Sex-specific genetic architecture of late-life memory performance

BACKGROUND

Women demonstrate a memory advantage when cognitively healthy yet lose this advantage to men in Alzheimer's disease. However, the genetic underpinnings of this sex difference in memory performance remain unclear.

METHODS

We conducted the largest sex-aware genetic study on late-life memory to date (Nmales  = 11,942; Nfemales  = 15,641). Leveraging harmonized memory composite scores from four cohorts of cognitive aging and AD, we performed sex-stratified and sex-interaction genome-wide association studies in 24,216 non-Hispanic White and 3367 non-Hispanic Black participants.

RESULTS

We identified three sex-specific loci (rs67099044-CBLN2, rs719070-SCHIP1/IQCJ-SCHIP), including an X-chromosome locus (rs5935633-EGL6/TCEANC/OFD1), that associated with memory. Additionally, we identified heparan sulfate signaling as a sex-specific pathway and found sex-specific genetic correlations between memory and cardiovascular, immune, and education traits.

DISCUSSION

This study showed memory is highly and comparably heritable across sexes, as well as highlighted novel sex-specific genes, pathways, and genetic correlations that related to late-life memory.

HIGHLIGHTS

Demonstrated the heritable component of late-life memory is similar across sexes. Identified two genetic loci with a sex-interaction with baseline memory. Identified an X-chromosome locus associated with memory decline in females. Highlighted sex-specific candidate genes and pathways associated with memory. Revealed sex-specific shared genetic architecture between memory and complex traits.

Longitudinal change in memory performance as a strong endophenotype for Alzheimer's disease

INTRODUCTION

Although large-scale genome-wide association studies (GWAS) have been conducted on AD, few have been conducted on continuous measures of memory performance and memory decline.

METHODS

We conducted a cross-ancestry GWAS on memory performance (in 27,633 participants) and memory decline (in 22,365 participants; 129,201 observations) by leveraging harmonized cognitive data from four aging cohorts.

RESULTS

We found high heritability for two ancestry backgrounds. Further, we found a novel ancestry locus for memory decline on chromosome 4 (rs6848524) and three loci in the non-Hispanic Black ancestry group for memory performance on chromosomes 2 (rs111471504), 7 (rs4142249), and 15 (rs74381744). In our gene-level analysis, we found novel genes for memory decline on chromosomes 1 (SLC25A44), 11 (BSX), and 15 (DPP8). Memory performance and memory decline shared genetic architecture with AD-related traits, neuropsychiatric traits, and autoimmune traits.

DISCUSSION

We discovered several novel loci, genes, and genetic correlations associated with late-life memory performance and decline.

HIGHLIGHTS

Late-life memory has high heritability that is similar across ancestries. We discovered four novel variants associated with late-life memory. We identified four novel genes associated with late-life memory. Late-life memory shares genetic architecture with psychiatric/autoimmune traits.

DNA from multiple viral species is associated with Alzheimer's disease risk

INTRODUCTION

Multiple infectious agents, including viruses, bacteria, fungi, and protozoa, have been linked to Alzheimer's disease (AD) risk by independent lines of evidence. We explored this association by comparing the frequencies of viral species identified in a large sample of AD cases and controls.

METHODS

DNA sequence reads that did not align to the human genome in sequences were mapped to viral reference sequences, quantified, and then were tested for association with AD in whole exome sequences (WES) and whole genome sequences (WGS) datasets.

RESULTS

Several viruses were significant predictors of AD according to the machine learning classifiers. Subsequent regression analyses showed that herpes simplex type 1 (HSV-1) (odds ratio [OR] = 3.71, p = 8.03 × 10-4) and human papillomavirus 71 (HPV-71; OR = 3.56, p = 0.02), were significantly associated with AD after Bonferroni correction. The phylogenetic-related cluster of Herpesviridae was significantly associated with AD in several strata of the data (p < 0.01).

DISCUSSION

Our results support the hypothesis that viral infection, especially HSV-1, is associated with AD risk.

Progranulin mutations in clinical and neuropathological Alzheimer's disease

INTRODUCTION

Progranulin (GRN) mutations occur in frontotemporal lobar degeneration (FTLD) and in Alzheimer's disease (AD), often with TDP-43 pathology.

METHODS

We determined the frequency of rs5848 and rare, pathogenic GRN mutations in two autopsy and one family cohort. We compared Braak stage, β-amyloid load, hyperphosphorylated tau (PHFtau) tangle density and TDP-43 pathology in GRN carriers and non-carriers.

RESULTS

Pathogenic GRN mutations were more frequent in all cohorts compared to the Genome Aggregation Database (gnomAD), but there was no evidence for association with AD. Pathogenic GRN carriers had significantly higher PHFtau tangle density adjusting for age, sex and APOE ε4 genotype. AD patients with rs5848 had higher frequencies of hippocampal sclerosis and TDP-43 deposits. Twenty-two rare, pathogenic GRN variants were observed in the family cohort.

DISCUSSION

GRN mutations in clinical and neuropathological AD increase the burden of tau-related brain pathology but show no specific association with β-amyloid load or AD.

Neuropathological lesions and their contribution to dementia and cognitive impairment in a heterogeneous clinical population

INTRODUCTION

Alzheimer disease (AD) and related dementias are characterized by damage caused by neuropathological lesions in the brain. These include AD lesions (plaques and tangles) and non-AD lesions such as vascular injury or Lewy bodies. We report here an assessment of lesion association to dementia in a large clinic-based population.

METHODS

We identified 5272 individuals with neuropathological data from the National Alzheimer's Coordinating Center. Individual lesions, as well as a neuropathological composite score (NPCS) were tested for association with dementia, and both functional and neurocognitive impairment using regression models.

RESULTS

Most individuals exhibited mixed pathologies, especially AD lesions in combination with non-AD lesions. All lesion types were associated with one or more clinical outcomes; most even while controlling for AD pathology. The NPCS was also associated with clinical outcomes.

DISCUSSION

These data suggest mixed-type pathologies are extremely common in a clinic-based population and may contribute to dementia and cognitive impairment.

Protein phosphatase 2A and complement component 4 are linked to the protective effect of APOE ɛ2 for Alzheimer's disease

INTRODUCTION

The apolipoprotein E (APOE) ɛ2 allele reduces risk against Alzheimer's disease (AD) but mechanisms underlying this effect are largely unknown.

METHODS

We conducted a genome-wide association study for AD among 2096 ɛ2 carriers. The potential role of the top-ranked gene and complement 4 (C4) proteins, which were previously linked to AD in ɛ2 carriers, was investigated using human isogenic APOE allele-specific induced pluripotent stem cell (iPSC)-derived neurons and astrocytes and in 224 neuropathologically examined human brains.

RESULTS

PPP2CB rs117296832 was the second most significantly associated single nucleotide polymorphism among ɛ2 carriers (P = 1.1 × 10-7 ) and the AD risk allele increased PPP2CB expression in blood (P = 6.6 × 10-27 ). PPP2CB expression was correlated with phosphorylated tau231/total tau ratio (P = .01) and expression of C4 protein subunits C4A/B (P = 2.0 × 10-4 ) in the iPSCs. PPP2CB (subunit of protein phosphatase 2A) and C4b protein levels were correlated in brain (P = 3.3 × 10-7 ).

DISCUSSION

PP2A may be linked to classical complement activation leading to AD-related tau pathology.

Association of mitochondrial variants and haplogroups identified by whole exome sequencing with Alzheimer's disease

INTRODUCTION

Findings regarding the association between mitochondrial DNA (mtDNA) variants and Alzheimer's disease (AD) are inconsistent.

METHODS

We developed a pipeline for accurate assembly and variant calling in mitochondrial genomes embedded within whole exome sequences (WES) from 10,831 participants from the Alzheimer's Disease Sequencing Project (ADSP). Association of AD risk was evaluated with each mtDNA variant and variants located in 1158 nuclear genes related to mitochondrial function using the SCORE test. Gene-based tests were performed using SKAT-O.

RESULTS

Analysis of 4220 mtDNA variants revealed study-wide significant association of AD with a rare MT-ND4L variant (rs28709356 C>T; minor allele frequency = 0.002; P = 7.3 × 10-5 ) as well as with MT-ND4L in a gene-based test (P = 6.71 × 10-5 ). Significant association was also observed with a MT-related nuclear gene, TAMM41, in a gene-based test (P = 2.7 × 10-5 ). The expression of TAMM41 was lower in AD cases than controls (P = .00046) or mild cognitive impairment cases (P = .03).

DISCUSSION

Significant findings in MT-ND4L and TAMM41 provide evidence for a role of mitochondria in AD.

Leveraging videoconferencing supports the continuity of Alzheimer research during the COVID‐19 pandemic and beyond

Background

The COVID‐19 pandemic has placed a demand on researchers to limit in‐person contact with participants, greatly impacting Alzheimer Disease (AD) research. To address this problem, we describe here an approach to using digital technology to continue nationwide clinical recruitment and ascertainment of biological samples while adhering to COVID‐19 guidelines and travel restrictions.

Method

To accomplish this, we considered a videoconferencing approach for remote delivery of cognitive assessments. A multi‐site panel of neurologists and clinical psychologists and a detailed literature review ensured a protocol that captures the best‐practices for administering assessments through videoconferencing while ensuring consistency between remote and in‐person administration. Clinical coordinators underwent training to ensure good agreement with in‐person administration. Most aspects of the cognitive assessments easily transferred to videoconferencing, though Trail Making A and B, and Digit Symbol‐Coding were removed to protect the integrity of the evaluation. Additionally, we coordinated the collection of biological samples with a national company, Quest Diagnostics, to provide phlebotomy services at the participant’s residence. All protocols were developed under the guidance of the Human Subjects Research Office at the University of Miami and with approval of local IRB.

Result

Our clinical coordinators completed over two dozen remote assessments using these protocols. Both cases and controls were enrolled, across various ethnic populations within our study. The distributions of age and 3MS were similar between in‐person and remote assessments. The uptake of videoconferencing enrollment varied among the age groups, level of impairment, at‐home support system and telemedicine readiness. For example, earlier‐onset groups had the best uptake, while older‐onset groups showed the least uptake due to a higher prevalence of telemedicine unreadiness (Lam et al., 2020; Bossen et al.,2015).

Conclusion

This study demonstrates that remote enrollment and ascertainment of biological samples through videoconferencing and partnering with national mobile phlebotomy services is feasible. This approach allows researchers to continue ascertainment efforts while maintaining their participants’ autonomy through informed consent and privacy throughout the process and minimizing their exposure to COVID‐19.

Outreach and recruitment of African Americans for Alzheimer’s disease studies during the COVID‐19 pandemic

Background

Recruiting African Americans in AD studies remains a challenge, particularly during a pandemic, where major health disparities in this population are illuminated. The recruitment literature suggests myriad factors that contribute to the underrepresentation of AAs, including, but not limited to “mistrust” in researchers and their institutions. Maintaining a continuous presence in the AA community builds trust even when traditional outreach methods are not allowed. We continued to provide outreach and recruitment opportunities through COVID education and food for families as we educated them about AD, and opportunities for study participation.

Method

While our traditional outreach methods for recruiting AAs were interrupted, we continued to conduct AD outreach using virtual platforms, mobile phone calls, family conference calls and food distributions. We hosted nine webinars on COVID‐19 to maintain a presence in local and national AA communities and to remain connected to existing AD participants. We reached over 160,000 persons through webinars and social media. We established new relationship new faith leaders in the AA community who co‐hosted COVID‐19 webinars and also expressed interest in forming partnerships on AD education. In addition, we hosted food drives in AA communities that not only addressed food insecurity and COVID prevention, but also AD education and AD research opportunities. At the food drives we distributed bags with masks, hand sanitizers, AD brochures, booklets and study participation information.

Result

Between October and December of 2020, 64 AAs who attended food drives expressed interest in AD studies that required blood draws and cognitive testing. Fifteen enrolled in our genetic study, 15 requested additional follow‐up and 13 expressed interest in participating in more than one study.

Conclusion

Prior research suggests that recruiting AAs into AD studies requires continuous engagement. We used multiple strategies to maintain contact with the AA community and existing research participants, and successfully increased enrollment in the last quarter of the year. Maintaining consistent and continuous engagement facilitates trustworthiness with AAs and yields positive recruitment outcomes, even in a pandemic where traditional recruitment methods are limited.