Feasibility and Safety of Multicenter Tissue and Biofluid Sampling for α-Synuclein in Parkinson's Disease: The Systemic Synuclein Sampling Study (S4)

Predicting Cerebrospinal Fluid Alpha-Synuclein Seed Amplification Assay Status from Demographics and Clinical Data

Objective

To develop and externally validate models to predict probabilities of alpha-synuclein (a-syn) positive or negative status in vivo in a mixture of people with and without Parkinson's disease (PD) using easily accessible clinical predictors.

Methods

Uni- and multi-variable logistic regression models were developed in a cohort of participants from the Parkinson Progression Marker Initiative (PPMI) study to predict cerebrospinal fluid (CSF) a-syn status as measured by seeding amplification assay (SAA). Models were externally validated in a cohort of participants from the Systemic Synuclein Sampling Study (S4) that had also measured CSF a-syn status using SAA.

Results

The PPMI model training/testing cohort consisted of 1260 participants, of which 76% had manifest PD with a mean (± standard deviation) disease duration of 1.2 (±1.6) years. Overall, 68.7% of the overall PPMI cohort (and 88.0% with PD of those with manifest PD) had positive CSF a-syn SAA status results. Variables from the full multivariable model to predict CSF a-syn SAA status included age- and sex-specific University of Pennsylvania Smell Identification Test (UPSIT) percentile values, sex, self-reported presence of constipation problems, leucine-rich repeat kinase 2 (LRRK2) genetic status and pathogenic variant, and GBA status. Internal performance of the model on PPMI data to predict CSF a-syn SAA status had an area under the receiver operating characteristic curve (AUROC) of 0.920, and sensitivity/specificity of 0.881/0.845. When this model was applied to the external S4 cohort, which included 71 participants (70.4% with manifest PD for a mean 5.1 (±4.8) years), it performed well, achieving an AUROC of 0.976, and sensitivity/specificity of 0.958/0.870. Models using only UPSIT percentile performed similarly well upon internal and external testing.

Conclusion

Data-driven models using non-invasive clinical features can accurately predict CSF a-syn SAA positive and negative status in cohorts enriched for people living with PD. Scores from the UPSIT were highly significant in predicting a-syn SAA status.

Harnessing Graphdiyne for Selective Cu2+ Detection: A Promising Tool for Parkinson's Disease Diagnostics and Pathogenesis

Cu2+ accelerates the viral-like propagation of α-synuclein fibrils and plays a key role in the pathogenesis of Parkinson's disease (PD). Therefore, the accurate detection of Cu2+ is essential for the diagnosis of PD and other neurological diseases. The Cu2+ detection process is impeded by substances that have similar electrochemical properties. In this study, graphdiyne (GDY), a new kind of carbon allotrope with strong electron-donating ability, was utilized for the highly selective detection of Cu2+ by taking advantage of its outstanding adsorption capacity for Cu2+. Density functional theory (DFT) calculations show that Cu atoms are adsorbed in the cavity of GDY, and the absorption energy between Cu and C atoms is higher than that of graphene (GR), indicating that the cavity of GDY is favorable for the adsorption of Cu atoms and electrochemical sensing. The GDY-based electrochemical sensor can effectively avoid the interference of amino acids, metal ions and neurotransmitters and has a high sensitivity of 9.77 μA·μM-1·cm-2, with a minimum detectable concentration of 200 nM. During the investigating pathogenesis and therapeutic process of PD with α-synuclein as the diagnostic standard, the concentration of Cu2+ in cells before and after L-DOPA and GSH treatments were examined, and it was found that Cu2+ exhibits high potential as a biomarker for PD. This study not only harnesses the favorable adsorption of the GDY and Cu2+ to improve the specificity of ion detection but also provide clues for deeper understanding of the role of Cu2+ in neurobiology and neurological diseases.

Combined measure of salivary alpha-synuclein species as diagnostic biomarker for Parkinson's disease

Parkinson's disease (PD) diagnosis is still vulnerable to bias, and a definitive diagnosis often relies on post-mortem neuropathological diagnosis. In this regard, alpha-synuclein (αsyn)-specific in vivo biomarkers remain a critical unmet need, based on its relevance in the neuropathology. Specifically, content changes in αsyn species such as total (tot-αsyn), oligomeric (o-αsyn), and phosphorylated (p-αsyn) within the cerebrospinal fluid (CSF) and peripheral fluids (i.e., blood and saliva) have been proposed as PD biomarkers possibly reflecting the neuropathological outcome. Here, we measured the p-αsyn levels in the saliva from 15 PD patients along with tot-αsyn, o-αsyn and their ratios, and compared the results with those from 23 healthy subjects (HS), matched per age and sex. We also calculated the optimal cutoff values for different αsyn species to provide information about their capability to discriminate PD from HS. We found that p-αsyn was the most abundant alpha-synuclein species in the saliva. While p-αsyn concentration did not differ between PD and HS when adjusted for total salivary proteins, the ratio p-αsyn/tot-αsyn was largely lower in PD patients than in HS. Moreover, the concentration of o-αsyn was increased in the saliva of PD patients, and tot-αsyn did not differ between PD and HS. The ROC curves indicated that no single αsyn form or ratio could provide an accurate diagnosis of PD. On the other hand, the ratio of different items, namely p-αsyn/tot-αsyn and o-αsyn, yielded more satisfactory diagnostic accuracy, suggesting that the combined measure of different species in the saliva may show more promises as a diagnostic means for PD.

Skin Biopsy as a Diagnostic Tool for Synucleinopathies

Studies published in the last decade identified skin biopsies as a promising source of material for detecting alpha-synuclein (αSN). Alpha-synuclein gets deposited in the skin of patients with synucleinopathies, and therefore, a skin biopsy can be used to diagnose and confirm these diseases histopathologically. A skin biopsy can also be helpful for studies focusing on the nature of αSN deposits. The most important aspects of a biomarker are sensitivity, specificity, and technical feasibility. The potential for a skin biopsy to become the clinical tool of choice as a reliable biomarker for diagnosing synucleinopathies appears to be high, with consistently high sensitivity (>80%) and specificity approaching 100%. The review aims to provide an overview of the factors impacting skin biopsy's sensitivity, specificity, and feasibility in detecting dermal αSN deposits.

Central and peripheral α-synuclein in Parkinson disease detected by seed amplification assay

OBJECTIVES

Detection of α-synuclein aggregates by seed amplification is a promising Parkinson disease biomarker assay. Understanding intraindividual relationships of α-synuclein measures could inform optimal biomarker development. The objectives were to test accuracy of α-synuclein seed amplification assay in central (cerebrospinal fluid) and peripheral (submandibular gland) sources, compare to total α-synuclein measures, and investigate within-subject relationships.

METHODS

The Systemic Synuclein Sampling Study aimed to characterize α-synuclein in multiple tissues and biofluids within Parkinson disease subjects (n = 59) and compared to healthy controls (n = 21). Motor and non-motor measures and dopamine transporter scans were obtained. Four measures of α-synuclein were compared: seed amplification assay in cerebrospinal fluid and formalin-fixed paraffin-embedded submandibular gland, total α-synuclein quantified in biofluids using enzyme-linked immunoassay, and aggregated α-synuclein in submandibular gland detected by immunohistochemistry. Accuracy of seed amplification assay for Parkinson disease diagnosis was examined and within-subject α-synuclein measures were compared.

RESULTS

Sensitivity and specificity of α-synuclein seed amplification assay for Parkinson disease diagnosis was 92.6% and 90.5% in cerebrospinal fluid, and 73.2% and 78.6% in submandibular gland, respectively. 25/38 (65.8%) Parkinson disease participants were positive for both cerebrospinal fluid and submandibular gland seed amplification assay. Comparing accuracy for Parkinson disease diagnosis of different α-synuclein measures, cerebrospinal fluid seed amplification assay was the highest (Youden Index = 83.1%). 98.3% of all Parkinson disease cases had ≥1 measure of α-synuclein positive.

INTERPRETATION

α-synuclein seed amplification assay (cerebrospinal fluid>submandibular gland) had higher sensitivity and specificity compared to total α-synuclein measures, and within-subject relationships of central and peripheral α-synuclein measures emerged.

Path to Parkinson Disease Prevention: Conclusion and Outlook

Tremendous progress in our understanding of the pathophysiology and clinical manifestations of the prodromal phase of Parkinson disease (PD) offers a unique opportunity to start therapeutic interventions as early as possible to slow or even stop the progression to clinically manifest motor PD. A Parkinson's Prevention Conference, "Planning for Prevention of Parkinson's: A trial design symposium and workshop" was convened to discuss all issues that need to be addressed before the launch of the first PD prevention study. In this review, we summarize the major opportunities and challenges in designing prevention trials in PD, organized by the following critical trial design questions: Who (should be enrolled)? What (to test)? How (to measure prevention)? and the pivotal question, When during the prodromal disease (should we start these trials)? We outline the implications of these questions and their meaning for a responsible, sustainable, and fruitful further planning for prevention trials. Despite the great progress that has been made, it needs to be acknowledged that several queries remain to be carefully considered and addressed because prevention trials are being planned and become a reality.

Antemortem detection of Parkinson's disease pathology in peripheral biopsies using artificial intelligence

The diagnosis of Parkinson's disease (PD) is challenging at all stages due to variable symptomatology, comorbidities, and mimicking conditions. Postmortem assessment remains the gold standard for a definitive diagnosis. While it is well recognized that PD manifests pathologically in the central nervous system with aggregation of α-synuclein as Lewy bodies and neurites, similar Lewy-type synucleinopathy (LTS) is additionally found in the peripheral nervous system that may be useful as an antemortem biomarker. We have previously found that detection of LTS in submandibular gland (SMG) biopsies is sensitive and specific for advanced PD; however, the sensitivity is suboptimal especially for early-stage disease. Further, visual microscopic assessment of biopsies by a neuropathologist to identify LTS is impractical for large-scale adoption. Here, we trained and validated a convolutional neural network (CNN) for detection of LTS on 283 digital whole slide images (WSI) from 95 unique SMG biopsies. A total of 8,450 LTS and 35,066 background objects were annotated following an inter-rater reliability study with Fleiss Kappa = 0.72. We used transfer learning to train a CNN model to classify image patches (151 × 151 pixels at 20× magnification) with and without the presence of LTS objects. The trained CNN model showed the following performance on image patches: sensitivity: 0.99, specificity: 0.99, precision: 0.81, accuracy: 0.99, and F-1 score: 0.89. We further tested the trained network on 1230 naïve WSI from the same cohort of research subjects comprising 42 PD patients and 14 controls. Logistic regression models trained on features engineered from the CNN predictions on the WSI resulted in sensitivity: 0.71, specificity: 0.65, precision: 0.86, accuracy: 0.69, and F-1 score: 0.76 in predicting clinical PD status, and 0.64 accuracy in predicting PD stage, outperforming expert neuropathologist LTS density scoring in terms of sensitivity but not specificity. These findings demonstrate the practical utility of a CNN detector in screening for LTS, which can translate into a computational tool to facilitate the antemortem tissue-based diagnosis of PD in clinical settings.

Detection of Dermal Alpha-Synuclein Deposits as a Biomarker for Parkinson's Disease

Alpha-synuclein deposits are detectable in skin biopsies of patients with Parkinson’s disease and other synucleinopathies like multiple system atrophy by immunohistochemical staining. As they are easily to obtain, they appear a promising tool for the pre-mortem histopathological confirmation of the disease and as a potential outcome measure in studies targeting alpha-synuclein aggregates. Good sensitivity, specificity, and practicability are the most important requirements of a biomarker. The review gives an overview on all three aspects, addresses methodological problems and the lack of standardized procedures as a major problem and gives an outlook on the future of skin biopsy as a potential diagnostic tool in synucleinopathies.

Proteomic Profile of Saliva in Parkinson's Disease Patients: A Proof of Concept Study

Parkinson’s disease (PD) is a progressive neurodegenerative disorder. It affects many organs. Lewy bodies—a histopathological “hallmark” of PD—are detected in about 75% of PD submandibular gland samples. We hypothesize that saliva can be a source of biomarkers of PD. The aim of the study was to evaluate and compare the salivary proteome of PD patients and healthy controls (HC). Salivary samples from 39 subjects (24 PD patients, mean age 61.6 ± 8.2; 15 HC, mean age 60.9 ± 6.7) were collected. Saliva was collected using RNA-Pro-Sal kits. Label-free LC-MS/MS mass spectrometry was performed to characterize the proteome of the saliva. IPA analysis of upstream inhibitors was performed. A total of 530 proteins and peptides were identified. We observed lower concentrations of S100-A16, ARP2/3, and VPS4B in PD group when compared to HC. We conclude that the salivary proteome composition of PD patients is different than that of healthy controls. We observed a lower concentration of proteins involved in inflammatory processes, exosome formation, and adipose tissue formation. The variability of expression of proteins between the two groups needs to be considered.

Alpha-synuclein seeds in olfactory mucosa of patients with isolated REM sleep behaviour disorder

Isolated REM sleep behaviour disorder (RBD) is an early-stage α-synucleinopathy in most, if not all, affected subjects. Detection of pathological α-synuclein in peripheral tissues of patients with isolated RBD may identify those progressing to Parkinson's disease, dementia with Lewy bodies or multiple system atrophy, with the ultimate goal of testing preventive therapies. Real-time quaking-induced conversion (RT-QuIC) provided evidence of α-synuclein seeding activity in CSF and olfactory mucosa of patients with α-synucleinopathies. The aim of this study was to explore RT-QuIC detection of α-synuclein aggregates in olfactory mucosa of a large cohort of subjects with isolated RBD compared to patients with Parkinson's disease and control subjects. This cross-sectional case-control study was performed at the Medical University of Innsbruck, Austria, the Hospital Clinic de Barcelona, Spain, and the University of Verona, Italy. Olfactory mucosa samples obtained by nasal swab in 63 patients with isolated RBD, 41 matched Parkinson's disease patients and 59 matched control subjects were analysed by α-synuclein RT-QuIC in a blinded fashion at the University of Verona, Italy. Median age of patients with isolated RBD was 70 years, 85.7% were male. All participants were tested for smell, autonomic, cognitive and motor functions. Olfactory mucosa was α-synuclein RT-QuIC positive in 44.4% isolated RBD patients, 46.3% Parkinson's disease patients and 10.2% control subjects. While the sensitivity for isolated RBD plus Parkinson's disease versus controls was 45.2%, specificity was high (89.8%). Among isolated RBD patients with positive α-synuclein RT-QuIC, 78.6% had olfactory dysfunction compared to 21.4% with negative α-synuclein RT-QuIC (P < 0.001). The extent of olfactory dysfunction was more severe in isolated RBD patients positive than negative for olfactory mucosa a-synuclein RT-QuIC (P < 0.001). We provide evidence that the α-synuclein RT-QuIC assay enables the molecular detection of neuronal α-synuclein aggregates in olfactory mucosa of patients with isolated RBD and Parkinson's disease. Although the overall sensitivity was moderate in this study, nasal swabbing is attractive as a simple, non-invasive test and might be useful as part of a screening battery to identify subjects in the prodromal stages of α-synucleinopathies. Further studies are needed to enhance sensitivity, and better understand the temporal dynamics of α-synuclein seeding in the olfactory mucosa and spreading to other brain areas during the progression from isolated RBD to overt α-synucleinopathy, as well the impact of timing, disease subgroups and sampling technique on the overall sensitivity.

Skin α-Synuclein Aggregation Seeding Activity as a Novel Biomarker for Parkinson Disease

IMPORTANCE

Deposition of the pathological α-synuclein (αSynP) in the brain is the hallmark of synucleinopathies, including Parkinson disease (PD), Lewy body dementia (LBD), and multiple system atrophy (MSA). Whether real-time quaking-induced conversion (RT-QuIC) and protein misfolding cyclic amplification (PMCA) assays can sensitively detect skin biomarkers for PD and non-PD synucleinopathies remains unknown.

OBJECTIVE

To develop sensitive and specific skin biomarkers for antemortem diagnosis of PD and other synucleinopathies.

DESIGN, SETTING, AND PARTICIPANTS

This retrospective and prospective diagnostic study evaluated autopsy and biopsy skin samples from neuropathologically and clinically diagnosed patients with PD and controls without PD. Autopsy skin samples were obtained at 3 medical centers from August 2016 to September 2019, and biopsy samples were collected from 3 institutions from August 2018 to November 2019. Based on neuropathological and clinical diagnoses, 57 cadavers with synucleinopathies and 73 cadavers with nonsynucleinopathies as well as 20 living patients with PD and 21 living controls without PD were included. Specifically, cadavers and participants had PD, LBD, MSA, Alzheimer disease, progressive supranuclear palsy, or corticobasal degeneration or were nonneurodegenerative controls (NNCs). A total of 8 approached biopsy participants either refused to participate in or were excluded from this study due to uncertain clinical diagnosis. Data were analyzed from September 2019 to April 2020.

MAIN OUTCOMES AND MEASURES

Skin αSynP seeding activity was analyzed by RT-QuIC and PMCA assays.

RESULTS

A total of 160 autopsied skin specimens from 140 cadavers (85 male cadavers [60.7%]; mean [SD] age at death, 76.8 [10.1] years) and 41 antemortem skin biopsies (27 male participants [66%]; mean [SD] age at time of biopsy, 65.3 [9.2] years) were analyzed. RT-QuIC analysis of αSynP seeding activity in autopsy abdominal skin samples from 47 PD cadavers and 43 NNCs revealed 94% sensitivity (95% CI, 85-99) and 98% specificity (95% CI, 89-100). As groups, RT-QuIC also yielded 93% sensitivity (95% CI, 85-97) and 93% specificity (95% CI, 83-97) among 57 cadavers with synucleinopathies (PD, LBD, and MSA) and 73 cadavers without synucleinopathies (Alzheimer disease, progressive supranuclear palsy, corticobasal degeneration, and NNCs). PMCA showed 82% sensitivity (95% CI, 76-88) and 96% specificity (95% CI, 85-100) with autopsy abdominal skin samples from PD cadavers. From posterior cervical and leg skin biopsy tissues from patients with PD and controls without PD, the sensitivity and specificity were 95% (95% CI, 77-100) and 100% (95% CI, 84-100), respectively, for RT-QuIC and 80% (95% CI, 49-96) and 90% (95% CI, 60-100) for PMCA.

CONCLUSIONS AND RELEVANCE

This study provides proof-of-concept that skin αSynP seeding activity may serve as a novel biomarker for antemortem diagnoses of PD and other synucleinopathies.

Phosphorylated Alpha-Synuclein Within Cutaneous Autonomic Nerves of Patients With Parkinson's Disease: The Implications of Sample Thickness on Results

The detection of cutaneous phosphorylated alpha-synuclein (P-syn) in patients with Parkinson's disease (PD) has ranged from 30% to 100% across different studies. We hypothesize that part of the variability in P-syn detection is due to methodological differences using sections of different tissue thickness. Three skin biopsies were obtained from 29 individuals with PD and 21 controls. Tissues were cut into 10-, 20-, and 50-µm-thick sections and double-stained with protein gene product (PGP) 9.5 and P-syn. We quantified the deposition of P-syn with and without PGP 9.5 in sweat glands, pilomotor muscle, and blood vessels using confocal digital images of autonomic structures. Overall, the P-syn-positive rates with PGP 9.5 colocalization in subjects with PD were 100% using 50 µm sections, 90% using 20 µm sections, and 73% using 10 µm sections with 100% specificity. (No P-syn was detected within control subjects.) Without PGP 9.5, colocalization of the P-syn-positive rates was 100% for all samples, but specificity dropped below 70%. In this study, double-immunostained 50 µm skin biopsy tissue sections are superior to 20 and 10 µm tissue sections at detecting P-syn in subjects with PD. The increased sensitivity is likely secondary to a combination of greater volume of tissue analyzed and improved visualization of nerve fiber architecture.

In vivo distribution of α-synuclein in multiple tissues and biofluids in Parkinson disease

Objective

The Systemic Synuclein Sampling Study (S4) measured α-synuclein in multiple tissues and biofluids within the same patients with Parkinson disease (PD) vs healthy controls (HCs).

Methods

S4 was a 6-site cross-sectional observational study of participants with early, moderate, or advanced PD and HCs. Motor and nonmotor measures and dopamine transporter SPECT were obtained. Biopsies of skin, colon, submandibular gland (SMG), CSF, saliva, and blood were collected. Tissue biopsy sections were stained with 5C12 monoclonal antibody against pathologic α-synuclein; digital images were interpreted by neuropathologists blinded to diagnosis. Biofluid total α-synuclein was quantified using ELISA.

Results

The final cohort included 59 patients with PD and 21 HCs. CSF α-synuclein was lower in patients with PD vs HCs; sensitivity/specificity of CSF α-synuclein for PD diagnosis was 87.0%/63.2%, respectively. Sensitivity of α-synuclein immunoreactivity for PD diagnosis was 56.1% for SMG and 24.1% for skin; specificity was 92.9% and 100%, respectively. There were no significant relationships between different measures of α-synuclein within participants.

Conclusions

S4 confirms lower total α-synuclein levels in CSF in patients with PD compared to HCs, but specificity is low. In contrast, α-synuclein immunoreactivity in skin and SMG is specific for PD but sensitivity is low. Relationships within participants across different tissues and biofluids could not be demonstrated. Measures of pathologic forms of α-synuclein with higher accuracy are critically needed.

Classification of evidence

This study provides Class III evidence that total CSF α-synuclein does not accurately distinguish patients with PD from HCs, and that monoclonal antibody staining for SMG and skin total α-synuclein is specific but not sensitive for PD diagnosis.

α-Synuclein real-time quaking-induced conversion in the submandibular glands of Parkinson's disease patients

BACKGROUND

Identification of a peripheral biomarker is a major roadblock in the diagnosis of PD. Immunohistological identification of p-serine 129 α-synuclein in the submandibular gland tissues of PD patients has been recently reported.

OBJECTIVE

We report on a proof-of-principle study for using an ultra-sensitive and specific, real-time quaking-induced conversion assay to detect pathological α-synuclein in the submandibular gland tissues of PD patients.

METHODS

The α-synuclein real-time quaking-induced conversion assay was used to detect and quantify pathological α-synuclein levels in PD, incidental Lewy body disease, and control submandibular gland tissues as well as in formalin-fixed paraffin-embedded sections.

RESULTS

We determined the quantitative seeding kinetics of pathological α-synuclein present in submandibular gland tissues from autopsied subjects using the α-synuclein real-time quaking-induced conversion assay. A total of 32 cases comprising 13 PD, 3 incidental Lewy body disease, and 16 controls showed 100% sensitivity and 94% specificity. Interestingly, both PD and incidental Lewy body disease tissues showed 100% concordance for elevated levels of pathological α-synuclein seeding activity compared to control tissues. End-point dilution kinetic analyses revealed that the submandibular gland had a wide dynamic range of pathological α-synuclein seeding activity.

CONCLUSIONS

Our results are the first to demonstrate the utility of using the real-time quaking-induced conversion assay on peripherally accessible submandibular gland tissues and formalin-fixed paraffin-embedded tissue sections to detect PD-related pathological changes with high sensitivity and specificity. Additionally, the detection of seeding activity from incidental Lewy body disease cases containing immunohistochemically undetected pathological α-synuclein demonstrates the α-synuclein real-time quaking-induced conversion assay's potential utility for identifying prodromal PD in submandibular gland tissues. © 2019 International Parkinson and Movement Disorder Society.

Feasibility of repeat and bilateral submandibular gland needle biopsies in Parkinson's disease

INTRODUCTION

Submandibular gland (SMG) biopsies detect pathological alpha-synuclein (aSyn) in patients with Parkinson's disease (PD). The objectives of this study were to determine 1) the feasibility of performing a second SMG biopsy in previously biopsied patients, 2) the feasibility of doing bilateral SMG biopsies, 3) laterality of aSyn density, 4) whether aSyn density changes over time.

METHODS

Seven PD patients (6 males) previously having positive unilateral SMG biopsies underwent bilateral needle biopsies. Staining with a validated antibody to pathologic p-serine 129 aSyn was performed.

RESULTS

Mean age at time of second biopsy was 76 years and mean time between biopsies was 4.1 years. Five subjects had sufficient SMG tissue bilaterally and two only unilaterally for a total of 12/14 glands biopsied having sufficient tissue, all 7 subjects having sufficient tissue on at least one side, and all 12 glands being aSyn positive. There was a 4x increase in aSyn density on average in the repeat biopsy, with 5 subjects having an increase, one no change, and one a decrease in density. Side effects were similar to previous reports; mainly bruising, swelling, slight bleeding.

CONCLUSIONS

This is the first published study of bilateral transcutaneous needle biopsies of the SMG in living patients with PD which showed better tissue acquisition and a change in aSyn density over time. While further study is needed, there is potential for SMG biopsies to serve as a tissue biomarker for PD disease progression and potentially as a peripheral outcome measure for anti-aSyn treatment.