Sickle cell trait and risk of cognitive impairment in African-Americans: The REGARDS cohort

Measuring Hemoglobin A1C with Frozen Packed Cell and Frozen Whole Blood Samples in an Epidemiologic Study: The Reasons for Geographic and Racial Differences in Stroke Study

INTRODUCTION

Hemoglobin A1c (HbA1c) measurement in epidemiology studies could be increased if reliability of measurements in frozen stored samples was known. In the Reasons for Geographic And Racial Differences in Stroke, a longitudinal study of 30,239 Black and White U.S. adults, we investigated reliability of HbA1c measurements for two types of samples stored at -80°C for up to 14 years.

METHODS

Among 917 participants without diabetes, HbA1c was measured in 2017 in frozen packed cells from the first visit (2003-2007) and in frozen whole blood samples from the second visit (2013-2016). To study reliability, associations between HbA1c and glycemia-related characteristics were examined.

RESULTS

Each 10 mg/dL greater fasting glucose was associated with 0.08% (95% CI: 0.05%-0.11%) greater HbA1c in frozen packed cells (Visit 1) and 0.10% (95% CI: 0.08%-0.12%) greater HbA1c in whole blood (Visit 2). HbA1c was also similarly higher with both methods with increasing age, gender, systolic blood pressure, body mass index, high-density lipoprotein, triglycerides, C-reactive protein, and hemoglobin. Using both methods, ≤ 3.5% would be classified with diabetes based on HbA1c ≥ 6.5%.

CONCLUSIONS

In REGARDS participants without diabetes, HbA1c measurement appeared reliable in frozen packed cells or whole blood under long-term storage, suggesting acceptability for study of the epidemiology of HbA1c.

A Scoping Review on Sex and Gender Differences in the Adverse Health Outcomes of Individuals with Sickle Cell Trait

Although there is an emerging body of evidence that addresses the adverse health outcomes of individuals with sickle cell trait (SCT), it is not clear if the findings are generalizable from a sex and gender perspective. The purpose of this scoping review was to complete an assessment of main concepts, identify knowledge gaps, and determine the potential value of conducting an eventual systematic review. The research question guiding this scoping review is: In SCT individuals with adverse health outcomes, what is known about sex and gender differences? We conducted a scoping review of research on SCT from 2016 to 2022 across five databases, with 36 research studies included in the review. The majority of the included studies were cohort studies (67%) in the United States (61%) focusing on a variety of health outcomes. One-third reported health outcomes by both SCT status and sex, and one-third controlled for sex; no studies addressed gender. Further research is needed on the role of sex and gender for individuals with SCT.

Methods of a Study to Assess the Contribution of Cerebral Small Vessel Disease and Dementia Risk Alleles to Racial Disparities in Vascular Cognitive Impairment and Dementia

Background Non-Hispanic Black adults have a higher proportion of vascular cognitive impairment and Alzheimer's disease and related dementias compared with non-Hispanic White adults that may be due to differences in the burden of cerebral small vessel disease and risk alleles for Alzheimer's disease and related dementias. We describe here the methods of an ancillary study to the REGARDS (Reason for Geographic and and Racial Difference in Stroke) study, which will examine the role of magnetic resonance imaging markers of cerebral small vessel disease and vascular as well as genetic risk factors for Alzheimer's disease and related dementias in racial disparity in the prevalence and trajectory of vascular cognitive impairment and dementia in non-Hispanic White and non-Hispanic Black participants. Methods In participants with no prior history of stroke who had an incident stroke or transient ischemic attack after enrollment in the study, magnetic resonance imaging scans will be evaluated using the Standards for Reporting Vascular Changes on Neuroimaging international consensus criteria and automated analysis pipelines for quantification of cerebral small vessel disease. Participants will be genotyped for APOE ε4 and TREM2 risk alleles for Alzheimer's disease and related dementias. The 6-item screener will define global cognitive function and be the primary cognitive outcome. Conclusions With at least 426 non-Hispanic Black and 463 non-Hispanic White participants who have at least 2 prior and 2 poststroke or transient ischemic attack cognitive assessments, we will have at least 80% power to detect a minimum effect size of 0.09 SD change in Z score, with correction for as many as 20 tests (ie, at P<0.0025, after adjusting for up to 20 covariates) for cognitive decline.

Silent Infarcts, White Matter Integrity, and Oxygen Metabolic Stress in Young Adults With and Without Sickle Cell Trait

BACKGROUND

Individuals with sickle cell anemia have heightened risk of stroke and cognitive dysfunction. Given its high prevalence globally, whether sickle cell trait (SCT) is a risk factor for neurological injury has been of interest; however, data have been limited. We hypothesized that young, healthy adults with SCT would show normal cerebrovascular structure and hemodynamic function.

METHODS

As a case-control study, young adults with (N=25, cases) and without SCT (N=24, controls) underwent brain magnetic resonance imaging to quantify brain volume, microstructural integrity (fractional anisotropy), silent cerebral infarcts (SCI), intracranial stenosis, and aneurysms. Pseudocontinuous arterial spin labeling and asymmetric spin echo sequences measured cerebral blood flow and oxygen extraction fraction, respectively, from which cerebral metabolic oxygen demand was calculated. Imaging metrics were compared between SCT cases and controls. SCI volume was correlated with baseline characteristics.

RESULTS

Compared with controls, adults with SCT demonstrated similar normalized brain volumes (SCT 0.80 versus control 0.81, P=0.41), white matter fractional anisotropy (SCT 0.41 versus control 0.43, P=0.37), cerebral blood flow (SCT 62.04 versus control, 61.16 mL/min/100 g, P=0.67), oxygen extraction fraction (SCT 0.27 versus control 0.27, P=0.31), and cerebral metabolic oxygen demand (SCT 2.71 versus control 2.70 mL/min/100 g, P=0.96). One per cohort had an intracranial aneurysm. None had intracranial stenosis. The SCT cases and controls showed similar prevalence and volume of SCIs; however, in the subset of participants with SCIs, the SCT cases had greater SCI volume versus controls (0.29 versus 0.07 mL, P=0.008). Of baseline characteristics, creatinine was mildly elevated in the SCT cohort (0.9 versus 0.8 mg/dL, P=0.053) and correlated with SCI volume (ρ=0.49, P=0.032). In the SCT cohort, SCI distribution was similar to that of young adults with sickle cell anemia.

CONCLUSIONS

Adults with SCT showed normal cerebrovascular structure and hemodynamic function. These findings suggest that healthy individuals with SCT are unlikely to be at increased risk for early or accelerated ischemic brain injury.

Silent cerebral infarcts in patients with sickle cell disease: a systematic review and meta-analysis

BACKGROUND AND PURPOSE

Silent cerebral infarcts (SCIs) are the most common neurological complication in children and adults with sickle cell disease (SCD). In this systematic review, we provide an overview of studies that have detected SCIs in patients with SCD by cerebral magnetic resonance imaging (MRI). We focus on the frequency of SCIs, the risk factors involved in their development and their clinical consequences.

METHODS

The databases of Embase, MEDLINE ALL via Ovid, Web of Science Core Collection, Cochrane Central Register of Trials via Wiley and Google Scholar were searched from inception to June 1, 2019.

RESULTS

The search yielded 651 results of which 69 studies met the eligibility criteria. The prevalence of SCIs in patients with SCD ranges from 5.6 to 80.6% with most studies reported in the 20 to 50% range. The pooled prevalence of SCIs in HbSS and HbSβ⁰ SCD patients is 29.5%. SCIs occur more often in patients with the HbSS and HbSβ⁰ genotype in comparison with other SCD genotypes, as SCIs are found in 9.2% of HbSC and HbSβ⁺ patients. Control subjects showed a mean pooled prevalence of SCIs of 9.8%. Data from included studies showed a statistically significant association between increasing mean age of the study population and mean SCI prevalence. Thirty-three studies examined the risk factors for SCIs. The majority of the risk factors show no clear association with prevalence, since more or less equal numbers of studies give evidence for and against the causal association.

CONCLUSIONS

This systematic review and meta-analysis shows SCIs are common in patients with SCD. No clear risk factors for their development were identified. Larger, prospective and controlled clinical, neuropsychological and neuroimaging studies are needed to understand how SCD and SCIs affect cognition.