Abstract
Fragile X syndrome (FXS) is a common genetic disorder in which temporal processing may be impaired. To our knowledge however, no studies have examined the neural basis of temporal discrimination in individuals with FXS using functional magnetic resonance imaging (fMRI). Ten girls with fragile X syndrome and ten developmental age-matched typically developing controls performed an auditory temporal discrimination task in a 3T scanner. Girls with FXS showed significantly greater brain activation in a left-lateralized network, comprising left medial frontal gyrus, left superior and middle temporal gyrus, left cerebellum, and left brainstem (pons), when compared to a developmental age-matched typically developing group of subjects who had similar in-scanner task performance. There were no regions that showed significantly greater brain activation in the control group compared to individuals with FXS. These data indicate that networks of brain regions involved in auditory temporal processing may be dysfunctional in FXS. In particular, it is possible that girls with FXS employ left hemispheric resources to overcompensate for relative right hemispheric dysfunction.
Highlights
Fragile X Syndrome (FXS) is the most common cause of inherited mental retardation, affecting up to one in 4,000 individuals in the general population [5]
FXS most commonly occurs in association with an expansion of a CGG trinucleotide sequence within the FMR1 gene located at band 27.3q of the X chromosome [35]
Ten female subjects diagnosed with FXS and ten female developmental age-matched typically developing (TD) controls with no known history of neurological or psychiatric disorder participated in the study
Summary
Fragile X Syndrome (FXS) is the most common cause of inherited mental retardation, affecting up to one in 4,000 individuals in the general population [5]. FXS most commonly occurs in association with an expansion of a CGG trinucleotide sequence within the FMR1 gene located at band 27.3q of the X chromosome [35]. This expansion generally leads to hypermethylation of the gene, resulting in reduced production of FMR1 protein (FMRP). The deficiency of FMRP observed in FXS leads to abnormalities in both brain development and function, primarily thought to be related to aberrant development and plasticity of synapses [10]. Previous research has indicated that individuals with FXS possess characteristic structural abnormalities in specific brain regions including increased volume of the caudate nucleus [6, 15]. Other brain regions show reduction in size in comparison to control subjects, including the cerebellar vermis and the superior temporal gyrus [22, 29], key brain regions involved in motor control and auditory processing [17]
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