Longitudinal neuroanatomical and cognitive progression of posterior cortical atrophy.

Posterior cortical atrophy is a clinico-radiological syndrome characterized by progressive decline in visual processing and atrophy of posterior brain regions. With the majority of cases attributable to Alzheimer's disease and recent evidence for genetic risk factors specifically related to posterior cortical atrophy, the syndrome can provide important insights into selective vulnerability and phenotypic diversity. The present study describes the first major longitudinal investigation of posterior cortical atrophy disease progression. Three hundred and sixty-one individuals (117 posterior cortical atrophy, 106 typical Alzheimer's disease, 138 controls) fulfilling consensus criteria for posterior cortical atrophy-pure and typical Alzheimer's disease were recruited from three centres in the UK, Spain and USA. Participants underwent up to six annual assessments involving MRI scans and neuropsychological testing. We constructed longitudinal trajectories of regional brain volumes within posterior cortical atrophy and typical Alzheimer's disease using differential equation models. We compared and contrasted the order in which regional brain volumes become abnormal within posterior cortical atrophy and typical Alzheimer's disease using event-based models. We also examined trajectories of cognitive decline and the order in which different cognitive tests show abnormality using the same models. Temporally aligned trajectories for eight regions of interest revealed distinct (P < 0.002) patterns of progression in posterior cortical atrophy and typical Alzheimer's disease. Patients with posterior cortical atrophy showed early occipital and parietal atrophy, with subsequent higher rates of temporal atrophy and ventricular expansion leading to tissue loss of comparable extent later. Hippocampal, entorhinal and frontal regions underwent a lower rate of change and never approached the extent of posterior cortical involvement. Patients with typical Alzheimer's disease showed early hippocampal atrophy, with subsequent higher rates of temporal atrophy and ventricular expansion. Cognitive models showed tests sensitive to visuospatial dysfunction declined earlier in posterior cortical atrophy than typical Alzheimer's disease whilst tests sensitive to working memory impairment declined earlier in typical Alzheimer's disease than posterior cortical atrophy. These findings indicate that posterior cortical atrophy and typical Alzheimer's disease have distinct sites of onset and different profiles of spatial and temporal progression. The ordering of disease events both motivates investigation of biological factors underpinning phenotypic heterogeneity, and informs the selection of measures for clinical trials in posterior cortical atrophy.

Effect of age at onset on cortical thickness and cognition in posterior cortical atrophy.

Age at onset (AAO) has been shown to influence the phenotype of Alzheimer's disease (AD), but how it affects atypical presentations of AD remains unknown. Posterior cortical atrophy (PCA) is the most common form of atypical AD. In this study, we aimed to investigate the effect of AAO on cortical thickness and cognitive function in 98 PCA patients. We used Freesurfer (v5.3.0) to compare cortical thickness with AAO both as a continuous variable, and by dichotomizing the groups based on median age (58 years). In both the continuous and dichotomized analyses, we found a pattern suggestive of thinner cortex in precuneus and parietal areas in earlier-onset PCA, and lower cortical thickness in anterior cingulate and prefrontal cortex in later-onset PCA. These cortical thickness differences between PCA subgroups were consistent with earlier-onset PCA patients performing worse on cognitive tests involving parietal functions. Our results provide a suggestion that AAO may not only affect the clinico-anatomical characteristics in AD but may also affect atrophy patterns and cognition within atypical AD phenotypes.

Genetic risk factors for the posterior cortical atrophy variant of Alzheimer's disease.

INTRODUCTION: The genetics underlying posterior cortical atrophy (PCA), typically a rare variant of Alzheimer's disease (AD), remain uncertain. METHODS: We genotyped 302 PCA patients from 11 centers, calculated risk at 24 loci for AD/DLB and performed an exploratory genome-wide association study. RESULTS: We confirm that variation in/near APOE/TOMM40 (P = 6 × 10(-14)) alters PCA risk, but with smaller effect than for typical AD (PCA: odds ratio [OR] = 2.03, typical AD: OR = 2.83, P = .0007). We found evidence for risk in/near CR1 (P = 7 × 10(-4)), ABCA7 (P = .02) and BIN1 (P = .04). ORs at variants near INPP5D and NME8 did not overlap between PCA and typical AD. Exploratory genome-wide association studies confirmed APOE and identified three novel loci: rs76854344 near CNTNAP5 (P = 8 × 10(-10) OR = 1.9 [1.5-2.3]); rs72907046 near FAM46A (P = 1 × 10(-9) OR = 3.2 [2.1-4.9]); and rs2525776 near SEMA3C (P = 1 × 10(-8), OR = 3.3 [2.1-5.1]). DISCUSSION: We provide evidence for genetic risk factors specifically related to PCA. We identify three candidate loci that, if replicated, may provide insights into selective vulnerability and phenotypic diversity in AD.

Neuropsychiatric Symptoms in Posterior Cortical Atrophy and Alzheimer Disease.

BACKGROUND: Posterior cortical atrophy (PCA) is a rare neurodegenerative syndrome characterized by early progressive visual dysfunction in the context of relative preservation of memory and a pattern of atrophy mainly involving the posterior cortex. The aim of the present study is to characterize the neuropsychiatric profile of PCA. METHODS: The Neuropsychiatric Inventory was used to assess 12 neuropsychiatric symptoms (NPS) in 28 patients with PCA and 34 patients with typical Alzheimer disease (AD) matched by age, disease duration, and illness severity. RESULTS: The most commonly reported NPS in both groups were depression, anxiety, apathy, and irritability. However, aside from a trend toward lower rates of apathy in patients with PCA, there were no differences in the percentage of NPS presented in each group. All those patients presenting visual hallucinations in the PCA group also met diagnostic criteria for dementia with Lewy bodies (DLB). Auditory hallucinations were only present in patients meeting diagnosis criteria for DLB. CONCLUSION: Prevalence of the 12 NPS examined was similar between patients with PCA and AD. Hallucinations in PCA may be helpful in the differential diagnosis between PCA-AD and PCA-DLB.

Restoration of conceptual knowledge in a case of semantic dementia.

Patients with semantic dementia (SD) may undergo successful relearning of object names, but these gains are usually restricted to the trained exemplars, demonstrating poor generalization. We hypothesized that generalization could be improved by restoring an item's semantic network through specific strategies that recruit the remaining personal semantic memories (conceptual enrichment therapies). We describe the case of a patient with SD who showed greater generalization of learning following a conceptual enrichment therapy than when learning items in a word-retrieval therapy. Our results suggest that enhancing an item's semantic network connections may result in improved generalization of learning in SD. A learning mechanism in the presence of compromised hippocampi is also discussed.

Utility of neuropsychiatric tools in the differential diagnosis of dementia with Lewy bodies and Alzheimer's disease: quantitative and qualitative findings.

BACKGROUND: Discerning dementia with Lewy bodies (DLB) from Alzheimer's disease (AD) is one of the most common and challenging differential diagnoses at the memory clinic. Although the neuropsychiatric manifestations have been widely reported as one of the main key points in the differential diagnosis between these two diseases, to date no neuropsychiatric questionnaire has been specifically devised for this purpose. METHODS: We administered the Neuropsychiatric Inventory (NPI) and the Columbia University Scale for Psychopathology in Alzheimer's Disease (CUSPAD) to a memory clinic sample of 80 patients with probable DLB and 85 age- and severity-matched patients with probable AD. Diagnosis of probable DLB was supported with a positive dopamine transporter SPECT scan. We examined the usefulness of these two neuropsychiatric tools designed for AD in the differential diagnosis between DLB and AD. We also investigated the correlations between psychotic symptoms and measures of cognitive and functional decline. RESULTS: Auditory hallucinations were very specific of DLB and were usually preceded by visual hallucinations. Misinterpretation of real visual stimuli (illusions) was more frequent in DLB. Delusions were both quantitatively and qualitatively different between DLB and AD: delusional misidentifications were significantly more characteristic of DLB, while paranoid delusions did not show specificity for DLB. CONCLUSIONS: Neuropsychiatric tools are useful to discriminate DLB from AD. Hallucinations and delusions are not only more frequent in DLB than in AD but also have distinct qualitative characteristics and patterns of progression that can help clinicians to make a more accurate differential diagnosis.

C9ORF72 hexanucleotide expansions of 20-22 repeats are associated with frontotemporal deterioration.

OBJECTIVE: Expansions of more than 30 hexanucleotide repetitions in the C9ORF72 gene are a common cause of frontotemporal dementia (FTD) or amyotrophic lateral sclerosis (ALS). However, the range of 20-30 repetitions is rarely found and still has unclear significance. A screening of our cohort of cases with FTD (n = 109) revealed 4 mutation carriers (>30 repetitions) but also 5 probands with 20-22 confirmed repetitions. This study explored the possible pathogenic correlation of the 20-22 repeats expansion (short expansion). METHODS: Comparison of clinical phenotypes between cases with long vs short expansions; search for segregation in the families of probands with short expansion; analysis of the presence of the common founder haplotype, described for expansions >30 repeats, in the cases having the short expansion; and analysis of the distribution of hexanucleotide repeat alleles in a control population. RESULTS: No different patterns were found in the clinical phenotype or aggressiveness of the disease when comparing cases with long or short expansions. Cases in both groups had psychiatric symptoms during 1-3 decades before evolving insidiously to cognitive deterioration. The study of the families with short expansion showed clear segregation of the 20-22 repeats allele with the disease. Moreover, this 20-22 repeats allele was associated in all cases with the pathogenic founder haplotype. None of 216 controls had alleles with more than 14 repetitions. CONCLUSIONS: Description of these families suggests that short C9ORF72 hexanucleotide expansions are also related to frontotemporal cognitive deterioration.

Abnormal sensorimotor plasticity in CADASIL correlates with neuropsychological impairment.

OBJECTIVE: Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is a small vessel disease of the brain caused by mutations in the NOTCH3 gene. CADASIL progresses, in some cases, to subcortical dementia with a particular cognitive impairment. Different diseases in the dementia spectrum share a central cholinergic and sensorimotor plasticity alteration. We aimed to study different intracortical circuits and sensorimotor plasticity in CADASIL patients using transcranial magnetic stimulation protocols, and to determine whether these characteristics correlated with the results of clinical neuropsychological evaluation. METHODS: Ten CADASIL patients and 10 healthy subjects were included in the study. All subjects underwent a transcranial magnetic stimulation study examining different intracortical circuits. Sensorimotor plasticity was also assessed using a paired associative stimulation and extensive neuropsychological tests. RESULTS: CADASIL patients showed a lack of intracortical facilitation, short latency afferent inhibition and sensorimotor plasticity when compared with control subjects. CADASIL patients also showed an altered neuropsychological profile. Correlation between sensorimotor plasticity and neuropsychological alterations was observed in CADASIL patients. CONCLUSIONS: These results suggest that acetylcholine and glutamate could be involved in the dementia process in CADASIL and that abnormal sensorimotor plasticity correlates with the neuropsychological profile in CADASIL patients.

Disturbed sleep patterns in elders with mild cognitive impairment: the role of memory decline and ApoE ε4 genotype.

Sleep disturbances are prevalent in patients with Alzheimer' disease (AD), being one of the most troubling symptoms during the progression of disease. However, little research has been made to determine if impaired sleep patterns appear years before AD diagnosis. This study tries to shed light on this issue by performing polysomnographic recordings in healthy elders and patients with mild cognitive impairment (MCI). We further investigated whether changes in sleep patterns parallel memory decline as well as its relationship with the Apolipoprotein E (ApoE) ɛ4 genotype. Results showed a significant shortening of rapid eye movement (REM) sleep together with increased fragmentations of slow-wave sleep in MCI patients relative to healthy elders. Interestingly, we further showed that reduction of REM sleep in MCI patients with ApoE ɛ4 was more noticeable than in ɛ4 non-carriers. Contrary to our initial hypothesis, changes in sleep patterns were not correlated with memory performance in MCI patients. Instead, increased REM sleep accompanied enhanced immediate recall in MCI ɛ4 non-carriers. Taken together, these results suggest that sleep disruptions are evident years before diagnosis of AD, which may have implications for early detection of dementia and/or therapeutic management of sleep complaints in MCI patients.

Clinical-genetic correlations in familial Alzheimer's disease caused by presenilin 1 mutations.

We describe the clinical phenotype of nine kindred with presenile Alzheimer's disease (AD) caused by different presenilin 1 (PS1) point mutations, and compare them with reported families with mutations in the same codons. Mutations were in exon 4 (Phe105Val), exon 5 (Pro117Arg, Glu120Gly), exon 6 (His163Arg), exon 7 (Leu226Phe), exon 8 (Val261Leu, Val272Ala, Leu282Arg), and exon 12 (Ile439Ser). Three of these amino acid changes (Phe105Val, Glu120Gly, and Ile439Ser) had not been previously reported. Distinct clinical features, including age of onset, symptoms and signs associated with the cortical-type dementia and aggressiveness of the disease, characterized the different mutations and were quite homogeneous across family members. Age of onset fell within a consistent range: some mutations caused the disease in the thirties (P117R, L226F, V272A), other in the forties (E120G, H163R, V261L, L282R), and other in the fifties (F105V, I439S). Associated features also segregated with specific mutations: early epileptic activity (E120G), spastic paraparesis (V261L), subcortical dementia and parkinsonism (V272A), early language impairment, frontal signs, and myoclonus (L226F), and late myoclonus and seizures (H163R, L282R). Neurological deterioration was particularly aggressive in PS1 mutations with earlier age of onset such as P117R, L226F, and E120G. With few exceptions, a similar clinical phenotype was found in families reported to have either the same mutation or different amino acid changes in the same codons. This series points to a strong influence of the specific genetic defect in the development of the clinical phenotype.

Reduction of basal forebrain cholinergic system parallels cognitive impairment in patients at high risk of developing Alzheimer's disease.

Neuropathological studies suggest that the basal forebrain cholinergic system (BFCS) is affected in Alzheimer's disease (AD), but there is no in vivo evidence of early damage to this system in subjects at high risk of developing AD. Here, we found that mild cognitive impairment (MCI) patients exhibited significant volume reduction of the nucleus basalis of Meynert (NbM) using recently developed probabilistic maps of the BFCS space. In addition, volumes of different magnocellular compartments varied significantly with regional gray matter atrophy in regions known to be affected by AD and were found to correlate with cognitive decline in MCI patients. Bilateral reductions of the horizontal nucleus of the diagonal band of Broca (Ch3) and frontal lobe (medial frontal, orbital, subcallosal gyrus, anterior cingulate, and middle frontal gyrus) were significantly associated with a global decline in cognitive status, whereas volume reduction of the posterior compartment of Ch4 (NbM) and temporal lobe (including hippocampus, entorhinal cortex, and amygdala) were associated with impaired delayed recall in MCI patients. These findings establish, for the first time, a link between degeneration of specific cholinergic compartments of the BFCS and cognitive-related deficits in subjects at high risk of developing AD.

Functional integrity of thalamocortical circuits differentiates normal aging from mild cognitive impairment.

Resonance in thalamocortical networks is critically involved in sculpting oscillatory behavior in large ensembles of neocortical cells. Neocortical oscillations provide critical information about the integrity of thalamocortical circuits and functional connectivity of cortical networks, which seem to be significantly disrupted by the neuronal death and synapse loss characterizing Alzheimer's disease (AD). By applying a novel analysis methodology to overcome volume conduction effects between scalp electroencephalographic (EEG) measurements, we were able to estimate the temporal activation of EEG-alpha sources in the thalamus and parieto-occipital regions of the cortex. We found that synaptic flow underlying the lower alpha band (7.5-10 Hz) was abnormally facilitated in patients with mild cognitive impairment (MCI) as compared to healthy elderly individuals, particularly from thalamus to cortex (approximately 38% higher). In addition, the thalamic generator of lower alpha oscillations was also abnormally activated in patients with MCI. Regarding the upper alpha subdivision (10.1-12.5 Hz), both controls and patients with MCI showed a bidirectional decrease of thalamocortical synaptic transmission, which was age-dependent only in the control group. Altogether, our results suggest that functional dynamics of thalamocortical networks differentiate individuals at high risk of developing AD from healthy elderly subjects, supporting the hypothesis that neurodegeneration mechanisms are active years before the patient is clinically diagnosed with dementia.

Increased synchronization and decreased neural complexity underlie thalamocortical oscillatory dynamics in mild cognitive impairment.

Abnormal patterns of electroencephalographic (EEG) alpha oscillations in preclinical stages of dementia reveal a selective vulnerability of thalamocortical circuits to the cascade of neurodegenerative events heralding Alzheimer's disease (AD). EEG-alpha slowing characterizes both mild cognitive impairment (MCI) and healthy aging, but it remains ambiguous whether different neural mechanisms underlie this oscillatory behavior in normal and pathological senescence. In this study, we show that the strength of phase coupling and the level of phase predictability between thalamocortical and cortico-cortical EEG sources of low alpha frequency are abnormally facilitated in MCI patients when compared to healthy elderly subjects. Additionally, we found a loss of neural complexity intrinsic to both thalamic and cortical generators of lower alpha in MCI patients, which likely influenced the aberrant phase synchronization behavior between EEG-alpha sources in this high risk group of AD. Taken together, these results suggest that different neural mechanisms account for the well known slowing of alpha rhythm present in normal aging and MCI patients. Whether these anomalous neural coding mechanisms of lower alpha generation in MCI patients represent a potential electrophysiological marker of mild AD is a topic for future research.

Relationship between the efficacy of rivastigmine and apolipoprotein E (epsilon4) in patients with mild to moderately severe Alzheimer disease.

Alzheimer disease is the most common form of dementia in Western countries and the leading cause of disability in the over-65 population. Apolipoprotein E (APOE) is a multifunctional protein implied in lipid metabolism and neurobiology. Polymorphisms of the APOE gene have been associated with a variety of medical disorders, from arteriosclerosis to AD. A high frequency of the APOE epsilon4 allele has been found in patients with AD and they seem to have a higher risk of developing the disease. Various authors have suggested a possible relationship between the efficacy of cholinesterase inhibitors and the presence of the APOE epsilon4 allele. The purpose of the present study was to compare prospectively the efficacy of rivastigmine in patients with mild to moderately severe AD presenting different polymorphisms of the APOE gene on chromosome 19 and to determine if there was a difference in the response to rivastigmine treatment in AD patients with the APOE epsilon4 allele (heterozygous or homozygous) versus patients who had other forms of APOE, such as epsilon2 and epsilon3. This was an open-label, nonrandomized, multicenter study in patients over 50 years of age diagnosed with mild to moderately severe AD. The results of the analysis of this study indicate that the presence of at least one APOE epsilon4 allele does not determine a difference in the response to treatment with rivastigmine. The data indicate that knowledge of the patient's genotype is not necessary for treatment with rivastigmine. It would be interesting in the future to analyze the interaction between these 2 factors using other available anticholinesterase drugs.

Left hemicranial hypoplasia in 2 patients with primary progressive aphasia.

BACKGROUND: Primary progressive aphasia (PPA) leads to a gradual and relatively isolated dissolution of language function. The factors that determine the selectivity of the disease process remain unknown. We had speculated that PPA may occasionally arise as a tardive manifestation of genetic or acquired vulnerabilities involving the language network of the brain. OBJECTIVE: To explore predisposing factors for PPA. RESULTS: In 2 patients, PPA developed with a background of mild left hemicranial hypoplasia. CONCLUSION: In keeping with other observations of PPA in patients with dyslexia and childhood injury to the left temporal lobe, these 2 patients support the contention that some cases of PPA may arise in settings where the language network has become a locus of least resistance.

Mitochondrial DNA A4336G mutation in Alzheimer's and Parkinson's diseases.

OBJECTIVES: To determine whether the mitochondrial DNA (mtDNA) A4336G mutation represents a risk factor for Spanish patients with both Alzheimer's disease (AD) and Parkinson's disease (PD). MATERIAL AND METHODS: One hundred and sixty-one AD and 106 PD unrelated patients were included in the study. Seventy-eight age-matched and 144 randomly chosen healthy subjects served as controls. The frequency of the A4336G mutation in these groups was compared using the chi(2) and Fisher's exact tests. p < 0.05 was established as a statistically significant differential value. RESULTS: The mtDNA A4336G mutation was present in 1/161 of AD patients (0.6%), in 3/106 of PD patients (2.8%), in 1/78 of age-matched controls (1.3%) and in 2/144 of the randomly chosen controls (1.4%). These differences were not statistically significant. CONCLUSION: Our results do not support the hypothesis that this mutation represents a risk factor for either AD or PD patients, at least in the case of this Spanish sample.