Clinical findings in nondemented mutation carriers predisposed to Alzheimer's disease: a model of mild cognitive impairment

Skin-brain axis in Alzheimer's disease - Pathologic, diagnostic, and therapeutic implications: A Hypothetical Review

The dynamic interaction between the brain and the skin is termed the 'skin-brain axis.' Changes in the skin not only reflect conditions in the brain but also exert direct and indirect effects on the brain. Interestingly, the connection between the skin and brain is crucial for understanding aging and neurodegenerative diseases. Several studies have shown an association between Alzheimer's disease (AD) and various skin disorders, such as psoriasis, bullous pemphigoid, and skin cancer. Previous studies have shown a significantly increased risk of new-onset AD in patients with psoriasis. In contrast, skin cancer may reduce the risk of developing AD. Accumulating evidence suggests an interaction between skin disease and AD; however, AD-associated pathological changes mediated by the skin-brain axis are not yet clearly defined. While some studies have reported on the diagnostic implications of the skin-brain axis in AD, few have discussed its potential therapeutic applications. In this review, we address the pathological changes mediated by the skin-brain axis in AD. Furthermore, we summarize (1) the diagnostic implications elucidated through the role of the skin-brain axis in AD and (2) the therapeutic implications for AD based on the skin-brain axis. Our review suggests that a potential therapeutic approach targeting the skin-brain axis will enable significant advances in the treatment of AD.

Clinical considerations in early-onset cerebral amyloid angiopathy

Cerebral amyloid angiopathy (CAA) is an important cerebral small vessel disease associated with brain haemorrhage and cognitive change. The commonest form, sporadic amyloid-β CAA, usually affects people in mid- to later life. However, early-onset forms, though uncommon, are increasingly recognized and may result from genetic or iatrogenic causes that warrant specific and focused investigation and management. In this review, we firstly describe the causes of early-onset CAA, including monogenic causes of amyloid-β CAA (APP missense mutations and copy number variants; mutations of PSEN1 and PSEN2) and non-amyloid-β CAA (associated with ITM2B, CST3, GSN, PRNP and TTR mutations), and other unusual sporadic and acquired causes including the newly-recognized iatrogenic subtype. We then provide a structured approach for investigating early-onset CAA, and highlight important management considerations. Improving awareness of these unusual forms of CAA amongst healthcare professionals is essential for facilitating their prompt diagnosis, and an understanding of their underlying pathophysiology may have implications for more common, late-onset, forms of the disease.

Findings from the Swedish Study on Familial Alzheimer's Disease Including the APP Swedish Double Mutation

This is a brief summary of the findings from the Swedish study on familial Alzheimer's disease (FAD). Similar to other FAD studies, it includes prospective assessments of cognitive function, tissue sampling, and technical analyses such as MRI and PET. This 24-year-old study involves 69 individuals with a 50% risk of inheriting a disease-causing mutation in presenilin 1 (PSEN1 H163Y or I143T), or amyloid precursor protein (the Swedish APP or the arctic APP mutation) who have made a total of 169 visits. Our results show the extraordinary power in this study design to unravel the earliest changes in preclinical AD. The Swedish FAD study will continue and future research will focus on disentangling the order of pathological change using longitudinal data as well as modeling the changes in patient derived cell systems.

Cerebrospinal Fluid Biomarkers in Familial Forms of Alzheimer's Disease and Frontotemporal Dementia

As dementia is a fast-growing health care problem, it is becoming an increasingly urgent need to provide an early diagnosis in order to offer patients the best medical treatment and care. Validated biomarkers which reflect the pathology and disease progression are essential for diagnosis and are important when developing new therapies. Today, the core protein biomarkers amyloid-β42, total tau and phosphorylated tau in the cerebrospinal fluid (CSF) are used to diagnose Alzheimer's disease (AD), because these biomarkers have shown to reflect the underlying amyloid and tau pathology. However, the biomarkers have proved insufficient predictors of dementias with a different pathology, e.g. frontotemporal dementia (FTD); furthermore, the biomarkers are not useful for early AD diagnosis. Familial dementias with a known disease-causing mutation can be extremely valuable to study; yet the biomarker profiles in patients with familial dementias are not clear. This review summarizes CSF biomarker findings from studies on symptomatic and presymptomatic individuals carrying a mutation in one of the genes known to cause early-onset familial AD or FTD. In conclusion, the biomarker profile of inherited AD is quite similar between carriers of different mutations as well as similar to the profile found in sporadic AD, whereas familial FTD does not seem to have a clear biomarker profile. Hence, new biomarkers are needed for FTD.

ERP generator anomalies in presymptomatic carriers of the Alzheimer's disease E280A PS-1 mutation

Although subtle anatomical anomalies long precede the onset of clinical symptoms in Alzheimer's disease, their impact on the reorganization of brain networks underlying cognitive functions has not been fully explored. A unique window into this reorganization is provided by presymptomatic cases of familial Alzheimer's disease (FAD). Here we studied neural circuitry related to semantic processing in presymptomatic FAD cases by estimating the intracranial sources of the N400 event-related potential (ERP). ERPs were obtained during a semantic-matching task from 24 presymptomatic carriers and 25 symptomatic carriers of the E280A presenilin-1 (PS-1) mutation, as well as 27 noncarriers (from the same families). As expected, the symptomatic-carrier group performed worse in the matching task and had lower N400 amplitudes than both asymptomatic groups, which did not differ from each other on these variables. However, N400 topography differed in mutation carrier groups with respect to the noncarriers. Intracranial source analysis evinced that the presymptomatic-carriers presented a decrease of N400 generator strength in right inferior-temporal and medial cingulate areas and increased generator strength in the left hippocampus and parahippocampus compared to the controls. This represents alterations in neural function without translation into behavioral impairments. Compared to controls, the symptomatic-carriers presented a similar anatomical shift in the distribution of N400 generators to that found in presymptomatic-carriers, albeit with a larger reduction in generator strength. The redistribution of N400 generators in presymptomatic-carriers indicates that early focal degeneration associated with the mutation induces neural reorganization, possibly contributing to a functional compensation that enables normal performance in the semantic task.

Glucose metabolism and PIB binding in carriers of a His163Tyr presenilin 1 mutation

Six young related pre-symptomatic carriers of a His163Tyr mutation in the presenilin 1 gene who will develop early onset familial Alzheimer's disease (eoFAD), and a control group of 23 non-carriers underwent (18)F-fluorodeoxyglucose positron emission tomography (FDG PET). The mutation carriers were followed-up after 2 years. Multivariate analysis showed clear separation of carriers from non-carriers on both occasions, with the right thalamus being the region contributing most to group differentiation. Statistical parametric mapping (SPM) revealed in the carriers non-significantly lower thalamic cerebral glucose metabolism (CMRglc) at baseline and significantly decreased CMRglc in the right thalamus at follow-up. One mutation carrier was followed-up with FDG PET 10 years after baseline and showed reductions in cognition and CMRglc in the posterior cingulate and the frontal cortex. This subject was diagnosed with AD 1 year later and assessed with an additional FDG as well as an (11)C-PIB PET scan 12 years after baseline. Global cortical CMRglc and cognition were distinctly decreased. PIB binding was comparable with sporadic AD patterns but showing slightly higher striatal levels.

Relative hyperperfusion by SPECT in a family with a presenilin 1 (T245P) mutation

Clinical characteristics of autosomal dominant Alzheimer's disease often differ clinically from sporadic disease with the onset of seizures, spasticity and myoclonus early in the disease course. Similarly imaging characteristics may also differ. We report the findings of relative hyperperfusion by Tc-99m HMPAO SPECT in the medial orbitofrontal cortex and anterior temporal lobe in four affected family members carrying a presenilin 1 mutation. SPECT of the four individuals was compared to an age-matched normal database. We speculate that the findings of relative medial orbitofrontal and anterior temporal lobe hyperperfusion may be a marker of early onset Alzheimer's disease in this family.

Age-dependent loss of NGF signaling in the rat basal forebrain is due to disrupted MAPK activation

The loss of nerve growth factor (NGF) and its high affinity receptor TrkA has been implicated in the loss of cholinergic tone and function in Alzheimer's disease (AD) and normal aging. We employed an animal model of aging, the aged rat, which also exhibits memory loss and NGF alterations. Basal forebrain TrkA levels increased after injection of NGF in the hippocampus within 1h in young rats, but this response was diminished in aged animals as determined by Western blot analysis. Further, NGF activated MAPK pathways without changing total ERK levels and the activation of these pathways was also diminished in aged animals. The exogenous NGF injection did not appear to activate the PI-3K pathway or alter total levels of Akt significantly. These data shed light on mechanisms of NGF signaling in the CNS, and alterations in this signaling cascade associated with age and memory loss. These findings might lead to development of novel treatment therapies for the memory loss associated with AD and other age-associated neurodegenerative diseases.

What the study of persons at risk for familial Alzheimer's disease can tell us about the earliest stages of the disorder: a review

As the proportion of elderly persons continues to expand, understanding the pathobiology of Alzheimer's disease and being able to diagnose it at an early stage become more critical. A minority of Alzheimer's disease cases are inherited as a fully-penetrant, autosomal dominant trait with a young age of onset. The molecular study of the pathogenic mutations has led to insights regarding the etiology of sporadic Alzheimer's disease. Clinical studies in persons at risk for these mutations have confirmed early episodic memory and executive deficits in Alzheimer's disease and suggested that dysphoria may precede the cognitive changes of Alzheimer's disease. Imaging studies have indicated that medial temporal lobe atrophy begins 3 to 4 years before cognitive symptoms, and quantitative cerebral metabolic changes are also present from early on. Studies of biochemical markers suggest that elevations of plasma A 1-42 occur early in familial Alzheimer's disease but that tau may not be elevated in cerebrospinal fluid until the disease is more advanced.

Black-white disparities in functional decline in older persons: the role of cognitive function

BACKGROUND

Black elders have a greater frequency of functional decline than do white elders. The impact of cognitive function on explaining black-white disparities in functional decline has not been extensively explored.

METHODS

To compare the extent to which different risk domains (comorbidity, smoking, socioeconomic status (SES), self-rated health, and cognitive function) explain more frequent functional decline in black elders, we studied 779 black and 4892 white community-dwelling adults aged 70 and older from the Assets and Health Dynamics Among the Oldest Old (AHEAD), a population-based cohort study begun in 1993. Our primary outcome was worse functional status at 2 years than at baseline. We used logistic regression to compare the unadjusted with the adjusted black-white odds ratios (ORs) after adjusting for each risk domain.

RESULTS

At baseline black participants aged 70-79 had higher rates of smoking, diabetes, and hypertension; lower SES; and worse cognitive function than did white participants (p <.05 for all). The mean cognitive score was 15.7 in black and 21.8 in white participants (p <.01). Black participants had a higher frequency of 2-year functional decline than did white participants (10.9% vs 4.7%; OR = 2.61, 95% confidence interval [CI], 1.69-4.03 adjusted for age and sex). Adjustment for comorbidity and smoking did not significantly change the black-white OR, whereas self-rated health and SES accounted for about half the risk. Adjustment for cognitive function accounted for nearly all the associated decline (OR = 1.10, 95% CI, 0.67-1.79). Among participants aged 80 and over, those who were black had significantly lower risk for functional decline after adjustment for cognitive function (OR = 0.61, 95% CI, 0.38-0.96 vs OR = 1.08, 95% CI, 0.70-1.66 adjusted for age and sex only).

CONCLUSIONS

Cognitive function mediated the higher frequency of functional decline among black elders. Efforts to understand cognitive function may enhance our understanding of black-white disparities in health outcomes.

The phenotypes of bipolar disorder: relevance for genetic investigations

The search for susceptibility genes for bipolar disorder (BD) depends on appropriate definitions of the phenotype. In this paper, we review data on diagnosis and clinical features of BD that could be used in genetic studies to better characterize patients or to define homogeneous subgroups. Clinical symptoms, long-term course, comorbid conditions, and response to prophylactic treatment may define groups associated with more or less specific loci. One such group is characterized by symptoms of psychosis and linkage to 13q and 22q. A second group includes mainly bipolar II patients with comorbid panic disorder, rapid mood switching, and evidence of chromosome 18 linkage. A third group comprises typical BD with an episodic course and favourable response to lithium prophylaxis. Reproducibility of cognitive deficits across studies raises the possibility of using cognitive profiles as endophenotypes of BD, with deficits in verbal explicit memory and executive function commonly reported. Brain imaging provides a more ambiguous data set consistent with heterogeneity of the illness.

Differential effects of everyday stress on the episodic memory test performances of young, mid-life, and older adults

This research explored the differential association of everyday stress with the episodic memory test performances of young, mid-life, and older adults. Participants included 98 community-dwelling adults ranging in age from 19-89 years. Everyday stress was assessed via the Perceived Stress Scale and the Elder Life Stress Inventory. A brief battery of episodic memory tasks was administered which included tests of Logical Memory, Verbal Paired Associates, Digit Symbol Substitution, and Digit Symbol Incidental Learning. Results suggest that everyday hassles and irritations as well as the accumulation of challenging life events may exacerbate age-related decline on episodic memory tests that require greater executive resources and more integrated and elaborative processing. The functional relationship between affective status and risk for dementia is discussed, and consideration of individual differences in everyday stress is suggested so as to allow more sensitive interpretation of episodic memory tests commonly used to discern mild cognitive impairment.

Prospects of genetic research of mild cognitive impairment

Mild cognitive impairment (MCI) is a common problem in the elderly. Genetic research may yield valuable clues to improve the diagnostic and prognostic tools for MCI. As the majority of patients progress into Alzheimer's disease (AD) and other forms of dementia, the genetics of MCI cannot be separated from the genetics of AD and dementia in general. Follow-up studies of carriers of mutations underlying AD may yield valuable clues for the development of new diagnostic tools for MCI. In particular, large-scale studies of carriers of the apolipoprotein E 4 allele may still be of interest. Our knowledge of the genes involved in MCI is still very limited. In addition, we need powerful and carefully designed candidate gene studies aiming to discover new genes involved in the risk and progression of MCI. Although the genetics of MCI will be difficult to disentangle, there is ample opportunity to improve research of the genes involved.