Abstract
Objectives
Four-and-a-half LIM domains 1 (FHL1) is a muscle-specific protein. Autoantibodies against FHL1 were recently discovered in adults with idiopathic inflammatory myopathies (IIMs) and were found to be associated with clinical features and outcomes indicative of increased disease severity. Anti-FHL1 autoantibodies have not been described in children. Here, the prevalence and clinical features associated with anti-FHL1 autoantibodies were examined in a large North American cohort of juvenile patients with IIM.
Methods
Sera from 338 juvenile IIM patients and 91 juvenile healthy controls were screened for anti-FHL1 autoantibodies by ELISA. Clinical characteristics and HLA alleles of those with and without anti-FHL1 autoantibodies were compared among those with juvenile IIM.
Results
Anti-FHL1 autoantibodies were present in 10.9% of juvenile IIM patients and 1.1% of controls. The frequency of anti-FHL1 autoantibodies among clinical and serologic subgroups did not differ. A higher percentage of Asian patients had anti-FHL1 autoantibodies (11% vs 0.7%; P = 0.002). Myositis-associated autoantibodies (MAAs) [odds ratio (OR) 2.09 (CI 1.03, 4.32)], anti-Ro52 autoantibodies specifically [OR 4.17 (CI 1.83, 9.37)] and V-sign rash [OR 2.59 (CI 1.22, 5.40)] were associated with anti-FHL1 autoantibodies. There were no differences in other features or markers of disease severity. No HLA associations with anti-FHL1 autoantibodies in Caucasian myositis patients were identified.
Conclusion
Anti-FHL1 autoantibodies are present in ∼11% of juvenile IIM patients and commonly co-occur with MAAs, including anti-Ro52 autoantibodies. In contrast to adult IIM, anti-FHL1 autoantibodies in juvenile myositis are associated with V-sign rash but not with other distinctive clinical features or worse outcomes.
Keywords: myositis, juvenile idiopathic inflammatory myopathies, FHL1 autoantibodies, myositis-associated autoantibodies
Rheumatology key messages.
Myositis-associated autoantibodies, specifically anti-Ro52, commonly co-occur with anti-FHL1 autoantibodies in juvenile myositis.
Anti-FHL1 autoantibodies in juvenile myositis are associated with V-sign rash but not with a distinct phenotype or severe disease.
Introduction
The idiopathic inflammatory myopathies (IIMs) are a heterogeneous group of systemic autoimmune diseases characterized by skeletal muscle inflammation and frequent multiorgan involvement. Autoantibodies are found in most patients with IIM [1, 2]. Myositis-specific autoantibodies (MSAs) exist only in patients with IIM and define distinct clinical phenotypes. Myositis-associated autoantibodies (MAAs) are present in patients with myositis as well as other autoimmune diseases and commonly co-occur with other MSAs or MAAs. MAAs may also portend increased morbidity, such as more frequent interstitial lung disease (ILD) and worse prognosis in juvenile IIM patients with anti-Ro52 autoantibodies [3].
Autoantibodies against the muscle-specific four-and-a-half LIM domains 1 (FHL1) protein were recently identified in a Swedish cohort of adult IIM [4]. Anti-FHL1 autoantibodies were associated with a more severe phenotype that included an increased frequency of distal weakness, muscle atrophy, myofiber damage, dysphagia and vasculitis. Additionally, the DRB1*03/DRB1*13 genotype was found more often in those with anti-FHL1 autoantibodies. However, these findings were not replicated in an Australian adult myositis cohort in which anti-FHL1 autoantibodies were more common in those without other myositis autoantibodies [5]. This study also found anti-FHL1 autoantibodies in adults with SSc, suggesting that anti-FHL1 is an MAA.
Anti-FHL1 autoantibodies were detected in one patient with juvenile dermatomyositis (JDM) in the original study, but they otherwise remain undescribed in children [4]. The purpose of the present study was to determine the prevalence of as well as the clinical features and HLA alleles associated with anti-FHL1 autoantibodies in a large North American cohort of juvenile IIM.
Patients and methods
Patients and serum samples
Of 560 patients from the Childhood Myositis Heterogeneity Collaborative Study enrolled in National Institutes of Health institutional review board–approved studies between 1989 and 2020 with probable or definite juvenile-onset myositis by Bohan and Peter criteria, 338 patients with sera available for autoantibody testing were included [2, 6, 7]. Myositis clinical subgroups included JDM, juvenile polymyositis (JPM) and juvenile myositis overlapping with another autoimmune or juvenile connective tissue myositis (JCTM). Sera were available from 91 juvenile healthy controls enrolled in the same studies. All subjects and their parents provided written informed consent. A physician questionnaire captured demographics, clinical and laboratory features, treatments and outcomes. Questionnaires were completed by medical records review and patient interviews [6]. Disease onset speed and severity from first symptom to the time of diagnosis were graded according to Likert scales per the enrolling physician, as previously described [6, 8]. Organ system symptom scores at diagnosis as well as complete clinical response and remission were determined, as previously described [9–11].
Anti-FHL1 autoantibodies were detected using an enhanced-performance FHL1 ELISA, as previously described [5]. Results were normalized and transformed into arbitrary units (AU). A cut-off of 1.38 AU, which was 3 s.d. above the control mean, was considered positive. Other myositis autoantibodies were tested using validated immunoprecipitation, immunoblotting or ELISA methods [3, 6, 12, 13]. Genotyping of HLA class II (DQA1 and DRB1) alleles was also performed, as previously described [14, 15].
Analysis
Categorical variables were expressed as absolute frequency and percentage and continuous variables were reported as median and interquartile range (IQR). Comparisons between groups were made using the chi-squared or Fisher’s exact test for categorical variables and Wilcoxon rank sum test for continuous variables. Logistic or linear regression was used to determine whether anti-FHL1 autoantibody titer was predictive of outcome variables. The frequency of HLA DQA1 and DRB1 alleles in Caucasian anti-FHL1 autoantibody-positive juvenile myositis patients was compared with Caucasian anti-FHL1 autoantibody-negative myositis patients and healthy controls. Multivariable logistic regression was performed for statistically significant clinical features from the univariate analysis, controlling for the presence of MSA, year of diagnosis and duration of the disease. A two-sided P-value <0.05 was considered significant in this exploratory analysis, except for HLA analyses in which the Benjamini–Hochberg procedure was used to correct for multiple comparisons if there were any significant results. All analyses were performed using RStudio (version 1.4.1717; RStudio, Boston, MA, USA).
Results
Prevalence of anti-FHL1 autoantibodies, demographics and myositis autoantibodies
Anti-FHL1 autoantibodies were more prevalent in juvenile myositis patients than in healthy controls (10.9% vs 1.1%) (Fig. 1). Among clinical subgroups, anti-FHL1 autoantibodies were found in 10.8% of patients with JDM, 13% with JPM and 10.5% with JCTM. None of the anti-FHL1 autoantibody-positive patients with JCTM had SSc.
Fig. 1.
Swarm plot of anti-FHL1 autoantibody ELISA results for juvenile healthy controls and juvenile myositis patients
The dashed line of 1.38 AU indicates the cutoff level for anti-FHL1 autoantibody positivity. One of 91 healthy controls and 37 of 338 juvenile patients with IIM were above this threshold. Of the IIM patients, 30 had JDM, 3 had JPM and 4 had JCTM.
There was no difference in clinical subgroup distribution, gender or age between juvenile myositis patients with and without anti-FHL1 autoantibodies (Table 1). Patients with anti-FHL1 autoantibodies were more frequently Asian (11% vs 0.7%; P = 0.002). Compared with those without anti-FHL1 autoantibodies, patients with anti-FHL1 autoantibodies more often presented within 1 week of the first symptoms (8.1 vs 0.3%; P = 0.005), specifically with muscle or skin involvement or both. Those with anti-FHL1 autoantibodies did not have more severe disease at onset.
Table 1.
General features of juvenile myositis patients with and without anti-FHL1 autoantibodies
| Characteristics | Anti-FHL1 autoantibody positive (n = 37) | Anti-FHL1 autoantibody negative (n = 301) | P-valuea |
|---|---|---|---|
| Clinical subgroup, % (n/N) | |||
| JDM | 81 (30/37) | 82 (247/301) | 0.9 |
| JPM | 8.1 (3/37) | 6.6 (20/301) | 0.7 |
| JCTM | 11 (4/37) | 11 (34/301) | >0.9 |
| Female, % (n/N) | 76 (28/37) | 72 (216/301) | 0.6 |
| Raceb, % (n/N) | |||
| Caucasian | 70 (26/37) | 64 (193/301) | 0.5 |
| Black | 11 (4/37) | 17 (50/301) | 0.4 |
| Hispanic | 5.4 (2/37) | 6.6 (20/301) | >0.9 |
| Asian | 11 (4/37) | 0.7 (2/301) | 0.002 |
| Other | 2.7 (1/37) | 12 (36/301) | 0.10 |
| Age at diagnosis, years, median (IQR) | 6.6 (4.0–11.1) | 8.3 (5.5–12.2) | 0.094 |
| Delay in diagnosis, months, median (IQR) | 3.0 (1.0–5.5) | 4.0 (2.0–9.0) | 0.13 |
| Duration from diagnosis to enrolment, months, median (IQR) | 20.5 (3.6– 41.6) | 19.3 (5.6– 44.3) | 0.4 |
| Speed of onset, % (n/N) | |||
| Very rapid (<1 week) | 8.1 (3/37) | 0.3 (1/297) | 0.005 |
| Rapid (<1 month) | 11 (4/37) | 12 (35/297) | >0.9 |
| Moderate (<3 months) | 27 (10/37) | 23 (69/297) | 0.6 |
| Slow (3-6 months) | 30 (11/37) | 28 (83/297) | 0.8 |
| Very slow (>6 months) | 24 (9/37) | 37 (109/297) | |
| Severity of onset, % (n/N) | 0.14 | ||
| Mild | 8.1 (3/37) | 11 (33/298) | 0.8 |
| Moderate | 57 (21/37) | 54 (162/298) | 0.8 |
| Severe | 27 (10/37) | 32 (95/298) | 0.5 |
| Very severe | 8.1 (3/37) | 2.7 (8/298) | 0.11 |
| Myositis autoantibodies, % (n/N) | |||
| MSAc | 73 (27/37) | 81 (244/301) | 0.2 |
| Anti-p155/140 (TIF-1) | 30 (11/37) | 37 (110/301) | 0.4 |
| Anti-NXP2 | 24 (9/37) | 27 (81/301) | 0.7 |
| Anti-MDA5 | 11 (4/37) | 8.0 (24/301) | 0.5 |
| Anti-Mi2 | 0 (0/37) | 5.0 (15/301) | 0.4 |
| Anti-aminoacyl tRNA synthetase | 5.4 (2/37) | 4.0 (12/301) | 0.7 |
| Anti-SRP | 2.7 (1/37) | 2.3 (7/301) | >0.9 |
| Anti-HMGCR | 0 (0/37) | 1.3 (4/301) | >0.9 |
| MAA | 57 (21/37) | 38 (113/301) | 0.024 |
| Anti-PM/Scl | 2.7 (1/37) | 3.7 (11/301) | >0.9 |
| Anti-U1RNP | 8.1 (3/37) | 6.0 (18/301) | 0.5 |
| Anti-Ro60 | 11 (4/37) | 7.0 (21/301) | 0.3 |
| Anti-Ro52 | 35 (13/37) | 13 (38/301) | <0.001 |
| Anti-NT5c1A | 30 (11/37) | 26 (77/301) | 0.6 |
| Autoantibody negative | 16 (6/37) | 10.0 (30/301) | 0.3 |
Pearson’s chi-squared test, Fisher’s exact test or Wilcoxon rank sum test. P < 0.05; significant values are in bold.
Asian race includes Korean, Japanese, Chinese, Indian and Filipino.
Nine patients were positive for two MSAs [eight with anti-p155/140 (TIF-1) and Mi2 and one with anti-p155/140 (TIF-1) and HMGCR; none were positive for anti-FHL1].
HMGCR: 3-hydroxy-3-methylglutaryl-coenzyme A reductase; MDA5: melanoma differentiation associated protein 5; NT5c1A: cytosolic 5′-nucleotidase 1A; NXP2: nuclear matrix protein 2; PM/Scl: polymyositis/scleroderma; RNP: ribonucleoprotein; SRP: signal recognition particle; TIF-1: transcription intermediary factor 1; tRNA: transfer RNA.
While most pediatric IIM patients had an MSA, there were no differences in the prevalence of individual MSAs between those with and without anti-FHL1 autoantibodies (Table 1). However, those with anti-FHL1 autoantibodies had a higher frequency of MAAs (57% vs 38%; P = 0.024), and specifically anti-Ro52 autoantibodies (35% vs 13%; P < 0.001).
Clinical features, treatment characteristics and outcomes of juvenile myositis patients with anti-FHL1 autoantibodies
Patients with anti-FHL1 autoantibodies had more frequent V-sign rash (41 vs 25%; P = 0.042) (Table 2). The frequency of distal weakness, muscle atrophy, dysphagia, vasculitic rashes and other manifestations did not differ between patients with or without anti-FHL1 autoantibodies. There was also no difference in peak muscle enzyme levels or early system symptom scores (data not shown).
Table 2.
Clinical features, treatments and outcomes of juvenile myositis patients with and without anti-FHL1 autoantibodies
| Characteristics | Anti-FHL1 autoantibody positive (n = 37) | Anti-FHL1 autoantibody negative (n = 301) | P-valuea |
|---|---|---|---|
| Muscle involvement, % (n/N) | |||
| Myalgia | 58 (21/36) | 66 (193/294) | 0.4 |
| Distal weakness | 51 (18/35) | 47 (139/297) | 0.6 |
| Asymmetric weakness | 11 (4/36) | 16 (49/300) | 0.4 |
| Muscle atrophy | 38 (14/37) | 37 (109/298) | 0.9 |
| Falling | 46 (17/37) | 45 (134/297) | >0.9 |
| Joint involvement, % (n/N) | |||
| Arthritis | 57 (21/37) | 49 (148/300) | 0.4 |
| Joint contracture | 59 (22/37) | 61 (183/300) | 0.9 |
| Mucocutaneous involvement, % (n/N) | |||
| Heliotrope rash | 78 (28/36) | 80 (239/300) | 0.8 |
| Gottron’s papules | 89 (33/37) | 83 (249/301) | 0.3 |
| Raynaud’s phenomenon | 19 (7/37) | 14 (41/300) | 0.4 |
| Mechanic’s hands | 8 (3/37) | 6 (19/297) | 0.7 |
| V-sign rash | 41 (15/37) | 25 (75/301) | 0.042 |
| Shawl sign rash | 19 (7/37) | 17 (52/300) | 0.8 |
| Skin ulceration | 19 (7/37) | 20 (61/301) | 0.8 |
| Mucous membrane involvement | 41 (15/37) | 37 (110/300) | 0.6 |
| Vasculitic rash | 8 (3/37) | 5 (16/301) | 0.4 |
| Calcinosis | 32 (12/37) | 31 (93/301) | 0.8 |
| Lipodystrophy | 5 (2/37) | 8 (23/299) | >0.9 |
| Gastrointestinal involvement, % (n/N) | |||
| Dysphagia | 35 (13/37) | 41 (123/301) | 0.5 |
| Regurgitation | 28 (10/36) | 21 (62/301) | 0.3 |
| Pulmonary involvement, % (n/N) | |||
| Dysphonia | 32 (12/37) | 34 (100/298) | 0.9 |
| Dyspnea on exertion | 31 (11/36) | 31 (93/298) | >0.9 |
| Interstitial lung disease | 11 (4/37) | 8 (25/300) | 0.5 |
| Cardiac involvement, % (n/N) | |||
| Chest pain | 14 (5/37) | 10 (30/301) | 0.6 |
| Palpitations | 3 (1/37) | 10 (31/299) | 0.2 |
| Systemic involvement, % (n/N) | |||
| Fever | 49 (18/37) | 38 (113/300) | 0.2 |
| Weight loss | 32 (12/37) | 42 (125/299) | 0.3 |
| Muscle enzymes, median (IQR) | |||
| Peak creatine kinase (IU/L) | 810 (379–3442) | 1021 (324–5600) | 0.5 |
| Peak aldolase (IU/L) | 15.9 (9.7–37.5) | 11.4 (8.4–23.2) | 0.090 |
| Duration from start of treatment, months, median (IQR) | 35.9 (19.1–70.8) | 40.8 (17.4–76.0) | 0.8 |
| Medication useb, % (n/N) | |||
| Steroid treatment duration (months) | 22.4 (14.5, 42.1) | 26.3 (12.0, 46.1) | 0.8 |
| Prednisone (oral) | 100 (34/34) | 99 (262/264) | >0.9 |
| Methylprednisolone (i.v.) | 56 (19/34) | 57 (151/264) | 0.9 |
| Methotrexate | 82 (28/34) | 75 (198/264) | 0.3 |
| IVIG | 44 (15/34) | 35 (93/264) | 0.3 |
| Antimalarial | 44 (15/34) | 44 (117/264) | >0.9 |
| Other DMARD | 29 (10/34) | 23 (60/264) | 0.4 |
| Cytotoxic or biologic | 18 (6/34) | 16 (43/264) | 0.8 |
| Total number of major medications, median (IQR) | 3.0 (2.0–5.0) | 3.0 (2.0–4.0) | 0.4 |
| Combination of four or more major medications, % (n/N) | 29 (10/34) | 22 (58/264) | 0.3 |
| Disease coursec, % (n/N) | |||
| Monocyclic | 16 (5/31) | 21 (51/239) | 0.5 |
| Polycyclic | 29 (9/31) | 23 (54/239) | 0.4 |
| Chronic continuous | 55 (17/31) | 56 (134/239) | 0.9 |
| ACR functional class (worst ever), % (n/N) | |||
| Median (IQR) | 4.0 (2.5–4.0) | 4.0 (2.0–4.0) | >0.9 |
| I | 0 (0/15) | 6 (6/108) | >0.9 |
| II | 27 (4/15) | 21 (23/108) | 0.7 |
| III | 20 (3/15) | 19 (21/108) | >0.9 |
| IV | 53 (8/15) | 54 (58/108) | >0.9 |
| Outcomes, % (n/N) | |||
| Hospitalized | 64 (23/36) | 56 (162/288) | 0.4 |
| Wheelchair use | 20 (7/35) | 19 (56/293) | 0.9 |
| Complete clinical responsed | 26 (9/34) | 32 (82/260) | 0.5 |
| Remissione | 18 (6/34) | 22 (58/264) | 0.6 |
| Mortality | 3 (1/37) | 3 (10/301) | >0.9 |
Pearson’s chi-squared test, Fisher’s exact test or Wilcoxon rank sum test. P < 0.05; significant values are in bold.
Major drugs include steroids (i.v. methylprednisolone, oral prednisone), methotrexate, other DMARDs (azathioprine, mycophenolate mofetil, ciclosporin, tacrolimus, leflunomide, Janus kinase inhibitor), cytotoxic drugs (cyclophosphamide, chlorambucil), biologics (etanercept, infliximab, rituximab, abatacept) and immunoglobulin (i.v./s.c.). Antimalarial drugs include hydroxychloroquine, chloroquine and quinacrine.
Disease course available for those with at least 2 years of follow-up.
No evidence of active disease for 6 continuous months while on therapy.
No evidence of active disease for 6 continuous months while off all therapy.
There was no difference in the type or number of medications used between patients with and without anti-FHL1 autoantibodies (Table 2). Although a higher percentage of patients with anti-FHL1 autoantibodies received IVIG (44% vs 35%), this difference was not significant. Additionally, there was no difference in the distribution of disease courses or outcomes, including the frequency of complete clinical response and remission, between those with and without anti-FHL1 autoantibodies.
Among 51 patients with anti-Ro52 autoantibodies, 13 were anti-FHL1 autoantibody positive. In those with both anti-Ro52 and anti-FHL1 autoantibodies, there was a higher frequency of gastroesophageal regurgitation compared with those positive only for anti-Ro52 autoantibodies (54% vs 18%; P = 0.027). There were no other differences in clinical features, including ILD, treatments received or outcomes, between anti-Ro52 autoantibody-positive patients with and without anti-FHL1 autoantibodies (data not shown).
Among 36 patients negative for other known MSAs and MAAs (i.e. seronegative), the six with anti-FHL1 autoantibodies had JDM. Asian race was also more common among seronegative patients with anti-FHL1 autoantibodies (33% vs 0%; P = 0.024). V-sign rash (50% vs 23%) and calcinosis (67% vs 37%) were present in higher percentages of seronegative patients with anti-FHL1 autoantibodies compared with those without, although these differences were not statistically significant. Demographics, clinical features and outcomes did not otherwise differ between these two groups (data not shown). Additionally, there were no significant differences in clinical features or outcomes based on anti-FHL1 autoantibody titer among patients with these autoantibodies (data not shown).
Multivariable analysis
In a multivariable logistic regression model examining significant clinical features, positive MAA [odds ratio (OR) 2.09 (CI 1.03, 4.32)], anti-Ro52 autoantibodies [OR 4.17 (CI 1.83, 9.37)] and V-sign rash [OR 2.59 (CI 1.22, 5.40)] were independently associated with anti-FHL1 autoantibodies.
HLA alleles of Caucasian juvenile myositis patients with anti-FHL1 autoantibodies
There were no statistically significant associations between anti-FHL1 autoantibodies and HLA DQA1 or DRB1 alleles in juvenile myositis patients compared with anti-FHL1 autoantibody-negative juvenile myositis patients or healthy controls (Table 3). Among myositis patients, there was no difference in the percentage of DRB1*07 and DRB1*15 alleles between those with and without anti-FHL1 autoantibodies. Additionally, the DRB1*03/DRB1*13 genotype was not present in any juvenile myositis patient with anti-FHL1 autoantibodies.
Table 3.
HLA alleles in Caucasian juvenile myositis patients and juvenile healthy controls
| Alleles | Anti-FHL1 autoantibody positive juvenile myositis (n = 20)a, % (n) | Anti-FHL1 autoantibody negative juvenile myositis (n = 143)a, % (n) | P-valueb,c | Controls (n = 434)a | P-valueb,d |
|---|---|---|---|---|---|
| DQA1*01:01 | 20 (4) | 22 (31) | >0.9 | 26 (114) | >0.9 |
| DQA1*01:02 | 40 (8) | 24 (34) | 0.6 | 35 (151) | >0.9 |
| DQA1*01:03 | 0 (0) | 17 (24) | 0.3 | 19 (84) | 0.3 |
| DQA1*01:04 | 5.0 (1) | 2.1 (3) | >0.9 | 3.2 (14) | >0.9 |
| DQA1*01:05 | 5.0 (1) | 0.7 (1) | 0.8 | 1.8 (8) | >0.9 |
| DQA1*02:01 | 20 (4) | 19 (27) | >0.9 | 29 (124) | >0.9 |
| DQA1*03:01 | 25 (5) | 20 (28) | >0.9 | 11 (46) | 0.3 |
| DQA1*03:03 | 5.0 (1) | 8.4 (12) | >0.9 | 9.0 (39) | >0.9 |
| DQA1*04:01 | 20 (4) | 14 (20) | >0.9 | 7.4 (32) | 0.3 |
| DQA1*05:01 | 25 (5) | 52 (74) | 0.3 | 40 (172) | 0.7 |
| DQA1*05:05 | 5.0 (1) | 7.7 (11) | >0.9 | 4.8 (21) | >0.9 |
| DRB1*01:01 | 15 (3) | 13 (19) | >0.9 | 19 (84) | >0.9 |
| DRB1*01:02 | 5.0 (1) | 0.7 (1) | >0.9 | 3.0 (13) | >0.9 |
| DRB1*01:03 | 15 (3) | 4.2 (6) | >0.9 | 2.8 (12) | 0.9 |
| DRB1*03:01 | 20 (4) | 46 (66) | >0.9 | 22 (96) | >0.9 |
| DRB1*04:01 | 20 (4) | 14 (20) | >0.9 | 8.8 (38) | 0.9 |
| DRB1*04:03 | 5.0 (1) | 1.4 (2) | >0.9 | 0.9 (4) | >0.9 |
| DRB1*04:04 | 15 (3) | 8.4 (12) | >0.9 | 4.8 (21) | 0.9 |
| DRB1*07:01 | 20 (4) | 20 (28) | >0.9 | 29 (124) | >0.9 |
| DRB1*08:01 | 15 (3) | 11 (16) | >0.9 | 5.8 (25) | 0.9 |
| DRB1*08:04 | 5.0 (1) | 0.7 (1) | >0.9 | 1.4 (6) | >0.9 |
| DRB1*10:01 | 5.0 (1) | 2.1 (3) | >0.9 | 1.8 (8) | >0.9 |
| DRB1*11:01 | 5.0 (1) | 10 (15) | >0.9 | 7.4 (32) | >0.9 |
| DRB1*11:04 | 10 (2) | 4.9 (7) | >0.9 | 6.0 (26) | >0.9 |
| DRB1*13:01 | 0 (0) | 15 (21) | >0.9 | 16 (70) | 0.9 |
| DRB1*13:02 | 5.0 (1) | 7.0 (10) | >0.9 | 9.7 (42) | >0.9 |
| DRB1*14:01 | 5.0 (1) | 2.1 (3) | >0.9 | 4.6 (20) | >0.9 |
| DRB1*14:02 | 5.0 (1) | 0.7 (1) | >0.9 | 0.2 (1) | 0.9 |
| DRB1*15:01 | 20 (4) | 9.8 (14) | >0.9 | 22 (97) | >0.9 |
| DRB1*16:01 | 5.0 (1) | 1.4 (2) | >0.9 | 3.9 (17) | >0.9 |
Alleles with a carriage rate <5% are not presented.
Pearson’s chi-squared test or Fisher’s exact test with Benjamini–Hochberg correction for multiple comparisons.
Anti-FHL1 autoantibody-positive juvenile myositis compared with anti-FHL1 autoantibody-negative juvenile myositis.
Anti-FHL1 autoantibody-positive juvenile myositis compared with juvenile healthy controls.
Discussion
In this study of a large North American cohort of juvenile IIM patients, anti-FHL1 autoantibodies had an overall prevalence of ∼11% and were present in all clinical and most serologic subgroups. Moreover, anti-FHL1 autoantibodies frequently co-occurred with MAAs, especially anti-Ro52 autoantibodies, and were associated with V-sign rash but not with more severe manifestations or a distinct clinical phenotype.
Compared with the current study of pediatric IIM patients, anti-FHL1 autoantibodies were more prevalent in the adult IIM cohorts (25% in Albrecht et al. [4] and 14% in Galindo-Feria et al. [5]). Furthermore, in adult myositis patients, these autoantibodies were more frequently found in certain clinical subgroups, particularly PM and IBM. Of note, the relative incidence of JPM is lower than PM, and the present study may have been underpowered to detect an association with this subgroup. Alternatively, the distribution of anti-FHL1 autoantibodies may differ between adult and juvenile IIM clinical subgroups. Unlike the present cohort of juvenile myositis, adult IIM patients with anti-FHL1 autoantibodies were found more often to be seronegative for MSAs and other MAAs [4, 5]. However, this may be related in part to the smaller number of MSAs for which these cohorts were tested. In this juvenile cohort, there were only six seronegative patients with anti-FHL1 autoantibodies; all of them had JDM with the characteristic features of proximal weakness and Gottron’s papules and three had V-sign rash. A major strength of this study was evaluation of myositis autoantibodies by immunoprecipitation, which detects a broader range of autoantibodies and appears to have superior test characteristics compared with commercial assays used in the adult IIM studies [16].
In contrast to both adult IIM cohorts with anti-FHL1 autoantibodies, in the present study of juvenile IIM patients, anti-Ro52 autoantibodies were independently associated with anti-FHL1 autoantibodies [4, 5]. Although anti-Ro52 autoantibodies are associated with ILD, increased disease severity and a chronic disease course in juvenile IIM, those associations were not present in juvenile IIM patients with both anti-FHL1 and anti-Ro52 autoantibodies [3]. Patients positive for both anti-Ro52 and anti-FHL1 autoantibodies did have a higher frequency of gastroesophageal regurgitation compared with those positive only for anti-Ro52 autoantibodies. Albrecht et al. [4] also noted upper gastrointestinal involvement, specifically dysphagia, in adult IIM patients with anti-FHL1 autoantibodies. However, dysphagia was not a prominent feature of juvenile IIM patients with anti-FHL1 autoantibodies broadly or within the anti-Ro52 autoantibody-positive subgroup.
In the first description of anti-FHL1 autoantibodies in adult IIM patients there was an association with certain disease features, including dysphagia, clinical muscle atrophy and worse clinical outcomes [4]. Here, only V-sign rash was associated with anti-FHL1 autoantibodies. V-sign rash in juvenile myositis has previously been found to be associated with certain MSAs, such as anti-p155/140 (TIF-1) autoantibodies, as well as with a chronic disease course [2, 9, 17]. The association of V-sign rash with anti-FHL1 autoantibodies in the present cohort was independent of the presence of MSA, year of diagnosis and duration of disease, and patients with anti-FHL1 autoantibodies did not more frequently have a chronic disease course or worse prognosis. Although V-sign rash is more common in JDM compared with JPM and JCTM, this clinical subgroup was not overrepresented among those with anti-FHL1 autoantibodies [6].
The present findings overall align more closely with the recent adult IIM study of Galindo-Feria et al. [5]. in which neither distinctive nor severe features were identified in association with anti-FHL1 autoantibodies. The differences in these three studies on anti-FHL1 autoantibodies in IIM may be due to inherent characteristics of the distinct cohorts, which differ in country as well as in the distribution of race, age and clinical subgroup. It is clear from recent reports of anti-cortactin and anti-mitochondrial autoantibodies that not only prevalence but also associated clinical features of autoantibodies may vary between adult and juvenile myositis patients [18, 19]. The differences may also be related in part to the particular anti-FHL1 autoantibody ELISA methodology, which was consistent between Galindo-Feria et al. [5] and the present study.
The lack of severe disease features or poor prognostic factors here is surprising, as it has been proposed that production of anti-FHL1 autoantibodies may be related to prolonged exposure to FHL1 antigen from damaged muscle. As a consequence of the natural history study from which patients were included, sera were not collected at a standardize time point, such as at diagnosis of myositis. The prevalence of anti-FHL1 autoantibodies, then, may be skewed towards the group with a longer duration of disease. However, in the present cohort, delay to diagnosis, time from diagnosis to enrolment and disease duration were not significantly longer in anti-FHL1 autoantibody-positive patients. This may suggest that the development of anti-FHL1 autoantibodies is not related to long-standing muscle inflammation. Indeed, disease duration also was not different between those with and without anti-FHL1 autoantibodies in the previous studies of adult myositis patients [4, 5].
Lastly, HLA alleles have been found to be associated with certain MSAs and even potentially to differentiate juvenile from adult DM [20–22]. Anti-FHL1 autoantibodies in adult IIM were initially found to be associated with the DRB1*03/*13 genotype [4]. More recently, DRB1*07 and DRB1*15 were found in higher percentages of those with anti-FHL1 autoantibodies, although these associations were not significant after correction for multiple comparisons [5]. Here there were no significant associations of anti-FHL1 autoantibodies with either DRB1 or DQA1 alleles in Caucasian juvenile IIM patients and none of the previously reported HLA findings from the adult IIM cohorts was replicated. Moreover, neither risk nor protective factors, such as DRB1*03:01 and DRB1*15:01, respectively, were identified in Caucasian anti-FHL1 autoantibody-positive juvenile myositis patients. That DRB1*03:01 was not associated with anti-FHL1 autoantibodies may suggest that the pathogenesis of juvenile IIM in patients with these autoantibodies proceeds through an alternative mechanism.
This study has several limitations. First, some of the clinical data were collected from a natural history study ongoing since 1989, resulting in some missing data and the potential for chronology bias. Second, anti-FHL1 autoantibody titers were not measured longitudinally, given the cross-sectional nature of the natural history study. Third, patients were classified according to Bohan and Peter criteria rather than the more recent EULAR/ACR classification criteria, given incomplete data for the latter criteria. Fourth, disease severity of patients seen in the research studies may not be representative of the general spectrum of juvenile IIM. Fifth, the sample size of Caucasian juvenile myositis patients with anti-FHL1 autoantibodies was relatively small and may be underpowered to reveal potential HLA allele associations; the size and matching ethnicity of the control group are strengths. Finally, anti-FHL1 autoantibody-positive adult myositis patients were found to have increased frequencies of fiber necrosis and fatty replacement; muscle biopsies were not available in an adequate number to examine characteristics associated with these autoantibodies in juvenile myositis patients [4].
In summary, anti-FHL1 autoantibodies are present in juvenile myositis patients and are associated with other MAAs in general and anti-Ro52 autoantibodies specifically. Unlike the reported cohorts of adult IIM patients, anti-FHL1 autoantibodies in juvenile myositis were found to be associated with V-sign rash but not with other distinct clinical features, more severe manifestations or a worse prognosis. At this time, the clinical utility of anti-FHL1 autoantibodies in juvenile myositis patients is modest; future studies may uncover more useful applications.
Acknowledgements
We thank Edvard Wigren and Susanne Gräslund at the Structural Genomics Consortium, Karolinska Institutet, for access to recombinantly produced FHL1 protein. We thank Sarthak Gupta and Mariana J. Kaplan for critical review of the manuscript. This paper was presented as a poster entitled ‘Anti-FHL1 autoantibodies in juvenile myositis are associated with myositis-associated autoantibodies but not distinctive clinical features’ at the 4th Global Conference on Myositis, Prague, Czech Republic, 7 June 2022.
Members of the Childhood Myositis Heterogeneity Collaborative Study Group who contributed to this project: Daniel A. Albert, Bita Arabshahi, Imelda M. Balboni, Susan Ballinger, Lilliana Barillas-Arias, Mara L. Becker, C April Bingham, John F. Bohnsack, Ruy Carrasco, Victoria W. Cartwright, Randy Q. Cron, Rodolfo Curiel, Jason A. Dare, Wendy de la Pena, Marietta M. DeGuzman, B. Anne Eberhard, Barbara S. Edelheit, Terri H. Finkel, Stephen W. George, Harry L. Gewanter, Ellen A. Goldmuntz, Brandt P. Groh, Hillary H. Haftel, William P. Hannan, Michael Henrickson, Gloria C. Higgins, Patricia M. Hobday, Russell J. Hopp, Adam M. Huber, Lisa Imundo, C. J. Inman, Anna Jansen, James Jarvis, Olcay Y. Jones, Ankur Kamdar, Hanna Kim, Daniel J. Kingsbury, Carol B. Lindsley, Gulnara Mamyrova, Paul L. McCarthy, Stephen R. Mitchell, Frederick T. Murphy, Kabita Nanda, Terrance O’Hanlon, Elif A. Oral, Lauren M. Pachman, Maria D. Perez, Donald A. Person, C. Egla Rabinovich, Tova Ronis, Adam Schiffenbauer, Bracha Shaham, Sara H. Sinal, Jennifer Soep, Matthew L. Stoll, Sangeeta Sule, Stacey Tarvin, Scott A. Vogelgesang, Rita Volochayev, Jennifer C. Wargula and Patience H. White.
Funding: This research was supported by the Intramural Research Programs of the National Institute of Arthritis and Musculoskeletal and Skin Diseases (ZIA AR041203), National Institute of Environmental Health Sciences (ZIA ES101074, ZIA ES101081) and the Clinical Center (ZIC CL002128) of the National Institutes of Health. S.E.S. and T.K. were partially supported by the Cure JM Foundation. I.E.L. is supported by the Swedish Research Council (Vetenskapsrådet; 2020-01378), King Gustaf V 80-year Foundation (Stiftelsen Konung Gustaf V; s 80-årsfond), Swedish Rheumatism Association (Reumatikerförbundet) and Stockholm Region Council (ALF project). G.M. has received grants/research support from the Cure JM Foundation.
Disclosure statement: I.N.T. is a consultant to the Oklahoma Medical Research Foundation Clinical Immunology Laboratory with regard to myositis autoantibody testing. I.E.L. has filed a patent for use of the autoantigen FHL1 in autoantibody assays (US Patent No. 10254281; European Patent No. 3220948). All other authors have declared no relevant conflicts of interest.
Contributor Information
Matthew A Sherman, Muscle Disease Unit, Laboratory of Muscle Stem Cells and Gene Regulation, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD.
Rose Graf, Muscle Disease Unit, Laboratory of Muscle Stem Cells and Gene Regulation, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD.
Sara E Sabbagh, Division of Rheumatology, Department of Pediatrics, Medical College of Wisconsin, Milwaukee, Wisconsin, USA.
Angeles S Galindo-Feria, Division of Rheumatology, Department of Medicine, Solna, Karolinska Institutet; Center for Molecular Medicine, Karolinska Institutet, Karolinska University Hospital Solna, Stockholm, Sweden.
Iago Pinal-Fernandez, Muscle Disease Unit, Laboratory of Muscle Stem Cells and Gene Regulation, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD; Department of Neurology, Johns Hopkins University School of Medicine, Baltimore.
Katherine Pak, Muscle Disease Unit, Laboratory of Muscle Stem Cells and Gene Regulation, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD.
Takayuki Kishi, Environmental Autoimmunity Group, National Institute of Environmental Health Sciences.
Willy A Flegel, Department of Transfusion Medicine, NIH Clinical Center, National Institutes of Health, Bethesda, MD.
Ira N Targoff, Veteran's Affairs Medical Center, University of Oklahoma Health Sciences Center, and Oklahoma Medical Research Foundation, Oklahoma City, OK.
Frederick W Miller, Environmental Autoimmunity Group, National Institute of Environmental Health Sciences.
Ingrid E Lundberg, Division of Rheumatology, Department of Medicine, Solna, Karolinska Institutet; Center for Molecular Medicine, Karolinska Institutet, Karolinska University Hospital Solna, Stockholm, Sweden.
Lisa G Rider, Environmental Autoimmunity Group, National Institute of Environmental Health Sciences.
Andrew L Mammen, Muscle Disease Unit, Laboratory of Muscle Stem Cells and Gene Regulation, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD; Department of Neurology, Johns Hopkins University School of Medicine, Baltimore; Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
for the Childhood Myositis Heterogeneity Collaborative Study Group:
Daniel A Albert, Bita Arabshahi, Imelda M Balboni, Susan Ballinger, Lilliana Barillas-Arias, Mara L Becker, C April Bingham, John F Bohnsack, Ruy Carrasco, Victoria W Cartwright, Randy Q Cron, Rodolfo Curiel, Jason A Dare, Wendy de la Pena, Marietta M DeGuzman, B Anne Eberhard, Barbara S Edelheit, Terri H Finkel, Stephen W George, Harry L Gewanter, Ellen A Goldmuntz, Brandt P Groh, Hillary H Haftel, William P Hannan, Michael Henrickson, Gloria C Higgins, Patricia M Hobday, Russell J Hopp, Adam M Huber, Lisa Imundo, C J Inman, Anna Jansen, James Jarvis, Olcay Y Jones, Ankur Kamdar, Hanna Kim, Daniel J Kingsbury, Carol B Lindsley, Gulnara Mamyrova, Paul L McCarthy, Stephen R Mitchell, Frederick T Murphy, Kabita Nanda, Terrance O’Hanlon, Elif A Oral, Lauren M Pachman, Maria D Perez, Donald A Person, C Egla Rabinovich, Tova Ronis, Adam Schiffenbauer, Bracha Shaham, Sara H Sinal, Jennifer Soep, Matthew L Stoll, Sangeeta Sule, Stacey Tarvin, Scott A Vogelgesang, Rita Volochayev, Jennifer C Wargula, and Patience H White
Data availability statement
The data underlying this article will be shared on reasonable request to the corresponding author.
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Data Availability Statement
The data underlying this article will be shared on reasonable request to the corresponding author.