Abstract
Introduction/Aims:
The amyotrophic lateral sclerosis (ALS) functional rating scale-revised (ALSFRS-R) is commonly used to track ALS disease progression; however, there are gaps in the literature regarding the extent to which ALSFRS-R relates to underlying central nervous system (CNS) pathology. The current study explored the association between ALSFRS-R (total and subdomain) scores and postmortem neuropathology (both ALS-specific and comorbid disease).
Methods:
We utilized hierarchical cluster analysis (HCA) conducted using ALSFRS-R subdomain scores to identify profiles of motor dysfunction within our sample of 93 military veterans with autopsy-confirmed ALS. We examined whether emergent clusters were associated with neuropathology. Separate analyses of variance and covariance with post-hoc comparisons were performed to examine relevant cluster differences.
Results:
Analyses revealed significant correlations between ALSFRS-R total and subdomain scores with some but not all neuropathological variables. The HCA illustrated three groups: Cluster 1 - predominantly diffuse functional impairment; Cluster 2 - spared respiratory/bulbar and impaired motor function; and Cluster 3 - spared bulbar and impaired respiratory, fine, and gross motor function. Individuals in Cluster 1 (and to a lesser degree, Cluster 3) exhibited greater accumulation of ALS-specific neuropathology and less comorbid neuropathology than those in Cluster 2.
Discussion:
These results suggest that discrete patterns of motor dysfunction based on ALSFRS-R subdomain scores are related to postmortem neuropathology. Findings support utilization of ALSFRS-R subdomain scores to capture the heterogeneity of clinical presentation and disease progression in ALS, and may assist researchers in identifying endophenotypes for separate assessment in clinical trials.
Keywords: AMYOTROPHIC LATERAL SCLEROSIS, FUNCTIONAL RATING SCALE, NEUROPATHOLOGY, CLUSTER ANALYSIS
INTRODUCTION:
The amyotrophic lateral sclerosis (ALS) functional rating scale-revised (ALSFRS-R)1,2 is a commonly used measure to track disease progression and severity in persons with ALS (PALS). Given that disease progression results in increasing muscle weakness due to motor neuron loss, ALSFRS-R ratings have been theorized to be a surrogate marker of ALS-related central nervous system (CNS) neurodegeneration3–6. This concept has been examined in neuroimaging studies7–9, which have demonstrated an association between the ALSFRS-R and diffuse neuronal damage10, including spinal cord atrophy, cortical thinning11, and volume loss in the basal ganglia and frontal lobe (e.g., Brodmann area 10)12. However, it remains unknown to what extent ALSFRS-R is associated with specific postmortem neuropathological substrates. Such comparisons may provide more detailed analyses of brain involvement and underlying pathomechanisms in ALS than can be seen with neuroimaging. These findings may also assist researchers assessing the efficacy of therapeutic agents, which target specific neuropathological mechanisms.
The ALSFRS-R total score is commonly employed in Phase II and III ALS trials as an outcome measure13,14; however, the ALSFRS-R is limited by multidimensionality as the measure is a summation of discrete subscales and prevents reliable comparison between patients with identical total scores15,16. Investigators have recently questioned whether the ALSFRS-R total score or individual subdomain scores (bulbar, respiratory, fine and gross motor) better capture the heterogeneity of ALS symptoms and disease severity in relation to underlying neuropathology17,18. This is a critical issue as certain patterns of motor dysfunction differ in prognosis and rate of survival, which may reflect severity of atrophy or neuronal damage19. Researchers have theorized that performances on subdomains reflect divergent phenotypes of ALS20,13,14. These phenotypes may respond differentially in clinical drug trials and drug efficacy may be obscured if a clinical trial fails to consider heterogeneity in clinical presentation and survival rates.
Thus, the aims of the current study are twofold: First, given the heterogeneity of the ALS population, we sought to characterize profiles of motor dysfunction based on the ALSFRS-R subdomain scores. Second, we investigated the association between these emergent clusters and neuropathology commonly seen in ALS and co-occurring neurodegenerative conditions. Based on a review of the literature21–25 and expertise of a board certified neurologist (M.T-J) and neuropathologist (T.D.S), we hypothesized that emergent clusters of performance on ALSFRS-R correspond to underlying neuropathological changes, such that: 1) diffuse functional motor impairment will be associated with common markers of ALS disease-specific neurodegeneration, including anterior horn cell loss (AHCL), hypoglossal nerve degeneration, pallor of the lateral corticospinal tract, ventral root degeneration, and/or TAR DNA-binding protein 43 (TDP-43) burden in the spinal cord, 2) preserved respiratory function will be associated with relative sparing of CN-XII and anterior horn cells in the cervicothoracic region, and 3) preserved bulbar function will be associated with greater conservation of CN-XII nuclei. Additionally, we postulated that ALSFRS-R profiles will be relatively unchanged by comorbid pathologies, such as neuropathological markers of Alzheimer’s disease (AD-NP) and vascular burden.
METHODS:
The Department of Veterans Affairs Biorepository Brain Bank (VABBB) is a national prospective observational cohort study and data/tissue repository that collects extensive longitudinal antemortem health data and postmortem CNS tissue from veterans with ALS or related motor neuron diseases26–28. Only veterans with a neuropathologically-confirmed ALS diagnosis and an ALSFRS-R administered within 6 months of death by VABBB staff were selected for the current study. These cases represent a subset of a previously reported sample from the VABBB cohort27,28. All assessments were completed between September 2012 and April 2020. Procedures were in accordance with ethical standards of the VA Boston Healthcare System Institutional Review Board and VA Office of Research and Development.
Clinical Data.
Study staff collected demographic and health data via telephone interviews and/or mailed questionnaires conducted with either the participant or a proxy (in cases where the participant was unable to speak) at enrollment and semi-annually thereafter until the participants’ death. Additional health data was collected from VA’s Compensation and Pension Record Interchange medical record system. Genotyping for known ALS mutations was conducted on a subset of the sample by previously noted methods28.
Motor/Functional Status.
The ALSFRS-R consists of 12 questions divided into 4 subdomains: [1] Bulbar; items 1–3, [2] Fine Motor; items 4–6, [3] Gross Motor; items 7–9, and [4] Respiratory; items 10–12. The maximum score is 12 on each subdomain and accordingly, 48 for the total score. The participant’s ALSFRS-R total and subdomain scores within six months of autopsy were selected for analysis.
Neuropathological Examination.
Neuropathological analyses followed previously established procedures26,27 and PALS were screened for all known neurodegenerative pathologies. Neuropathologists were blinded to clinical features of the participants and neuropathological diagnoses were based on well-defined criteria. ALS was defined as the degeneration of upper and lower motor neurons, pallor of lateral and ventral corticospinal tracts of the spinal cord, and loss of anterior horn cells from cervical, thoracic and lumbar spinal cord with gliosis29,30. Scores in these regions as well as ventral root degeneration, hypoglossal cranial nerve loss, and cervical TDP-43 burden were rated by a team of neuropathologists on a scale of 0–3 (0-no degeneration, 1- mild, 2- moderate, and 3-severe). TDP-43 pathology was determined within the spinal cord, medulla, midbrain, motor cortex, orbitofrontal gyrus, middle frontal gyrus, amygdala, entorhinal cortex, and hippocampus. We utilized Brettschneider staging31 to assess distribution of TDP-43 in these regions. We also calculated presence (vs. absence) of TDP-43 in the spinal cord. Cervical TDP-43 in the spinal cord was selected over thoracic and lumbar regions given the availability and relative completeness of the data set. Please refer to Supplemental Methods for information on comorbid neuropathology32–37.
Data Analysis Plan.
We examined whether patterns of ALS-related motor dysfunction indexed by the ALSFRS-R total and subdomain scores were associated with ALS and comorbid neuropathology. Correlational analyses were used to explore clinicopathological relationships between ALSFRS-R total and subdomain scores and neuropathological variables of interest. Strong or very strong correlations were defined by coefficients of 0.70–1.00, moderate correlations ranged between 0.40–0.69, and weak were defined as 0.10–0.3938. We utilized hierarchical cluster analysis (HCA) to identify clinical profiles of motor dysfunction based on the ALSFRS-R within our sample. HCA is a statistical technique to identify latent structures, or clusters, within a population by grouping entities with similar characteristics (i.e., within group similarities in ALSFRS-R subdomain patterns) into homogenous groups while maximizing heterogeneity between groups. The current study formed clusters via agglomerative nesting (AGNES) and compared the similarity of resultant clusters via Ward’s method39.
The summed score for each ALSFRS-R subdomain was utilized for HCA. Using Ward’s method and review of the AGNES table, we confirmed which solution was the most parsimonious and clinically relevant. Additionally, graphs illustrating all available clustering solutions were presented a priori and at discrete junctures to a board-certified neuropathologist and a neurologist board certified in neuromuscular disorders. After individual meetings with each expert to make predictions, any differences were resolved through a third consensus meeting with both experts present.
Analyses of variance (ANOVA) were performed to examine whether the ALSFRS-R-based clusters exhibited differences in neuropathological variables consistent with a priori derived hypotheses on cluster differences in the clinicopathological relations. Separate ANOVAs were conducted on the ALS-NPs described above. Secondary ANOVAs were also conducted on the following comorbid neuropathology: atherosclerosis, arteriolosclerosis, and AD-NP. Supplementary ANCOVAs were performed to control for the effect of age of death on the clinicopathological findings. An alpha level of 0.05 was used for all statistical tests with Bonferroni correction for multiple post-hoc comparisons. All statistical analyses were performed using IBM SPSS Statistics for Windows, version 20 (IBM Corp., Armonk, NY).
RESULTS:
Cohort Overview.
Data for the ALSFRS-R and neuropathological variables for our hypotheses were available for 93 cases with a primary neuropathological diagnosis of ALS. Within our sample (Table 1), veterans were largely Caucasian and male. A total of 38 PALS were standard duration cases (defined as less than 10 years from symptom onset to death) and 55 PALS were long-duration cases (greater than or equal to 10 years). Genotyping for known ALS mutations was performed on 65 of the present 93 cases. Of these, all but 1 case (SOD1+) yielded negative results. Only one PALS in the present sample met the pathological criteria for a diagnosis of frontal temporal lobar degeneration (FTLD) at autopsy.
Table 1.
Cohort Demographic Summary
| Cohort Demographics | N | |||
| Gender | ||||
| Male | 91 | |||
| Female | 2 | |||
| Ethnicity | ||||
| Caucasian | 90 | |||
| Hispanic | 3 | |||
| NPD | N (%) | |||
| ALS | 93 (100) | |||
| PALS Clinical Features | M (SD) | |||
| Age at Symptom Onset, Y | 59.37 (10.99) | |||
| Age at Death, Y | 73.28 (10.79) | |||
| Disease Duration, Y | 13.91 (9.87) | |||
| ALSFRS-R Total Score | 12.97 (8.31) | |||
| ALSFRS-R Bulbar | 5.13 (3.57) | |||
| ALSFRS-R Fine | 1.85 (2.34) | |||
| ALSFRS-R Gross | 1.48 (1.82) | |||
| ALSFRS-R Respiratory | 4.51 (3.74) | |||
| Riluzole@ (N) | 43 | |||
| Site of Disease Onset (N)* | Bulbar | Upper | Lower | Respiratory |
| 15 | 27 | 48 | 1 | |
| Pathological Features | None | Mild | Moderate | Severe |
| AD-NP (N=90) | 53 | 24 | 13 | 0 |
| Atherosclerosis (N=88) | 48 | 22 | 11 | 7 |
| Arteriolosclerosis (N=91) | 2 | 24 | 45 | 20 |
| LVCST (N=88) | 3 | 22 | 31 | 32 |
| Ventral Roots (N=84) | 1 | 15 | 25 | 43 |
| AHCL (N=91) | 0 | 9 | 23 | 59 |
| CN-XII (N=77) | 14 | 21 | 31 | 11 |
| Cervical TDP-43 (N=86) | 40 | 27 | 16 | 3 |
| Stage 1 | Stage 2 | Stage 3 | Stage 4 | |
| Brettschneider TDP-43 (N=88)^ | 44 | 14 | 2 | 1 |
Note. Total number of PALS with identified neuropathology collected, N.; Percentage of PALS with neuropathology present at death, %. Neuropathological diagnosis at death, NPD; Pathologically-confirmed Amyotrophic Lateral Sclerosis, ALS; Y, years; Alzheimer’s Disease Neuropathological Changes, AD-NP; Lateral and Ventral Corticospinal Tract degeneration, LVCST; Anterior Horn Cell Loss, AHCL; TAR DNA-binding protein 43, TDP-43; Hypoglossal Nerve Degeneration, CN-XII.
Only PALS with known site of disease onset are provided
Only PALS with TDP-43+ inclusions (according to the criteria of Brettschneider et.al,40) were staged
No cases reported edaravone use; one case reported dextromethorphan HBr/quinidine use.
ALSFRS-R Total /Subdomains Scores and ALS-NP/Comorbid Neuropathology.
As seen in Table 2, there were largely weak associations between ALSFRS-R total score and neuropathology such that greater functional impairment was associated with more severe ALS-NP burden and with less accumulation of comorbid neuropathological changes. Moreover, total score showed a moderate correlation with only CN-XII.
Table 2.
Correlations‡ Between ALSFRS-R Total Score, ALSFRS-R Subdomains and Neuropathology
| Variable | n # | Total Score | Bulbar | Fine | Gross | Respiratory |
|---|---|---|---|---|---|---|
| ALSFRS-R Total Score | 93 | - | 0.74** | 0.69** | 0.68** | 0.78** |
| Bulbar Function | 93 | 0.74** | - | 0.32** | 0.33** | 0.39** |
| Fine Motor Function | 93 | 0.69** | 0.32** | - | 0.68** | 0.40** |
| Gross Motor Function | 93 | 0.68** | 0.33** | 0.68** | - | 0.39** |
| Respiratory Function | 93 | 0.78** | 0.39** | 0.40** | 0.39** | - |
| LVCST | 88 | −0.32** | −0.29** | −0.25* | −0.45** | −0.22* |
| Ventral Roots | 84 | −0.34** | −0.13 | −0.30* | −0.31** | −0.42** |
| AHCL | 91 | −0.39** | −0.15 | −0.39** | −0.42** | −0.38** |
| Brettschneider TDP-43 | 88 | −0.14 | −0.03 | −0.14 | −0.04 | −0.15 |
| Cervical TDP-43 | 86 | −0.12 | −0.01 | −0.15 | −0.05 | −0.13 |
| CN-XII | 77 | −0.41** | −0.19 | −0.41** | −0.27* | −0.32** |
| AD-NP Changes | 90 | 0.32** | 0.15 | 0.27** | 0.27** | 0.28** |
| Atherosclerosis | 88 | 0.28** | 0.24* | 0.16 | 0.12 | 0.21* |
| Arteriolosclerosis | 91 | 0.07 | 0.12 | 0.03 | -0.09 | 0.13 |
Note:
Spearman Rho correlations.
n’s varied due to missing data on some of the neuropathological variables.
Lateral and Ventral Corticospinal Tract degeneration, LVCST; Anterior Horn Cell Loss, AHCL; TAR DNA-binding protein 43,TDP-43; Hypoglossal Nerve Degeneration, CN-XII; Alzheimer’s Disease Neuropathological Changes, AD-NP.
p < .05;
p < 0.01.
Table 2 indicates that, compared to the total score, the four subdomain scores exhibited largely similar correlations with ALS-NP variables, however, the relative strength of the correlations differed to some degree. Additionally, the bulbar score was not significantly correlated with ventral root degeneration or anterior horn cell loss. Given these discrepancies, we utilized individual subdomains scores to examine the relationship between discrete clinical profiles of functional impairment (determined via cluster analysis) and neuropathology.
ALSFRS-R Cluster Analysis.
A three-cluster solution was deemed most representative of the heterogeneity seen clinically and neuropathologically in ALS (Figure 1 and Table 3). The three groups were characterized as follows:
Cluster 1 (n=44)—diffuse functional impairment across all ALSFRS-R subdomains (LABEL: Diffuse Impairment)
Cluster 2 (n=27)—relatively spared respiratory and bulbar functioning, and impaired fine and gross motor ability (LABEL: Spared Respiratory/Bulbar—Impaired Motor)
Cluster 3 (n=22)—relatively spared bulbar and impaired respiratory, fine motor, and gross motor ability (LABEL: Spared Bulbar—Impaired Respiratory/Motor).
Figure 1.
Emergent Profiles of Motor Dysfunction Based on Hierarchical Cluster Analysis of ALSFRS-R Subdomain Scores
Table 3.
ALSFRS-R Scores and Disease Duration Information by Cluster Membership
| Cluster 1 | Cluster 2 | Cluster 3 | ||||||
|---|---|---|---|---|---|---|---|---|
| ALSFRS-R Score | Mean | SD | Mean | SD | Mean | SD | ||
| Total Score | 5.98 | 4.86 | 21.7 | 4.92 | 16.23 | 3.56 | ||
| Bulbar | 2.23 | 2.09 | 6.56 | 2.45 | 9.18 | 1.44 | ||
| Fine | 0.80 | 1.29 | 3.81 | 2.91 | 1. 55 | 1.63 | ||
| Gross | 0.86 | 1.36 | 2.67 | 2.3 | 1.27 | 1.2 | ||
| Respiratory | 2.09 | 2.42 | 8.67 | 2.76 | 4.23 | 2.27 | ||
| Age of Onset | 58.15 | 9.1 | 59.58 | 12.18 | 61.54 | 12.99 | ||
| Age at Death | 69.51 | 9.71 | 79.31 | 10.81 | 73.4 | 9.82 | ||
| Disease Duration, (y) | 11.36 | 7.14 | 19.73 | 9.99 | 11.86 | 11.7 | ||
Note. Amyotrophic Lateral Sclerosis Functional Rating Scale - Revised; ALSFRS-R. y = years.
Cluster Membership (CM) and Neuropathology.
The ANOVAs revealed significant main effects of cluster membership on ALS-NP: anterior horn cell loss [F (2, 90) = 5.69, p < 0.01], ventral root degeneration [F (2, 83) = 5.58, p < 0.01], CN-XII [F (2, 76) = 7.06, p < 0.01], and cervical TDP-43 burden [F (2, 85) = 3.47, p < 0.05]. Results of post-hoc comparisons (Supplementary Tables 1 and 2) indicated the following significant differences among the Clusters:
Anterior Horn Cell Loss: Cluster 1 and Cluster 3 exhibited significantly greater anterior horn cell loss as compared to Cluster 2.
Ventral Root Degeneration and Cranial Nerve XII: Cluster 1 exhibited significantly greater ventral root degeneration and CN-XII loss as compared individuals in Cluster 2.
Cervical TDP-43: Cluster 3 exhibited significantly greater cervical TDP-43 burden as compared to Cluster 2.
Analyses (Supplementary Table 3) indicated that age at death was correlated with the neuropathological variables and varied across the cluster groups. Supplementary ANCOVAs controlling for age at death revealed significant main effects of cluster membership on anterior horn cell loss (F (2, 91) = 3.22, p < 0.05) and CN-XII (F (2, 77) = 4.01, p < 0.05) with ventral root degeneration approaching significance (F (2, 84) = 3.05, p = 0.053). Results of post-hoc comparison (Supplementary Table 4) demonstrated that 1) Cluster 1 exhibited significantly greater CN-XII loss as compared to Cluster 2 and 2) Cluster 1 and 3 exhibited marginally (p < 0.09) greater anterior horn cell loss as compared to Cluster 2.
Cluster Membership and Comorbid Neuropathology.
ANOVAs revealed significant main effects of cluster membership on comorbid NP: AD-NP (F (2, 89) = 5.60, p < 0.01) and atherosclerosis (F (2, 87) = 3.98, p < 0.01). Results of post-hoc comparisons (Supplementary Tables 1 and 2) indicated that Cluster 1 had significantly less AD-NP and atherosclerosis as compared to Cluster 2. These associations were no longer statistically significant when controlling for age of death.
DISCUSSION
Our initial analyses showed significant, albeit weak correlations between ALSFRS-R total score and ALS-NP. Cross comparisons between total score and the four subdomain scores revealed similar patterns of association with ALS-NP; however, there were discrepancies in the strength of these associations and the bulbar subdomain score was not significantly associated with certain ALS neuropathology. Given the differential sensitivity of subdomain scores to types of neuropathology and the weak association between total score and neuropathology, we utilized individual subdomain scores to explore the relationship between discrete clinical profiles of functional impairment (determined via cluster analysis) and neuropathology.
Emergent Functional Profiles/Cluster Findings.
Based on a priori predictions and HCA, we identified clusters of ALSFRS-R subdomain performance within our sample. Analyses revealed differences in the demographic characteristics among clusters: individuals in Cluster 1 on average had a shorter disease duration since symptom onset and younger age of death (suggestive of relatively more rapid disease progression) than individuals in Cluster 2, who contrastingly had a longer disease duration and the oldest age at death (suggestive of slower disease progression and less motor dysfunction at time of death). Individuals in Cluster 3 were the “midway” cluster, with a shorter disease duration (comparable to Cluster 1), and an age of death equivalent to the cohort at large.
Clinicopathological Findings.
Consistent with our predictions, we found differences in degree and type of disease burden associated with cluster membership. Participants in Cluster 1 had greater ALS-NP and less comorbid disease burden as compared to Cluster 2. Specifically, we found that diffuse functional impairment, which was present to a greater degree in both Cluster 1 and Cluster 3, was associated with characteristic markers of ALS (e.g., greater anterior horn cell loss and CN-XII loss). Moreover, these results largely remained after controlling for age of death. Regarding CN-XII, we found that Cluster 2 demonstrated relative sparing of the hypoglossal nerve as compared to Cluster 1, yet did not differ significantly from Cluster 3. This may suggest that the compounded burden of respiratory and bulbar dysfunction may signal underlying neuropathological change. Secondary analyses revealed that cluster membership was also associated with comorbid disease pathology. Individuals in Cluster 2 exhibited greater atherosclerosis and AD-NP than did individuals in Cluster 1 (note: Cluster 3 did not differ significantly from either group). However, consistent with our hypotheses, these associations were no longer significant when controlling for age of death.
These findings highlight the potential of ALSFRS-R derived clusters for predicting underlying neuropathology. Individuals who exhibited a more characteristic ALS disease progression marked by diffuse functional impairment (i.e., lower score on all subscales of the ALSFRS-R), earlier age of death, and relatively more rapid disease progression had greater ALS-NP, whereas those with less impaired motor function, older age of death, and longer disease duration may be at greater risk for developing comorbid neuropathology such as Alzheimer’s disease and/or vascular burden. Moreover, our results support the theory that ALS appears to be a “multifactorial and multisystem” disorder merely unified by motor neuron involvement40. While all three groups had impaired fine/gross motor function and similar causes of death, our findings raise the possibility of distinct variants or endophenotypes of ALS, which may have differential responses to pharmacological interventions.
Limitations.
First, given that we selected the last available ALSFRS-R within 6 months of death, the score is considered a snapshot of patient motor function and further motor deterioration (and/or accumulation of neuropathology) may have occurred just before death. Second, our VABBB cohort may not be representative of the broader ALS population given the relatively few cases of FTLD and C9ORF72 as well as the high number of participants with long-duration ALS (> than 10 years) and later average age of onset (>55 years)28. Regarding the latter characterization, opportunities for accumulation of neuropathological markers of ALS may be greater in the current cohort than in the ALS population at large. As postulated previously, military related factors such as detailed health screening28 may alter expected proportions of certain genetic variants in the VABBB cohort (e.g., C9ORF72) that are otherwise present in the civilian ALS population. A significant proportion of long-duration participants also lacked a clear pathological substrate (i.e., TDP-43, SOD1, or FUS). Third, there are limitations to our use of HCA in a cross-sectional sample. The sample sizes of our cluster groups were unequal which limited the power of post hoc analyses, particularly when controlling for age of death. Additionally, although we assessed the stability of emergent clusters using both statistical methodology and expert consensus, analyses should also be conducted on cohorts over time and across different settings. As with any investigation, the characteristics of our clusters are limited to our data and setting. Replicating these analyses in other settings and other patient populations, such as younger and/or civilian cohorts with shorter disease duration, may potentially yield different clusters.
Conclusions.
Overall, cluster membership derived from ALSFRS-R subdomain scores was associated with differences in neuropathological markers of disease, such that individuals in Cluster 1 exhibited greater ALS-NP and less comorbid disease pathology as compared to individuals in Cluster 2. Our study showed that the ALSFRS-R total and subdomain scores are related to underlying ALS neuropathology. Consistent with work by van Eijk and colleagues18, analyses also indicated that while ALSFRS-R total score may be a sensitive marker of neuropathological burden, subdomain scores may convey more complex relationships with neuropathology and better capture the clinical heterogeneity of ALS. Indeed, future clinical trials and neuroimaging studies should include subdomain scores as they may assist researchers in identifying and defining endophenotypes for separate assessment.
Supplementary Material
ACKNOWLEDGMENTS:
This work was supported by the Department of Veterans Affairs, Veterans Health Administration, Biomedical Laboratory Research and Development Merit Awards, Veterans Affairs Biorepository (BX002466); Gulf War Veterans’ Illnesses Biorepository (BX003063); Clinical Sciences Research and Development Merit Award (I01-CX001038); National Institute of Aging (RF1AG054156, R56AG057768); National Institute of Aging Boston University AD Center (P30AG13846; supplement 0572063345-5). All content, statements, opinions, or views are solely of the author(s) and do not reflect official views of the Department of Veterans Affairs or the National Institutes of Health. We gratefully acknowledge Kerry Cormier, Rebecca Mathias, and Caroline Kubilus for the histological and immunohistochemical work as well as all the veterans and their families whose participation and contributions made this work possible.
List of Abbreviations:
- ALS
Amyotrophic lateral sclerosis
- ALSFRS-R
Amyotrophic lateral sclerosis functional rating scale-revised
- CNS
Central nervous system
- VABBB
Department of Veterans Affairs Biorepository Brain Bank
- FTLD
Frontal temporal lobar degeneration
- HCA
Hierarchical cluster analysis
- Cranial Nerve 12, CN-XII
Hypoglossal nerve
- PALS
Persons with ALS
- TDP-43
TAR DNA-binding protein 43
Footnotes
DECLARATION OF INTEREST STATEMENT:
The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this article.
ETHICS APPROVAL AND CONSENT TO PARTICIPATE:
IRB approval for the brain donation program was obtained through the VA Boston Healthcare System.
Ethical Publication Statement: We confirm that we have read the Journal’s position on issues involved in ethical publication and affirm that this report is consistent with those guidelines.
AVAILABILITY OF DATA AND MATERIALS:
The data that support the findings of this study are available from the corresponding author upon reasonable request.
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This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Data Availability Statement
The data that support the findings of this study are available from the corresponding author upon reasonable request.