Learning and memory in monozygotic twins discordant for schizophrenia

Abstract

SynopsisLearning and memory were assessed in 24 monozygotic (MZ) pairs of individuals discordant for schizophrenia or delusional disorder and seven normal pairs of MZ twins. On declarative memory tasks, the affected group displayed a pattern that might best be characterized as dysmnesic in that they performed significantly worse than the discordant unaffected group on story recall, paired associated learning, and visual recall of designs, but they learned over time, had relatively preserved recognition memory, and did not show profoundly accelerated rates of forgetting. Effortful, volitional retrieval from the lexicon, measured by verbal fluency, was also compromised in the affected group. On the other hand, procedural learning of the motor skill in a pursuit rotor task was relatively intact in the affected group. Comparisons of the normal group and unaffected group indicated that the latter group had very mild impairments in some aspects of episodic memory, namely, immediate and delayed recall of stories and delayed recall of designs. It is highly unlikely that the impairments observed in the affected group can be attributed to differences in genome, family environment, socioeconomic circumstance, or educational opportunity, as all of these were controlled by the twin paradigm. Rather, the impairments appear to be related to the intercession of disease. The neuropsychological profile is consistent with frontal lobe and medial temporal lobe dysfunction, as noted in this sample as well as other samples of schizophrenic singletons. Significant correlations between many measures of memory and global level of social and vocational functioning within the discordant group were also found. Thus difficulties in rapidly acquiring new information and propitiously retrieving old information may burden patients with schizophrenia in many of the transactions of everyday life.

Psychomotor slowing and planning deficits in schizophrenia

“…A great advantage of this type of task is that the figures to be copied are rather simple and, by mirroring the stimuli, the perceptual and memory load is kept constant. As was to be expected from studies showing that schizophrenia is associated with intact procedural learning (Clare et al, 1993;Goldberg, et al, 1993;Watanabe et al, 2002), the results demonstrated that patients with schizophrenia performed within the normal range when they copied the 'non-conflicting' patterns. However, in copying 'conflicting' patterns patients performed differently compared to the healthy controls.…”

Catechol-O-methyl transferase Val158Met gene polymorphism in schizophrenia: working memory, frontal lobe MRI morphology and frontal cerebral blood flow

“…In this study, only the total raw score of the number of correct items from the backward portion of the test is used, since previous studies suggest that the backward span task is a more robust measure of working memory. 17,66 The Trail Making test is a measure of executive functioning and set alternation. 69 Trail A involves connecting numbers in succession, while Trail B requires subjects to connect numbers and letters alternately in successive order.…”

“…12 Schizophrenia patients as well as their unaffected relatives perform poorly on tasks that assess working memory function. [13][14][15][16][17][18][19][20][21][22][23] Working memory is moderately heritable with 43-49% of its variability accounted by genetic factors 24 In a series of studies involving a population isolate, a significant additive genetic heritability estimate was found in verbal working memory, and for visual working memory at a trend level. 20,21,25 Spatial working memory performance was more highly correlated in monozygotic twins than in dizygotic twin pairs.…”

Verbal recall and recognition in twins discordant for schizophrenia

“…A study that included non-ill relatives with either one or multiple first-degree relatives diagnosed with schizophrenia showed that deficits in story recall scaled with the level of genetic predisposition for the disorder (Faraone et al, 2000). Three twin reports including MZ twin pairs discordant for schizophrenia as well as control twins found that patients performed significantly worse than their co-twins, who performed significantly worse than the healthy twins on a story recall task, suggesting disease-related as well as familial influences on verbal memory performance in schizophrenia (Goldberg et al, 1990;Goldberg et al, 1993;Goldberg et al, 1995). Furthermore, one report showed that patients from concordant pairs did not differ from patients from discordant pairs, suggesting a similar etiology of the observed performance deficits in both groups (Goldberg et al, 1995).…”