Abstract
Carriers of the fragile X premutation allele (fXPCs) have an expanded CGG trinucleotide repeat size within the FMR1 gene and are at increased risk of developing fragile x-associated tremor/ataxia syndrome (FXTAS). Previous research has shown that male fXPCs with FXTAS exhibit cognitive decline, predominantly in executive functions such as inhibitory control and working memory. Recent evidence suggests fXPCs may also exhibit impairments in processing temporal information. The attentional blink (AB) task is often used to examine the dynamics of attentional selection, but disagreements exist as to whether the AB is due to excessive or insufficient attentional control. In this study, we used a variant of the AB task and neuropsychological testing to explore the dynamics of attentional selection, relate AB performance to attentional control, and determine whether fXPCs exhibited temporal and/or attentional control impairments. Participants were adult male fXPCs, aged 18–48 years and asymptomatic for FXTAS (n = 19) and age-matched male controls (n = 20). We found that fXPCs did not differ from controls in the AB task, indicating that the temporal dynamics of attentional selection were intact. However, they were impaired in the letter-number sequencing task, a test of executive working memory. In the combined fXPC and control group, letter-number sequencing performance correlated positively with AB magnitude. This finding supports models that posit the AB is due to excess attentional control. In our two-pronged analysis approach, in control participants we replicated a previously observed effect and demonstrated that it persists under more stringent theoretical constraints, and we enhance our understanding of fXPCs by demonstrating that at least some aspects of temporal processing may be spared.
Highlights
Fragile X premutation carriers are defined as individuals who have a 55–200 CGG repeat expansion in the FMR1 gene, which is located on the X chromosome
ADHD self-report data were available from 19 controls and 18 fragile x premutation carrier (fXPC), and observer-report data were available www.frontiersin.org
Our main finding is that fXPCs do not differ from controls in attentional blink (AB) magnitude, indicating that the temporal dynamics of attentional selection are intact in fXPCs
Summary
Fragile X premutation carriers (fXPCs) are defined as individuals who have a 55–200 CGG repeat expansion in the FMR1 gene, which is located on the X chromosome. The FXTAS phenotype is thought to be due to a toxic gain of function of excess FMR1 mRNA, which is associated with increasing CGG repeat length (Hagerman and Hagerman, 2004). This potential mechanism is supported by associations between CGG repeat length and age of onset of FXTAS (Tassone et al, 2007); level of motor impairment in fXPCs (Leehey et al, 2008); negative associations of CGG repeat length with brain volume, packing density of middle cerebellar peduncle, and gray matter density of the dorsomedial frontal lobes (Cohen et al, 2006; Hashimoto et al, 2011a,b); and negative associations of both CGG repeat length and FMR1 mRNA with the connectivity strength of the superior cerebellar peduncle (Wang et al, 2013)
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