Algeciras‐Schimnich, Alicia

Background: The National Institute on Aging-Alzheimer’s Association Research Framework proposes defining Alzheimer’s disease by grouping imaging and fluid biomarkers by their respective pathologic processes. The AT(N) structure proposes several neurodegenerative fluid biomarkers (N) including total tau (t-tau), neurogranin (Ng), and neurofilament light chain (NfL). However, pathologic drivers influencing each biomarker remain unclear. Objective: To determine whether cerebrospinal fluid (CSF)-neurodegenerative biomarkers (N) map differentially to Alzheimer’s disease pathology measured by Aβ 42 (an indicator of amyloidosis, [A]), p-tau (an indicator of tau deposition, [T]), and MRI vascular pathology indicators (measured by white-matter integrity, infarcts, and microbleeds [V]). Methods: Participants were from Mayo Clinic Study of Aging (MCSA) with CSF measures of NfL, Ng, t-tau, Aβ 42 , and p-tau and available MRI brain imaging. Linear models assessed associations between CSF neurodegeneration (N) markers, amyloid markers (A), tau (T), and vascular pathology (V). Results: Participants ( n = 408) had a mean age of 69.2±10.7; male, 217 (53.2%); cognitively unimpaired, 359 (88%). All three neurodegeneration biomarkers correlated with age ( p < 0.001 for NfL and t-tau, p = 0.018 for Ng). Men had higher CSF-NfL levels; women had higher Ng ( p < 0.001). NfL and t-tau levels correlated with infarcts ( p = 0.009, p = 0.034 respectively); no biomarkers correlated with white-matter integrity. N biomarkers correlated with p-tau levels (T, p < 0.001). Higher Aβ 42 levels associated with higher N-biomarker levels but only among cognitively unimpaired (A, p < 0.001). Conclusion: The influence of vascular pathology in the general population on CSF (N) biomarkers is modest, with greater influence of infarcts than white-matter disruption. Neurodegeneration markers more closely correlated with tau than amyloid markers.

Abstract Staging the severity of Alzheimer’s disease pathology using biomarkers is useful for therapeutic trials and clinical prognosis. Disease staging with amyloid and tau PET has face validity; however, this would be more practical with plasma biomarkers. Our objectives were, first, to examine approaches for staging amyloid and tau PET and, second, to examine prediction of amyloid and tau PET stages using plasma biomarkers. Participants (n = 1136) were enrolled in either the Mayo Clinic Study of Aging or the Alzheimer’s Disease Research Center; had a concurrent amyloid PET, tau PET and blood draw; and met clinical criteria for cognitively unimpaired (n = 864), mild cognitive impairment (n = 148) or Alzheimer’s clinical syndrome with dementia (n = 124). The latter two groups were combined into a cognitively impaired group (n = 272). We used multinomial regression models to estimate discrimination [concordance (C) statistics] among three amyloid PET stages (low, intermediate, high), four tau PET stages (Braak 0, 1–2, 3–4, 5–6) and a combined amyloid and tau PET stage (none/low versus intermediate/high severity) using plasma biomarkers as predictors separately within unimpaired and impaired individuals. Plasma analytes, p-tau181, Aβ1–42 and Aβ1–40 (analysed as the Aβ42/Aβ40 ratio), glial fibrillary acidic protein and neurofilament light chain were measured on the HD-X Simoa Quanterix platform. Plasma p-tau217 was also measured in a subset (n = 355) of cognitively unimpaired participants using the Lilly Meso Scale Discovery assay. Models with all Quanterix plasma analytes along with risk factors (age, sex and APOE) most often provided the best discrimination among amyloid PET stages (C = 0.78–0.82). Models with p-tau181 provided similar discrimination of tau PET stages to models with all four plasma analytes (C = 0.72–0.85 versus C = 0.73–0.86). Discriminating a PET proxy of intermediate/high from none/low Alzheimer’s disease neuropathological change with all four Quanterix plasma analytes was excellent but not better than p-tau181 only (C = 0.88 versus 0.87 for unimpaired and C = 0.91 versus 0.90 for impaired). Lilly p-tau217 outperformed the Quanterix p-tau181 assay for discriminating high versus intermediate amyloid (C = 0.85 versus 0.74) but did not improve over a model with all Quanterix plasma analytes and risk factors (C = 0.85 versus 0.83). Plasma analytes along with risk factors can discriminate between amyloid and tau PET stages and between a PET surrogate for intermediate/high versus none/low neuropathological change with accuracy in the acceptable to excellent range. Combinations of plasma analytes are better than single analytes for many staging predictions with the exception that Quanterix p-tau181 alone usually performed equivalently to combinations of Quanterix analytes for tau PET discrimination.

AbstractBackgroundNeurofilament light chain (NfL) is an emerging blood‐based biomarker useful for assessing neuro‐axonal injury in several neurological conditions. Plasma NfL concentrations reflect the extent of axonal damage, making it a general marker of neurodegenerative disease progression. This study evaluates the analytical performance characteristics of the Quanterix NfL Advantage method in EDTA‐plasma.MethodThe assay was performed per manufacturer’s instructions on the Quanterix Simoa HD‐X Analyzer. Analytical validation included analyte stability, imprecision, lower limit of quantification (LLOQ), analytical measurement range (AMR), accuracy, and interferences. One‐sided reference intervals were established using quantile regression methods among 1100 cognitive normal individuals, age 20 to 95 years without known chronic kidney disease, stroke, or myocardial infarction.ResultNfL was stable in plasma three days ambient, seven days refrigerate, 90 days frozen (‐20C), and over 3 freeze/thaw cycles. Intra and inter‐assay imprecision, expressed as % coefficient of variation (%CV), ranged from 3.4 – 6.0% and 5.9 – 11.6% respectively. The LLOQ was evaluated using patient plasma pools at concentrations of 1.7 and 3.6 pg/mL. %CVs were 16.8% and 9.7% respectively, and the LLOQ was set at 3.0 pg/mL. Accuracy was assessed by spiking 5 plasma samples with NfL calibratoran 87% average recovery (range 81‐94%) was observed. The AMR of 3.0 – 1500 pg/mL was verified with a regression slope of 0.93 and r2 > 0.99. Additionally, plasma admixtures covering the AMR showed acceptable linear response (slope of 1.02 and r² >0.99). The assay was not affected by icterus to 100 mg/dL, lipemia to 1000 mg/dL, hemolysis to 1000 mg/dL at NfL concentrations >30 pg/mL or to 200 mg/dL at NfL concentrations ≤30 pg/mL. NfL increased with age but did not differ by sex. The data supported age‐based reference intervals broken down into 10‐year intervals. The 97.5th percentile limits were: 20s: ≤8.4 pg/mL, 30s: ≤11.4 pg/mL, 40s: ≤15.4 pg/mL, 50s: ≤20.8 pg/mL, 60s: ≤28.0 pg/mL, 70s: ≤37.9 pg/mL, 80+: ≤51.2 pg/mL.ConclusionThe analytical performance characteristics of the plasma Quanterix NfL advantage assay were deemed acceptable for clinical laboratory implementation. The establishment of NfL reference intervals will aid in the clinical interpretation of patient plasma NfL concentrations.

AbstractContextThyroglobulin autoantibodies (TgAbs) affect thyroglobulin immunometric assays (TgIMAs), causing falsely low results. Conversely, heterophilic antibodies (HAs) may cause falsely elevated results. Thyroglobulin (Tg) measurements by mass spectrometry (MS) resist antibody interference. The most effective use of TgIMA/TgMS in the evaluation of Tg remains unclear.ObjectiveThe objective of this work was to study the usefulness of TgMS vs TgIMA in the presence of Tg measurement interference by HA and TgAb.MethodsIn 163 thyroid cancer patients, Tg was postoperatively measured by TgIMA and TgMS. When TgIMA was elevated and TgMS undetectable, HA was assessed by serial dilution and pretreatment with HA blocking reagent. TgIMA and TgMS were compared in TgAb-positive patients with well-characterized clinical status.Results6 out of 45 cases with TgIMA &gt;1 ng/mL had undetectable TgMS. HA interference was confirmed by serial dilution and HA blocking reagent addition. In TgAb-positive cases, TgIMA and TgMS were highly correlated (R2 = 0.86). In patients with structural disease and TgAb, TgIMA and TgMS were detectable in 6/19 patients, and 9/19 cases, respectively. The TgMS concentration range in the 3 discrepant cases ranged from 0.5 to 2.0 ng/mL. Hence, the presence of TgAb was associated with inappropriately reduced Tg concentrations with both TgIMA and TgMS.ConclusionHA cause falsely elevated TgIMA with undetectable TgMS with significant frequency. TgMS can be used to rule out HA interference. Albeit resistant to TgAb in vitro, TgMS detects little Tg in patients with TgAb and structural disease. Hence, TgAb may reduce Tg concentrations in vivo. The implication is that no assay design may be able to overcome this problem. TgMS may not detect structural disease in TgAb-positive patients.

AbstractObjectiveTo investigate the effect of CRYSVITA® (burosumab‐twza) on FGF23 measurements in an intact and a C‐terminal immunoassay.MethodsAn intact serum FGF23 (MedFrontier) and a C‐terminal plasma FGF23 assay (Immutopics) were used. Serum/plasma pools were spiked to span the burosumab therapeutic range (1.4–11.3 μg/ml) and FGF23 recovery was assessed. Patient serum and plasma samples obtained pre and post‐burosumab treatment were evaluated on both assays and compared with corresponding phosphorus measurementsResultsSpiking burosumab (1.4–11.3 μg/ml) into sample pools resulted in a dose‐dependent negative analytical interference on intact FGF23 measurements and no significant interference for C‐terminal FGF23 measurements. However, more than a 500‐fold median increase (post‐ vs. pre‐burosumab administration) in in vivo FGF23 concentrations were observed by both assays.ConclusionsTherapeutic concentrations of burosumab result in a negative analytical interference of the intact, but not the C‐terminal FGF23 immunoassay. Despite this in vitro analytical interference in the intact assay, relatively large elevations of both intact FGF23 and C‐terminal FGF23 measurements were observed in vivo following burosumab administration. Following burosumab administration, FGF23 measurements must be interpreted within the clinical context of the patient and other relevant biomarker results.SummaryThis article describes a negative analytical interference by burosumab in an intact FGF23 immunoassay. The recovery of C‐terminal FGF23 is not significantly affected by the presence of burosumab. In vivo, both assays demonstrate extreme FGF23 elevations in the presence of the drug. Furthermore, the measurement of FGF23 blocked by burosumab is not clinically useful regarding hypophosphataemia.

AbstractBackground and purposeAutoimmune encephalitis (AE) is a potentially treatable cause of rapidly progressive dementia that may mimic Creutzfeldt–Jakob disease (CJD). Alzheimer disease (AD) cerebrospinal fluid (CSF) biomarkers may discriminate CJD from AD, but utility in discriminating CJD and AE is unclear. This study compared AD CSF biomarkers in CJD and AE.MethodsPatients with probable or definite CJD and probable or definite AE who underwent Roche Elecsys AD CSF biomarker testing at Mayo Clinic from March 2020 through April 2021 were included. Total‐tau, phosphorylated181 tau and amyloid‐β42 levels were compared.ResultsOf 11 CJD cases, four were autopsy proven; the rest had positive real‐time quaking‐induced conversion testing. Disease‐associated autoantibodies were detected in 8/15 cases of AE: leucine‐rich glioma‐inactivated 1 and neuronal intermediate filaments (two cases each), and N‐methyl‐d‐aspartate receptor, contactin‐associated protein‐like 2, dipeptidyl‐peptidase‐like protein 6 and immunoglobulin‐like cell adhesion molecule IgLON family member 5. Total‐tau provided excellent discrimination between CJD and AE in a univariate model (odds ratio 1.46 per 100 pg/ml, 95% confidence interval 1.17–2.11, p < 0.05, c = 0.93). Total‐tau was elevated in 91% of CJD cases (median > 1300, range 236–>1300 pg/ml), of which 55% were above the limit of assay measurement (>1300 pg/ml). Total‐tau was elevated in 20% of AE cases (median 158, range 80–>1300 pg/ml).ConclusionTotal‐tau was greater in CJD than AE. Given that amyloid‐β42 and phosphorylated181 tau were comparable, the ratio differences were probably driven by elevated total‐tau in CJD. This study supports the role for AD biomarker testing in patients with rapidly progressive dementia.

Background: Cerebral microbleeds (CMBs) are a common vascular pathology associated with future intracerebral hemorrhage. Plasma biomarkers of amyloid, tau, and neurodegeneration may provide a screening avenue to identify those with CMBs, but evidence is conflicting. Objective: To determine the association between plasma biomarkers (Aβ40, Aβ42, t-tau, p-tau181, p-tau217, neurofilament light chain (NfL)) and CMBs in a population-based study of aging and whether these biomarkers predict higher signal on Aβ-PET imaging in patients with multiple CMBs. Methods: 712 participants from the Mayo Clinic Study of Aging with T2* GRE MRI and plasma biomarkers were included. Biomarkers were analyzed utilizing Simoa (Aβ40, Aβ42, t-tau, NfL) or Meso Scale Discovery (p-tau181, p-tau217) platforms. Cross-sectional associations between CMBs, plasma biomarkers and Aβ-PET were evaluated using hurdle models and multivariable regression models. Results: Among the 188 (26%) individuals with≥1 CMB, a lower plasma Aβ42/Aβ40 ratio was associated with more CMBs after adjusting for covariables (IRR 568.5 95% CI 2.8–116,127). No other biomarkers were associated with risk or number CMBs. In 81 individuals with≥2 CMBs, higher plasma t-tau, p-tau181, and p-tau217 all were associated with higher Aβ-PET signal, with plasma p-tau217 having the strongest predictive value (r2 0.603, AIC –53.0). Conclusion: Lower plasma Aβ42/Aβ40 ratio and higher plasma p-tau217 were associated with brain amyloidosis in individuals with CMBs from the general population. Our results suggest that in individuals with multiple CMBs and/or lobar intracranial hemorrhage that a lower plasma Aβ42/Aβ40 ratio or elevated p-tau217 may indicate underlying cerebral amyloid angiopathy.

Abstract Background Multiple sclerosis (MS) is an immune-mediated central nervous system (CNS) inflammatory demyelinating disease in which analysis of clinical presentation, imaging studies, and laboratory tests aid in diagnosis. Content This review discusses laboratory tests ordered to rule out and rule in MS, such as the traditional measurement of cerebrospinal fluid (CSF) IgG index and oligoclonal bands. Biomarkers discovered in the past 2 decades, such as aquaporin-4 (AQP4) antibodies and myelin oligodendrocyte glycoprotein (MOG) antibodies, have been incorporated into clinical practice in the diagnosis of disorders referred to as MS mimics. The importance of test selection, assay methodology, optimal sample for testing, and diagnostic utility of these biomarkers is reviewed. Other laboratory testing that can aid in the differentiation between MS and these biomarker-defined CNS demyelinating diseases is described. There is a focus on emerging biomarkers such as the use of kappa immunoglobulin free light chain concentration in CSF and kappa CSF index measurement as an alternative to oligoclonal bands which has a potential for an improvement in laboratory workflows. Finally, the role of biomarkers of disease activity and prognosis are discussed, including neurofilament light chain, glial fibrillary acidic protein, and myelin basic protein. Future perspectives with improved laboratory testing tools and discovery of additional biomarkers are provided. Summary Laboratory testing for demyelinating disorders using CSF and serum are routine practices that can benefit from an update, as novel biomarker-defined entities have reduced the potential for MS misdiagnosis, and CSF/serum biomarkers reinstated in the diagnostic criteria of MS.

Abstract Introduction : Plasma glial fibrillary acidic protein (GFAP) may be associated with amyloid burden, neurodegeneration, and stroke but its specificity for Alzheimer's disease (AD) in the general population is unclear. We examined associations of plasma GFAP with amyloid and tau positron emission tomography (PET), cortical thickness, white matter hyperintensities (WMH), and cerebral microbleeds (CMBs). Methods : The study included 200 individuals from the Mayo Clinic Study of Aging who underwent amyloid and tau PET and magnetic resonance imaging and had plasma GFAP concurrently assayed; multiple linear regression and hurdle model analyses were used to investigate associations controlling for age and sex. Results : GFAP was associated with amyloid and tau PET in multivariable models. After adjusting for amyloid, the association with tau PET was no longer significant. GFAP was associated with cortical thickness, WMH, and lobar CMBs only among those who were amyloid‐positive. Discussion : This cross‐sectional analysis demonstrates the utility of GFAP as a plasma biomarker for AD‐related pathologies.