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Evaluation of a new biomarker 14-3-3 Eta protein in diagnosis of rheumatoid arthritis

1 Department of Biochemistry, Nizam's Institute of Medical Sciences, Hyderabad, Telangana, India
2 Department of Clinical Immunology and Rheumatology, Nizam's Institute of Medical Sciences, Hyderabad, Telangana, India

Date of Submission17-Feb-2020
Date of Acceptance07-May-2020

Correspondence Address:
Noorjahan Mohammed,
Department of Biochemistry, Nizam's Institute of Medical Sciences, Punjagutta, Hyderabad - 500 082, Telangana
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/injr.injr_30_20


Context: The lack of sensitivity and specificity of the existing diagnostic markers in Rheumatoid arthritis (RA) stimulates the search for new biomarkers to improve diagnostic sensitivity especially in seronegative cases. Aims: To estimate the levels of 14-3-3 η in RA cases, to assess the positivity of 14-3-3 η in seronegative RA and to correlate rheumatoid factor (RF) positivity with 14-3-3 η positivity in seropositive RA. Settings and Design: This was cross sectional case control study by the Departments of Biochemistry and Rheumatology and clinical immunology. Subjects and Methods: A total of 61 RA cases and 20 healthy controls were included. Erythrocyte sedimentation rate, high sensitivity C reactive protein, RF, anti-citrullinated peptide antibodies (CCP) and 14-3-3 η protein were estimated. RA cases were further classified as seropositive (n = 23) and seronegative (n = 38) based on the positivity of either RF or anti-CCP result. Statistical Analysis: Prism 7 (GraphPad Software Inc.). Results: The median levels of 14-3-3 η (ng/ml) in cases (0.66 [0.2–1.1]) were significantly high compared to controls (0.1 [0.07–0.28]), P < 0.0001. It had a sensitivity of 74% and specificity of 90% at >0.3 ng/ml. 14-3-3 η showed statistically significant difference between seronegative cases and controls (P = 0.0003). The sensitivity and specificity of RF and anti-CCP were 33% and 85% and 37% and 90% respectively. The combination of 14-3-3 η, RF and anti-CCP showed sensitivity and specificity of 85.4% and 100% respectively with area under the curve 0.927. Conclusions: Our study demonstrated that serum levels of 14-3-3 η were significantly higher in cases compared to controls. Seronegative RA cases showed 14-3-3 η positivity in 71% of cases. 14-3-3 η appears to be a useful and highly specific marker in RA.

Keywords: Anti-citrullinated peptide antibodies, rheumatoid factor, seronegative and seropositive

How to cite this URL:
Yarlagadda LD, Jacob R, Rajasekhar D L, Iyyapu KM, S. Kompella SB, Madrol VB, Sreedevi N N, Khan SA, Mohammed N. Evaluation of a new biomarker 14-3-3 Eta protein in diagnosis of rheumatoid arthritis. Indian J Rheumatol [Epub ahead of print] [cited 2021 Jan 18]. Available from:

  Introduction Top

Rheumatoid arthritis (RA) is a chronic autoimmune disease that affects 0.3%–1% of the population according to WHO.[1] It is driven by multiple pathophysiological factors and manifests with high heterogeneity both among and within patients along the disease course. It is the most common form of chronic inflammatory arthritis and often results in joint damage and physical disability.[2] Early diagnosis, combined with an accurate prognostic assessment at presentation, is a central tenet in the effective management of RA patients.[3]

The diagnosis of RA is primarily based on clinical, radiological and immunological features.

The most frequent serological test is the measurement of rheumatoid factor (RF).[4] Although the RF test has good sensitivity, it is not specific for RA, as it is often positive in healthy individuals and patients with other rheumatic or inflammatory diseases, autoimmune diseases or chronic infections.[5]

Both RF and anti citrullinated peptide antibodies (CCP) antibodies (anti-cyclic citrullinated protein peptide antibodies) have been found to be present very early in the disease, often with the absence of clinical symptoms and many reports indicate that elevated levels of anti CCP antibodies can predict the development of erosive disease.[6],[7],[8],[9],[10],[11] The sensitivity of the anti CCP test is around 50%–60% at the onset of RA and can rise as high as 85% later in the course of the disease.[11] As 10%–15% patients with RA will be RF and anti-CCP antibody negative, there is a need for a new biomarker that will improve diagnostic sensitivity in these seronegative patients.

14-3-3 protein

14-3-3 proteins represent a family of ubiquitously expressed intracellular chaperonins that are exclusively expressed in eukaryotic cells. The family consists of seven isoforms and share more than 50% amino acid homology between them: Beta (β), epsilon (ε), gamma (γ), eta (η), tau (τ), zeta (ζ), and sigma (σ).[12] Serum 14-3-3 η is a novel joint-derived proinflammatory mediator implicated in the pathogenesis of RA.[13] Unlike RF or anti CCP antibodies, which can arise as a consequence of disease in sites distinct from inflamed joints, 14-3-3 η hyper expression in RA is restricted to synovial joints with a significantly higher expression in synovial fluid than in serum.[14] In established RA an association has been observed between the serum levels of 14-3-3 η and the degree of joint damage.

RA, like many other chronic diseases, has a significant impact on patient's functional ability and quality of life and it represents a huge economic burden, not only for patients and their families, but also for the society as a whole. The lack of sensitivity and specificity of the present diagnostic panel of parameters have led to the search for newer biomarkers to add to the present panel to identify the disease earlier and halt the progression of the disease and prevent the disability to greater extent.

So we aimed: (i) To estimate the levels of 14-3-3 η in established cases of RA and healthy controls, (ii) to assess the prevalence of 14-3-3 η in seronegative RA and also to correlate RF positivity with 14-3-3 η positivity in seropositive RA.

  Subjects and Methods Top

This study was cross sectional case control study conducted in the Department of Biochemistry in collaboration with Department of Clinical Immunology and Rheumatology, Nizam's Institute of Medical Sciences, Punjagutta, Hyderabad, Telangana. This study included 61 subjects aged between 18 and 60 years clinically diagnosed as RA as per American College of Rheumatology 2010 criteria as cases (taking into consideration joint involvement, serology, acute phase reactants (erythrocyte sedimentation rate [ESR], C-reactive protein [CRP]) and duration of symptoms) and 20 age and gender matched subjects as healthy controls. RA cases were further classified as seropositive (n = 23) and seronegative (n = 38) based on the positivity of either RF or anti-CCP result. Cut-off considered positive for RF and anti-CCP are >20 IU/ml and >5 U/ml respectively. Patients with bacterial or crystal-induced arthritis or a defined connective tissue disease or systemic vasculitis and patients not willing to provide informed consent were excluded.

After obtaining approval from Institutional Ethics Committee and taking informed written consent from the study subjects, 8 ml of blood was collected from each patient and healthy volunteers in plain and ethylenediaminetetraacetic acid tubes. Serum was separated after 1 h. ESR (Westergren method), high sensitivity CRP (hsCRP) (immunoturbidimetry), RF (IgM rhuematoid factor enzyme-linked immunosorbent assay [ELISA], Euroimmun, Germany), and Anti-CCP antibody (ELISA from HYCOR company) were estimated. Part of serum was aliquoted and stored at −80°C for subsequent analysis of 14-3-3 η protein by using Sandwich technique ELISA kit (Cusabio, Houston, Texas, USA).

Statistical methods

Statistical analysis was performed using Prism 7 (GraphPad Prism version 7.00 for Windows, GraphPad Software, La Jolla California USA). Distribution normality was established by the Shapiro-Wilk normality test. Median 14-3-3 η serum levels between the RA and control groups were tested for statistical significance using a 2-tailed Mann–Whitney U test. Kruskal-Wallis test with the post hoc Dunn's multiple comparison method was used to determine the statistical significance across the three groups (sero + ve, sero–ve and controls). Receiver operator characteristics (ROC) curves were used to evaluate the diagnostic utility of RF, anti-CCP and 14-3-3 η as estimated by the area under the curve (AUC), sensitivity, specificity, positive predictive value and negative predictive value. P < 0.05 is considered as statistically significant.

  Results Top

A total of 81 subjects (61 RA cases and 20 healthy controls) were included in the study. Among 61 cases, 54 (89%) were females and 7 (11%) males. In the control group of 20 healthy subjects, there were 18 (90%) females and 2 (10%) males.

[Table 1] lists the demographic variables of controls and RA cases. Mean levels of ESR (mm/1st h) (48.6 ± 20.1 vs. 10.2 ± 5.4, P < 0.0001) were significantly higher in cases when compared to controls. Medians of hsCRP (mg/L) were significantly higher in RA cases when compared to controls (7.5 [3.5–21.6] and 2.3 [0.8–5.3], P = 0.0003) respectively [Figure 1].
Table 1: Demographic data of controls and rheumatoid arthritis cases

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Figure 1: Comparison of 14-3-3η levels between controls and cases

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Though median serum levels of 14-3-3 η were significantly higher in both seropositive and seronegative cases than in controls, there is no significant difference between these two groups (P > 0.99) [Figure 2].
Figure 2: Comparison of serum 14-3-3η levels among the three groups

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Positivity of 14-3-3 η in seronegative and seropositive rheumatoid arthritis

Out of 61 RA patients included in our study, 38 were seronegative for RF and anti-CCP. Of these 38 patients, 27 were found to be positive for 14-3-3 η (with cut-off of >0.3 ng/ml) [Table 2]. Thus the prevalence of this marker in seronegative population in our study was found to be 71% whereas seropositive cases showed 78% positivity for 14-3-3 η.
Table 2: Descriptive statistics of seropositive and seronegative rheumatoid arthritis cases

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To assess the diagnostic performance of various biomarkers, ROC analysis was done. 14-3-3 η had a sensitivity of 74% and specificity of 90% at a cut-off of >0.3 ng/ml [Figure 3] for diagnosis of RA. RF had a sensitivity of 33% and specificity of 85% and AntiCCP has a sensitivity of 35% and specificity of 90% [Table 3].
Figure 3: Comparison of receiver operator characteristics curves of various biomarkers

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Table 3: Utility of various markers in diagnosis of rheumatoid arthritis

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The combination 14-3-3 η, RF and anti-CCP showed sensitivity and specificity of 85.42% and 100% respectively with AUC 0.927 [Figure 4].
Figure 4: Receiver operator characteristics – Combination of biomarkers (14-3-3eta, rheumatoid factor and anti-citrullinated peptide antibodies)

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As shown in [Table 4], serum 14-3-3 η has significant positive correlation with hsCRP. 14-3-3 η showed a positive correlation with RF (ρ = 0.42, P = 0.008) and anti-CCP (ρ = 0.51, P = 0.01) in seropositive RA cases.
Table 4: Correlation of serum 14-3-3η with other variables in rheumatoid arthritis

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Logistic regression analysis

When logistic regression is done, 14-3-3 η and ESR were found to be significant independent predictors of RA as shown in [Table 5].
Table 5: Logistic regression analysis for rheumatoid arthritis

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  Discussion Top

Early diagnosis of RA has been a challenge for clinicians because symptoms are often subtle and can be similar to those of other diseases. Diagnosis and initiation of treatment of RA within 12 weeks of symptom onset, window of opportunity for therapy intervention, can only help prevent joint destruction and improve long-term function and patient prognosis. Unfortunately, many of these patients are not diagnosed during this time frame. The current laboratory markers used for diagnosis of RA are RF, anti-CCP, and CRP. These laboratory markers are normal in many patients, particularly in early disease. RF and anti-CCP have low sensitivity in early RA. In view of low sensitivity with current serological markers, there is need for better marker for early detection of RA. 14-3-3 protein is uniquely present in RA. This protein distributed throughout the body, particularly in synovium. Serum measurement of 14.3.3 η could play a valuable role in early diagnosis of RA to enable timely intervention.

This study has been undertaken to determine the effectiveness of the newer biomarker 14-3-3 η protein to diagnose more number of RA patients at an earlier stage. The synovial fluid determination of 14-3-3 η protein is more specific than the serum. As it is an invasive procedure, serum levels of 14-3-3 η protein have been assessed in this study which has been previously determined by many studies across the world.[13],[15]

14-3-3 η

The median levels of 14-3-3 η in RA cases and healthy controls in our study are 0.66 ng/ml and 0.1 ng/ml, respectively [Figure 2]. The values are significantly higher in RA cases when compared to control group. 14-3-3 eta is a joint derived biomarker that is expressed at significantly higher levels in patients with RA than in healthy subjects, other autoimmune diseases, or viral and bacterial arthritides.[16] In a study done by Maksymowych et al.,[17] the median 14-3-3 η levels are significantly higher in RA patients with established disease versus healthy subjects (1.12 vs. 0.001 ng/ml) and subjects with other arthropathies, connective tissue disorders and autoimmune diseases (0.02 ng/mL). In our study, ROC curve analysis of 14-3-3 η comparing RA cases to healthy subjects showed a sensitivity of 73.8% and specificity of 90% with AUC of 0.82. In a similar study done by Walter P. Maksymowych et al.[18] sensitivity and specificity of 14-3-3 η was 77.0% and 92.6%, respectively. This difference in sensitivity could be due to low cut-off (≥0.19 ng/ml) as compared to our cut off (>0.3 ng/ml).

Comparison of 14-3-3 η, rheumatoid factor and anti-citrullinated peptide antibodies

Our study found a significant difference between established RA cases and healthy controls with respect to serum 14-3-3 η, RF and anti-CCP levels. 14-3-3 η has high sensitivity and specificity when compared to RF and anti-CCP. ROC-AUC for 14-3-3 η (0.82) is higher when compared to RF (0.59) and anti-CCP (0.68). In a study by Martinez-Prat et al.,[19] showed a sensitivity and specificity of 71.0% and 86.9%, respectively with AUC 0.82 (95% confidence interval [CI] 0.80–0.84) for anti-CCP. They also reported a sensitivity and specificity of 63.0% and 87%, respectively with AUC 0.79 (95% CI 0.77–0.81) for IgM RF. The high sensitivity for anti-CCP and RF in their study could be due to large sample size and low sensitivity in our study may be explained by inclusion of more number of seronegative cases. Out of 61 RA patients included in our study, 38 were seronegative for RF and anti-CCP. Of these 38 patients, 27 were found to be positive for 14-3-3 η making it a good marker in seronegative cases.

Utility of combination of markers

As anti-CCP and RF are often used together to diagnose RA, the benefit of adding 14-3-3 η to the existing markers was assessed. Addition of 14-3-3 η to RF and/or anti-CCP improved the sensitivity from 32.8% to 75% and from 35.4% to 83%, respectively. Combination all the three markers (RF + anti-CCP + 14-3-3 η) further increased the sensitivity to 85%. In the study conducted by W. P. Maksymowych et al. demonstrated that adding 14-3-3 η to anti-CCP resulted in an identification rate of 72% compared to 59% for anti-CCP alone.[18] Adding RF to anti-CCP increased diagnostic sensitivity from 59% to 72% and this is-further increased to78% when 14-3-3 η was added.

  Conclusions Top

Our study demonstrated that the serum levels of new biomarker 14-3-3 η were significantly higher in RA patients when compared to healthy controls. 14-3-3 η has 73.77% sensitivity and 90% specificity at a cut-off of >0.3 ng/ml. Seronegative RA cases showed 14-3-3 η positivity in 71% of cases. Our study shows that 14-3-3 η is a useful, highly specific marker in RA. Addition of new biomarker14-3-3 η to RF and anti-CCP further improves detection of patients with RA. Future large sample size studies are warranted to examine the diagnostic role of 14-3-3 η in early detection of RA.

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Conflicts of interest

There are no conflicts of interest.

  References Top

WHO; 2020. Available from: [Last accessed on 2020 May 26].  Back to cited text no. 1
Feldmann M, Brennan FM, Maini RN. Rheumatoid arthritis. Cell 1996;85:307-10.  Back to cited text no. 2
Rasker JJ, Cosh JA. Course and prognosis of early rheumatoid arthritis. Scand J Rheumatol Suppl 1989;79:45-56.  Back to cited text no. 3
Wolfe F. The natural history of rheumatoid arthritis. J Rheumatol Suppl 1996;44:13-22.  Back to cited text no. 4
van Venrooij WJ, Hazes JM, Visser H. Anticitrullinated protein/peptide antibody and its role in the diagnosis and prognosis of early rheumatoid arthritis. Neth J Med 2002;60:383-8.  Back to cited text no. 5
Rantapää-Dahlqvist S, de Jong BA, Berglin E, Hallmans G, Wadell G, Stenlund H, et al. Antibodies against cyclic citrullinated peptide and IgA rheumatoid factor predict the development of rheumatoid arthritis. Arthritis Rheum 2003;48:2741-9.  Back to cited text no. 6
Nielen MM, Schaardenburg DV, Reesink HW, Stadt RJ, Horst-Bruinsma IE, Margret HM, et al. Specific autoantibodies precede the symptoms of rheumatoid arthritis: A study of serial measurements in blood donors. Arthritis Rheum 2004;50:380-6.  Back to cited text no. 7
van Gaalen FA, Linn-Rasker SP, van Venrooij WJ, de Jong BA, Breedveld FC, Verweij CL, et al. Autoantibodies to cyclic citrullinated peptides predict progression to rheumatoid arthritis in patients with undifferentiated arthritis: A prospective cohort study. Arthritis Rheum 2004;50:709-15.  Back to cited text no. 8
Meyer O, Labarre C, Dougados M, Goupille P, Cantagrel A, Dubois A, et al. Anticitrullinated protein/peptide antibody assays in early rheumatoid arthritis for predicting five year radiographic damage. Ann Rheum Dis 2003;62:120-6.  Back to cited text no. 9
Forslind K, Ahlmén M, Eberhardt K, Hafström I, Svensson B; BARFOT Study Group. Prediction of radiological outcome in early rheumatoid arthritis in clinical practice: Role of antibodies to citrullinated peptides (anti-CCP). Ann Rheum Dis 2004;63:1090-5.  Back to cited text no. 10
Kastbom A, Strandberg G, Lindroos A, Skogh T. Anti-CCP antibody test predicts the disease course during 3 years in early rheumatoid arthritis (the Swedish TIRA project). Ann Rheum Dis 2004;63:1085-9.  Back to cited text no. 11
Jin J, Smith FD, Stark C, Wells CD, Fawcett JP, Kulkarni S, et al. Proteomic, functional, and domain-based analysis of in vivo 14-3-3 binding proteins involved in cytoskeletal regulation and cellular organization. Curr Biol 2004;14:1436-50.  Back to cited text no. 12
Maksymowych WP, Heijde DV, Allaart CF, Landewé R, Boire G, Tak PP, et al. 14-3-3η is a novel mediator associated with the pathogenesis of rheumatoid arthritis and joint damage. Arthritis Res Ther 2014;16:R99.  Back to cited text no. 13
Kilani RT, Maksymowych WP, Aitken A, Boire G, St-Pierre Y, Li Y, et al. Detection of high levels of 2 specific isoforms of 14-3-3 proteins in synovial fluid from patients with joint inflammation. J Rheumatol 2007;34:1650-7.  Back to cited text no. 14
Mohamed AH, Abdellatif A, El-Noshokaty EH. Serum level of 14-3-3η (eta) protein as a diagnostic marker for rheumatoid arthritis and potential correlation with 'disease activity. MOJ Orthop Rheumatol 2018;7:280.  Back to cited text no. 15
Hirata S, Marotta A, Gui Y, Hanami K, Tanaka Y. Serum 14-3-3η level is associated with severity and clinical outcomes of rheumatoid arthritis, and its pretreatment level is predictive of DAS28 remission with tocilizumab. Arthritis Res Ther 2015;17:280.  Back to cited text no. 16
Maksymowych WP, Naides SJ, Bykerk V, Siminovitch KA, Schaardenburg DV, Boers M, et al. Serum 14-3-3η is a novel marker that complements current serological measurements to enhance detection of patients with rheumatoid arthritis. J Rheumatol 2014;41:2104-13.  Back to cited text no. 17
Maksymowych WP, Marotta A. 14-3-3η: A novel biomarker platform for rheumatoid arthritis. Clin Exp Rheumatol 2014;32 Suppl 85:S35-9.  Back to cited text no. 18
Martinez-Prat L, Nissen MJ, Lamacchia C, Bentow C, Cesana L, Roux-Lombard P, et al. Comparison of serological biomarkers in rheumatoid arthritis and their combination to improve diagnostic performance. Front Immunol 2018;9:1113.  Back to cited text no. 19


  [Figure 1], [Figure 2], [Figure 3], [Figure 4]

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]


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