Distinctive patterns of memory function in subgroups of females with Turner syndrome: evidence for imprinted loci on the X-chromosome affecting neurodevelopment.
Bishop DV., Canning E., Elgar K., Morris E., Jacobs PA., Skuse DH.
X-monosomy is a form of Turner syndrome (TS) in which an entire X chromosome is missing. It is usually assumed that neuropsychological deficits in females with TS result from insufficient dosage of gene products from alleles on the sex chromosomes. If so, then parental origin of the single X chromosome should be immaterial. However, if there are imprinted genes on the X chromosome affecting brain development, neuropsychological development will depend on the parental origin of the single X chromosome. We contrasted verbal and visuospatial memory in females with a single paternal X chromosome (45,X(p)) and those with a single maternal X (45,X(m)). Neither group showed any impairment on immediate story recall; if anything, performance was above control levels. Groups did not differ on a measure of delayed recall. However, when delayed recall was considered after adjusting for level of immediate recall, 45,X(m) females showed enhanced verbal forgetting relative to controls over a delay. On the Rey figure, both groups were poor at copying the figure, but, after adjusting scores for initial copy score and strategy, only the 45,X(p) females showed disproportionate forgetting relative to controls. We propose there may be one or more imprinted genes on the X chromosome that affect the development of lateralised brain regions important for memory function.