Age-related cortical grey matter reductions in non-demented Down's syndrome adults determined by MRI with voxel-based morphometry.

Ageing in Down's syndrome is accompanied by amyloid and neurofibrillary pathology the distribution of which replicates pathological features of Alzheimer's disease. With advancing age, an increasing proportion of Down's syndrome subjects >40 years old develop progressive cognitive impairment, resembling the cognitive profile of Alzheimer's disease. Based on these findings, Down's syndrome has been proposed as a model to study the predementia stages of Alzheimer's disease. Using an interactive anatomical segmentation technique and volume-of-interest measurements of MRI, we showed recently that non-demented Down's syndrome adults had significantly reduced hippocampus, entorhinal cortex and corpus callosum sizes with increasing age. In this study, we applied the automated and objective technique of voxel-based morphometry, implemented in SPM99, to the analysis of structural MRI from 27 non-demented Down's syndrome adults (mean age 41.1 years, 15 female). Regional grey matter volume was decreased with advancing age in bilateral parietal cortex (mainly the precuneus and inferior parietal lobule), bilateral frontal cortex with left side predominance (mainly middle frontal gyrus), left occipital cortex (mainly lingual cortex), right precentral and left postcentral gyrus, left transverse temporal gyrus, and right parahippocampal gyrus. The reductions were unrelated to gender, intracranial volume or general cognitive function. Grey matter volume was relatively preserved in subcortical nuclei, periventricular regions, the basal surface of the brain (bilateral orbitofrontal and anterior temporal) and the anterior cingulate gyrus. Our findings suggest grey matter reductions in allocortex and association neocortex in the predementia stage of Down's syndrome. The most likely substrate of these changes is alterations or loss of allocortical and neocortical neurons due to Alzheimer's disease-type pathology.

Differential diagnosis of Alzheimer disease with cerebrospinal fluid levels of tau protein phosphorylated at threonine 231.

BACKGROUND: Phosphorylation of tau protein at threonine 231 (using full-length tau, 441 amino acids, for the numbering scheme) (p-tau(231)) occurs specifically in postmortem brain tissue of patients with Alzheimer disease (AD) and can be sensitively detected in cerebrospinal fluid (CSF). OBJECTIVES: To determine to what extent CSF levels of p-tau(231) distinguish patients with AD from control subjects and from patients with other dementias, and to investigate whether p-tau(231) levels are a better diagnostic marker than levels of total tau protein (t-tau) in CSF. DESIGN AND SETTING: Cross-sectional, multicenter, memory clinic-based studies. PARTICIPANTS: One hundred ninety-two patients with a clinical diagnosis of AD, frontotemporal dementia (FTD), vascular dementia, Lewy body dementia, or other neurological disorder and healthy controls. MAIN OUTCOME MEASURES: Levels of CSF tau proteins as measured with enzyme-linked immunosorbent assays. RESULTS: Mean CSF levels of p-tau(231) were significantly elevated in the AD group compared with all other groups. Levels of p-tau(231) did not correlate with dementia severity in AD, and discriminated with a sensitivity of 90.2% and a specificity of 80.0% between AD and all non-AD disorders. Moreover, p-tau(231) levels improved diagnostic accuracy compared with t-tau levels when patients with AD were compared with healthy controls (P =.03) and demented subjects (P<.001), particularly those with FTD (P<.001), but not those with vascular and Lewy body dementias. Sensitivity levels between AD and FTD were raised by p-tau(231) compared with t-tau levels from 57.7% to 90.2% at a specificity level of 92.3% for both markers. CONCLUSION: Increased levels of CSF p-tau(231) may be a useful, clinically applicable biological marker for the differential diagnosis of AD, particularly for distinguishing AD from FTD.

Progression of corpus callosum atrophy in Alzheimer disease.

BACKGROUND: Atrophy of the corpus callosum in the absence of primary white matter degeneration reflects loss of intracortical projecting neocortical pyramidal neurons in Alzheimer disease (AD). OBJECTIVES: To determine individual rates of atrophy progression of the corpus callosum in patients with AD and to correlate rates of atrophy progression with clinical disease severity and subcortical disease. METHODS: Magnetic resonance imaging-derived measurements of corpus callosum size were studied longitudinally in 21 patients clinically diagnosed as having AD (mean observation time, 17.0 +/- 8.5 months) and 10 age- and sex-matched healthy controls (mean observation time, 24.1 +/- 6.8 months). RESULTS: Corpus callosum size was significantly reduced in AD patients at baseline. Annual rates of atrophy of total corpus callosum, splenium, and rostrum were significantly larger in AD patients (-7.7%, -12.1%, and -7.3%, respectively) than in controls (-0.9%, -1.5%, and 0.6%, respectively). Rates of atrophy of the corpus callosum splenium were correlated with progression of dementia severity in AD patients (rho = 0.52, P<.02). The load of subcortical lesions at baseline (P<.05) predicted rate of anterior corpus callosum atrophy in healthy controls. Rates of atrophy of corpus callosum areas were independent of white matter hyperintensity load in patients with AD. CONCLUSIONS: Measurement of corpus callosum size allows in vivo mapping of neocortical neurodegeneration in AD over a wide range of clinical dementia severities and may be used as a surrogate marker for evaluation of drug efficacy.