Publications by authors named "Ihab Hajjar"

Background: The SARS-CoV-2 pandemic accelerated development of innovative methods for conducting research remotely via digital technologies. However, few studies have examined participant technological literacy skills or access as key social determinants of brain health in aging populations at risk of Alzheimer's disease and other dementias.

Objective: To identify associations of sociodemographic and clinical characteristics, cognitive status and geolocation with digital technology access and skill within dementia research cohorts.

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Introduction: Essential tremor (ET) is a highly-prevalent neurological disease. At present, there are no clinical biomarkers. Neurofilament light (NfL) has been studied as a measure of neuronal damage in a considerable number of neurological disorders.

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High-density lipoprotein cholesterol efflux function may prevent brain amyloid beta deposition and neurodegeneration. However, the relevance of this finding has not been established in the diverse middle-aged population. We examined 1826 adults (47% Black adults) who participated in the Dallas Heart Study to determine associations between high-density lipoprotein (HDL) measures and brain structure and function.

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Background: Previous studies have linked cardiovascular risk factors during midlife to cognitive function in later life. However, few studies have looked at the association between cardiac function, brain structure, and cognitive function and even less have included diverse middle-aged populations.

Objectives: The objective of this study was to determine associations between cardiac and brain structure and function in a multiethnic cohort of middle-aged adults.

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Objective: Alzheimer's disease (AD) is believed to be more common in African Americans (AA), but biomarker studies in AA populations are limited. This report represents the largest study to date examining cerebrospinal fluid AD biomarkers in AA individuals.

Methods: We analyzed 3,006 cerebrospinal fluid samples from controls, AD cases, and non-AD cases, including 495 (16.

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Introduction: Recent Alzheimer's disease (AD) clinical trials have used cerebrospinal fluid (CSF) biomarker levels for screening and enrollment. Preliminary evidence suggests that AD risk is related to impaired renal function. The impact of kidney function on commonly used AD biomarkers remains unknown.

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Background: "Super-agers" are adults aged ≥80 with cognitive performance similar to persons two to three decades younger. Characteristics such as larger hippocampal volume, APOE-ε4 allele absence, higher educational attainment, female sex, and lifelong cognitive stimulation are associated with cognitive performance compatible with super-aging. These findings are based on predominantly white research samples.

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The biology of individual lipid species and their relevance in Alzheimer's disease (AD) remains incompletely understood. We utilized non-targeted mass spectrometry to examine brain lipids variations across 316 post-mortem brains from participants in the Religious Orders Study (ROS) or Rush Memory and Aging Project (MAP) cohorts classified as either control, asymptomatic AD (AAD), or symptomatic AD (SAD) and integrated the lipidomics data with untargeted proteomic characterization on the same individuals. Lipid enrichment analysis and analysis of variance identified significantly lower abundance of lysophosphatidylethanolamine (LPE) and lysophosphatidylcholine (LPC) species in SAD than controls or AAD.

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Positron emission tomography (PET) and magnetic resonance imaging (MRI) are both widely used neuroimaging techniques to study brain function. Although whole brain resting functional MRI (fMRI) connectomes are widely used, the integration or association of whole brain functional connectomes with PET data are rarely done. This likely stems from the fact that PET data is typically analyzed by using a regions of interest approach, while whole brain spatial networks and their connectivity (covariation) receive much less attention.

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Positron emission tomography (PET) and magnetic resonance imaging (MRI) are two commonly used imaging techniques to visualize brain function. The use of inter-network covariation (a functional connectome) is a widely used approach to infer links among different brain networks. While whole brain resting fMRI connectomes are widely used, PET data has mostly been analyzed using a few regions of interest.

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Anti-amyloid therapies (AATs), such as anti-amyloid monoclonal antibodies, are emerging treatments for people with early Alzheimer's disease (AD). AATs target amyloid β plaques in the brain. Amyloid-related imaging abnormalities (ARIA), abnormal signals seen on magnetic resonance imaging (MRI) of the brain in patients with AD, may occur spontaneously but occur more frequently as side effects of AATs.

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Background: Subjective cognitive complaints are frequent following COVID-19 infection, but assessment of whether these complaints map onto objective cognitive findings may not be routine in busy clinical settings. Consequently, opportunities to confirm these complaints and to provide follow-up referrals and appropriate care may be missed, thereby impacting patients' functional independence and quality of life. African Americans are vulnerable to poor outcomes from COVID-19, and thus represent a minority group in whom subjective concerns are especially important to investigate.

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Subjective cognitive complaints (SCC) in cognitively intact older adults have been investigated as a clinically important symptom that may portend the onset of a neurodegenerative disorder such as Alzheimer's disease. Few studies have concurrently incorporated demographic features, depressive symptoms, neuropsychological status, and neuroimaging correlates of SCC and evaluated whether these differ in White and African American older adults. In the current study, 131 (77 White, 54 African American) healthy participants ≥50 years old completed the Cognitive Function Instrument (CFI) to assess SCC, and they underwent objective cognitive testing, assessment of mood, and brain magnetic resonance imaging.

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Background: The impact of COVID-19 severity on development of long-term sequelae remains unclear, and symptom courses are not well defined.

Methods: This ambidirectional cohort study recruited adults with new or worsening symptoms lasting ≥3 weeks from confirmed SARS-CoV-2 infection between August 2020-December 2021. COVID-19 severity was defined as severe for those requiring hospitalization and mild for those not.

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Importance: Perceived stress can have long-term physiological and psychological consequences and has shown to be a modifiable risk factor for Alzheimer disease and related dementias.

Objective: To investigate the association between perceived stress and cognitive impairment in a large cohort study of Black and White participants aged 45 years or older.

Design, Setting, And Participants: The Reasons for Geographic and Racial Differences in Stroke (REGARDS) study is a national population-based cohort of 30 239 Black and White participants aged 45 years or older, sampled from the US population.

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Introduction: Advances in natural language processing (NLP), speech recognition, and machine learning (ML) allow the exploration of linguistic and acoustic changes previously difficult to measure. We developed processes for deriving lexical-semantic and acoustic measures as Alzheimer's disease (AD) digital voice biomarkers.

Methods: We collected connected speech, neuropsychological, neuroimaging, and cerebrospinal fluid (CSF) AD biomarker data from 92 cognitively unimpaired (40 Aβ+) and 114 impaired (63 Aβ+) participants.

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Background: Cerebral microvascular dysfunction is commonly seen in Alzheimer's disease (AD) and vascular cognitive impairment (VCI). Cerebrovascular reactivity (CVR) to CO reflects cerebral microvascular health and may be modulated by the renin-angiotensin system (RAS). This study aimed to investigate the effects of RAS modulation on CVR in individuals with mild cognitive impairment (MCI) due to underlying vascular or AD etiologies.

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Background: Functional decline in Alzheimer's disease (AD) is impacted by impaired ability to integrate and modulate complex cognitive and motor abilities, commonly known as motor-cognitive integration. Impaired motor-cognitive integration occurs in the early stages of AD, prodromal AD (pAD), and may precede other symptoms. Combined motor and cognitive training have been recommended for people with pAD and need to be better researched.

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Observational studies suggest that angiotensin receptor blockers in hypertensive adults are associated with lower post-mortem indicators of Alzheimer's disease pathology. Candesartan, an angiotensin receptor blocker, has a positive cognitive effect in mild cognitive impairment with hypertension. However, its safety and effects in non-hypertensive individuals with Alzheimer's disease are unclear.

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Importance: Differences in cerebrospinal fluid (CSF) tau Alzheimer dementia (AD) biomarkers by self-identified race have been observed in prior studies. More recently, plasma biomarkers have been gaining recognition, but whether they exhibit similar differences is unclear. Furthermore, the underlying explanation for these differences in AD biomarkers is still unexplored.

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The APOE-ε4 allele is a known genetic risk for Alzheimer's disease (AD). Thus, it can be reasoned that the APOE-ε4 allele would also impact neurodegeneration-associated structural brain changes. Here we probe if the APOE-ε4 genotype directly modulates the human brain's gray matter using a neural network trained on the whole-brain gray matter images from the cognitively normally aging (CN) and AD individuals.

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