CSF and blood neuronal injury biomarkers in spinal bulbar muscular atrophy and amyotrophic lateral sclerosis 4

Abstract

Spinal and bulbar muscular atrophy (SBMA) and amyotrophic lateral sclerosis 4 (ALS4) are two forms of motor neuron disease characterized by clinically slow disease progression. Based on the current limited human studies, the contribution of central nervous neurodegeneration to these diseases and the rate of clinical progression is unclear. Neuronal proteins glial fibrillary acidic protein (GFAP), neurofilament light (NfL) chain, or Total-tau measured in either cerebrospinal fluid or blood could serve as sensitive markers of neurodegeneration. We studied 56 adult participants (32 SBMA, 7 ALS4, and 17 controls) who were enrolled at the National Institutes of Health, of whom 22 (10 SBMA, 7 ALS4, and 5 controls) underwent paired CSF and serum sampling, and of whom 6 participants were assessed longitudinally up to 24 months from initial visit. An additional 7 controls completed CSF sampling only. CSF GFAP, NfL chain, and Total-tau correlated with corresponding levels in serum (r = 0.74, r = 0.47, and r = 0.70, respectively). CSF GFAP was increased in patients with SBMA (median, 8840 pg/mL, interquartile range (IQR) 5780-10489) as compared to controls (median, 5315 pg/mL, IQR 1822-6657; P = 0.029) but not compared with ALS4 (median, 5015 pg/mL, IQR 3172-9803; P = 0.31). Patients with SBMA had increased concentrations of CSF NfL chain (median, 719 pg/mL, IQR 483-773) as compared to ALS4 (median, 307 pg/mL, IQR 187-629; P = 0.034) or controls (median, 395 pg/mL, IQR 307-497; P = 0.024). In contrast, serum concentrations of either biomarker did not differ significantly between SBMA, ALS4, or controls. Higher CSF GFAP and NfL chain levels were associated with lower SBMA Functional Rating Scale scores (r = -0.49 and r = -0.42, respectively). Over the course of 24 months, the average change in SBMA Functional Rating Scale was -0.83 points, while the changes in CSF GFAP and NfL chain were progressive (increased 1.4-fold and 1.3-fold, respectively). Our data suggest that SBMA patients have increased concentrations of CSF GFAP and NfL chain as compared to ALS4 and controls, and higher levels of these biomarkers are associated with disease severity. Importantly, these results indicate that SBMA is associated with progressive neurodegeneration and that either CSF GFAP or NfL chain may be useful for patient stratification and monitoring treatment effects in clinical trials.

Keywords: ALS4; CSF; GFAP; NfL; SBMA.

Graphical Abstract

Figure 1

Correlation between CSF and serum biomarkers. Scatter plots showing the pairwise relationship between CSF and serum level of (A) GFAP, (B) NfL, and (C) T-tau in all participants (SBMA, ALS4 and controls). Each data point represents a study participant (n = 23). All correlations were calculated using the Pearson method. CSF, cerebrospinal fluid; GFAP, glial fibrillary acidic protein; NfL, neurofilament light chain; T-tau, total-tau.

Figure 2

CSF NfL and GFAP are increased in patients with SBMA compared with ALS4, or controls. Scatterplots show the differences in GFAP, NfL and T-tau measured in CSF (A–C) and serum (D–F) across SBMA, ALS4 and controls. Each data point represents a study participant. Values are presented as medians; error bars indicate interquartile range. P values are from the Kruskal-Wallis test of variance followed by Mann-Whitney U test. Significant group differences are displayed, except for CSF NfL that was also significantly higher in SBMA compared with ALS4 (P = 0.034). CSF, cerebrospinal fluid; GFAP, glial fibrillary acidic protein; NfL, neurofilament light chain; T-tau, total-tau. 11 age-and sex matched controls to SBMA from NIH blood bank.

Figure 3

Association between fluid biomarkers and SBMA outcome measures. Panel (A) shows the correlation between fluid biomarkers and functional outcome measures. Plots (B–F) show examples of correlations indicated in the heatmap. Warmer colours indicate positive correlation, while cooler colours indicate negative correlations. Bold outlines, P < 0.01; dashed outlines P < 0.05. Each data point represents a study participant sample. All correlations were calculated using the Pearson method. 6MWT, 6-minute walk test; AMAT, total adult myopathy assessment tool; SBMAFRS, spinal bulbar muscular atrophy functional rating scale; TUG, timed up and go. SBMA, n (CSF) = 30 (23). TUG, n (CSF) = 28 (22). AMAT, n (CSF) = 27 (21). MWT, n (CSF) = 27 (21).

Figure 4

Longitudinal changes in fluid and SBMA functional outcome measures. Plot (A) shows the absolute fold changes over 24 months for the fluid biomarkers measured in CSF and serum. Plot (B) shows the absolute fold changes over 24 months for the SBMA outcome measures for comparison. Data in plot (A) and (B) are based on the 22 patients with SBMA who underwent paired CSF and serum sampling; of whom six underwent longitudinal sampling (2 at 12 months and 4 at 12 and 24 months from initial visit). 6MWT, 6-minute walk test; AMAT, total adult myopathy assessment tool; CSF, cerebrospinal fluid; GFAP, glial fibrillary acidic protein; NfL, neurofilament light chain; SBMAFRS, spinal bulbar muscular atrophy functional rating scale; T-tau, total-tau; TUG, timed up and go.