Prediction and prevention of schizophrenia: what has been achieved and where to go next?

Since the traditional clinical paradigm has been replaced by the modern molecular one, medicine set off into new directions. “Prediction”, “prevention” and “personalization” are the programmatic key words of this new approach. Like other medical disciplines, psychiatry has broadened its focus from diagnosis and treatment to the detection and estimation of the risk of disease development, the prediction of its onset and strategies to avoid its manifestation 1,2,3,4. Although treatment of schizophrenia has greatly advanced over the last decades, a significant number of patients continue to take an unfavorable chronic course 5,6. This makes schizophrenia the leading cause for permanent occupational disability among people under 40 years of age in Germany 7, and the 8th most common cause for disability adjusted life years (DALYs) lost among the 15 to 34-year olds worldwide 8, despite its low prevalence. Moreover, schizophrenia involves tremendous direct and indirect societal costs 9 and a huge burden on patients and their families 8,10. It is becoming increasingly clear that schizophrenia is a complex disorder with polygenic heredity and that its pathogenesis is greatly influenced by interactions between different genes and between genes and environment. Associations to variants of the genes for dysbindin and neuregulin-1, the genetic locus G72 and the DAOA (D-amino acid oxidase activator) gene have now been repeatedly confirmed. As with all other complex diseases, research is focusing now on characterizing the polygenetic predisposition and clarifying its influence on the development of the phenotype 11. Research methods range from molecular genetics via proteome research to cell biology, neurophysiology, brain structural and functional imaging and neuropsychology. With all these methods, several indicators for an increased risk of schizophrenia have been identified. However, the currently recognized neurobiological risk factors are not sufficiently predictive to allow the development and application of “selective” prevention measures targeting asymptomatic persons at risk. For neuro-psychological risk factors, this has just become evident in the large-scale attempt of the North American Prodrome Longitudinal Study (NAPLS) group to improve their multivariate model by integrating the examined neurocognitive variables 12. There are also established environmental risk factors for schizophrenia, such as pregnancy or birth complications, growing up in a large city, IQ low but normal and drug consumption. However, with odds ratios around 2, each of these factors appears to increase the lifetime risk of the disease only slightly 13. Thus, the currently known risk factors, either alone or taken together, cannot be used for prediction and prevention without knowledge of the complete predispositional basis and the gene-gene and gene-environment interactions, which are probably numerous. In view of this situation, it may be argued that the current efforts towards prediction and prevention are still premature and that further progress of etiological research is needed. However, a different perspective has emerged from the work of the centers for early recognition and prevention, established first in Melbourne, Australia and in Cologne, Germany in the mid 1990s, and later on in many other places around the world. This resulted from retrospective research of the early course of psychosis, in which the pathophysiologically active disturbances in brain development extend beyond early abnormalities in behavior into psychopathologically definable early risk and ultra high risk (UHR) symptoms, depending on the individual combination of stressors and resilience factors. First episode psychosis (FEP) research has shown that the outbreak of the disease is preceded in about 70% to nearly 100% of cases by an initial prodrome, which lasts for an average of five to six years. Even in highly developed health care systems, an average of one year thereafter elapses from the first manifestation of psychotic positive symptoms to the initiation of adequate treatment 14,15. The period over which the FEP remains untreated (duration of untreated psychosis, DUP) correlates with: delayed and incomplete remission of the symptoms; necessity of more protracted treatment and greater risk of relapse; lower compliance, greater burden on the family, and a higher level of “expressed emotion”; increased risk of depression and suicide; greater impact on the individual's employment or education; increased drug abuse and delinquent behavior; markedly increased costs of treatment 16. These correlations have recently been confirmed by a meta-analysis 17, with coefficients ranging from 0.285 to 0.434 (95% CI). This does not only provide strong arguments in favor of treating the FEP as early as possible, but has also led to a systematic effort to decrease the incidence of psychosis through indicated prevention. Two important studies concerning the early stage prior to the conversion to FEP have demonstrated that the earliest and most common symptoms, which generally dominate during the prodrome, are unspecific and cannot be distinguished from impairment in mood, drive, contact, and concentration of depressive episodes. These are the Age-Beginning-Course (ABC) study of schizophrenia, a retrospective study with optimized methods 14, and the Cologne Early Recognition (CER) Study, a long-term prospective study with an average follow-up period just below 10 years 18. These studies also found striking cognitive impairments in the form of self-experienced disturbances in thought, speech, and perception processes. This subgroup of so-called basic symptoms, which were found in more than a quarter of patients, had high specificity and a high positive predictive power, accompanied by only low rates of false positive predictions 19,20,21. Basic symptoms were first operationalized in the Bonn Scale for the Assessment of Basic Symptoms (BSABS). Shorter versions of the scale for adults and for children and adolescents — the Schizophrenia Proneness Instrument, Adult version (SPI-A) and the Schizophrenia Proneness Instrument, Child and Youth version (SPI-CY) — were later developed from dimensional analyses 22,23,24. While the BSABS only allows an assessment of the current state, the SPI-A and the SPI-CY also allow severity ratings according to the maximum frequency of occurrence within the past 3 months. In the CER study, 385 patients who were presumably in the prodromal phase of schizophrenia were followed up for an average of 9.6 (±7.6) years past baseline. Twenty percent of the initial criterion-positive cases (1 of 66 basic symptoms) who agreed to be followed up developed schizophrenia after 12 months, a further 17% after 24 months, a further 13% after 36 months, and finally a total of 70% after an average of 4.5 years. Thus, only 30% did not convert to schizophrenia. The overall presence/absence of at least one basic symptom correctly predicted presence/absence of a subsequent transition to schizophrenia in 78.1% of cases. From further analyses, two partially overlapping basic symptom criteria for defining at risk mental states (ARMS) for psychosis, primarily schizophrenia, were developed (Table 1). The first criterion, which consists of ten cognitive-perceptive basic symptoms and is abbreviated as COPER, was based on findings concerning the predictive accuracy of individual basic symptoms 18,25. The second was based on a methodological re-analysis of the same data set, in which a cluster of nine cognitive basic symptoms had repeatedly been selected as the most predictive. This cluster was called “cognitive disturbances” (COGDIS). In terms of general predictive accuracy, the two criteria slightly differed in the CER study, as COGDIS tended to be more conservative than COPER, i.e. to perform better in ruling in subsequent schizophrenia at the cost of performing worse in ruling it out. The transition rate throughout the average follow-up period of roughly 10 years was 65% for COPER and 79% for COGDIS, with the majority of transitions occurring within the first 3 years past baseline. In a second prospective study 26, conducted with the SPI-A and with a systematic follow-up of 24 months, 38% of the initially included 146 at-risk subjects developed a frank psychosis, mainly schizophrenia, within 12.3 (±10.4) months on average (1–48; median=9) according to COPER. Thus, the positive results of the CER study were confirmed. Again, COGDIS appeared to be more specific but less sensitive than COPER. As a consequence of these findings, predictive basic symptoms have been established as a set of criteria for risk assessment in international research on the early recognition of psychosis. In particular, the German Research Network on Schizophrenia used these symptoms, together with a combined criterion of functional deterioration and biological risk, in defining an “early at-risk of psychosis state” (ERPS), thereby suggesting a clinical risk staging model (Figure 1). Early and late initial prodromal state: a clinical staging approach The positive symptoms typical of schizophrenia — such as delusions, hallucinations or formal thought disorders — often first appear in an attenuated or transient form during the initial prodromal phase. These symptoms provide a valid prediction of conversion into FEP, particularly in the short term. Warning signs of this sort have been used as ultra-high risk (UHR) criteria 27,28. Notwithstanding their differences across studies, these criteria are generally composed of three alternative elements: attenuated positive symptoms (APS), brief limited intermittent psychotic symptoms (BLIPS), or a combination of one or more risk factors (always including genetic risk) and functional decline within a certain recent period. For the ascertainment of the UHR criteria, the Melbourne group gradually developed a specific instrument, the Comprehensive Assessment of At Risk Mental States (CAARMS) 29. Based on the Australian definition of the UHR criteria, the Structured Interview for Prodromal Syndromes (SIPS), the Scale for Prodromal Syndromes (SOPS) and, subsequently, the Criteria of Prodromal Syndromes (COPS) were developed 30,31. Different UHR-related approaches to an early detection of FEP, particularly schizophrenia, were developed by the Hillside Recognition and Prevention (RAP) program in New York 32 and the Basel Früherkennung von Psychosen (FEPSY) study 33. There have been at least 15 prediction studies using UHR criteria, some of which with large samples 34,35,36,37,38,39,40,41. The 12-month rates of transition into FEP published so far range between approximately 13% and 50%. A substantial variance is even observed with comparable observation periods in the same center 34,35. Yet, as the annual incidence for all forms of psychosis in the general population is only about 0.034% 42, even the lowest conversion rates still indicate a dramatic increase in the relative risk of illness, at least in the help-seeking samples of specialized centers. Table 2 depicts the predictive accuracy measures published so far, with the last five listed studies representing secondary predictor analyses of samples meeting at risk criteria. As a result, in the German Research Network on Schizophrenia, the UHR approach was combined with the basic symptom approach and applied in a slightly modified form for the definition of “late at-risk of psychosis state” (LRPS) (Figure 1). This clinical staging model, which suggests a syndromal sequence for the development of FEP progressing from unspecific prodromal symptoms to predictive basic symptoms, and then to APS, to BLIPS and to full-blown psychotic symptoms, was recently strongly supported 15. Universal or selective prevention measures target healthy population groups or clinically still healthy risk carriers, respectively 43. Indicated prevention, instead, targets individuals with basic symptoms and UHR symptoms. Even at the early stages when these individuals seek advice and help at the early recognition and prevention centers, they must be regarded as ill and in need of treatment. Furthermore, the impending deterioration of psychosocial performance in schizophrenia often already occurs in the initial prodromal phase, even prior to the conversion into FEP 14,15. These clinical and psychosocial impairments justify defining the interventions in EPRS and LPRS as indicated prevention, pursuing the following three objectives: a) improvement in the current burden of prodromal symptoms; b) avoidance or perhaps delay in the development of psychosocial handicap; c) prevention of or at least delay or attenuation of psychosis. Five international intervention studies have attempted to find out whether or to what extent these three objectives can be reached 44,45,46,47,48,49,50,51 (Table 3). The preventive measures used were either cognitive behavioral therapy (CBT), adapted to the requirements of the persons at risk, or atypical antipsychotics (risperidone, olanzapine, and amisulpride). These were randomized controlled studies, but there were problems with the blinding condition in the two CBT interventions. This and other methodological shortcomings currently limit conclusions and have encouraged the research groups working in this area to set up new, optimized intervention studies. For example, the protocol of the ongoing parallel group PREVENT study includes careful comparative analyses and superiority and inferiority tests of the psychological and pharmacological treatments 52. A staging of risk, thereby implying a temporal dimension, was considered for the first time in the two intervention studies of the German Research Network on Schizophrenia. One of these studies covered ERPS and only offered CBT as a preventive measure 49,50. The other study was designed for LRPS and used only preventive treatment with amisul-pride 51. When the symptom development in the initial prodromal state follows the sequence shown in Figure 1, it would be beneficial for scientific and especially ethical reasons to focus on psychological interventions in ERPS, which are well tolerated and highly accepted. As soon as the first attenuated or transient psychotic symptoms occur, it seems justifiable to apply well tolerated antipsychotics with few side effects. This differential prevention strategy is now pursued in all German early recognition centers and is also increasingly gaining support in other countries. Another pharmacological option is aripiprazole, tested in a pilot study in UHR states 53. Its possible preventive effects are currently being analyzed in the PREVENT study. Antidepressants were used in a naturalistic, non-randomized observational study of an adolescent sample employing only the APS criterion for inclusion, but, for methodological reasons, this study does not allow any conclusion about differential preventive effects of these medications 54. A critical evaluation of the achievements over the past 15 years through continuous efforts to enhance prediction and prevention of psychoses, particularly of schizophrenia, reveals quite impressive results. However, the results achieved thus far need to be evaluated in the light of the ambitious, initially mentioned objectives of modern predictive and preventive medicine. Once predictive basic symptoms and UHR symptoms have occurred, the underlying pathophysiological process might have already progressed. For such a complex disease with a long-term course and a pre-dispositional basis, this kind of risk identification and risk-oriented prevention may possibly come too late. A more substantial reduction in incidence could be reached with selective and universal prevention measures. Therefore, symptom-based prediction and prevention need to be further developed into the direction of selective prevention for symptom-free risk carriers. In the future, it is necessary to strive for: a) an improvement of risk enrichment with the inclusion of biological risk factors; b) a stronger individualization of the risk estimation by stratification; c) the inclusion of sub-psychotic mental states, as cross-sectionally by current at risk criteria, in the the application of prevention strategies more with the of the the initial prodromal phase for as as then most of the follow-up periods shown in Table 2 are not to the transition A significant number of later may be as and, the predictive of the risk may be 12. 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