Effects of misclassification on estimates of relative risk in family history studies

Two types of misclassification that commonly occur in family-genetic studies are distinguished: 1) nondifferential misclassification, in which the probability of error as to phenotype (presence or absence of psychiatric disorder) does not depend on exposure status (being kin to a case or control proband) and 2) differential misclassification, in which it does. Nondifferential misclassification of phenotype reduces the observed relative risk towards the null value, sometimes quite dramatically. Differential misclassification can bias the observed relative risk in either direction, depending on the different values of sensitivity and specificity among relatives of cases and controls. The impact of these biases on genetic-epidemiologic studies is reviewed and discussed. In particular, the ability to detect major gene effects from the pattern of relative risks in first-, second-, and third-degree relatives can be severely compromised. Although there are some methods available to correct the effects of nondifferential misclassification, a major priority for family history studies is to minimize differential misclassification.

High functioning autism and Childhood Disintegrative Disorder in half brothers

Childhood Disintegrative Disorder (CDD) is grouped with autism as a subtype of Pervasive Developmental Disorder (PDD) in ICD-10 and DSM-IV. This is the first report of autism and CDD cosegregating within a sibship. J. P. and M. P. are half-brothers with the same mother. J. P. is an 18-year-old with impairments in communication, social reciprocity, and stereotypies and was diagnosed with autism. M. P. is a 7-year-old who developed normally to 2 years 4 months. He then underwent a profound regression, becoming nonverbal and socially withdrawn, and lost adaptive skills. Investigations did not reveal any neurodegenerative process. M. P. was diagnosed with CDD. The rarity of the two conditions suggests a shared transmissible mechanism. The implications for autism/PDD genetic studies are discussed.

Ring chromosome 22 and autism: report and review

Ring chromosome 22 has been described in over 50 cases. A characteristic phenotype has not been fully delineated; however, long face, thick eyebrows, 2-3 toe syndactyly, mental retardation, adequate somatic growth and the absence of major malformations are noted in many cases. An 11-year-old boy with ring chromosome 22 and 46,XY,r(22)(p11.31-q13.31 approximately q13.33) karyotype presented with global developmental delay, autistic disorder, and dolichocephaly, apparently low-set and large ears, midface hypoplasia, and 2-3 toe syndactyly. This is the second report of a ring chromosome 22 with autistic disorder. There appears to be an association between abnormalities of chromosome 22, including r(22), and autistic disorder; however, this occurrence may be a result of the association of autistic disorder with mental retardation rather than specifically due to r(22). The physical findings in this case also suggest that ring chromosome 22 causes a subtle but distinct phenotype which has previously been proposed.

Evidence of linkage in subtypes of alcoholism

We believed that subtyping alcoholism might be an efficient strategy for mapping susceptibility genes. Cluster analysis is one of the possible statistical techniques for such a purpose. We required that, ideally, the variables to be used in cluster analysis should be: 1) related to alcoholism, 2) related to the severity of alcoholism, and 3) familial, i.e., correlated within families. Only three variables met all three conditions. Those included age of onset of ALDX1, smoking, and TPQ-HA. A global score of symptoms of alcoholism was systematically introduced as one of the variables composing a subset for cluster analysis, although this score did not show any familial aggregation. Our strategy led to a strong evidence of linkage at D15S230 in only 20 families whose members are mainly characterized by heavy smoking.

Imaging of autism: lessons from the past to guide studies in the future

OBJECTIVE

To review the scientific literature on the imaging of autism with a view to understanding how imaging can contribute to future studies.

METHODS

Medline was searched, and bibliographies from retrieved articles were reviewed. Inclusion criteria were a diagnosis of autism according to Diagnostic and Statistical Manual of Mental Disorders (DSM) criteria, third edition or later, and a control group without autism.

RESULTS

The field suffers from a lack of replication studies and poor methodology in terms of not controlling for confounding variables. Enlarged brain size, particularly in the temporoparietal brain region, and decreased size of the posterior corpus callosum are the only findings that have been independently replicated.

CONCLUSION

Future imaging studies should attempt to investigate more homogeneous subgroups of patients such as those with "the lesser variant of PDD" and high-functioning patients with PDD who do not have comorbid medical conditions. A different approach, examining the individual behaviours that constitute the PDD spectrum and exploring these separately along with other associated variables such as neuropsychological deficits, structural and functional brain abnormalities, and genetic information could help identify biological mechanisms that do not follow diagnostic boundaries.

Age-of-onset classification of conduct disorder: reliability and validity in a prospective cohort study

OBJECTIVE

To test in a prospective clinical cohort study the reliability and validity of the age-of-onset subtyping of conduct disorder.

METHOD

Participants were adolescents referred to psychiatric clinics who met DSM-III-R criteria for conduct disorder by structured diagnostic interview. Age of onset was the reported age of the first conduct disorder symptom. The reliability of age-of-onset report was tested by assessing agreement within informant on interviews 2 to 4 weeks apart. Age-of-onset groups were compared within informant on rates of correlates and symptom and social functioning outcomes over a period of 3 years.

RESULTS

The reliability of age-of-onset report was low (kappa of 0.1 and 0.4 by adolescent and parent informant, respectively). Although the early-onset group had elevated rates of attention-deficit/hyperactivity disorder, family disadvantage, and aggressive and nonaggressive antisocial behaviors at inclusion, growth curve analysis showed that age-of-onset subtyping had no predictive validity.

CONCLUSIONS

The reliability of ascertainment of age of onset of antisocial behavior requires further study. While age-of-onset subtyping has heuristic value with respect to the study of the causal pathways to conduct disorder, it is premature to use this system in clinic settings.

Familial factors influence level of functioning in pervasive developmental disorder

OBJECTIVE

To determine whether siblings with pervasive developmental disorders (PDD) tend to have the same type and number of PDD symptoms or a similar level of functioning.

METHOD

The familial correlations for PDD subtype, symptom totals, adaptive behaviors, and nonverbal IQ were calculated for 94 children with PDD from 46 families.

RESULTS

On variables measuring PDD symptoms, only impairments in nonverbal communication and verbal/nonverbal status tended to run true within families. There was no familial aggregation of PDD subtype. In contrast, measures of nonverbal IQ and adaptive behaviors in socialization and communication showed a moderate degree of familial resemblance. The degree of familial resemblance did not change if the analysis was restricted only to those families in which both affected children met criteria for autism.

CONCLUSION

Insofar as the familial resemblance seen in PDD is due to genetic factors, these data provide some evidence that higher- and lower-functioning PDD children may arise from separate genetic mechanisms. Current gene-mapping studies of PDD may need to take this evidence of genetic heterogeneity into account.

Highly somatizing young adolescents and the risk of depression

OBJECTIVE

To determine if high levels of somatization symptoms in 13- to 16-year-olds from the general population predict risk of major depression and other psychiatric disorders 4 years later.

METHOD

Cohort study, using interview and self-report survey data from the 1983 Ontario Child Health Study (OCHS) and 1987 OCHS Follow-up. The study population included 1015 13- to 16-year-olds from the general community within Ontario. Baseline levels of somatization and emotional disorder were measured by the Survey Diagnostic Instrument, a checklist based on DSM-III criteria. Data were also collected for a range of sociodemographic factors, as well as the presence of chronic health problems. Major depression, anxiety disorders, and substance abuse and dependency at follow-up were measured using a self-administered questionnaire derived from the Diagnostic Interview Schedule. Bivariate and multiple logistic regression techniques were used to assess the relationship between high levels of somatization symptoms (>90th percentile) and later emotional morbidity, with adjustment for potential confounding factors, including gender and baseline disorders.

RESULTS

Highly somatizing adolescents are at increased risk of major depression 4 years later, an association that is not explained by detectable emotional disorder at baseline or gender differences between groups. There is an important interaction between somatization and emotional disorder in predicting risk of major depression. It is primarily the group of 13- to 16-year-olds not recognized as being emotionally disordered at the initial OCHS survey in which somatization symptoms increased risk of later depression. The young teen with high levels of somatic complaints had as much risk of later depression as his/her peer with more typical symptoms of emotional disorder. Highly somatizing adolescents were also more likely to describe panic attacks at 4-year follow-up. There was no increased risk of substance abuse/dependency in the highly somatizing group or in generalized anxiety.

CONCLUSIONS

High levels of somatic symptoms identified in young adolescents in the community represent a significant risk factor for major depression 4 years later, particularly in those individuals who do not present with more typical symptoms of emotional disorder. To detect the emergence of this serious emotional morbidity, adequate follow-up and continuity of care for these challenging patients are needed.

Heterogeneity and the genetics of autism

The objective of this review is to summarize recent data on the genetics of autism, highlight the evidence for genetic heterogeneity and extend the implications of these findings for the identification of susceptibility genes in this disorder. Family studies have shown that autism runs in families and twin studies indicate that the basis of that familial aggregation is genetic. As a result the prospects for the identification of susceptibility genes using either linkage or association studies are quite good. However, recent evidence is accumulating suggesting that the disorder is genetically heterogeneous; higher functioning individuals with autism may arise from separate genetic mechanisms that lower functioning ones. If true, this will make the detection of linkage and association much more difficult.

Influence of parental concordance for psychiatric disorders on psychopathology in offspring

OBJECTIVE

To examine the influence of parental mating types for substance abuse and anxiety/affective disorders on the risk of psychopathology among child and adolescent offspring.

METHOD

Emotional and behavioral disorders were assessed in offspring, aged 7 to 17 years, of male and female parents who served as probands from a family study of comorbidity of substance abuse and anxiety disorders.

RESULTS

The findings indicated that (1) patterns of psychopathology among offspring were similar for mothers and fathers; (2) spouse concordance for psychopathology was greater among parents with substance abuse than among those with anxiety, particularly among female substance abusers; (3) there was a direct relationship between the number of affected parents and the magnitude of psychopathology in children, particularly with respect to the anxiety disorders; and (4) by contrast, rates of conduct disorder were elevated only among offspring of dually affected parents, irrespective of the specific parental disorders.

CONCLUSIONS

These findings underscore the importance of the contribution of both mothers and fathers, particularly those with concordance for psychiatric disorders, to the development of psychopathology in offspring.

Genetics of autism: overview and new directions

Genetic epidemiology is the study of inherited factors involved in the etiology of a disease or disorder and uses the methods of both medical genetics and clinical epidemiology. In general, genetic epidemiology tries to answer the following four questions: Is the disorder inherited; What phenotype is inherited; How is it inherited or what is the mode of transmission; and What is the nature of the genetic mutation, if any, that gives rise to the disorder? The hope is that by identifying the gene or genes involved in pathophysiology, a much better understanding of the steps from gene product to phenotype will be possible, leading to improvements in diagnosis, an opportunity for thoughtful family planning, and perhaps, most important, to the development of treatments based on an understanding of the biochemistry of the disorder. We review the current knowledge of the genetic epidemiology of autism and the other pervasive developmental disorders (PDDs) and highlight promising new directions. There seems to be widespread agreement that the PDDs are caused, at least in part, by genetic factors. There is also some agreement on the phenotypic boundaries associated with these same genetic factors. However, many points of uncertainty remain, and several methodologic issues need to be resolved before further progress in mapping susceptibility genes is possible. We do not specifically review molecular studies, medical conditions associated with autism, or the broader autism phenotype, as these topics are covered in other papers in this special issue.

Psychopathology among offspring of parents with substance abuse and/or anxiety disorders: a high-risk study

This paper reports the results of a high-risk study of children under age 18 of parents who served as probands in a family study of comorbidity of substance abuse and anxiety disorders. There was a strong degree of specificity of familial aggregation of both the anxiety disorders and substance disorders. Rates of conduct disorder and depression were elevated among offspring of all affected parents. Inclusion of co-parent disorders in the evaluation of familial transmission in the present study strengthened the findings regarding the specificity of transmission of the anxiety disorders and the links between both parental substance abuse and antisocial personality with child conduct disorder.

Reliability and accuracy of differentiating pervasive developmental disorder subtypes

OBJECTIVE

To evaluate the ability of the DSM-IV criteria for the pervasive developmental disorders (PDD) to reliably and accurately differentiate PDD subtypes.

METHOD

The sample consisted of 143 children with various types of developmental disabilities. A diagnosis of PDD and PDD subtype was made by one clinician using information obtained from the Autism Diagnostic Interview-Revised and the Autism Diagnostic Observation Schedule. The raw data from the Autism Diagnostic Interview-Revised, clinical notes (excluding diagnostic opinion), Autism Diagnostic Observation Schedule, IQ, and other available data were independently assessed by three experienced raters, each of whom then made a separate, blind diagnosis. If there was any disagreement, a consensus best-estimate (CBE) diagnosis was made after discussion. To assess reliability, the agreement between the three raters was calculated using k. Accuracy was assessed by calculating the agreement between the clinician's diagnosis and the CBE and by calculating the error rates associated with the three raters using latent class analysis.

RESULTS

The current DSM-IV criteria show good to excellent reliability for the diagnosis of PDD, Asperger's disorder (AsD), and autism, but they show poor reliability for the diagnosis of atypical autism. The clinician (compared to the CBE) had little difficulty differentiating PDD from non-PDD children and autism from AsD but had more difficulty identifying children with atypical autism. The latent class analysis also showed that the average error rates of the three raters for a differentiation of atypical autism from autism were unacceptably high.

CONCLUSIONS

Although the psychometric properties of the current DSM-IV criteria for autism and AsD appear quite acceptable, there is likely to be a high rate of misclassification of children given a diagnosis of atypical autism.

Clinical and methodological factors related to reliability of the best-estimate diagnostic procedure

OBJECTIVE

The reliability and accuracy of the best-estimate diagnostic procedure were examined, and factors associated with reliability were determined.

METHOD

The subjects were 134 members of large multigenerational pedigrees densely affected by bipolar disorders or schizophrenia. Three best-estimate diagnoses were derived: first, by a research psychiatrist and research assistant unblind to the relatives' diagnoses; second, by two blind independent psychiatrists; third, by a panel of four blind psychiatrists. The subjects were characterized on several clinical and methodological variables, which were used to compare the agreements of two types of best-estimate diagnoses with the disagreements.

RESULTS

There was satisfactory agreement between the unblind and blind consensus best-estimate diagnoses and between the two blind independent psychiatrists. Latent class analyses revealed that limited sensitivity was the main source of imperfect reliability. Confusability analyses revealed that the most problematic diagnostic distinctions involved schizoaffective disorder, which was confused with schizophrenia, bipolar I disorder, and schizophreniform disorder. Blindness significantly affected diagnostic outcome in latent class analyses. Moreover, for diagnostic disagreements, unblind diagnoses had greater continuity with the most predominant diagnosis in the pedigree than did blind diagnoses. Diagnostic disagreements were associated with the presence of mixed affective and psychotic symptoms, less diagnostic certainty, and shorter duration of illness.

CONCLUSIONS

These results suggest that it is possible to identify cases that are more likely to lead to diagnostic disagreements in family and epidemiological studies and that blind diagnoses may help to prevent false positive diagnoses, which may be particularly detrimental to genetic linkage analyses.

Adequacy of interviews vs checklists for classifying childhood psychiatric disorder based on parent reports

BACKGROUND

The advantages and disadvantages of lay-administered structured interviews and self-administered problem checklists for estimating prevalence and associated features of childhood psychiatric disorder have attracted little comment. This article compares the scientific adequacy of these 2 instruments for classifying DSM-III-R categories of childhood psychiatric disorder in general population samples.

METHODS

Study data are from parental assessments of 251 children aged 6 to 16 years participating in a 2-stage measurement evaluation study. Reliability and validity were compared between the Diagnostic Interview for Children and Adolescents (the structured interview in the study) and the revised Ontario Child Health Study scales (the self-administered problem checklist used in the study).

RESULTS

Reliability estimates based on the kappa statistic were comparable for the 2 instruments and ranged from 0.21 (conduct disorder) to 0.70 (depression) on the lay interview and from 0.17 (depression) to 0.61 (oppositional defiant disorder) on the self-administered checklist. Validity coefficients tended to favor the checklist categories, but only marginally.

CONCLUSIONS

On balance, differences in reliability and validity were small between the 2 instruments. These differences would appear to have no discernible impact on the knowledge about prevalence and associated features of disorder generated by use of such instruments in general population surveys.

The effect of selection criteria on outcome studies of children with pervasive developmental disorders (PDD)

The objective of this paper is to see whether regression to the mean biases the differences on outcome observed between children with Asperger syndrome and autism. Children with pervasive developmental disorders (PDD) and normal nonverbal IQ were divided into those with Asperger syndrome and autism. It was hypothesized that IQ in the autistic children would fall at the 2-year outcome assessments since the autistic group represented a subgroup selected on the basis of extreme scores on a single measure. In fact, the Asperger syndrome group experienced a significant drop in nonverbal IQ contrary to expectation. Serial measurements of nonverbal IQ at inception indicated that this drop was probably a function of high initial nonverbal IQ scores that fall over time due to increasing complexity of problem-solving tests. The results are discussed in relation to outcome studies of high functioning children with PDD.

A high-risk pilot study of the children of adults with social phobia

OBJECTIVE

Children of patients with social phobia were studied to estimate their rates of psychiatric disorder.

METHOD

Twenty-six social-phobic outpatients who had at least one child between the ages of 4 and 18 years participated in the study. Information was collected from parents on all 47 children and from the children between 12 and 18 years of age. Diagnoses in the children were made based on DSM-III-R and were done by a best-estimate method, using parent and child reports from a modified Anxiety Disorders Interview Schedule for Children, the Survey Diagnostic Instrument, the Current Self-Report Childhood Inhibition Scale, and the Alcohol Dependence Survey.

RESULTS

Of the 47 children, 49% had at least one lifetime anxiety disorder diagnosis. The most common diagnoses were overanxious disorder (30%), social phobia (23%), and separation anxiety disorder (19%). Sixty-five percent had more than one anxiety disorder diagnosis. Lifetime major depression was found, in 8.5% of the children. Parents whose children met criteria for an anxiety disorder had a greater mean number of comorbid diagnoses than did the parents of unaffected children.

CONCLUSION

This pilot study suggests that children of social-phobic parents may have increased rates of psychiatric disorder. Further studies incorporating a control group are needed.

Risk and protective factors affecting the adjustment of siblings of children with chronic disabilities

OBJECTIVE

To examine the adjustment of nondisabled siblings of handicapped children.

METHOD

In a 3-year longitudinal study, 46 siblings of children with pervasive developmental disorder (PDD), 45 siblings of children with Down syndrome, and 46 siblings of developmentally normal children (serving as controls) were examined at time 1 using the sibling, primary caretaker, and teacher as informants. Both direct and indirect variables related to sibling adjustment were considered.

RESULTS

Significantly more difficulties were found in the siblings of children with PDD compared with the other two groups. Different correlates of adjustment were present in the siblings of the disabled compared with nondisabled children, and mediating factors differed in parent and teacher reports of internalizing difficulties in siblings of children with PDD. Marital satisfaction, lack of parental depression, a cohesive family, and a warm, nonconflictual sibling relationship were protective for normal control and Down syndrome siblings but not for PDD siblings.

CONCLUSION

Findings underline the risks for the siblings of children with PDD and suggest the importance of a transactional mechanism rather than identification of single risk or protective factors in predicting sibling adjustment. Subsequent data analysis in this longitudinal study will assist in defining these mechanisms and allow for improved intervention strategies.

Identifying thresholds for classifying childhood psychiatric disorder: issues and prospects

OBJECTIVE

To evaluate empirically the implications of choosing different thresholds to classify conduct disorder and attention-deficit hyperactivity disorder for estimating prevalence, test-retest reliability of measurement, and informant (parent/teacher) agreement and for evaluating comorbidity and associated features of disorder.

METHOD

Data for the study came from problem checklist assessments done by parents and teachers of children aged 6 to 16 years (N = 1,229) selected with known probability from a general population sample and from structured interviews obtained in a stratified, random subsample (n = 251).

RESULTS

Estimates varied widely depending on the rationale used to set thresholds. Percent prevalence went from 0.1 to 39.2; kappa estimates of test-retest reliability went from .19 to .82. Parent-teacher agreement based on kappa went from .0 to .38. Relative odds between disorder and associated features varied twofold.

CONCLUSION

Use of different rationales to set thresholds for classifying childhood psychiatric disorder in the general population has profound implications for what we learn about the epidemiology of childhood disorder.