Familial frontotemporal dementia with neuronal intranuclear inclusions is not a polyglutamine expansion disease.

Abstract

BACKGROUND:

Many cases of frontotemporal dementia (FTD) are familial, often with an autosomal dominant pattern of inheritance. Some are due to a mutation in the tau- encoding gene, on chromosome 17, and show an accumulation of abnormal tau in brain tissue (FTDP-17T). Most of the remaining familial cases do not exhibit tau pathology, but display neuropathology similar to patients with dementia and motor neuron disease, characterized by the presence of ubiquitin-immunoreactive (ub-ir), dystrophic neurites and neuronal cytoplasmic inclusions in the neocortex and hippocampus (FTLD-U). Recently, we described a subset of patients with familial FTD with autopsy-proven FTLD-U pathology and with the additional finding of ub-ir neuronal intranuclear inclusions (NII). NII are a characteristic feature of several other neurodegenerative conditions for which the genetic basis is abnormal expansion of a polyglutamine-encoding trinucleotide repeat region. The genetic basis of familial FTLD-U is currently not known, however the presence of NII suggests that a subset of cases may represent a polyglutamine expansion disease.

METHODS:

We studied DNA and post mortem brain tissue from 5 affected members of 4 different families with NII and one affected individual with familial FTLD-U without NII. Patient DNA was screened for CAA/CAG trinucleotide expansion in a set of candidate genes identified using a genome-wide computational approach. Genes containing CAA/CAG trinucleotide repeats encoding at least five glutamines were examined (n = 63), including the nine genes currently known to be associated with human disease. CAA/CAG tract sizes were compared with published normal values (where available) and with those of healthy controls (n = 94). High-resolution agarose gel electrophoresis was used to measure allele size (number of CAA/CAG repeats). For any alleles estimated to be equal to or larger than the maximum measured in the control population, the CAA/CAG tract length was confirmed by capillary electrophoresis. In addition, immunohistochemistry using a monoclonal antibody that recognizes proteins containing expanded polyglutamines (1C2) was performed on sections of post mortem brain tissue from subjects with NII.

RESULTS:

No significant polyglutamine-encoding repeat expansions were identified in the DNA from any of our FTLD-U patients. NII in the FTLD-U cases showed no 1C2 immunoreactivity.

CONCLUSION:

We find no evidence to suggest that autosomal dominant FTLD-U with NII is a polyglutamine expansion disease.

• Authors: Ian R Mackenzie, Stefanie L Butland, Rebecca S Devon, Emily Dwosh, Howard Feldman, Caroline Lindholm, Scott J Neal, B F Francis Ouellette, Blair R Leavitt
• Journal: BMC neurology (BMC Neurol) Vol. 6 Pg. 32 (Aug 31 2006) ISSN: 1471-2377 [Electronic] England
• PMID: 16945149 (Publication Type: Comparative Study, Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Peptides
• polyglutamine

Topics

• Brain (pathology)
• Dementia (genetics, pathology)
• Diagnosis, Differential
• Humans
• Intranuclear Inclusion Bodies (genetics, pathology)
• Peptides (genetics)
• Trinucleotide Repeat Expansion (genetics)