Cees Mulder

Amyloid-β(1–42), Total Tau, and Phosphorylated Tau as Cerebrospinal Fluid Biomarkers for the Diagnosis of Alzheimer Disease

BACKGROUND To improve ante mortem diagnostic accuracy of Alzheimer disease (AD), measurement of the biomarkers amyloid-beta(1-42) (Abeta42), total tau (Tau), and tau phosphorylated at threonine(181) (pTau) in cerebrospinal fluid (CSF) has been proposed. We have used these markers and evaluated their performance. METHODS From January 2001 to January 2007, we assessed Abeta42, Tau, and pTau by commercial ELISAs in CSF from 248 consecutive AD patients and 131 patients with subjective memory complaints attending our outpatient memory clinic. Diagnoses were made blind to the results of the biomarker assays. We assessed sensitivity and specificity and analyzed trends over time. RESULTS Interassay CVs from analysis of pools of surplus CSF specimens were mean 11.3% (SD 4.9%) for Abeta42; 9.3% (1.5%) for Tau, and 9.4% (2.5%) for pTau, respectively (n = 7-18). To achieve 85% sensitivity, cutoff values were 550 (95% CI 531-570) ng/L for Abeta42; 375 (325-405) ng/L for Tau, and 52 (48-56) ng/L for pTau. Corresponding specificities were 83% (95% CI 76%-89%) for Abeta42, 78% (70%-85%) for Tau, and 68% (60%-77%) for pTau. Logistic regression to investigate the simultaneous impact of the 3 CSF biomarkers on the diagnosis yielded a sensitivity of 93.5% and specificity of 82.7%, at a discrimination line of Abeta42 = 373 + 0.82 x Tau. The area under the ROC curves of Tau and pTau showed significant fluctuation over time. CONCLUSIONS CSF biomarkers Abeta42 and Tau can be used as a diagnostic aid in AD. pTau did not have additional value over these 2 markers. Cutoff values, sensitivities, specificities, and discrimination lines depend on the patient groups studied and laboratory experience.

Amyloid β 38, 40, and 42 species in cerebrospinal fluid: More of the same?

Various C‐terminally truncated amyloid β peptides (Aβ) are linked to Alzheimers disease (AD) pathogenesis. Cerebrospinal fluid (CSF) concentrations of Aβ38, Aβ40, and Aβ42 were measured by enzyme‐linked immunosorbent assay in 30 patients with AD and 26 control subjects. CSF Aβ42 levels was decreased in patients with AD, whereas CSF Aβ38 and Aβ40 levels were similar in patients with AD and control subjects. All three Aβ peptides were interrelated, particularly CSF Aβ38 and Aβ40. Diagnostic accuracy of CSF Aβ42 concentrations was not improved by applying the ratios of CSF Aβ42 to Aβ38 or Aβ40. Ann Neurol 2005;58:139–142

BACE1 Activity in Cerebrospinal Fluid and Its Relation to Markers of AD Pathology

Several studies have shown that reduced amyloid-beta 1-42 (Abeta(42)) and increased tau levels in cerebrospinal fluid (CSF) reflect increased Alzheimers disease (AD) pathology in the brain. beta-site APP cleaving enzyme (BACE1) is thought to be the major beta-secretase involved in Abeta production in the brain, and therefore we investigated the relation between BACE1 activity and CSF markers Abeta(40), Abeta(42), total tau (t-tau), and tau phosphorylated at threonine 181 (p-tau) in CSF of control (n=12), mild cognitive impairment (n=18), and AD (n=17) subjects. Patients were classified according to their Abeta(42), t-tau, and p-tau CSF biomarker levels, with either an AD-like biomarker profile (two or three biomarkers abnormal: Abeta(42) < 495 pg/ml in combination with t-tau > 356 pg/ml, and/or p-tau > 54 pg/ml) or a normal biomarker profile (<or= one biomarker abnormal). This resulted in 19 subjects with an AD-like biomarker profile (66 +/- 6 years, 53% female, and Mini-Mental Status Examination (MMSE) score: 23 +/- 5) and 28 subjects with a normal biomarker profile (62 +/- 11 years, 43% female, and MMSE score: 27 +/- 4). Subjects with an AD-like biomarker profile had higher CSF BACE1 activity levels, compared to patients with a normal biomarker profile (20 pg/ml and 16 pg/ml respectively; p=0.01), when controlled for age and gender. In the whole sample, BACE1 activity correlated with CSF levels of Abeta(40), t-tau, and p-tau (r=0.38, r=0.63, and r=0.65; all p< 0.05), but not with Abeta(42). These data suggest that increased BACE1 activity in CSF relates to AD pathology in the brain.

Use of Serum Tumor Markers in the Differential Diagnosis between Ovarian and Colorectal Adenocarcinomas

In the search for a method to facilitate the preoperative discrimination of ovarian carcinomas from colorectal carcinomas serum levels of 6 tumor markers were measured in 47 patients presenting with ovarian cancer and compared to levels found in 24 female patients with advanced, untreated colorectal cancer. The markers studied were CA 125, CA 15.3, CA 19.9, CEA and two recently developed mucin markers, CA M29 and CA M26. Levels of CA 125, CA 15.3, CEA and CA M29 showed significant differences between both groups. In predicting ovarian cancer, sensitivity was highest for CA 125 at 94% (35 U/ml cutoff level). However, the specificity of CA 125 was at 71% low. Specificity increased significantly by using a combination of a CA 125-positive score (greater than 35 U/ml) and a simultaneous negative CEA score (less than or equal to 5 ng/ml) (specificity 100%, sensitivity 81%). A CA 125/CEA serum ratio greater than 25 resulted in the highest discriminative power with a specificity of 100% and a sensitivity of 91% resulting in an overall test accuracy of 94%. It is concluded that the serum tumor markers used, especially a combination of CA 125 and CEA, are helpful in the preoperative differential diagnosis between adenocarcinomas of ovarian and colorectal origin.

CSF Neurofilaments in Frontotemporal Dementia Compared with Early Onset Alzheimer’s Disease and Controls

Background: Frontotemporal dementia (FTD) is pathologically heterogeneous, sometimes revealing intraneuronal inclusions of neurofilaments. We therefore measured CSF neurofilament profiles in patients with FTD, patients with early onset Alzheimer’s disease (EAD) and healthy control subjects to explore the discriminative potential of CSF neurofilaments compared with the existing CSF biomarkers amyloid-β(1–42), tau and tau phosphorylated at threonine-181. Methods: CSF levels of light chain, heavy chain and hyperphosphorylated heavy chain neurofilaments (NfL, t-NfH and P-NfH) were compared between 17 subjects with FTD, 20 with EAD and 25 cognitively healthy controls. Results: A subgroup of FTD patients had remarkably high CSF levels of both NfL and NfH. The degree of NfH phosphorylation was increased in FTD compared to both other groups. The levels of CSF NfL were significantly higher in EAD compared to controls. Conclusion: Differences in CSF biomarker profiles might reflect differential involvement of neurofilaments and tau in FTD and EAD. The subgroup of FTD patients with high CSF neurofilament levels may have a different neuropathological substrate and future studies addressing this specific issue are needed.

Genetic and biochemical markers for Alzheimer's disease: recent developments

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder of unknown aetiology, characterized by irreversible cognitive and physical deterioration. It is a major cause of morbidity and death in the elderly and a growing public health problem as life expectancy in the general population increases. AD is both genetically and phenotypically a heterogeneous disorder. An early-onset, familial type is recognized, as well as a later-onset, sporadic type. The diagnosis is made on clinical grounds, with the aid of a small number of additional investigations, using consensus criteria. 1 However, at autopsy about 10± 20% of clinically diagnosed AD patients are found to have conditions other than AD. Therefore, genetic and/or biochemical markers that support the clinical diagnosis and can distinguish AD from cognitive symptoms attributable to ageing and from other dementias will be of great value. The identi® cation of such accurate markers for the early diagnosis of AD is mandatory for the development of ef® cient pharmacological treatment, since therapy should be initiated at an early stage of the disease, before extensive and irreversible brain damage has occurred.

Serum amyloid p component as a biomarker in mild cognitive impairment and Alzheimer's disease.

Background: Serum amyloid P component (SAP), present in amyloid-β (Aβ) plaques in Alzheimer’s disease (AD), may protect Aβ deposits against proteolysis, thereby promoting plaque formation. The aim was to investigate if SAP levels in cerebrospinal fluid (CSF) and serum can be used to discriminate controls, AD and mild cognitive impairment (MCI) patients, and to identify incipient AD among MCI patients. Methods: SAP levels in CSF and serum were determined in 30 controls, 67 MCI and 144 AD patients. At follow-up, 39 MCI patients had progressed to dementia, while 25 had remained stable (mean follow-up time: 2.6 ± 1.0 and 2.1 ± 0.8 years). Results: Cross-sectionally no differences were found in SAP levels in CSF and serum between the groups. MCI patients that had progressed to dementia at follow-up had lower CSF SAP levels (13 mg/l, range 3.3–199.3 mg/l) than MCI nonprogressors (20.2 mg/l, range 7.0–127.7 mg/l; p < 0.05). A low CSF SAP level was associated with a 2-fold increased risk of progression to AD (hazard ratio = 2.2; 95% confidence interval = 0.9–5.4). Conclusion: Our data suggest that measurement of CSF SAP levels can aid in the identification of incipient AD among MCI patients.

LOW VITAMIN B6 LEVELS ARE ASSOCIATED WITH WHITE MATTER LESIONS IN ALZHEIMER'S DISEASE

To the Editor: Vitamin B6 is important in the reduction of a potentially toxic excess of homocysteine. Low levels of vitamin B6 are related to cognitive decline, but the underlying mechanism is not known. We hypothesized that vascular lesions in the brain may mediate this and studied the relation between vitamin B6 levels and the presence of white matter lesions (WMLs) on magnetic resonance imaging (MRI) in patients with Alzheimer’s disease (AD).

A Rapid and Sensitive Immunosorbent Assay for Urinary Albumin

We describe a fast, simple and sensitive microliter scale competitive ELISA for the determination of urinary albumin. All reagents are commercially available. In the standard procedure, a minimum concentration of 0·8 mg albumin/L can be measured, although, applying another dilution, 0·04 mg/L can be detected. Within-batch coefficient of variation was 6·9% and 5·6% (at 1:20 and 1:50 dilution, respectively); between-batch variation was 8·6% and 5·6% respectively. The influence of urine pH and other urine components is minimised in the assay diluting with a casein-containing buffer.

CSF levels of PSA and PSA-ACT complexes in Alzheimer's disease

Background Prostate-specific antigen (PSA) is a serine protease that in serum, is predominantly found complexed to the serine protease inhibitor alpha1-antichymotrypsin (ACT). ACT co-localizes with amyloid plaques in Alzheimers disease (AD) brain and both PSA and ACT are detectable in cerebrospinal fluid (CSF). Therefore, we aimed to determine whether PSA is produced in the brain and whether PSA and PSA–ACT complex levels in CSF can be used as a biomarker for AD. Methods Levels of ACT and PSA–ACT were determined by sandwich enzyme-linked immunosorbent assay in CSF and serum samples of AD (n = 16), frontotemporal lobe dementia (FTLD) (n = 19), mild cognitively impaired (MCI) patients (n = 19) and controls (n = 12). Total PSA was determined in a non-competitive immunoassay. Reverse transcriptase–polymerase chain reaction (RT–PCR) for PSA was performed on postmortem hippocampus and temporal cortex specimens from control and AD cases. Results PSA is expressed in the brain, as detected by RT–PCR. PSA and PSA–ACT complexes were detectable in CSF of almost all male and only very few female subjects. The levels of PSA and PSA–ACT complexes in CSF did not differ between AD, FTLD, MCI and control groups. PSA CSF/serum quotients highly correlated with albumin CSF/serum quotients. Furthermore, the hydrodynamic radius of PSA was found to be 3 nm and the theoretical PSA quotient, derived from the Felgenhauer plot, corresponded well with the measured PSA quotient. Conclusions PSA is locally produced in the human brain; however, brain PSA hardly contributes to the CSF levels of PSA. PSA and PSA–ACT levels in CSF are not suitable as a biomarker for AD.