Plasma proteome profiling identifies changes associated to AD but not to FTD

BACKGROUND

Frontotemporal dementia (FTD) is caused by frontotemporal lobar degeneration (FTLD), characterized mainly by inclusions of Tau (FTLD-Tau) or TAR DNA binding43 (FTLD-TDP) proteins. Plasma biomarkers are strongly needed for specific diagnosis and potential treatment monitoring of FTD. We aimed to identify specific FTD plasma biomarker profiles discriminating FTD from AD and controls, and between FTD pathological subtypes. In addition, we compared plasma results with results in post-mortem frontal cortex of FTD cases to understand the underlying process.

METHODS

Plasma proteins (n = 1303) from pathologically and/or genetically confirmed FTD patients (n = 56; FTLD-Tau n = 16; age = 58.2 ± 6.2; 44% female, FTLD-TDP n = 40; age = 59.8 ± 7.9; 45% female), AD patients (n = 57; age = 65.5 ± 8.0; 39% female), and non-demented controls (n = 148; 61.3 ± 7.9; 41% female) were measured using an aptamer-based proteomic technology (SomaScan). In addition, exploratory analysis in post-mortem frontal brain cortex of FTD (n = 10; FTLD-Tau n = 5; age = 56.2 ± 6.9, 60% female, and FTLD-TDP n = 5; age = 64.0 ± 7.7, 60% female) and non-demented controls (n = 4; age = 61.3 ± 8.1; 75% female) were also performed. Differentially regulated plasma and tissue proteins were identified by global testing adjusting for demographic variables and multiple testing. Logistic lasso regression was used to identify plasma protein panels discriminating FTD from non-demented controls and AD, or FTLD-Tau from FTLD-TDP. Performance of the discriminatory plasma protein panels was based on predictions obtained from bootstrapping with 1000 resampled analysis.

RESULTS

Overall plasma protein expression profiles differed between FTD, AD and controls (6 proteins; p = 0.005), but none of the plasma proteins was specifically associated to FTD. The overall tissue protein expression profile differed between FTD and controls (7-proteins; p = 0.003). There was no difference in overall plasma or tissue expression profile between FTD subtypes. Regression analysis revealed a panel of 12-plasma proteins discriminating FTD from AD with high accuracy (AUC: 0.99). No plasma protein panels discriminating FTD from controls or FTD pathological subtypes were identified.

CONCLUSIONS

We identified a promising plasma protein panel as a minimally-invasive tool to aid in the differential diagnosis of FTD from AD, which was primarily associated to AD pathophysiology. The lack of plasma profiles specifically associated to FTD or its pathological subtypes might be explained by FTD heterogeneity, calling for FTD studies using large and well-characterize cohorts.

Variations in consecutive serum neurofilament light levels in healthy controls and multiple sclerosis patients

Background Neurofilament light is a neuronal protein detectable in serum (sNfL), with high potential as disease activity biomarker in multiple sclerosis (MS). To date, little is known about sNfL fluctuations between 2 consecutive measurements in healthy controls (HC) and MS patients. Yet this information is critical, as it will help define a clinically significant variation. Methods sNfL was measured at 2 consecutive time points in a cohort of 90 MS patients (untreated relapsing remitting MS (uRRMS), n=35; treated relapsing remitting MS (tRRMS), n= 21; secondary progressive MS, SPMS, n=21; primary progressive MS, PPMS, n=13), and 90 age-matched HC, using the Simoa NfL light® assay. Results Mean sNfL was elevated in all MS subtypes compared to HC (p<0.0001), and positively associated with age in HC (r=0.70, p<0.001), confirming previous reports. Mean sNfL was higher at follow-up compared to baseline in HC (p<0.001), and lower in uRRMS(p=0.036) and tRRMS (p=0.008). At follow-up, a similar proportion of HC (50.0%), untreated RRMS (51.4%), treated RRMS (33.3%), SPMS (45.0%) and PPMS (46.2%) had variations in sNfL levels exceeding 20% of baseline levels. Conclusions Our data suggest variations in sNfL occur both in HC and MS populations to a similar extent and magnitude. Variations between two consecutive sNfL measurements may reflect natural variations and not necessarily variations in inflammatory disease activity.

Kappa free light chains is a valid tool in the diagnostics of MS: A large multicenter study

OBJECTIVE

To validate kappa free light chain (KFLC) and lambda free light chain (LFLC) indices as a diagnostic biomarker in multiple sclerosis (MS).

METHODS

We performed a multicenter study including 745 patients from 18 centers (219 controls and 526 clinically isolated syndrome (CIS)/MS patients) with a known oligoclonal IgG band (OCB) status. KFLC and LFLC were measured in paired cerebrospinal fluid (CSF) and serum samples. Gaussian mixture modeling was used to define a cut-off for KFLC and LFLC indexes.

RESULTS

The cut-off for the KFLC index was 6.6 (95% confidence interval (CI) = 5.2-138.1). The cut-off for the LFLC index was 6.9 (95% CI = 4.5-22.2). For CIS/MS patients, sensitivity of the KFLC index (0.88; 95% CI = 0.85-0.90) was higher than OCB (0.82; 95%CI = 0.79-0.85; p < 0.001), but specificity (0.83; 95% CI = 0.78-0.88) was lower (OCB = 0.92; 95% CI = 0.89-0.96; p < 0.001). Both sensitivity and specificity for the LFLC index were lower than OCB.

CONCLUSION

Compared with OCB, the KFLC index is more sensitive but less specific for diagnosing CIS/MS. Lacking an elevated KFLC index is more powerful for excluding MS compared with OCB but the latter is more important for ruling in a diagnosis of CIS/MS.

Brain endothelial cell expression of SPARCL-1 is specific to chronic multiple sclerosis lesions and is regulated by inflammatory mediators in vitro

AIMS

Cell matrix modulating protein SPARCL-1 is highly expressed by astrocytes during CNS development and following acute CNS damage. Applying NanoLC-MS/MS to CSF of RRMS and SPMS patients, we identified SPARCL-1 as differentially expressed between these two stages of MS, suggesting a potential as CSF biomarker to differentiate RRMS from SPMS and a role in MS pathogenesis.

METHODS

This study examines the potential of SPARCL-1 as CSF biomarker discriminating RRMS from SPMS in three independent cohorts (n = 249), analyses its expression pattern in MS lesions (n = 26), and studies its regulation in cultured human brain microvasculature endothelial cells (BEC) after exposure to MS-relevant inflammatory mediators.

RESULTS

SPARCL-1 expression in CSF was significantly higher in SPMS compared to RRMS in a Dutch cohort of 76 patients. This finding was not replicated in 2 additional cohorts of MS patients from Sweden (n = 81) and Switzerland (n = 92). In chronic MS lesions, but not active lesions or NAWM, a vessel expression pattern of SPARCL-1 was observed in addition to the expression by astrocytes. EC were found to express SPARCL-1 in chronic MS lesions, and SPARCL-1 expression was regulated by MS-relevant inflammatory mediators in cultured human BEC.

CONCLUSIONS

Conflicting results of SPARCL-1's differential expression in CSF of three independent cohorts of RRMS and SPMS patients precludes its use as biomarker for disease progression. The expression of SPARCL-1 by BEC in chronic MS lesions together with its regulation by inflammatory mediators in vitro suggest a role for SPARCL-1 in MS neuropathology, possibly at the brain vascular level.

Mutations in the fibrinogen aalpha gene account for the majority of cases of congenital afibrinogenemia

Congenital afibrinogenemia is a rare, autosomal, recessive disorder characterized by the complete absence of detectable fibrinogen. We previously identified the first causative mutations in a nonconsanguineous Swiss family; the 4 affected persons have homozygous deletions of approximately 11 kb of the fibrinogen alpha (FGA) gene. Haplotype data implied that these deletions occurred on distinct ancestral chromosomes, suggesting that this region may be susceptible to deletion by a common mechanism. We subsequently showed that all the deletions were identical to the base pair and probably resulted from a nonhomologous recombination mediated by 7-bp direct repeats. In this study, we have collected data on 13 additional unrelated patients to identify the causative mutations and to determine the prevalence of the 11-kb deletion. A common recurrent mutation, at the donor splice site of FGA intron 4 (IVS4 + 1 G > T), accounted for 14 of the 26 (54%) alleles. One patient was heterozygous for the previously identified deletion. Three more frameshift mutations, 2 nonsense mutations, and a second splice site mutation were also identified. Consequently, 86% of afibrinogenemia alleles analyzed to date have truncating mutations of FGA, though mutations in all 3 fibrinogen genes, FGG, FGA, and FGB, might be predicted to cause congenital afibrinogenemia.