Article

Rare Intranuclear Inclusions in the Brains of 3 Older Adult Males With Fragile X Syndrome: Implications for the Spectrum of Fragile X-Associated Disorders

NeuroTherapeutics Research Institute and Department of Neurological Surgery, University of California, Davis School of Medicine, USA.
Journal of Neuropathology and Experimental Neurology (Impact Factor: 4.37). 06/2011; 70(6):462-9. DOI: 10.1097/NEN.0b013e31821d3194
Source: PubMed

ABSTRACT The FMR1 gene is polymorphic for the length of CGG trinucleotide repeat expansions in the 5' untranslated region. Premutation (55-200 CGG repeats) and full-mutation (>200 CGG repeats) alleles give rise to their respective disorders by different pathogenic mechanisms: RNA gain-of-function toxicity leads to fragile X-associated tremor/ataxia syndrome in the premutation range, and transcriptional silencing and absence of fragile X mental retardation protein (FMRP) lead to fragile X syndrome in the full-mutation range. However, for the latter, incomplete silencing and/or size-mosaicism might result in some contribution to the disease process from residual messenger RNA production. To address this possibility, we examined the brains of 3 cases of fragile X syndrome for the presence of intranuclear inclusions in the hippocampal dentate gyrus. We identified low levels (0.1%-1.3%) of intranuclear inclusions in all 3 cases. Quantitative reverse transcription-polymerase chain reaction for FMR1 messenger RNA and immunofluorescence for FMRP revealed low but detectable levels of both RNA and protein in the 3 cases, consistent with the presence of small numbers of inclusions. The intranuclear inclusions were only present in FMRP-immunoreactive cells. The small numbers of inclusions and very low levels of both FMR1 RNA and protein suggest that the clinical course in these 3 subjects would not have been influenced by contributions from RNA toxicity.

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