Differences and similarities in the serotonergic diathesis for suicide attempts and mood disorders: a 22-year longitudinal gene-environment study

To investigate similarities and differences in the serotonergic diathesis for mood disorders and suicide attempts, we conducted a study in a cohort followed longitudinally for 22 years. A total of 1255 members of this cohort, which is representative of the French-speaking population of Quebec, were investigated. Main outcome measures included (1) mood disorders (bipolar disorder and major depression) and suicide attempts by early adulthood; (2) odds ratios and probabilities associated with 143 single nucleotide polymorphisms in 11 serotonergic genes, acting directly or as moderators in gene-environment interactions with childhood sexual or childhood physical abuse (CPA), and in gene-gene interactions; (3) regression coefficients for putative endophenotypes for mood disorders (childhood anxiousness) and suicide attempts (childhood disruptiveness). Five genes showed significant adjusted effects (HTR2A, TPH1, HTR5A, SLC6A4 and HTR1A). Of these, HTR2A variation influenced both suicide attempts and mood disorders, although through different mechanisms. In suicide attempts, HTR2A variants (rs6561333, rs7997012 and rs1885884) were involved through interactions with histories of sexual and physical abuse whereas in mood disorders through one main effect (rs9316235). In terms of phenotype-specific contributions, TPH1 variation (rs10488683) was relevant only in the diathesis for suicide attempts. Three genes contributed exclusively to mood disorders, one through a main effect (HTR5A (rs1657268)) and two through gene-environment interactions with CPA (HTR1A (rs878567) and SLC6A4 (rs3794808)). Childhood anxiousness did not mediate the effects of HTR2A and HTR5A on mood disorders, nor did childhood disruptiveness mediate the effects of TPH1 on suicide attempts. Of the serotonergic genes implicated in mood disorders and suicidal behaviors, four exhibited phenotype-specific effects, suggesting that despite their high concordance and common genetic determinants, suicide attempts and mood disorders may also have partially independent etiological pathways. To identify where these pathways diverge, we need to understand the differential, phenotype-specific gene-environment interactions such as the ones observed in the present study, using suitably powered samples.

Clinical diagnoses in young offspring from eastern Québec multigenerational families densely affected by schizophrenia or bipolar disorder

OBJECTIVE

The follow-up since 1989 of a large sample of multigenerational families of eastern Québec that are densely affected by schizophrenia (SZ) or bipolar disorder (BP) has permitted to look at the rates of DSM diagnoses in the young offspring of a SZ parent (HRSZ) and of a BP parent (HRBP) who had an extremely loaded family history.

METHOD

The sample (average age of 17.5, SD 4.5) consisted of 54 high-risk offspring (HR) having one parent affected by a DSM-IV SZ or BP. The parents descended from 21 multigenerational families that constitute a quasi-total sample of such kindred in eastern Québec. The HRs were administered a lifetime best estimate DSM-IV diagnosis.

RESULTS

We observed that the rates, the diversity of diagnoses, the high comorbidity, the severity and the age of onset of the clinical diagnoses tended to be similar with those already reported in the offspring of affected parents with a low familial loading. Although the sample size was small, HRSZ and HRBP also tended to show similarities in their clinical status.

CONCLUSION

Overall, taking into account methodological limitations, the observation early in life of some shared characteristics among HRSZ and HRBP in terms of non-psychotic diagnosis may be congruent with the accumulating evidence that several phenotypic features are shared in adulthood by the two major psychoses.

Possible association of the pro-melanin-concentrating hormone gene with a greater body mass index as a side effect of the antipsychotic olanzapine

Following our report of a linkage at 12q24 with a phenotype of obesity under antipsychotics, we tested the pro-melanin-concentrating hormone (PMCH) candidate gene for a possible association in humans with the body mass index (BMI; kg/m2) in unrelated schizophrenic patients (SZ) receiving antipsychotics (N = 300) and in controls (CTL; N = 150). Subjects were classified in obese (OB) (BMI > or = 30 kg/m2), overweight (25 < or = BMI < 30 kg/m2), and normal weight (BMI < 25 kg/m2) groups. Single nucleotide polymorphisms (SNP) rs7973796 and rs11111201, located 5' at -4.5 kb and 3' at +1.8 kb, respectively, of PMCH were genotyped. Interaction effects of genotypes and antipsychotic treatment on BMI were tested in a covariance analysis with age and gender as covariates. Interaction effects on the prevalence of obesity were tested in a logistic regression analysis. For subjects under 50 years, the effect of the rs7973796 genotype on BMI differed between the SZ patients taking olanzapine and CTL group (interaction P = 0.025). Olanzapine-treated SZ patients carrying the ancestral homozygote genotype showed a higher BMI for rs7973796 (P = 0.016 with the LSMeans t-test) than the variant homozygotes. Accordingly, the ORs for obesity associated with rs7973796 genotypes differed in the SZ patients taking olanzapine compared to the CTL group (interaction P = 0.0094). The G allele was associated with an increase in the odds of obesity in SZ patients taking olanzapine. No association was observed for those over 50 years, or for rs11111201. These results suggest that the common allele of PMCH rs7973796 may be associated with a greater BMI in olanzapine-treated SZ patients.

Epidemiology of insomnia: prevalence, self-help treatments, consultations, and determinants of help-seeking behaviors

BACKGROUND AND PURPOSE

To estimate the prevalence of insomnia symptoms and syndrome in the general population, describe the types of self-help treatments and consultations initiated for insomnia, and examine help-seeking determinants.

PATIENTS AND METHODS

A randomly selected sample of 2001 French-speaking adults from the province of Quebec (Canada) responded to a telephone survey about sleep, insomnia, and its treatments.

RESULTS

Of the total sample, 25.3% were dissatisfied with their sleep, 29.9% reported insomnia symptoms, and 9.5% met criteria for an insomnia syndrome. Thirteen percent of the respondents had consulted a healthcare provider specifically for insomnia in their lifetime, with general practitioners being the most frequently consulted. Daytime fatigue (48%), psychological distress (40%), and physical discomfort (22%) were the main determinants prompting individuals with insomnia to seek treatment. Of the total sample, 15% had used at least once herbal/dietary products to facilitate sleep and 11% had used prescribed sleep medications in the year preceding the survey. Other self-help strategies employed to facilitate sleep included reading, listening to music, and relaxation.

CONCLUSIONS

These findings confirm the high prevalence of insomnia in the general population. While few insomnia sufferers seek professional consultations, many individuals initiate self-help treatments, particularly when daytime impairments such as fatigue become more noticeable. Improved knowledge of the determinants of help-seeking behaviors could guide the development of effective public health prevention and intervention programs to promote healthy sleep.

Shared and specific susceptibility loci for schizophrenia and bipolar disorder: a dense genome scan in Eastern Quebec families

The goal of this study was to identify susceptibility loci shared by schizophrenia (SZ) and bipolar disorder (BP), or specific to each. To this end, we performed a dense genome scan in a first sample of 21 multigenerational families of Eastern Quebec affected by SZ, BP or both (N=480 family members). This probably constitutes the first genome scan of SZ and BP that used the same ascertainment, statistical and molecular methods for the concurrent study of the two disorders. We genotyped 607 microsatellite markers of which 350 were spaced by 10 cM and 257 others were follow-up markers in positive regions at the 10 cM scan. Lander and Kruglyak thresholds were conservatively adjusted for multiple testings. We maximized the lod scores (mod score) over eight combinations (2 phenotype severity levels x 2 models of transmission x 2 analyses, affected/unaffected vs affected-only). We observed five genomewide significant linkages with mod score >4.0: three for BP (15q11.1, 16p12.3, 18q12-q21) and two for the shared phenotype, that is, the common locus (CL) phenotype (15q26,18q12-q21). Nine mod scores exceeded the suggestive threshold of 2.6: three for BP (3q21, 10p13, 12q23), three for SZ (6p22, 13q13, 18q21) and three for the CL phenotype (2q12.3, 13q14, 16p13). Mod scores >1.9 might represent confirmatory linkages of formerly reported genomewide significant findings such as our finding in 6p22.3 for SZ. Several regions appeared to be shared by SZ and BP. One linkage signal (15q26) appeared novel, whereas others overlapped formerly reported susceptibility regions. Despite the methodological limitations we raised, our data support the following trends: (i) results from several genome scans of SZ and BP in different populations tend to converge in specific genomic regions and (ii) some of these susceptibility regions may be shared by SZ and BP, whereas others may be specific to each. The present results support the relevance of investigating concurrently SZ and BP within the same study and have implications for the modelling of genetic effects.

A genome wide linkage study of obesity as secondary effect of antipsychotics in multigenerational families of eastern Quebec affected by psychoses

Antipsychotics can induce in schizophrenic (SZ) and bipolar disorder (BP) patients serious body weight changes that increase risk for noncompliance to medication, and risk for cardiovascular diseases and diabetes. A genetic origin for this susceptibility to weight changes has been hypothesized because only a proportion of treated patients are affected, the degree of affection differing also in rates and magnitudes. In a first genome scan on obesity under antipsychotics in SZ and BP, we analyzed 21 multigenerational kindreds (508 family members) including several patients treated for a minimum of 3 years mainly with haloperidol or chlopromazine. Obesity was defined from medical files and was shown to be 2.5 times more frequent in patients treated with antipsychotics than in untreated family members (30 vs 12%). The nine pedigrees that showed at least two occurrences of obesity under antipsychotics were submitted to model-based linkage analyses. We observed a suggestive linkage with a multipoint Lod score (MLS) of 2.74 at 12q24. This linkage finding vanished when we used as phenotypes, obesity unrelated to antipsychotics, and when we used SZ or BP. This suggests that this positive linkage result with obesity is specific to the use of antipsychotics. A potential candidate gene for this linkage is the pro-melanin-concentrating hormone (PMCH) gene located at less then 1 cM of the linkage. PMCH encodes a neuropeptide involved in the control of food intake, energy expenditure, and in anxiety/depression. This first genome scan targeting the obesity side effect of antipsychotics identified 12q24 as a susceptibility region.

A search for specific and common susceptibility loci for schizophrenia and bipolar disorder: a linkage study in 13 target chromosomes

We report the first stage of a genome scan of schizophrenia (SZ) and bipolar disorder (BP) covering 18 candidate chromosomal areas. In addition to testing susceptibility loci that are specific to each disorder, we tested the hypothesis that some susceptibility loci might be common to both disorders. A total of 480 individuals from 21 multigenerational pedigrees of Eastern Québec were evaluated by means of a consensus best-estimate diagnosis made blind to diagnoses in relatives and were genotyped with 220 microsatellite markers. Two-point and multipoint model-based linkage analyses were performed and mod scores (Z, for max Z(max)) are reported. The strongest linkage signals were detected at D18S1145 (in 18q12; Z = 4.03) for BP, and at D6S334 (in 6p 22-24; Z(het) = 3.47; alpha = 0.66) for SZ. Three other chromosomal areas (3q, 10p, and 21q) yielded linkage signals. Chromosomes 3p, 4p, 5p, 5q, 6q, 8p, 9q, 11q, 11p, 12q, 13q, 18p and 22q showed no evidence of linkage. The 18q12 results met the Lander and Kruglyak (1995) criterion for a genome-wide significant linkage and suggested that this susceptibility region may be shared by SZ and BP. The 6p finding provided confirmatory evidence of linkage for SZ. Our results suggest that both specific and common susceptibility loci must be searched for SZ and BP.

Subtyping schizophrenia according to outcome or severity: a search for homogeneous subgroups

There is a growing consensus that current definitions of schizophrenia (SZ) include different disorders, or else different dimensions underlain by different pathophysiologies. This article reviews the evidence for the validity of three novel strategies to subtype SZ according to outcome or severity (deficit vs. nondeficit, Kraepelinian vs. non-Kraepelinian, congenital vs. adult-onset). Medline and bibliographies were used to locate articles. The methodology of the studies was reviewed, and their results were grouped according to seven validating criteria. Several differences were found between subtypes, particularly for the deficit/nondeficit subtypes. However, for most of these differences, replications have yet to be undertaken. Important indicators of etiology from the environmental risk factors and genetic domains have received very little attention. These three subtyping strategies represent promising attempts to address the etiologic heterogeneity of SZ. However, one cannot conclude whether these strategies identify etiologically distinct SZ subgroups. We propose ten methodological and conceptual recommendations for future studies aimed at the identification of valid SZ subtypes according to outcome or severity.

Male gender is associated with deficit schizophrenia: a meta-analysis

An association between deficit schizophrenia and male gender could be expected, since male schizophrenic subjects have been repeatedly found more severe than females on several dimensions of severity. Surprisingly, very few studies have confirmed such an association. We performed a more definitive test of this association using a meta-analysis. A pooled odds ratio was computed based on the 23 studies that reported the gender ratio in deficit vs. non-deficit schizophrenia. We tested for the heterogeneity of the association and examined the potential impact of the sampling method, the method used to assess the deficit syndrome, the breadth of diagnoses included and the mean duration of illness. A highly significant association between male gender and deficit schizophrenia was observed (pooled odds ratio=1.75). There was no definitive evidence that differences across studies in sampling methods, breadth of diagnoses included, mean duration of illness and methods to assess the deficit syndrome affected the strength of the association. However, the studies using the "Proxy Deficit Syndrome" method to assess the deficit syndrome yielded qualitatively weaker evidence. This significant association between male gender and deficit schizophrenia may reflect the influence of a gender related factor (e.g. sexual hormones) or gender differences in the liability to different etiologies of schizophrenia. The role of gender as a potential confounder must be closely examined in studies comparing deficit and non-deficit SZ.

Ascertainment and anticipation in family studies

Many human diseases show anticipation; that is, disease occurs earlier (or with greater severity) in successive generations. In a computer simulation, we assessed the degree of anticipation that one would expect to see in two-generation breast cancer families. Under reasonable assumed distributions for age at cancer onset, number of children, and mortality, we find a consistent earlier mean age at diagnosis in daughters than in mothers, but the same mean age at diagnosis in affected aunts and nieces. We compare these results with published pedigree data for familial breast cancer that show substantial anticipation in affected daughters compared to their mothers. We find that at least some anticipation is expected in human disease families even when the disease is stable and families are ascertained without obvious sampling bias. We further demonstrate that such anticipation is reduced when comparing affected children to the parents' affected siblings.

[Introduction to genetic psychiatry: progress in uncovering genetic susceptibility to psychiatric disorders]

The recent progress in human genetics suggests major benefits in clinical practice, including psychiatry. This article introduces the research methodology used in psychiatric genetics and explains how it is applied, for a better understanding of the challenges facing psychiatric genetics and the strategies being used to overcome them. We will review the evidence of genetic factors in psychiatric disorder etiology as well as the specificity or non-specificity of their expression. We will discuss problems associated with the approximate nature of diagnostic methods, the incomplete penetrance and the genetic heterogeneity of psychiatric disorders, the presence of phenocopies and our uncertainty concerning the mode of inheritance of psychiatric disorders. Finally, we will provide an overview of the most promising results and set out priorities for future studies.

Prolongation of brainstem auditory-evoked responses in autistic probands and their unaffected relatives

BACKGROUND

Brain function, as indexed by brain electrical activity, is heritable in humans, and it may be impaired in autism. Autism also has strong genetic determinants, and like all major psychiatric disorders, its complex clinical phenotype renders genetic studies difficult. Innovative strategies focused on alternative biological phenotypes are needed.

METHODS

The early brain auditory-evoked response was assessed in 73 autistic probands and 251 relatives who were compared with 521 normal controls.

RESULTS

We first confirmed in the autistic probands the presence of a slowing in nerve conduction in the auditory system as expressed by the prolongation of early brain auditory-evoked response under the form of I-III interpeak latencies (IPLs). Furthermore, we observed the same I-III IPL prolongation in the unaffected first degree relatives of the autistic probands compared with controls. Despite clear evidence of a coaggregation of autism and I-III IPL prolongation in families, the IPLs did not seem to be the sole liability factor for autism as suggested by the observation of 52% of families in which the autistic proband and relatives showed normal IPLs.

CONCLUSION

A prolongation of the early brain auditory-evoked response IPLs may be a marker for one of several deficits underlying autism and deserves further analysis as a potential alternative phenotype for the disorder.

Significant linkage for Tourette syndrome in a large French Canadian family

Family and twin studies provide strong evidence that genetic factors are involved in the transmission of Gilles de la Tourette syndrome (TS) and related psychiatric disorders. To detect the underlying susceptibility gene(s) for TS, we performed linkage analysis in one large French Canadian family (127 members) from the Charlevoix region, in which 20 family members were definitely affected by TS and 20 others showed related tic disorders. Using model-based linkage analysis, we observed a LOD score of 3.24 on chromosome 11 (11q23). This result was obtained in a multipoint approach involving marker D11S1377, the marker for which significant linkage disequilibrium with TS recently has been detected in an Afrikaner population. Altogether, 25 markers were studied, and, for level of significance, we derived a criterion that took into account the multiple testing arising from the use of three phenotype definitions and three modes of inheritance, a procedure that yielded a LOD score of 3.18. Hence, even after adjustment for multiple testing, the present study shows statistically significant evidence for genetic linkage with TS.

Longitudinal comparative study of risperidone and conventional neuroleptics for treating patients with schizophrenia. The Quebec Schizophrenia Study Group

This study compared the long-term (12 months) effectiveness of risperidone (RP) with that of conventional neuroleptics (CNs) in a population with chronic schizophrenia who had shown suboptimal response to CNs. A randomized, open, parallel, multicenter design was used. One hundred eighty-four subjects meeting DSM-IV criteria for schizophrenia were randomly assigned to receive either RP or a CN, and 165 of them completed the follow-up. Outcome measures were taken at 3, 6, and 12 months and included the Positive and Negative Syndrome Scale (PANSS) and the Extrapyramidal Symptom Rating Scale. Within this 12-month follow-up, RP was found to be superior to CNs in terms of both the average change in score from baseline on the PANSS (p = 0.006) and the proportion of good responders (as defined by a 20% decrease in total PANSS scores;p = 0.03). For positive symptoms, the effectiveness of the RP treatment tended to increase over time. At 12 months, the percentage of good responders in the RP group was twice as large as that in the CN group (30% vs. 15%;p = 0.03). The superiority of RP over CNs was constant over the three dose categories. In both the RP and the CN groups, the maximum decrease in psychopathology was achieved with the lowest dose range. A worsening of akathisia was less frequent in subjects receiving RP than in those receiving CNs (p = 0.02). In conclusion, this study showed that, compared with CNs, RP is beneficial in the treatment of patients with chronic schizophrenia and that some of these benefits may appear only after longer-term treatment.

Anticipation in schizophrenia and bipolar disorder controlling for an information bias

Anticipation was investigated in schizophrenia (SZ) and bipolar disorder (BP) while addressing several biases in 18 large families (154 subjects) from Eastern Québec densely affected by SZ, BP, or both over three generations. In particular, we controlled for an information bias using a measure of quality and quantity of clinical information (QOI) concerning the subjects' illness. Otherwise, spurious anticipation could have arisen because we found that QOI varied with the generations as well as with the severity of illness. Although anticipation was investigated separately for SZ and BP, both disorders were also included in one analysis that tested anticipation under the unitary hypothesis that the SZ and the BP spectrums represent a continuum of severity of the same disease. Age of onset (AOO) and five indices of severity were tested for anticipation. Two statistics were used: the difference in the mean AOO or severity between two successive generations, and the mean difference in parent-offspring pairs (POP). The study led to four main findings: 1) the choice of the statistics greatly influenced the results, POP yielding systematically greater biased estimates; 2) for SZ and BP, the evidence for anticipation with the five severity indices vanished after controlling for QOI; 3) as regards AOO a decrease of 8.6 years, p = 0.0001, and 5.3 years, p = 0.009 in AOO was found for SZ between Generations 1-2, and 2-3, respectively, despite controlling for QOI and addressing all biases; and 4) conversely for BP, anticipation with AOO may be due to censoring. Findings suggest that future anticipation studies should also control for QOI. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:61-68, 2000.

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.

Exploring the impact of extended phenotype in stratified samples

We have performed initial nonparametric sib-pair genome scans in the early (N = 52) and late (N = 53) onset subgroups of the COGA pedigrees, stratified near the median value of pedigree mean age of onset for ALDX1 diagnosis of alcoholism. Because the early group contained a higher proportion of smokers, traits of alcoholism, smoking, and addiction (defined as either alcoholism or smoking) were examined. Subgroups and phenotypic definitions influenced initial linkage results, corrected for the number of analyzed traits. Evidence for linkage to the ALDX1 alcoholism phenotype at the ADH3 functional candidate gene was increased in the late onset subgroup (Bonferroni corrected significance level < 0.002), as compared with the unstratified sample that replicated COGA linkage obtained in the same analysis; there was no evidence for linkage at this locus in the early onset subgroup. The theoretical implication of this result is that the loss of power due to contracting sample size through stratification may in some cases be more than offset by extraction of a more homogeneous subgroup from the etiologically complex trait.

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.

6p24-22 region and major psychoses in the Eastern Quebec population. Le Groupe IREP

Recent reports of a linkage trend in 6p24-22 for schizophrenia (SZ), in different samples, were tempered by the concurrent evidence of negative reports in other samples. In the studies showing positive results, different definitions of affection and a wide spectrum of diagnoses were used. Our objectives were not only to test for linkage at 6p24-22 in the Eastern Quebec population, but also to test whether this putative vulnerability locus was either selectively linked to schizophrenia (SZ), or to bipolar disorder (BP), or to both major psychoses. Parametric and nonparametric linkage analyses with 12 microsatellite markers in 6p24-p22 were performed on a sample of 18 large multigenerational pedigrees (N = 354) either affected by SZ, or by BP, or equally affected by both major psychoses (i.e., mixed pedigrees). Three affection definitions were usually tested in our program: one on schizophrenia (SZ), one on bipolar disorder (BP), and one that comprised SZ and BP under the hypothesis of a susceptibility locus common to both in major psychoses (common locus, CL). The results of parametric analyses did not support a major gene hypothesis. However, in one large mixed pedigree (#151), we observed with the common locus phenotype (CL) lod scores of 2.49 and 2.15, respectively, at the D6S296 and D6S277 loci under a dominant model. Our data suggest the presence of a potential vulnerability locus at 6p24-22 that could be related to both schizophrenia and bipolar affective disorder. These results may be seen as congruent with former studies that used schizoaffective as well as schizophrenia diagnoses as entry criteria for the affected families, and used an affection definition that comprised affective psychoses as well as schizophrenia.

Family history of cognitive disabilities in first-degree relatives of autistic and mentally retarded children

We compared with a family history method the rate of cognitive disabilities (CD) in 156 first-degree relatives of 49 autistic (AU) probands to that found in 55 first-degree relatives of 18 mentally retarded (MR) probands. Broadly defined CD were found in, respectively, 17 and 16% of the relatives of the AU and MR probands. However, the characteristics of the probands associated with a family history of CD are different in AU and MR: Female and low IQ AU probands have more first-degree relatives with CD. Our findings suggest that a positive family history of CD is not specific to autism when compared to mental retardation. The observation that female and low IQ probands have higher family history of CD may suggest heterogeneity within autistic children and provides leads for future family studies.

Childhood/early adolescence-onset and adult-onset schizophrenia. Heterogeneity at the dopamine D3 receptor gene

BACKGROUND

The dopamine D3 receptor gene (DRD3) is a meaningful candidate gene because it unifies the dopamine and the limbic hypotheses for schizophrenia. We tested for an allelic association between schizophrenia and the DRD3 Mscl alleles, hypothesising heterogeneity between childhood/early adolescence-onset schizophrenia (CO-SZ) and adult-onset schizophrenia (A-SZ).

METHOD

The frequencies of the DRD3 alleles were compared between 70 DSM-III-R schizophrenics (35 CO-SZ and 35 A-SZ) and 79 controls.

RESULTS

Compared with the controls, the subsample of A-SZ, but not CO-SZ, showed an over-proportion (P = 0.025) of allele 1. The association was not found in the total sample, combining the two subsamples.

CONCLUSIONS

Consistently with former studies, our data suggest an aetiological heterogeneity between CO-SZ and A-SZ and a possible specificity of the excess of allele 1 to the familial form of schizophrenia and to schizophrenia with a better outcome.

Long-term stability of diagnosis and symptom dimensions in a systematic sample of patients with onset of schizophrenia in childhood and early adolescence. II: Postnegative distinction and childhood predictors of adult outcome

BACKGROUND

The aim of this study was to verify the presence and stability across life of the positive/negative distinction in early-onset schizophrenia (EO-SZ) through a longitudinal factor analysis of the schizophrenic dimensions, and to identify the factors predicting several indices of long-term outcome for EO-SZ.

METHOD

Forty children consecutively referred for DSM-III-R schizophrenia (SZ) in a specific catchment area comprised the sample.

RESULTS

Across a 14.8-year follow-up, longitudinal factor analysis identified two separate factors corresponding to the positive and negative symptom dimensions. We also observed that: the GAS rated over the last three years of adult illness and the severity of negative symptoms during the stabilised interepisode intervals in adulthood were the indices of adult outcome that were most easily predicted; and the best childhood predictors of adult outcome were premorbid functioning and severity of positive and negative symptoms during acute episodes.

CONCLUSIONS

The presence of premorbid non-psychotic behaviour disturbances (NPBD) and premorbid developmental problems was not related to severity of outcome, in contrast to the former variables.

Long-term stability of diagnosis and symptom dimensions in a systematic sample of patients with onset of schizophrenia in childhood and early adolescence. I: nosology, sex and age of onset

BACKGROUND

Little is known about the long-term outcome of schizophrenia that has its onset during childhood and early adolescence (early-onset schizophrenia, or EO-SZ). Whether or not EO-SZ is an aetiologically separate form of schizophrenia (SZ) is unresolved.

METHOD

The study was a 14.8-year follow-up, using methods such as systematic sampling, evaluation of possible non-respondent bias, consensus best-estimate diagnoses (DSM-III-R) made independently in childhood and adulthood, measures of positive and negative dimensions, of non-psychotic behaviour disturbances (NPBD) and of developmental problems before the appearance of SZ.

RESULTS

There was high stability of EO-SZ (n = 40) diagnoses (mean onset at 14.0 years) until adulthood (mean age at follow-up 28.8 years) but a lower stability of positive and negative schizophrenic dimensions. There was a poor outcome of EO-SZ, a strong over-representation of males but few gender differences, and no effect of age of onset on clinical features and outcome.

CONCLUSIONS

EO-SZ taken as a whole shows no qualitative differences to adult-onset SZ. However, a distinction through the onset of preschizophrenic developmental problems or NPBD might be a way to investigate heterogeneity within EO-SZ.

Estimating parental relationship in linkage analysis of recessive traits

In linkage analysis of recessive traits, parental relationship is important. For the case that it is unknown, the question is investigated as to whether estimating parental relationship and using the estimated relationship in linkage analysis is beneficial. Results show that estimating parental relationship can reliably be carried out on the basis of 50-100 genetic marker loci (analysis based on theory by Thompson [1975: Am J Hum Genet 39:173-188]). Misspecification of parental relationship leads to a loss of linkage informativeness, but not to false-positive evidence for linkage. An asymptotic bias in the recombination fraction estimate occurs when parents are unrelated and falsely taken to be related, but no such bias is seen when related parents are taken to be unrelated. Results from this investigation suggest that an estimated parental relationship may be used in linkage analysis as if it were the correct relationship, when evidence for the estimated relationship is supported by a likelihood ratio of at least 10:1 against the parents being unrelated.

Identification and mapping of Mendelian subtypes of disease

We took as our working hypothesis the premise that there could be a single locus of major effect underlying a subset of cases in the simulated Problem 2 data set, and took as our primary goal the task of mapping that locus. Treating the disease as dichotomous and using discriminant function analysis, we were able to separate affected individuals into two disease categories: Disease Type I (DT-I) cases, whose disease was by hypothesis caused by the major locus; and Disease Type II (DT-II) cases, whose disease was by hypothesis produced by other causes. Segregation analysis showed evidence of simple recessive inheritance among the DT-I individuals. Linkage analysis under the best-fitting recessive model gave clear evidence of linkage to D1G2. In the generating model, this marker is linked to a major gene for disease with recombination fraction theta = 0, and the mode of inheritance at that locus is recessive (when the trait is considered as a dichotomy). We conclude that when the true model is complex, focussing on subtypes of disease that show evidence of simple Mendelian inheritance may be a useful first step in determining the underlying model and mapping major genes.

An investigation of genetic heterogeneity and linkage disequilibrium in 161 families with spinal muscular atrophy

We performed linkage analysis of 161 families with spinal muscular atrophy (SMA) in which affected individuals suffer from the intermediate or mild form of the disease (Types II or III). Markers for six loci encompassing the chromosome 5q11.2-q13.3 region were typed. The best map location for the disease locus was found to be between D5S6 and MAP1B. The corresponding 1 lod unit support intervals is confined to this interval and spans 0.5 cM. The data strongly support the hypothesis of linkage heterogeneity (likelihood ratio, 1.14 x 10(4)), with 5% of the families unlinked. Four families have a probability of less than 50% of segregating the SMA gene linked to the region 5q11.2-q13.3. A likelihood approach to test for linkage disequilibrium revealed no significant departure from Hardy-Weinberg equilibrium with any marker under study.

Molecular and statistical approaches to the detection and correction of errors in genotype databases

Errors in genotyping data have been shown to have a significant effect on the estimation of recombination fractions in high-resolution genetic maps. Previous estimates of errors in existing databases have been limited to the analysis of relatively few markers and have suggested rates in the range 0.5%-1.5%. The present study capitalizes on the fact that within the Centre d'Etude du Polymorphisme Humain (CEPH) collection of reference families, 21 individuals are members of more than one family, with separate DNA samples provided by CEPH for each appearance of these individuals. By comparing the genotypes of these individuals in each of the families in which they occur, an estimated error rate of 1.4% was calculated for all loci in the version 4.0 CEPH database. Removing those individuals who were clearly identified by CEPH as appearing in more than one family resulted in a 3.0% error rate for the remaining samples, suggesting that some error checking of the identified repeated individuals may occur prior to data submission. An error rate of 3.0% for version 4.0 data was also obtained for four chromosome 5 markers that were retyped through the entire CEPH collection. The effects of these errors on a multipoint map were significant, with a total sex-averaged length of 36.09 cM with the errors, and 19.47 cM with the errors corrected. Several statistical approaches to detect and allow for errors during linkage analysis are presented. One method, which identified families containing possible errors on the basis of the impact on the maximum lod score, showed particular promise, especially when combined with the limited retyping of the identified families. The impact of the demonstrated error rate in an established genotype database on high-resolution mapping is significant, raising the question of the overall value of incorporating such existing data into new genetic maps.

Assessment of nonallelic genetic heterogeneity of chronic (type II and III) spinal muscular atrophy

We have previously reported the mapping of the chronic (type II/intermediate and type III/mild/Kugelberg-Welander) form of the childhood-onset spinal muscular atrophies (SMA) to chromosome 5q11.2-13.3, with evidence for nonallelic genetic heterogeneity within a small sample of seven families [Brzustowicz et al., Nature 1990;344:540-541]. We now report the results of linkage analysis and heterogeneity testing on a set of 38 families with chronic SMA. Significant evidence for nonallelic heterogeneity was detected among these families, with the predominant locus for chronic SMA mapping to a 0.51-cM region on 5q, between the loci D5S6 and MAP1B. The estimated proportion of linked families, alpha, was 0.91, with a 2.3-unit support interval of 0.75 to 0.98. The indication that some families diagnosed with chronic SMA are not linked to chromosome 5q must be considered in strategies to map the SMA locus. The relevance of these findings to acute SMA (SMA type I, severe, Werdnig-Hoffmann disease) is still unknown.

Two new approaches toward linkage heterogeneity of FAD: two-locus models and age of onset as a discriminator

We present two new approaches to the problem of genetic heterogeneity encountered in linkage analysis of familial Alzheimer's disease. We used two-locus models to represent the possible existence of two disease genes while allowing for intrafamilial heterogeneity, and modeled the occurrence of the early onset form of the disease with epistasis. We developed a mixture model of heterogeneity where the early and late onset family types can be either linked to chromosome 19, 21, or unlinked, and where it is not necessary to arbitrarily preclassify a family into an early or late onset family type.

Reliability of best-estimate diagnosis in genetic linkage studies of major psychoses: results from the Quebec pedigree studies

OBJECTIVE

Diagnostic classification and reliability are critical in genetic linkage studies of schizophrenia and bipolar disorder. To establish an optimal diagnostic procedure, the authors drew 13 methodological elements from 38 major linkage studies and workshop reports. They determined reliability for a consensus best-estimate diagnostic method based on these 13 features.

METHOD

Each of 59 subjects from several large multiplex pedigrees, densely affected by either schizophrenia or bipolar disorder, received a best-estimate diagnosis from unblind diagnosticians in the field and also from a panel of four research psychiatrists who were blind to the proband's and relatives' clinical status. The best estimate was based on personal diagnostic interviews, all available medical records, and family history data.

RESULTS

The diagnostic concordance between the field team and the blind psychiatric board yielded 78% to 90% agreement for the whole sample (kappa = 0.83-0.88) and 71% to 87% agreement for the subjects given field diagnoses (kappa = 0.76-0.83). The diagnoses made by the unblind field diagnosticians were biased toward a greater severity (or certainty) level in the diagnostic hierarchy (schizophrenic or bipolar) and more consistency with the most prevalent diagnosis affecting the pedigree.

CONCLUSION

Since several previous linkage studies used diagnoses made by diagnosticians who were not blind to the status of the probands and the relatives or did not use a consensus best-estimate diagnosis, further reliability studies of different aspects of the best-estimate method and of its effect on linkage studies are needed. Such research is imperative given the serious impact of diagnostic misclassifications on genetic linkage results.

Heterogeneity analysis of breast cancer families by using age at onset as a covariate

An extension of the usual mixture model of heterogeneity (two family types, one with and one without linkage) is proposed by introducing age at onset as a covariate. The extended model defines age-dependent penetrances where the exact parametrization of age-at-onset distributions depends on the given genotype and family type (linked or unlinked). This extension was applied to breast cancer families. We postulated that the mean age at onset in individuals affected by the linked gene was lower than the mean age at onset in all other affected individuals. Linkage heterogeneity for breast cancer families was detected at a significance level of .003.

Psychiatric status of adolescents who had extreme temperaments at age 7

Two temperamentally extreme (extremely easy and extremely difficult) subgroups of children were selected at the age of 7 years from a large random sample of the general population of Quebec City. The clinical status, family functioning, IQ, and academic performance of these children were reassessed at 12 and 16 years of age. Findings suggest that extreme temperament at age 7 predicts psychiatric status in preadolescence and adolescence only when family functioning is also taken into account. The adolescents who had been temperamentally difficult children and who were living in families with dysfunctional behavior control displayed more clinical disorders.