Both Reaction Time and Accuracy Measures of Intraindividual Variability Predict Cognitive Performance in Alzheimer's Disease

Dementia researchers around the world prioritize the urgent need for sensitive measurement tools that can detect cognitive and functional change at the earliest stages of Alzheimer's disease (AD). Sensitive indicators of underlying neural pathology assist in the early detection of cognitive change and are thus important for the evaluation of early-intervention clinical trials. One method that may be particularly well-suited to help achieve this goal involves the quantification of intraindividual variability (IIV) in cognitive performance. The current study aimed to directly compare two methods of estimating IIV (fluctuations in accuracy-based scores vs. those in latency-based scores) to predict cognitive performance in AD. Specifically, we directly compared the relative sensitivity of reaction time (RT)—and accuracy-based estimates of IIV to cognitive compromise. The novelty of the present study, however, centered on the patients we tested [a group of patients with Alzheimer's disease (AD)] and the outcome measures we used (a measure of general cognitive function and a measure of episodic memory function). Hence, we compared intraindividual standard deviations (iSDs) from two RT tasks and three accuracy-based memory tasks in patients with possible or probable Alzheimer's dementia (n = 23) and matched healthy controls (n = 25). The main analyses modeled the relative contributions of RT vs. accuracy-based measures of IIV toward the prediction of performance on measures of (a) overall cognitive functioning, and (b) episodic memory functioning. Results indicated that RT-based IIV measures are superior predictors of neurocognitive impairment (as indexed by overall cognitive and memory performance) than accuracy-based IIV measures, even after adjusting for the timescale of measurement. However, one accuracy-based IIV measure (derived from a recognition memory test) also differentiated patients with AD from controls, and significantly predicted episodic memory performance. The findings suggest that both RT- and accuracy-based IIV measures may be useful indicators of underlying neuropathology. The present study therefore contributes toward an understanding of the relative utility of RT- and accuracy-based IIV measures in detecting neurocognitive impairment in older adults, and also advances the empirical evaluation of sensitive markers of cognitive change in patients with AD

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<p>Dementia researchers around the world prioritize the urgent need for sensitive measurement tools that can detect cognitive and functional change at the earliest stages of Alzheimer's disease (AD). Sensitive indicators of underlying neural pathology assist in the early detection of cognitive change and are thus important for the evaluation of early-intervention clinical trials. One method that may be particularly well-suited to help achieve this goal involves the quantification of intraindividual variability (IIV) in cognitive performance. The current study aimed to directly compare two methods of estimating IIV (fluctuations in accuracy-based scores vs. those in latency-based scores) to predict cognitive performance in AD. Specifically, we directly compared the relative sensitivity of reaction time (RT)—and accuracy-based estimates of IIV to cognitive compromise. The novelty of the present study, however, centered on the patients we tested [a group of patients with Alzheimer's disease (AD)] and the outcome measures we used (a measure of general cognitive function and a measure of episodic memory function). Hence, we compared intraindividual standard deviations (iSDs) from two RT tasks and three accuracy-based memory tasks in patients with possible or probable Alzheimer's dementia (n = 23) and matched healthy controls (n = 25). The main analyses modeled the relative contributions of RT vs. accuracy-based measures of IIV toward the prediction of performance on measures of (a) overall cognitive functioning, and (b) episodic memory functioning. Results indicated that RT-based IIV measures are superior predictors of neurocognitive impairment (as indexed by overall cognitive and memory performance) than accuracy-based IIV measures, even after adjusting for the timescale of measurement. However, one accuracy-based IIV measure (derived from a recognition memory test) also differentiated patients with AD from controls, and significantly predicted episodic memory performance. The findings suggest that both RT- and accuracy-based IIV measures may be useful indicators of underlying neuropathology. The present study therefore contributes toward an understanding of the relative utility of RT- and accuracy-based IIV measures in detecting neurocognitive impairment in older adults, and also advances the empirical evaluation of sensitive markers of cognitive change in patients with AD.</p

Phenotypic expansion of CACNA1C-associated disorders to include isolated neurological manifestations.

CACNA1C encodes the alpha-1-subunit of a voltage-dependent L-type calcium channel expressed in human heart and brain. Heterozygous variants in CACNA1C have previously been reported in association with Timothy syndrome and long QT syndrome. Several case reports have suggested that CACNA1C variation may also be associated with a primarily neurological phenotype. We describe 25 individuals from 22 families with heterozygous variants in CACNA1C, who present with predominantly neurological manifestations. Fourteen individuals have de novo, nontruncating variants and present variably with developmental delays, intellectual disability, autism, hypotonia, ataxia, and epilepsy. Functional studies of a subgroup of missense variants via patch clamp experiments demonstrated differential effects on channel function in vitro, including loss of function (p.Leu1408Val), neutral effect (p.Leu614Arg), and gain of function (p.Leu657Phe, p.Leu614Pro). The remaining 11 individuals from eight families have truncating variants in CACNA1C. The majority of these individuals have expressive language deficits, and half have autism. We expand the phenotype associated with CACNA1C variants to include neurodevelopmental abnormalities and epilepsy, in the absence of classic features of Timothy syndrome or long QT syndrome

Phenotypic expansion of CACNA1C-associated disorders to include isolated neurological manifestations

International audiencePurpose:CACNA1C encodes the alpha-1-subunit of a voltage-dependent L-type calcium channel expressed in human heart and brain. Heterozygous variants in CACNA1C have previously been reported in association with Timothy syndrome and long QT syndrome. Several case reports have suggested that CACNA1C variation may also be associated with a primarily neurological phenotype.Methods:We describe 25 individuals from 22 families with heterozygous variants in CACNA1C, who present with predominantly neurological manifestations.Results:Fourteen individuals have de novo, nontruncating variants and present variably with developmental delays, intellectual disability, autism, hypotonia, ataxia, and epilepsy. Functional studies of a subgroup of missense variants via patch clamp experiments demonstrated differential effects on channel function in vitro, including loss of function (p.Leu1408Val), neutral effect (p.Leu614Arg), and gain of function (p.Leu657Phe, p.Leu614Pro). The remaining 11 individuals from eight families have truncating variants in CACNA1C. The majority of these individuals have expressive language deficits, and half have autism.Conclusion:We expand the phenotype associated with CACNA1C variants to include neurodevelopmental abnormalities and epilepsy, in the absence of classic features of Timothy syndrome or long QT syndrome