Genetic epidemiological study of schizophrenia in Palau, Micronesia: prevalence and familiality

First episode of psychosis in Guam: The role of ethnicity and neighbourhood factors

OBJECTIVE

Ethnicity, neighbourhood ethnic density, and four additional neighbourhood factors (urbanicity, crime, voting, and poverty) were examined in relation to the incidence of first episode of psychosis (FEP) in the Pacific Island of Guam.

METHODS

All first contact patients seen at the Guam Department of Mental Health and Substance Abuse (DMHSA) between January 2005 and December 2007 that met DSM-IV criteria for the diagnosis of a psychotic disorder were included. At the time of the study, DMHSA was the only psychiatric facility in Guam.

RESULTS

After controlling for age and gender, Chamorros, the indigenous people of Guam, had a standardized incidence rate (IR = 151/100 000 person-years, 95%CI = 129-173) of FEP over twice that of Whites (IR = 66/100 000 person-years, 95%CI = 34-99). Individuals from Palau had the highest standardized incidence rate (IR = 832/100 000 person-years, 95%CI = 581-1083). Increased neighbourhood Chamorro density was associated with decreased incidence of FEP among Chamorro individuals (IRR = 0.11, 95%CI = 0.03-0.43). After controlling for age, gender, ethnicity, and other neighbourhood factors, urbanicity (IRR = 3.82, 95%CI = 1.86-7.81), voting (IRR = 2.06, 95%CI = 1.32-3.20), poverty (IRR = 1.94, 95%CI = 1.40-2.67), and crime (IRR = 1.18, 95%CI = 1.00-1.40) remained statistically associated with FEP incidence.

CONCLUSIONS

The findings add to prior research that suggests that rates of mental health problems are higher in indigenous than in settler communities and are highest for indigenous people who live in neighbourhoods with few other indigenous individuals. Findings also suggest that even on a small island, with only ~150 000 people, urbanicity is associated with FEP. Finally, results are consistent with other research suggesting that the reduction of crime and social adversity can play a positive role in reducing the incidence of first episode psychosis.

A Historical and Contemporary Review of the Contextualization and Social Determinants of Health of Micronesian Migrants in the United States

Hawai'i's Pacific Islander (PI) population has suffered a higher burden of coronavirus disease 2019 (COVID-19) infections, hospitalizations, and deaths compared to other groups in the state. The Hawai'i Emergency Management Agency Community Care Outreach Unit conducted an assessment across the state to gain an understanding of the impact of the COVID-19 pandemic on the health and social welfare of households. Survey data was collected from individuals across the state during a period of 3 weeks (August 12-September 5, 2020). The following are resulting recommendations from the Pacific Island community to mitigate the impact and disparities of the pandemic as immediate and medium-term structural requests: (1) ensure that Pacific Island communities are proactively represented in state and county committees that develop health interventions to ensure that relevant language and culturally tailored communications and strategies are included, (2) provide consistent funding and community centered support to ensure consistent COVID-19 impact services for the Pacific Island families, (3) enhance the capacity of PI health care navigators and interpreters through increased funding and program support, and (4) engage state policy makers immediately to understand and address the systemic structural barriers to health care and social services for Pacific Islanders in Hawai'i. These recommendations were developed to address the generational inequities and disparities that exist for Pacific islanders in Hawai'i which were exacerbated by the COVID-19 pandemic.

Prevalence of psychotic disorders and its association with methodological issues. A systematic review and meta-analyses

Objectives

The purpose of this study is to provide an updated systematic review to identify studies describing the prevalence of psychosis in order to explore methodological factors that could account for the variation in prevalence estimates.

Methods

Studies with original data related to the prevalence of psychosis (published between 1990 and 2015) were identified via searching electronic databases and reviewing manual citations. Prevalence estimates were sorted according to prevalence type (point, 12-months and lifetime). The independent association between key methodological variables and the mean effect of prevalence was examined (prevalence type, case-finding setting, method of confirming diagnosis, international classification of diseases, diagnosis category, and study quality) by meta-analytical techniques and random-effects meta-regression.

Results

Seventy-three primary studies were included, providing a total of 101 estimates of prevalence rates of psychosis. Across these studies, the pooled median point and 12-month prevalence for persons was 3.89 and 4.03 per 1000 respectively; and the median lifetime prevalence was 7.49 per 1000. The result of the random-effects meta-regression analysis revealed a significant effect for the prevalence type, with higher rates of lifetime prevalence than 12-month prevalence (p<0.001). Studies conducted in the general population presented higher prevalence rates than those carried out in populations attended in health/social services (p = 0.006). Compared to the diagnosis of schizophrenia only, prevalence rates were higher in the probable psychotic disorder (p = 0.022) and non-affective psychosis (p = 0.009). Finally, a higher study quality is associated with a lower estimated prevalence of psychotic disorders (p<0.001).

Conclusions

This systematic review provides a comprehensive comparison of methodologies used in studies of the prevalence of psychosis, which can provide insightful information for future epidemiological studies in adopting the most relevant methodological approach.

Analysis of Shared Haplotypes amongst Palauans Maps Loci for Psychotic Disorders to 4q28 and 5q23-q31

To localize genetic variation affecting risk for psychotic disorders in the population of Palau, we genotyped DNA samples from 203 Palauan individuals diagnosed with psychotic disorders, broadly defined, and 125 control subjects using a genome-wide single nucleotide polymorphism array. Palau has unique features advantageous for this study: due to its population history, Palauans are substantially interrelated; affected individuals often, but not always, cluster in families; and we have essentially complete ascertainment of affected individuals. To localize risk variants to genomic regions, we evaluated long-shared haplotypes, ≥10 Mb, identifying clusters of affected individuals who share such haplotypes. This extensive sharing, typically identical by descent, was significantly greater in cases than population controls, even after controlling for relatedness. Several regions of the genome exhibited substantial excess of shared haplotypes for affected individuals, including 3p21, 3p12, 4q28, and 5q23-q31. Two of these regions, 4q28 and 5q23-q31, showed significant linkage by traditional LOD score analysis and could harbor variants of more sizeable risk for psychosis or a multiplicity of risk variants. The pattern of haplotype sharing in 4q28 highlights <i>PCDH10</i>, encoding a cadherin-related neuronal receptor, as possibly involved in risk.

An evaluation of variation in published estimates of schizophrenia prevalence from 1990─2013: a systematic literature review

BACKGROUND

There is a lack of consistency in findings across studies on the prevalence of schizophrenia, and no recent systematic review of the literature exists. The purpose of this study is to provide an updated systematic review of population-based prevalence estimates and to understand the factors that could account for this variation in prevalence estimates.

METHODS

MEDLINE, Embase, and PsycInfo databases were searched for observational studies describing schizophrenia prevalence in general populations from 2003-2013 and supplemented by studies from a prior review covering 1990-2002. Studies reporting prevalence estimates from specialized populations such as institutionalized, homeless, or incarcerated persons were excluded. Prevalence estimates were compared both across and within studies by factors that might contribute to variability using descriptive statistics.

RESULTS

Sixty-five primary studies were included; thirty-one (48 %) were from Europe and 35 (54 %) were conducted in samples of ≥50,000 persons. Among 21 studies reporting 12-month prevalence, the median estimate was 0.33 % with an interquartile range (IQR) of 0.26 %-0.51 %. The median estimate of lifetime prevalence among 29 studies was 0.48 % (IQR: 0.34 %-0.85 %). Prevalence across studies appeared to vary by study design, geographic region, time of assessment, and study quality scores; associations between study sample size and prevalence were not observed. Within studies, age-adjusted estimates were higher than crude estimates by 17 %-138 %, the use of a broader definition of schizophrenia spectrum disorders compared to schizophrenia increased case identification by 18 %-90 %, identification of cases from inpatient-only settings versus any setting decreased prevalence by 60 %, and no consistent trends were noted by differing diagnostic criteria.

CONCLUSIONS

This review provides updated information on the epidemiology of schizophrenia in general populations, which is vital information for many stakeholders. Study characteristics appear to play an important role in the variation between estimates. Overall, the evidence is still sparse; for many countries no new studies were identified.

Characterizing runs of homozygosity and their impact on risk for psychosis in a population isolate

An increased abundance of runs of homozygosity (ROH) has been associated with risk for various diseases, including schizophrenia. Here we investigate the characteristics of ROH in Palau, an Oceanic population, evaluating whether these characteristics are related to risk for psychotic disorders and the nature of this association. To accomplish these aims we evaluate a sample of 203 cases with schizophrenia and related psychotic disorders-representing almost complete ascertainment of affected individuals in the population-and contrast their ROH to that of 125 subjects chosen to function as controls. While Palauan diagnosed with psychotic disorders tend to have slightly more ROH regions than controls, the distinguishing features are that they have longer ROH regions, greater total length of ROH, and their ROH tends to co-occur more often at the same locus. The nature of the sample allows us to investigate whether rare, highly penetrant recessive variants generate such case-control differences in ROH. Neither rare, highly penetrant recessive variants nor individual common variants of large effect account for a substantial proportion of risk for psychosis in Palau. These results suggest a more nuanced model for risk is required to explain patterns of ROH for this population.

Does originating from a genetic isolate affect the level of cognitive impairments in schizophrenia families?

Earlier studies have detected differences in the prevalence, symptomatology and genetic risk variants of schizophrenia between a north-eastern Finnish genetic isolate and the rest of Finland. This study compared a population-based isolate sample (145 persons with schizophrenia, 304 first-degree relatives and 32 controls) with a rest of Finland sample (73 persons with schizophrenia, 100 first-degree relatives and 80 controls) in cognitive functioning. Persons from the isolate outperformed persons in the rest of Finland sample in verbal learning, verbal ability and cognitive flexibility in the schizophrenia groups and in verbal learning, speeded processing and attentional control in the relatives groups. The differences between the subsamples remained significant after taking into account an intragenic Reelin STR allele, previously associated with cognitive impairments and almost absent from the isolate, in addition to disorder characteristics and familial loading. In control groups, we observed no differences between the isolate and the rest of Finland. In conclusion, cognitive impairments were milder in schizophrenia patients and their first-degree relatives within than outside the isolate. An absence of differences between the control samples suggests that the differences in schizophrenia families may relate to genetic background, possibly to partly distinct variants affecting the liability inside and outside the isolate.

Deletion at the SLC1A1 glutamate transporter gene co-segregates with schizophrenia and bipolar schizoaffective disorder in a 5-generation family

Growing evidence for genetic overlap between schizophrenia (SCZ) and bipolar disorder (BPD) suggests that causal variants of large effect on disease risk may cross traditional diagnostic boundaries. Extended multigenerational families with both SCZ and BPD cases can be a valuable resource for discovery of shared biological pathways because they can reveal the natural evolution of the underlying genetic disruptions and their phenotypic expression. We investigated a deletion at the SLC1A1 glutamate transporter gene originally identified as a copy number variant exclusively carried by members of a 5-generation Palauan family. Using an expanded sample of 21 family members, quantitative PCR confirmed the deletion in all seven individuals with psychosis, three "obligate-carrier" parents and one unaffected sibling, while four marry-in parents were non-carriers. Linkage analysis under an autosomal dominant model generated a LOD-score of 3.64, confirming co-segregation of the deletion with psychosis. For more precise localization, we determined the approximate deletion end points using alignment of next-generation sequencing data for one affected deletion-carrier and then designed PCR amplicons to span the entire deletion locus. These probes established that the deletion spans 84,298 bp, thus eliminating the entire promoter, the transcription start site, and the first 59 amino acids of the protein, including the first transmembrane Na(2+)/dicarboxylate symporter domain, one of the domains that perform the glutamate transport action. Discovery of this functionally relevant SLC1A1 mutation and its co-segregation with psychosis in an extended multigenerational pedigree provides further support for the important role played by glutamatergic transmission in the pathophysiology of psychotic disorders.

Transgenic mice overexpressing the extracellular domain of NCAM are impaired in working memory and cortical plasticity

The neural cell adhesion molecule, NCAM, is a pivotal regulator of neural development, with key roles in axonal and dendritic growth and synaptic plasticity. Alterations in NCAM expression or proteolytic cleavage have been linked to human neuropsychiatric disorders such as schizophrenia, bipolar disorder and Alzheimer's disease, and may contribute to cognitive dysfunction. We have generated mice overexpressing the NCAM extracellular (EC) proteolytic cleavage fragment which has been reported to be increased in schizophrenic versus normal brains. These mice show impaired GABAergic innervation and reduced number of apical dendritic spines on pyramidal neurons in the prefrontal cortex (PFC). Here, these NCAM-EC transgenic mice were subjected to behavioral tasks and electrophysiological measurements to determine the impact of structural abnormalities in the PFC on synaptic and cognitive functions. NCAM-EC mice exhibited impaired working memory in a delayed non-match-to-sample task, which requires PFC function, but showed no differences in anxiety, olfactory abilities, or sociability. Transgenic mice displayed impaired long- and short-term potentiation in the PFC but normal synaptic plasticity in the hippocampus, suggesting that the abnormal synaptic innervation in NCAM-EC mice impairs PFC plasticity and alters working memory. These findings may have implications for cognitive dysfunctions observed in neuropsychiatric disorders.

Familial transmission of schizophrenia in Palau: A 20-year genetic epidemiological study in three generations

Our genetic epidemiological studies of schizophrenia and other psychotic disorders (SCZ) in the isolated population of Palau have been ongoing for 20 years. Results from the first decade showed that Palau has an elevated prevalence of SCZ and that cases cluster in extended multigenerational pedigrees interconnected via complex genetic relationships after centuries of endogamous, but not consanguineous, marriages. The aim of our second decade of research, which extended data collection into a third generation of young, high-risk (HR) Palauans, was to identify significant predictors of intergenerational transmission of illness. Our findings revealed that degree of familial loading and gender effects on reproductive fitness are important modifiers of risk for transmission of SCZ. Among 45 distinct multiplex families, we identified 10 high-density (HD) Palauan families, each with 7-29 SCZ cases, which contain half of Palau's 260 SCZ cases and 80% of the 113 SCZ cases with one or more affected first-degree relatives, indicating that familial loading is a major risk factor for SCZ in Palau. Cases that belong to multiply affected sibships are more common than cases with an affected parent. Furthermore, only 6/38 multiply affected sibships have an affected parent, strong evidence that many unaffected parents are obligate carriers of susceptibility genes. Although reproductive fitness is dramatically reduced in affected males, the 30% minority who do become fathers are twice as likely as affected mothers to transmit SCZ to an offspring. As they evolve, these HD families can help to elucidate the genetic mechanisms that predict intergenerational transmission of SCZ.

Adoption, family relations and psychotic symptoms among Palauan adolescents who are genetically at risk for developing schizophrenia

PURPOSE

This paper focuses on the role of adoption and family relations as moderators of genetic risk for psychotic disorders.

METHODS

Participants included 184 adolescents in the Republic of Palau identified to be at genetic risk for schizophrenia and other psychotic disorders. Palau is an island nation in Micronesia with a lifetime prevalence of 1.99% for schizophrenia and 2.67% for psychotic disorders more broadly defined. In Palauan culture, kinship adoption is a common cultural practice; 47 of the 184 participants had been adopted at an early age. The current study was designed to test the hypothesis that adoption would function as a protective factor among Palauan youth at genetic risk for the development of psychotic symptoms. Participants were evaluated for psychotic and other psychiatric symptoms using KSADS-PL. Concurrently, the Youth Self Report was used to assess the perceived quality of family relationships.

RESULTS

Results indicated that adopted adolescents were more likely to develop psychotic symptoms than non-adopted adolescents. However, perceived family relations moderated the association between adoption status and psychotic symptoms, such that adopted adolescents with poorer family relations reported disproportionately higher rates of psychotic symptoms. Family relations also moderated the association between level of genetic risk and psychotic symptoms, independently of adoption status.

CONCLUSION

Consistent with previous research, adolescents at high genetic risk who reported more positive family relations also reported fewer psychotic symptoms.

Early signs and symptoms of psychosis among Palauan adolescents

AIM

This study was designed to identify early symptoms associated with the occurrence of psychosis during adolescence.

METHOD

Participants were recruited in the Republic of Palau, an isolated island nation in Micronesia with a prevalence rate for schizophrenia of 1.99%. Diagnostic interviews were used to obtain reports of early and current symptoms from 112 genetically high-risk (GHR) and 208 genetically low-risk (GLR) adolescents (ages 16-23). Based on current psychotic symptoms, participants were sorted into three groups: non-clinical, at-risk/symptomatic risk and clinically symptomatic.

RESULTS

Multivariate analysis of variance revealed several between-group differences on rates of early symptoms. Most notably, youth who were in the GHR-clinically symptomatic group reported significantly higher rates of early marijuana use than GLR-clinically symptomatic youth, who were significantly more likely to report early symptoms of depression and behaviour disorders. In addition, several gender based differences in the link between early symptoms and adolescent onset psychosis were noted.

CONCLUSIONS

Findings are generally consistent with previous research on early indicators, though several unexpected findings suggest that results from this study may not be fully generalizable beyond this relatively isolated and culturally distinct Micronesian nation.

Neuropsychological performance as endophenotypes in extended schizophrenia families from the Central Valley of Costa Rica

OBJECTIVE

The understanding of complex heritable psychiatric disorders such as schizophrenia could be clarified by examining endophenotypes within genetically isolated populations, such as the one found in the Central Valley of Costa Rica. The reduction of familial variability within a sample could allow the relationship between the cognitive and symptomatic manifestations of the illness and the genetic underpinnings to become more observable. This study investigates the neuropsychological test performances of 41 family members from four extended multiplex families within the Spanish origin population of the Central Valley of Costa Rica as potential endophenotypes for genetic studies.

METHODS

Individuals with a diagnosis of schizophrenia or schizoaffective disorder were compared with unaffected relatives and 15 unrelated controls with no family history of schizophrenia.

RESULTS

Although the sample size is small, the results confirm previous reports in the literature of deficits in working memory, executive function, processing speed, and verbal fluency in individuals with schizophrenia compared with controls and intermediate performance in nonpsychotic family members compared with controls. We also found several suggestive quantitative cognitive trait loci with log of the odds greater than 1.75.

CONCLUSION

These findings suggest that the cognitive deficits in schizophrenia are consistent aspects of the illness, although their usefulness as endophenotypes for genetic studies remains unclear.

Runs of homozygosity reveal highly penetrant recessive loci in schizophrenia

Evolutionarily significant selective sweeps may result in long stretches of homozygous polymorphisms in individuals from outbred populations. We developed whole-genome homozygosity association (WGHA) methodology to characterize this phenomenon in healthy individuals and to use this genomic feature to identify genetic risk loci for schizophrenia (SCZ). Applying WGHA to 178 SCZ cases and 144 healthy controls genotyped at 500,000 markers, we found that runs of homozygosity (ROHs), ranging in size from 200 kb to 15 mb, were common in unrelated Caucasians. Properties of common ROHs in healthy subjects, including chromosomal location and presence of nonancestral haplotypes, converged with prior reports identifying regions under selective pressure. This interpretation was further supported by analysis of multiethnic HapMap samples genotyped with the same markers. ROHs were significantly more common in SCZ cases, and a set of nine ROHs significantly differentiated cases from controls. Four of these 9 "risk ROHs" contained or neighbored genes associated with SCZ (NOS1AP, ATF2, NSF, and PIK3C3). Several of these risk ROHs were very rare in healthy subjects, suggesting that recessive effects of relatively high penetrance may explain a proportion of the genetic liability for SCZ. Other risk ROHs feature haplotypes that are also common in healthy individuals, possibly indicating a source of balancing selection.

Comorbid depressive symptoms in the developmental course of adolescent-onset psychosis

AIM: Depressive symptoms are common in the early prodromal phase of schizophrenia and other psychotic disorders. The objectives of the present study were to retrospectively examine the severity of depressive symptoms and their relationship to positive symptoms over the developmental course of adolescent-onset psychosis (AO-PSY). METHODS: The subjects were 62 unmedicated adolescents with DSM-IV psychosis and 104 normal controls from a Pacific island isolate with an elevated prevalence of schizophrenia. We used a modified K-SADS-PL to assess adolescents for a full range of Axis I psychopathology and quantified severity of depressive and positive symptoms over the adolescent's lifespan. RESULTS: Among AO-PSY subjects, 84% reported abnormal levels of depressive symptoms with mean onset 1.3 years prior to transition to psychosis. In 60% of the AO-PSY subjects with depressive symptoms, positive symptoms began first. A continuous linear increase in depressive symptom severity over the developmental course of illness mirrored the steady rise in positive symptom severity as psychosis emerged. CONCLUSIONS: We found that it is typically a combination of positive symptoms and depressive symptoms building in parallel that leads from the prodrome to frank psychosis. These results suggest that depressive symptoms represent more of an integral component of disease progression than an independent risk factor that predicts transition to early onset psychosis.

Schizophrenia and psychotic symptoms in families of two American Indian tribes

BACKGROUND

The risk of schizophrenia is thought to be higher in population isolates that have recently been exposed to major and accelerated cultural change, accompanied by ensuing socio-environmental stressors/triggers, than in dominant, mainstream societies. We investigated the prevalence and phenomenology of schizophrenia in 329 females and 253 males of a Southwestern American Indian tribe, and in 194 females and 137 males of a Plains American Indian tribe. These tribal groups were evaluated as part of a broader program of gene-environment investigations of alcoholism and other psychiatric disorders.

METHODS

Semi-structured psychiatric interviews were conducted to allow diagnoses utilizing standardized psychiatric diagnostic criteria, and to limit cultural biases. Study participants were recruited from the community on the basis of membership in pedigrees, and not by convenience. After independent raters evaluated the interviews blindly, DSM-III-R diagnoses were assigned by a consensus of experts well-versed in the local cultures.

RESULTS

Five of the 582 Southwestern American Indian respondents (prevalence = 8.6 per 1000), and one of the 331 interviewed Plains American Indians (prevalence = 3.02 per 1000) had a lifetime diagnosis of schizophrenia. The lifetime prevalence rates of schizophrenia within these two distinct American Indian tribal groups is consistent with lifetime expectancy rates reported for the general United States population and most isolate and homogeneous populations for which prevalence rates of schizophrenia are available. While we were unable to factor in the potential modifying effect that mortality rates of schizophrenia-suffering tribal members may have had on the overall tribal rates, the incidence of schizophrenia among the living was well within the normative range.

CONCLUSION

The occurrence of schizophrenia among members of these two tribal population groups is consistent with prevalence rates reported for population isolates and in the general population. Vulnerabilities to early onset alcohol and drug use disorders do not lend convincing support to a diathesis-stressor model with these stressors, commonly reported with these tribes. Nearly one-fifth of the respondents reported experiencing psychotic-like symptoms, reaffirming the need to examine sociocultural factors actively before making positive diagnoses of psychosis or schizophrenia.

Genetic liability to schizophrenia in Oceanic Palau: a search in the affected and maternal generation

While liability to schizophrenia (Scz) is due to genetic and environmental factors, specific factors are largely unknown. We postulate a two-hit model for Scz, in which initial liability is generated during fetal brain development: this "hit" is precipitated by environmental stressors biologically interacting with maternal genetic vulnerability to the stress. Additional liability to Scz is generated by individual genetic vulnerability. To evaluate these putative levels of vulnerability, we search in the genome of both affected individuals and their mothers for variation that differs, statistically, from that in the general population. For parental analyses, mothers were treated as "affected," rather than their offspring, and the fathers were treated as "controls". We used a sample from the Palauan population: 175 individuals diagnosed with Scz, broadly defined; 87 mothers and 45 fathers of affected individuals. Pedigree and diagnostic data were available on 2,953 living and deceased subjects. DNA from 553 individuals was genotyped for short tandem repeats (STR) spaced approximately every 10 cM across the genome. We tested for association between affection status and STR alleles; such an approach was reasonable, despite the widely spaced markers, because this population has far-ranging linkage disequilibrium (LD). Results for the truly affected individuals were modest, whereas results from the maternal generation were promising. For a recessive model and a test for excess allele matching across mothers, significant findings occurred for D20S481, D10S1221, D6S1021, D13S317, and D18S976. Regions in which at least two adjacent markers produced substantial association statistics include 2p12-11.2, 2q24.1-32.1, 6q12-14.1, 10q23.2-24.21, 12q23.2-24.21 and 17q23.2-23.3.

Recurrence risk to offspring in extended multiplex schizophrenia pedigrees from a Pacific Island isolate

Genetic transmission plays a major role in the pathogenesis of schizophrenia. Family, twin, and adoption studies have consistently shown that risks in relatives are many times greater than the general population risk of approximately 1%. McGue, Gottesman, and Rao (1983; Am J Hum Genet 35:1161-1178) calculated risk estimates of 12.8% for offspring and 3.5% for nieces/nephews of schizophrenia patients based on a large data set of Western European families. The present study evaluated corresponding risk levels in Palau, an isolated population in Micronesia where the prevalence of narrowly (broadly) defined schizophrenia is 1.99% (2.67%) and cases cluster in extended pedigrees, 20 of which contain 80% of affected individuals. We hypothesized that offspring in these extended families would have a higher risk for schizophrenia than offspring in smaller schizophrenia pedigrees from more genetically heterogeneous populations. RDC diagnostic data based on complete ascertainment of cases and their families covering the past two generations were used to quantify empirical recurrence risks in the offspring and nieces/nephews of Palauan schizophrenia patients. Risks to 1st- and 2nd-degree offspring were approximately double the rates found in the smaller Western European families: 23.4% in the offspring of an affected parent, 6.4% in offspring with one affected aunt/uncle, and 15.0% in offspring with two or more affected aunts/uncles. Recurrence rates in offspring of an affected parent were 1.6 times higher in males (27.9%) than in females (17.7%). The high risk levels we found in Palauan offspring reflect the elevated population prevalence, strong familial aggregation, and multi-lineal transmission pattern of schizophrenia in Palau.

The Palau Early Psychosis Study: distribution of cases by level of genetic risk

The Palau Early Psychosis Study (PEPS) was designed to examine the pathogenesis of early psychosis in a high-risk population isolate. This paper describes the characteristics of our community-based, non-help seeking sample of 404 Palauan adolescents and quantifies the presence of early psychosis by level of genetic risk. The sample included 53 offspring of a schizophrenic parent designated as "Genetically Highest Risk" (GHR+) and 68 nieces/nephews of sib-pairs/trios, designated as "Genetically High Risk" (GHR). The remaining subjects were recruited through a high school survey that identified 62 "Genetically Moderate Risk" (GMR) adolescents with an affected second or third degree relative and 221 "Genetically Low Risk" (GLR) subjects with no close affected relatives. The GLR adolescents included 117 symptomatic or "Clinically High Risk" (CHR) adolescents and 104 asymptomatic normal controls. Based on a modified K-SADS-PL assessment, we identified 221 adolescents with early psychosis, 62 or 28% of whom had already transitioned to a psychotic disorder. Together, the two highest risk groups contributed 31% of the adolescent-onset psychosis cases and 27% of the prodromals. More than half of the early psychosis cases (53%) were GLR adolescents. The mean age of onset for DSM-IV psychosis was 12.9 years, and males transitioned at an earlier age than females. Our results indicate that Palauan adolescents, even GLR adolescents with no close affected relatives, have elevated rates of early psychosis. These young subjects can contribute valuable information about the familial transmission of schizophrenia, the developmental course of the illness, and rates of transition to frank psychosis.

The Palau Early Psychosis Study: neurocognitive functioning in high-risk adolescents

OBJECTIVE

The purpose of the present study was to evaluate both the independent and joint effects of genetic risk and clinical status on neurocognitive functioning in adolescents from a population isolate with an elevated risk for schizophrenia and strong familial aggregation of cases.

METHOD

The subjects were 310 non-help seeking, drug-naïve adolescents 14-19 years of age from the Republic of Palau. The sample comprised 98 Genetically High Risk (GHR) adolescents, 54 of whom were symptomatic, and 212 Genetically Low Risk (GLR) adolescents, including 113 Clinically High Risk (CHR) subjects who were symptomatic and 99 normal controls who were non-symptomatic. Neurocognitive testing was conducted after the clinical assessment and included Wechsler Memory Scale tests of logical, visual and working memory, the perceptual organization and processing speed subtests of the WISC-III, CPT-IP measures of sustained attention, and tests of fine and gross neuromotor function.

RESULTS

GHR adolescents showed impairments in immediate logical memory, verbal working memory, CPT-IP performance, and fine motor skills. The only two cognitive components influenced by the presence of early psychosis symptoms were WISC-III perceptual organization and spatial working memory. Neurocognitive deficits did not increase with increasing levels of psychopathology. We found no significant interactive effects of genetic risk and clinical status on neurocognitive functioning.

CONCLUSIONS

Genetic risk and clinical status exert independent effects on neurocognitive function in HR adolescents, and genetic risk has a broader impact than clinical status. Our results suggest that many of the neurocognitive impairments associated with early psychosis are genetically mediated and can occur in genetically vulnerable individuals regardless of their clinical status. However, visuospatial processing appears to be uniquely disrupted by emerging symptomatology.

Applications and limitations of empiric data in provision of recurrence risks for schizophrenia: a practical review for healthcare professionals providing clinical psychiatric genetics consultations

Schizophrenia is a common disorder that may frequently be encountered when taking family histories in the genetics clinic, whether or not the referral is for a psychiatric indication. Like in other common disorders, the provision of recurrence risks for schizophrenia is a complex clinical issue because empiric recurrence risks (while reasonably well established) can rarely be used without individual tailoring. This review seeks to identify and detail some pertinent issues surrounding the clinical utility of empiric recurrence risks for schizophrenia, and to provide an overview of important factors to consider when tailoring empiric risks for individual patients.

Schizophrenia: An Update and Review

Schizophrenia is a common complex disorder characterized by psychosis, cognitive dysfunction and negative symptoms, whose etiology involves interactions between both genetic and environmental vulnerability factors. Recently, ongoing research attempting to elucidate the nature of these vulnerability factors has been generating exciting findings. The advances in understanding of environmental risk factors for mental illnesses and in genetic research into mental illnesses will be reviewed. Limitations of the findings and implications of these advances for genetic counseling practice will also be discussed.

P50 suppression in individuals at risk for schizophrenia: the convergence of clinical, familial, and vulnerability marker risk assessment

BACKGROUND

Identification of individuals at risk for the development of schizophrenia is important because it can lead to a greater understanding of the early stages of the illness. The aim of the present study was to determine whether individuals "at risk" for schizophrenia have deficits in P50 suppression, a preattentive measure of sensory gating.

METHODS

Thirty-one at-risk and 21 normal comparison subjects were referred to the CARE (Cognitive Assessment and Risk Evaluation) Program at University of California San Diego. The primary aim of the CARE Program is to identify individuals who are at the greatest risk for conversion to psychosis, with a combination of clinical, familial, and vulnerability markers, including P50 suppression.

RESULTS

As a group, the at-risk subjects had modestly lower levels (effect size=.43) of P50 suppression (55.1%, SD=39.8) relative to comparison subjects (71.5%, SD=34.7). At-risk subjects with a first-degree relative with schizophrenia had profoundly deficient P50 suppression (16.4%, SD=33.8) compared with other at-risk (p<.05) and comparison subjects (p<.005).

CONCLUSIONS

Ongoing longitudinal follow-up studies will determine whether it is possible to improve the predictive validity of the clinical and familial variables by using P50 suppression alone or in combination with other measures in determining which individuals are at greatest risk for schizophrenia.

Linkage analysis of a completely ascertained sample of familial schizophrenics and bipolars from Palau, Micronesia

We report on linkage analysis of a completely ascertained population of familial psychosis derived from the oceanic nation of Palau. Palau, an archipelago of islands in the Southern Pacific, currently has a population of approximately 23,000 individuals. The peoples of Palau populated these islands recently in human history, approximately 2,000 years ago. As both historical and genetic evidence suggest, the population is far more homogeneous than most other populations undergoing genetic studies, and should therefore prove quite useful for mapping genetic variants having a meaningful impact on susceptibility to psychotic disorders. Moreover, for our study, essentially all on-island schizophrenics (150) and individuals with other psychotic disorders (25) participated. By analysis of narrow (only schizophrenia) and broad (all psychosis) diagnostic schemes, two-point linkage analyses suggest that two regions of the genome harbor genetic variants affecting liability in most families, 3q28 (LOD = 3.03) and 17q32.2 (LOD = 2.80). Results from individual pedigrees also support 2q37.2, 2p14, and 17p13 as potentially harboring important genetic variants. Most of these regions have been implicated in other genetic studies of psychosis in populations physically quite distant from this Oceanic population, although some (e.g., 3q28) appear to be novel results for schizophrenia linkage analyses.

A systematic review of the prevalence of schizophrenia

BACKGROUND

Understanding the prevalence of schizophrenia has important implications for both health service planning and risk factor epidemiology. The aims of this review are to systematically identify and collate studies describing the prevalence of schizophrenia, to summarize the findings of these studies, and to explore selected factors that may influence prevalence estimates.

METHODS AND FINDINGS

Studies with original data related to the prevalence of schizophrenia (published 1965-2002) were identified via searching electronic databases, reviewing citations, and writing to authors. These studies were divided into "core" studies, "migrant" studies, and studies based on "other special groups." Between- and within-study filters were applied in order to identify discrete prevalence estimates. Cumulative plots of prevalence estimates were made and the distributions described when the underlying estimates were sorted according to prevalence type (point, period, lifetime, and lifetime morbid risk). Based on combined prevalence estimates, the influence of selected key variables was examined (sex, urbanicity, migrant status, country economic index, and study quality). A total of 1,721 prevalence estimates from 188 studies were identified. These estimates were drawn from 46 countries, and were based on an estimated 154,140 potentially overlapping prevalent cases. We identified 132 core studies, 15 migrant studies, and 41 studies based on other special groups. The median values per 1,000 persons (10%-90% quantiles) for the distributions for point, period, lifetime, and lifetime morbid risk were 4.6 (1.9-10.0), 3.3 (1.3-8.2), 4.0 (1.6-12.1), and 7.2 (3.1-27.1), respectively. Based on combined prevalence estimates, we found no significant difference (a) between males and females, or (b) between urban, rural, and mixed sites. The prevalence of schizophrenia in migrants was higher compared to native-born individuals: the migrant-to-native-born ratio median (10%-90% quantile) was 1.8 (0.9-6.4). When sites were grouped by economic status, prevalence estimates from "least developed" countries were significantly lower than those from both "emerging" and "developed" sites (p = 0.04). Studies that scored higher on a quality score had significantly higher prevalence estimates (p = 0.02).

CONCLUSIONS

There is a wealth of data about the prevalence of schizophrenia. These gradients, and the variability found in prevalence estimate distributions, can provide direction for future hypothesis-driven research.

P50 sensory gating in adolescents from a pacific island isolate with elevated risk for schizophrenia

BACKGROUND

Gating or inhibition of the P50 auditory evoked potential is a heritable neurobiological trait that has shown strong potential to serve as an endophenotype for schizophrenia. P50 sensory gating deficits have been found repeatedly in schizophrenic patients and in their unaffected first-degree relatives. P50 sensory gating has not yet been studied in high-risk (HR) offspring nor in prodromal adolescents.

METHODS

A paired-stimulus auditory event-related potential paradigm was used to examine P50 sensory gating in 44 genetically HR adolescent offspring and 43 clinically HR prodromal adolescents with the same low genetic liability as a comparison group of 39 normal adolescents.

RESULTS

Auditory sensory gating, as measured by the P50 ratio, was impaired in both genetically HR offspring and also in the clinically HR prodromal adolescents with no close affected relatives. In the genetically HR group, abnormal P50 sensory gating was found only in offspring who met criteria for the schizophrenia prodrome.

CONCLUSIONS

Our findings suggest that P50 deficits are associated with the presence of prodromal symptoms, regardless of genetic risk. The results are consistent with the hypothesis that genetic liability in HR offspring increases risk for prodromal symptoms, and prodromal symptoms, in turn, increase risk for impaired sensory gating.

Genome-wide scan in a large complex pedigree with predominantly male schizophrenics from the island of Kosrae: evidence for linkage to chromosome 2q

It is widely accepted that founder populations hold promise for mapping loci for complex traits. However, the outcome of these mapping efforts will most likely depend on the individual demographic characteristics and historical circumstances surrounding the founding of a given genetic isolate. The 'ideal' features of a founder population are currently unknown. The Micronesian islandic population of Kosrae, one of the four islands comprising the Federated States of Micronesia (FSM), was founded by a small number of settlers and went through a secondary genetic 'bottleneck' in the mid-19th century. The potential for reduced etiological (genetic and environmental) heterogeneity, as well as the opportunity to ascertain extended and statistically powerful pedigrees makes the Kosraen population attractive for mapping schizophrenia susceptibility genes. Our exhaustive case ascertainment from this islandic population identified 32 patients who met DSM-IV criteria for schizophrenia or schizoaffective disorder. Three of these were siblings in one nuclear family, and 27 were from a single large and complex schizophrenia kindred that includes a total of 251 individuals. One of the most startling findings in our ascertained sample was the great difference in male and female disease rates. A genome-wide scan provided initial suggestive evidence for linkage to markers on chromosomes 1, 2, 3, 7, 13, 15, 19, and X. Follow-up multipoint analyses gave additional support for a region on 2q37 that includes a schizophrenia locus previously identified in another small genetic isolate, with a well-established recent genealogical history and a small number of founders, located on the eastern border of Finland. In addition to providing further support for a schizophrenia susceptibility locus at 2q37, our results highlight the analytic challenges associated with extremely large and complex pedigrees, as well as the limitations associated with genetic studies of complex traits in small islandic populations.

Spatial working memory deficits in schizophrenia patients and their first degree relatives from Palau, Micronesia

Spatial working memory deficits associated with dorsolateral prefrontal dysfunction have been found in Caucasian samples of schizophrenia patients and their first-degree relatives. This study evaluated spatial working memory function in affected and unaffected members of multiplex schizophrenia families from the Republic of Palau to determine whether the spatial working memory deficits associated with schizophrenia extend to this non-Caucasian population. Palau is an isolated island nation in Micronesia with an elevated prevalence of schizophrenia and an aggregation of cases in large multigenerational families. Our objective was to evaluate the potential for spatial working memory function to serve as one of multiple endophenotypes in a genetic linkage study of these Palauan schizophrenia families. A spatial delayed response task requiring resistance to distraction and a sensorimotor control task were used to assess spatial working memory in 32 schizophrenia patients, 28 of their healthy first-degree relatives, and 19 normal control subjects. Schizophrenia patients and their relatives were significantly less accurate than normal control subjects on the spatial delayed response task but not on the sensorimotor control task. On both tasks, patients and relatives were slower to respond than the normal controls. There were no age or gender effects on accuracy, and working memory performance in schizophrenia patients was not significantly correlated with medication dosage. In summary, spatial working memory deficits that have been found in Caucasian schizophrenia patients and relatives were confirmed in this isolated Pacific Island family sample. These results suggest that spatial working memory deficits may be a potentially useful addition to the endophenotypic characterization of family members to be used in a comprehensive genome wide linkage analysis of these Palauan families.

Genetics of population isolates

Genetic isolates, as shown empirically by the Finnish, Old Order Amish, Hutterites, Sardinian and Jewish communities among others, represent a most important and powerful tool in genetically mapping inherited disorders. The main features associated with that genetic power are the existence of multigenerational pedigrees which are mostly descended from a small number of founders a short number of generations ago, environmental and phenotypic homogeneity, restricted geographical distribution, the presence of exhaustive and detailed records correlating individuals in very well ascertained pedigrees, and inbreeding as a norm. On the other hand, the presence of a multifounder effect or admixture among divergent populations in the founder time (e.g. the Finnish and the Paisa community from Colombia) will theoretically result in increased linkage disequilibrium among adjacent loci. The present review evaluates the historical context and features of some genetic isolates with emphasis on the basic population genetic concepts of inbreeding and genetic drift, and also the state-of-the-art in mapping traits, both Mendelian and complex, on genetic isolates.

Genomewide multipoint linkage analysis of seven extended Palauan pedigrees with schizophrenia, by a Markov-chain Monte Carlo method

Palauans are an isolated population in Micronesia with lifetime prevalence of schizophrenia (SCZD) of 2%, compared to the world rate of approximately 1%. The possible enrichment for SCZD genes, in conjunction with the potential for reduced etiological heterogeneity and the opportunity to ascertain statistically powerful extended pedigrees, makes Palauans a population of choice for the mapping of SCZD genes. We have used a Markov-chain Monte Carlo method to perform a genomewide multipoint analysis in seven extended pedigrees from Palau. Robust multipoint parametric and nonparametric linkage (NPL) analyses were performed under three nested diagnostic classifications-core, spectrum, and broad. We observed four regions of interest across the genome. Two of these regions-on chromosomes 2p13-14 (for which, under core diagnostic classification, NPL=6.5 and parametric LOD=4.8) and 13q12-22 (for which, under broad diagnostic classification, parametric LOD=3.6, and, under spectrum diagnostic classification, parametric LOD=3.5)-had evidence for linkage with genomewide significance, after correction for multiple testing; with the current pedigree resource and genotyping, these regions are estimated to be 4.3 cM and 19.75 cM in size, respectively. A third region, with intermediate evidence for linkage, was identified on chromosome 5q22-qter (for which, under broad diagnostic classification, parametric LOD=2.5). The fourth region of interest had only borderline suggestive evidence for linkage (on 3q24-28; for this region, under broad diagnostic classification, parametric LOD=2.0). All regions exhibited evidence for genetic heterogeneity. Our findings provide significant evidence for susceptibility loci on chromosomes 2p13-14 and 13q12-22 and support both a model of genetic heterogeneity and the utility of a broader set of diagnostic classifications in the population from Palau.

Clinical characteristics of schizophrenia in multiply affected Spanish origin families from Costa Rica

Sixty-six families from Costa Rica with multiply ill sets of siblings were examined in detailed clinical evaluations and compared with 59 similarly evaluated families from the USA. Eighty-six unrelated Costa Rican individuals with a schizophrenia spectrum diagnosis and no other ill siblings were an additional comparison group. This study was undertaken to examine whether schizophrenia in Costa Rica has similar clinical and demographic characteristics to that in the USA, whether a homogeneous population such as that in Costa Rica might harbor a specific definable subtype, and whether singletons have similar or differing characteristics from individuals in multiplex families. Overall, schizophrenia in Costa Rica is similar to that in any other geographic location. The same symptoms, sex ratio and age of onset characteristics predominate. However, there was significantly less prevalence of affective symptoms (depression and mania) and drug abuse among the Costa Rican multiplex families by comparison with those from the USA. The families with only one ill member from Costa Rica had significantly more alcohol abuse than the multiply affected families. Within multiplex families (both USA and Costa Rica), age of onset was found to have a familial component. Family sibship size was significantly greater in Costa Rica than the USA for the generation with illness studied. However, these siblings had overall fewer children. In Costa Rica, the male but not the female siblings with schizophrenia had reduced fecundity compared with their well siblings. These families from Costa Rica will be used in further molecular genetic studies to determine whether the illness etiology can be traced to one or more specific genetic linkages.

Molecular genetics of schizophrenia

1. Schizophrenia is a chronic, disabling brain disease that affects approximately 1% of the world's population. It is characterized by delusions, hallucinations and formal thought disorder, together with a decline in socio-occupational functioning. While the causes for schizophrenia remain unknown, evidence from family, twin and adoption studies clearly demonstrates that it aggregates in families, with this clustering largely attributable to genetic rather than cultural or environmental factors. Identifying the genes involved, however, has proven to be a difficult task because schizophrenia is a complex trait characterized by an imprecise phenotype, the existence of phenocopies and the presence of low disease penetrance. 2. The current working hypothesis for schizophrenia causation is that multiple genes of small to moderate effect confer compounding risk through interactions with each other and with non-genetic risk factors. The same genes may be commonly involved in conferring risk across populations or they may vary in number and strength between different populations. To search for evidence of such genetic loci, both candidate gene and genome-wide linkage studies have been used in clinical cohorts collected from a variety of populations. Collectively, these works provide some evidence for the involvement of a number of specific genes (e.g. the 5-hydroxytryptamine (5-HT) type 2a receptor (5-HT2a) gene and the dopamine D3 receptor gene) and as yet unidentified factors localized to specific chromosomal regions, including 6p, 6q, 8p, 13q and 22q. These data provide suggestive, but no conclusive, evidence for causative genes. 3. To enable further progress there is a need to: (i) collect fine-grained clinical datasets while searching the schizophrenia phenotype for subgroups or dimensions that may provide a more direct route to causative genes; and (ii) integrate recent refinements in molecular genetic technology, including modern composite marker maps, DNA expression assays and relevant animal models, while using the latest analytical techniques to extract maximum information in order to help distinguish a true result from a false-positive finding.

Effects of chewing betel nut (Areca catechu) on the symptoms of people with schizophrenia in Palau, Micronesia

BACKGROUND

Although millions of people with schizophrenia live in betel chewing regions, the effects of betel chewing on their symptoms are unknown. Betel nut alkaloids include potent muscarinic cholinomimetics: recent research suggests that these agents may be therapeutic in schizophrenia.

AIMS

To compare the primary and extrapyramidal symptom profiles and substance-using habits of betel chewing v. non-chewing people with schizophrenia.

METHOD

A cross-sectional study of 70 people with schizophrenia. Symptom ratings measured by the Positive and Negative Syndrome Scale (PANSS) and Extrapyramidal Symptom Rating Scale (ESRS), and demographic and substance-use data, were compared for 40 chewers and 30 non-chewers of betel nut.

RESULTS

Betel chewers with schizophrenia scored significantly lower on the positive (P = 0.001) and negative (P = 0.002) sub-scales of the PANSS than did non-chewers. There were no significant differences in extrapyramidal symptoms or tardive dyskinesia.

CONCLUSIONS

Betel chewing is associated with milder symptomatology and avoidance of more harmful recreational drugs. These initial results indicate that longitudinal research is merited.

The ascertainment of multiplex schizophrenia pedigrees from Daghestan genetic isolates (Northern Caucasus, Russia)

This article describes the preliminary ascertainment of multiplex schizophrenia pedigrees from the isolated mountain region of Daghestan (Northern Caucasus, Russia). Daghestan has a population of two million people and contains 26 aboriginal ethnic groups. Many of the ethnic groups reside in remote mountain villages that can be classified as 'primary isolates'. Prolonged reproductive isolation and severe environmental conditions in the highlands have created diverse, genetically isolated ethnic populations in Daghestan. A number of the isolates in this region contain large extended multiplex schizophrenia pedigrees that are ideal for genetic analyses. During summer expeditions of 1996 and 1997, 14 separate large multiplex schizophrenia pedigrees were ascertained from 14 different mountain villages. Of the 14 kindreds, one had 50 schizophrenic cases available for ascertainment, one had 32, and another had 24. Seven of the remaining pedigrees had between 11 and 23 living cases. Within the kindreds, the number of males with chronic schizophrenia was at least twice that of females. The average age of onset of schizophrenia is 21.2 years for offspring of consanguineous marriages and 17.4 years for offspring of nonconsanguineous marriages (P = 0.033). Although the pedigrees ascertained from the remote mountain villages may not be representative of the general population, they are unique kindreds for mapping schizophrenia susceptibility genes.

Gene mapping in isolated populations: new roles for old friends?

Population isolates are increasingly being used in attempts to map genes underlying complex diseases. To further explore the utility of isolates for this purpose, we explore linkage disequilibrium patterns in polymorphisms from two regions (VWF and NF1) in three isolated populations from Finland. At the NF1 locus, the Finnish populations have greater pairwise disequilibrium than populations from Africa, Asia, or northern Europe. However, populations from 'New Finland' and 'Old Finland' do not differ in their disequilibrium levels at either the NF1 or the VWF locus. In addition, disequilibrium patterns and haplotype diversity do not differ between a sample from the Aland Islands, Finland, and a collection of outbred Centre d'Etude du Polymorphisme Humain families. These results show that linkage disequilibrium patterns sometimes differ among populations with different histories and founding dates, but some putative isolated populations may not significantly differ from larger admixed populations. We discuss factors that should be considered when using isolated populations in gene-mapping studies.