruptive behavior and anxiety disorders, as well as early-onset depression, may be useful markers of risk for subsequent bipolar disorder in high-risk samples.

The cyclothymic temperament in healthy controls and familially at risk individuals for mood disorder: endophenotype for genetic studies?

BACKGROUND

The modern concept of affective disorders focuses increasingly on the study of subthreshold conditions on the border of manic or depressive episodes. Indeed, a spectrum of affective conditions spanning from temperament to clinical episodes has been proposed by the senior author. As bipolar disorder is a familial illness, an examination of cyclothymic temperament (CT) in controls and relatives of bipolar patients is of major relevance.

METHODS

We recruited a total sample of 177 healthy symptom-free volunteers. These controls were divided into three groups. The first one is comprised of 100 normal subjects with a negative familial affective history (NFH); the second of 37 individuals, with positive affective family history (PFH); and a third of 40 subjects, with at least one sib or first-degree kin with bipolar disorder type I according to the DSM-IV (BPR). The last two groups defined at risk individuals. We interviewed all subjects with CT, as described by the senior author.

RESULTS

We found a statistically significant difference in the rates of CT between the subjects in BPR versus others. CT was also more prevalent in the PFH compared with NFH. Additionally, the simple numeration of the CT traits exhibited gradation in the distribution of individuals inside the NFH, PFH and BPR. Finally, categorically defined CT and CT traits predominated in females. LIMITATION and

CONCLUSION

Although not all relatives of bipolar probands were studied, our results exhibit an aggregation of CT in families with affective disorder-and more specifically those with bipolar background. These results allow us to propose the importance of including CT for phenotypic characterization of bipolar disorder. Furthermore, our results support a spectrum concept of bipolar disorder, whereby CT is distributed in ascending order in the well-relatives of those with depressive and bipolar disorders. We submit that this temperament represents a behavioral endophenotype, serving as a link between molecular and behavioral genetics.

Functional magnetic resonance imaging during auditory verbal working memory in nonpsychotic relatives of persons with schizophrenia: a pilot study

BACKGROUND

First-degree relatives of persons with schizophrenia carry elevated genetic risk for the illness and show deficits on high-load information processing tasks. We used functional magnetic resonance imaging (fMRI) to test whether nonpsychotic relatives show altered functional activation in the prefrontal cortex (PFC), thalamus, hippocampus, and anterior cingulate during a working memory task requiring interference resolution.

METHODS

Twelve nonpsychotic relatives of persons with schizophrenia and 12 healthy control subjects were administered an auditory, verbal working memory version of the Continuous Performance Test during fMRI. An asymmetric, spin-echo, T2*-weighted sequence (15 contiguous, 7-mm axial slices) was acquired on a full-body MR scanner. Data were analyzed by Statistical Parametric Mapping (SPM).

RESULTS

Compared with control subjects, relatives showed greater task-elicited activation in the PFC and the anterior and dorsomedial thalamus. When task performance was controlled, relatives showed significantly greater activation in the anterior cingulate. When effects of other potentially confounding variables were controlled, relatives generally showed significantly greater activation in the dorsomedial thalamus and anterior cingulate.

CONCLUSIONS

This pilot study suggests that relatives of persons with schizophrenia have subtle differences in brain function in the absence of psychosis. These differences add to the growing literature identifying neurobiological vulnerabilities to schizophrenia.

Immune related genetic polymorphisms and schizophrenia among the Chinese

Genetic association studies were conducted among two independent cohorts of Chinese ethnicity. The samples consisted of cases and unrelated controls, ascertained from Guangzhou, China, and Singapore. The studies were prompted by our earlier report of an association between schizophrenia and HLA DQB1 alleles (HLA DQB1*0602 and HLA DQB1*0303) in the Singapore sample. Polymorphisms of HLA DQB1 and flanking markers on chromosome 6p21.3 were investigated in the first part of the study. A significant negative association with HLA DQB1*0402 was detected in the Guangzhou sample (Odds ratio, OR 0.26, 95% confidence intervals, CI 0.1, 0.6; p < 0.02, corrected for multiple comparisons). Additional analysis of the Guangzhou and Singapore samples revealed associations at three other anonymous markers flanking HLA DQB1. In the second part of the study, three polymorphisms at the Interleukin-1 gene cluster (IL-1, chromosome 2q13-q21) were investigated in both cohorts, since associations with schizophrenia have been reported in another sample. Persuasive evidence for an association at IL-1 was not detected in either sample. Our results suggest a susceptibility locus for schizophrenia in the HLA region among the Chinese, but further clarification is necessary.

Thalamic and amygdala-hippocampal volume reductions in first-degree relatives of patients with schizophrenia: an MRI-based morphometric analysis

BACKGROUND

Schizophrenia is characterized by subcortical and cortical brain abnormalities. Evidence indicates that some nonpsychotic relatives of schizophrenic patients manifest biobehavioral abnormalities, including brain abnormalities. The goal of this study was to determine whether amygdala-hippocampal and thalamic abnormalities are present in relatives of schizophrenic patients.

METHODS

Subjects were 28 nonpsychotic, and nonschizotypal, first-degree adult relatives of schizophrenics and 26 normal control subjects. Sixty contiguous 3 mm coronal, T1-weighted 3D magnetic resonance images of the brain were acquired on a 1.5 Tesla magnet. Cortical and subcortical gray and white matter and cerebrospinal fluid (CSF) were segmented using a semi-automated intensity contour mapping algorithm. Analyses of covariance of the volumes of brain regions, controlling for expected intellectual (i.e., reading) ability and diagnosis, were used to compare groups.

RESULTS

The main findings were that relatives had significant volume reductions bilaterally in the amygdala-hippocampal region and thalamus compared to control subjects. Marginal differences were noted in the pallidum, putamen, cerebellum, and third and fourth ventricles.

CONCLUSIONS

Results support the hypothesis that core components of the vulnerability to schizophrenia include structural abnormalities in the thalamus and amygdala-hippocampus. These findings require further work to determine if the abnormalities are an expression of the genetic liability to schizophrenia.

Sex differences in neuropsychological function in non-psychotic relatives of schizophrenic probands

Some recent studies suggest that men with schizophrenia may have greater neuropsychological deficits than women. It is not known, however, whether similar sex differences may be present in biological relatives of schizophrenic patients. We evaluated neuropsychological functioning of 54 relatives of schizophrenic patients and 72 normal volunteers. It was hypothesized that, if sex differences were present, they would be accounted for largely by deficits in male relatives. We were particularly interested in three neuropsychological functions that we previously identified as putative neuropsychological vulnerability indicators for schizophrenia: (1) abstraction/executive function; (2) verbal memory; and (3) auditory attention. There were significant group x sex interactions for verbal memory and motor function, and trends toward significant interactions for auditory attention and mental control/encoding. However, with the exception of motor function, it was the female relatives who accounted for most of the impairment. A speculative explanation for the findings is that women may have a higher threshold than men for developing schizophrenia. If so, female relatives might be able to withstand greater impairments than men before developing psychotic symptoms. Consequently, in a sample that was limited to non-psychotic relatives--as in the present study--there could be over-representation of both less impaired men and more impaired women. Alternative explanations and limitations of the study are also discussed.

Family history of depression in clinic and community samples

Because most published family studies of depression ascertained subjects from treatment settings, the reported familial aggregation of depression could be an artifact if a family history of depression increased the likelihood of seeking treatment. To investigate this possibility, we compared the family history of depression in three groups of probands aged 18-44; 54 women randomly selected from the community with depression in the prior year, 41 women who entered a clinical trial for depression and 37 women randomly selected from the community who had not been depressed in the prior year. The presence of depression in the parents and siblings of the probands was assessed by the family history method and quantified via family history scores which took the age, gender and number of relatives into account. Depressed probands ascertained from clinical sources had markedly higher family history scores of depression than other two groups (P < 0.00005 in each instance). In the absence of direct interviews with relatives, we cannot exclude the impact of differential reporting. A family history of depression might be associated with an increased probability of treatment or the differential reporting of family history. It is thus possible that the familial aggregation of depression observed in probands from treatment settings is an artifact.

Neuropsychological functioning among the elderly nonpsychotic relatives of schizophrenic patients

In our prior work with a young sample (age < 60), we showed that three neuropsychological functions were impaired among relatives of schizophrenic patients: abstraction, verbal memory, and auditory attention. In the present work we show that these results do not generalize to an older sample aged 60 years and greater. Thus, although we and others have put forth measures of neuropsychological function as indicators of the schizophrenia genotype, the present study suggests that conclusions may be limited to non-elderly samples. Further work is needed to address this issue definitively.

Childhood psychopathology in children from families of alcoholic female probands

OBJECTIVE

To determine the prevalence of DSM-III disorders among children who had been selected for study based on their maternal family history of alcoholism (either multigenerational alcoholism in the case of the high-risk group or no alcohol dependence in first- and second-degree relatives in the case of the control children).

METHOD

Thirty-four boys and 42 girls with a mean age of 11.3 years (range 8 to 18) were evaluated. An equal number of children comprised the high- and low-risk groups and were gender- and age-matched using a yoked control design.

RESULTS

The high-risk children manifested more psychiatric diagnoses overall, and significantly more internalizing disorders than controls. The relative odds of a high-risk child's having a diagnosed disorder were increased when the child lived with a biological mother and a custodial father (biological, step, or adoptive) who were both alcoholic. This relationship was exacerbated by the child's being older than 13 years of age.

CONCLUSIONS

Vertical transmission of maternal alcoholism is manifested in childhood and adolescence by the presence of increased psychopathology. This psychopathology occurred in offspring of alcoholics screened for major comorbidity, suggesting that it is unlikely that the increased psychopathology is due to cotransmission of affective or other psychopathology. The elevated risk of psychopathology in association with having an alcoholic mother was not further increased by the child's being older than 13 years of age, if the father (custodial or only biological) was not alcoholic.

Methodological issues in psychopathology research

We present an overview of methodological issues involved in conducting psychopathology research, including conceptual, analytic, and interpretive considerations. Research issues germane to structured diagnostic interviewed, comorbidity of mental disorders, and ascertainment and sampling are reviewed. Further, the problem of specificity (with respect to disorder, to differential deficit, and to time) is discussed. Specific issues concerning risk vs protective factors, conducting research with special populations, and the continuity of abnormal and normal functioning are highlighted. Finally, various analogue strategies (human subclinical syndromes, experimental study of "pathological" processes in normals, animal models, and computer simulations) are critiqued. Our review documents many of the impressive methodological developments that have emerged in this field, and we hope our review stimulates additional research that exploits recent methodological advances.

Selection biases during recruitment of patients and relatives for a family study in the elderly

The aim of the present study was to examine selection effects during recruitment of patients, controls and relatives for a family study in the elderly. The primary sample consisted of 368 in-patients (aged above 60 years) admitted in the years 1992 and 1993. One-hundred and eighty-four subjects (50%) suffering from dementia of Alzheimer type or major depression fulfilled the diagnostic inclusion criteria. Finally, 100 subjects participated in the family study. Demographic data of participants, ineligible subjects, uncooperative candidates, and control subjects from the general population was examined. Demographic parameters, reasons for refusal of personal interviews, and family history information were compared in first-degree relatives of participants and of 40 control subjects. According to demographic data, participants were representative for the whole sample of demented or depressed patients, and were comparable with the control sample. Demographic parameters of relatives were also equivalent in both groups. Rates of psychiatric disorders were equal in interviewed and unavailable relatives of patients (18.0% and 18.8%, respectively). However, interviewed relatives of controls had significantly fewer psychiatric disorders than unavailable relatives (7.8% vs 20%). This selection effect indicates the need for family history information on unavailable relatives in family studies on geriatric patients. Equivalence of demographic data alone was not a sufficient indicator of sample comparability. A second hospitalized comparison group might serve to increase the validity of conclusions resulting from comparative family studies.

Selecting control groups for studies of familial aggregation of disease

In genetic-epidemiologic studies to determine the association between the disease status of family members, this association is measured by comparing rates of the disease in relatives of probands (index cases) with the disease, with the rates of the disease among individuals in a control group. Either of two types of control groups are generally used: (1) a control group consisting of a random sample from the population or the entire population if available or (2) a control group consisting of relatives of individuals without the disease under study. We examine the advantages and disadvantages of using these different types of control groups. We show two major results for family studies: (1) when there are no other factors associated with the disease status of an individual other than the disease status of a family member, both types of control groups will give a valid test of the null hypothesis of no familial aggregation. However, tests using a population control group will always be less efficient statistically, than those performed with a control group of relatives of probands without the disease under study, the degree of efficiency decreasing with increasing population prevalence of the disease. (2) When factors other than the disease status of a family member are also associated with the disease status of an individual, if this factor is a proband characteristic (which is not shared by relatives) population control groups cannot be adjusted to eliminate possible bias due to the potential confounding effect of this factor (unlike control groups consisting of relatives of probands without the disorder).

The '3 Rs' and neuropsychological function in schizophrenia: a test of the matching fallacy in biological relatives

The 'matching fallacy' suggests that matching schizophrenic patients and normal control subjects on education or IQ may cause systematic mismatching of theoretically expected ability. This study supports a modest version of the matching fallacy effect in nonpsychotic biological relatives of schizophrenic patients. At equivalent levels of education, relatives and control subjects had similar Reading and Spelling scores on the Wide Range Achievement Test-Revised--measures that are largely unimpaired by schizophrenia-related processes. However, relatives showed a deficit in IQ (primarily verbal IQ) compared with what would be predicted from their Reading scores. A similar deficit in Arithmetic scores was found in non-college-educated relatives, but college-educated relatives showed an advantage. We discuss possible implications of the findings with regard to genetic and environmental factors.

Affective illness in family members and matched controls

As part of the US National Institute of Mental Health Collaborative Program on the Psychobiology of Depression study, a subset of 460 randomly chosen relatives of affectively ill probands were compared to a control group matched by the acquaintanceship method. The rate of major affective disorder in relatives was found to be 36%; the rate among controls was 28%. Relatives were also found to have significantly higher rates of bipolar II disorder, any Research Diagnostic Criteria (RDC) affective disorder and any RDC mental disorder. All of these rates were found to be significantly higher when female relatives were compared with their acquaintances, but only the rate of any RDC mental disorder was higher when this comparison was made in men. The acquaintanceship method enabled the selection of a control group that closely resembled the relatives, probably to the extent of "overmatching". When the match was evaluated to determine whether relatives tended to select comparably ill (or well) acquaintances, this was found to be the case only for alcoholic and never mentally ill relatives.

Schizotypal and paranoid personality disorder in the relatives of patients with schizophrenia and affective disorders: a review

This review considers the possible familial relationship of schizotypal and paranoid personality disorders (SPD, PPD) to schizophrenia (SCZ) and affective disorders (AD). There have been few controlled studies on familial risk of SPD and PPD based on direct semi-structured interviews of relatives, blind to proband diagnosis. Three of six studies reported increased familial risk of SPD for SCZ probands, but with considerable variability in estimates of this risk. None of four studies reported a significant relationship between AD and familial SPD. There is substantial but less consistent evidence for a familial relationship between PPD and SCZ: three of six studies supported such a relationship, but one large study reported increased familial risk of PPD for AD and not for SCZ probands. There is also some evidence that negative symptoms are most characteristic of SPD in relatives of SCZ probands. Also discussed are issues concerning the adequacy of current criteria for defining schizophrenia spectrum pathology, and of diagnostic methods in this area.

Psychiatric morbidity in the first-degree relatives of schizophrenic patients

First-degree relatives (FDRs) of 162 schizophrenic and 106 control probands were investigated [corrected]. Psychiatric morbidity was present in 34.8% of FDRs of schizophrenic probands and in 9.2% of FDRs of controls. There was significantly more psychiatric illness in the siblings and parents than in the offspring of both schizophrenic and control subjects. The morbidity risks for schizoid-schizotypal personality disorders, cannabis-use disorder and paranoid personality disorder were significantly higher in the FDRs of schizophrenic patients than in those of controls, suggesting a biological relationship.

The distinction of bipolar II disorder from bipolar I and recurrent unipolar depression: results of a controlled family study

The aim of the study was to differentiate bipolar II, bipolar I and recurrent unipolar depression by their familial load for affective disorders. Eighty bipolar, 108 unipolar, 80 control subjects and interviewed first-degree relatives were diagnosed according to Research Diagnostic Criteria using the Schedule for Affective Disorders and Schizophrenia--lifetime version. The morbid risks for bipolar I disorder were equivalent in relatives of bipolar I (3.6%) and bipolar II (3.5%) subjects and lower in relatives of unipolar subjects (1.0%). The morbid risks of relatives for bipolar II disorder distinguished bipolar II subjects (6.1%) from bipolar I subjects (1.8%), from unipolar depressives (0.3%) and from controls (0.5%). To promote further evaluation, bipolar II disorder should be included in DSM-IV as a distinct diagnostic category.

An extension of the acquaintanceship procedure in family studies of mental disorder

The acquaintanceship procedure is a method for obtaining a control group matched to relatives of probands on demographic variables. Relatives are asked to name six acquaintances who are the same gender, and who are about the same age and social class as themselves. An acquaintance is randomly selected from this list and contacted for recruitment. Rates of mental disorder in this group are assumed to approximate general population rates in a group with these demographic characteristics. This report focuses on an extension of the acquaintanceship procedure in which "super-normal" controls are used in a family study design. Two questions were addressed: (1) Does the acquaintance group (n = 166), as a whole, show a higher rate of illness than the relatives of acquaintances with no mental disorder (n = 129)? (2) Is there a relationship between mental disorder in acquaintances and in providers of acquaintance names? The prevalence of mental illness was significantly greater among acquaintances compared to relatives of "never ill" acquaintances. There was no evidence of assortative selection. We concluded that using the relatives of well acquaintances is a cost-effective control selection methodology which maximizes the detection of intergenerational transmission in family studies of mental disorder.

Determinants of expressed emotion in families of disturbed and normal children

Both high expressed emotion (EE) and psychiatric disorders were frequent in the parents of children and adolescents with disruptive behavior disorder (DBD, N = 34) and obsessive compulsive disorder (OCD, N = 49) compared to normal controls (NC, N = 41). Parental psychiatric diagnosis was significantly related to high-EE in fathers (p = .0002) and mothers (p = .0001) of all groups combined, and in parents of the ill groups (p = .03). Absence of diagnosis was associated with low-EE in fathers (p = .0006) and mothers (p = .04) of the controls. Psychiatric diagnosis was the only significant predictor for high-EE in fathers, while for mothers child's diagnosis was a stronger predictor.

Current perspectives on the genetics of unipolar depression

Evidence regarding the heritability of unipolar depression is evaluated. The data reviewed here support the involvement of genetic factors in the etiology of unipolar depression and its suitability for independent genetic inquiry, despite our inability to identify the mode(s) of transmission or identify a candidate locus. Continued progress in testing etiologic hypotheses requires (a) clarification of the mode of transmission; (b) resolution of phenotypic and potential genotypic heterogeneity; (c) general agreement on a "gold standard" for assessment of the unipolar phenotype; (d) the continued application of available quantitative methods to take into account the effects of ascertainment bias, sex effects, cohort effects, and variable/late age at onset; and (e) incorporation of quantitative indicators correlated with liability in multivariate analysis to improve the stability/validity of phenotypic determinations in segregation and linkage analysis. We present several recommendations regarding the extension of current methodologies in human population and quantitative genetics to help resolve these issues.