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Polyglutamine immunoreactivity is present in FTLD‐U and normal controls

1C2 is a monoclonal antibody raised against the N‐terminus of the human TATA‐box binding protein that contains a string of 38 glutamines. We have previously demonstrated 1C2 immunoreactivity in the substantia nigra, locus coeruleus, and globus pallidus of 2 FTLD‐Ub cases. To investigate this further, we stained sections of the midbrain, pons, and globus pallidus of 10 FTLD‐Ub cases and 2 normal controls using 1C2. In all cases 1C2 immunoreactivity was present in neuropil and in the cytoplasm of neurons, microglia, or both. 9 out of 10 FTLD‐U cases demonstrated 1C2 immunoreactivity in the substantia nigra, but only one revealed immunopositivity in the locus coeruleus. Chromogen deposition was independent of neuromelanin distribution. Granular 1C2 immunoreactivity was present within the neuropil or cytoplasm of globus pallidus microglia in all cases. This strong, reproducible, but previously undescribed 1C2 immunoreactivity warrants further assessment of its binding specificity. Alternatively, expanded CAG repeats may be present in selected CNS locations in normal individuals and those without known CAG repeat diseases. In either case, caution is indicated in interpreting 1C2 immunostaining results in diagnostic and pathogenetic studies of possible CAG repeat disorder cases.