Metabolic subtypes in patients with schizophrenia

Meta-analysis and the science of schizophrenia: variant evidence or evidence of variants?

Quantification (meta-analysis) of the neuroscience evidence on schizophrenia shows very modest average differences between patient and control distributions across a great variety of measures and literatures. The strongest findings involve cognitive and psychophysiological measures. Several possible explanations for this situation are reviewed including technical immaturity, methodological variability, dimensional and multiple illness models and the nature of cognitive measurement. An argument is developed that biological subtypes and endophenotypes within the broad diagnostic category of schizophrenia underpin the meta-analytic evidence. Considerations in the use of this evidence to identify illness variants are described and four candidate subtypes are proposed. Schizophrenia is a disease that will resist biological definition until its variants are isolated and extracted from the generic patient population.

Parsing schizophrenia with neurocognitive tests: evidence of stability and validity

The stability and validity of a neurocognitive typology for schizophrenia were studied in 55 chronic patients who met DSMIII-R criteria for the illness. Subtypes were based on an earlier cluster analytic study by Heinrichs and Awad (1993) that utilized the following variables: IQ (WAIS-R), categories (Wisconsin Card Sorting Test), free recall intrusions (California Verbal Learning Test), and bilateral motor performance (Purdue Pegboard). Stability was examined by analyzing subtype assignment at the original assessment and 3 years later at follow-up. Stability over this interval was variable with an overall kappa of .45 and individual kappas from .12 to .66. Adjunct cognitive and clinical data gathered at follow-up provide evidence for the validity of several subtypes, especially in terms of their cognitive and functional differences. There was no evidence of symptom differences in this relatively asymptomatic medicated sample of patients. The results are discussed in terms of the possibility that several patterns of neurocognitive dysfunction may underlie schizophrenia, with implications for understanding the heterogeneity of the illness and its variable functional outcomes.

Is cholinergic sensitivity a genetic marker for the affective disorders?

The recent literature on the involvement of cholinergic muscarinic mechanisms and adrenergic/cholinergic balance in affective disorders is reviewed and integrated with the older literature. There is strong evidence supporting the presence of exaggerated responses (behavioral, neuroendocrine, sleep) to cholinergic agents in affective disorder patients relative to normal controls and certain other psychiatric patients. There is also some, albeit less, conclusive evidence that these exaggerated responses may occur in euthymic individuals with a history of affective disorders, or in children at risk for development of affective disorders. Despite these promising results, suggesting a role for acetylcholine in the genetics of the affective disorders, further work in biochemistry and genetics is needed to link specific muscarinic receptors or other cholinergic variables to affective illness.