The Enigma of Uveitis in Juvenile Idiopathic Arthritis

Summary

In chapter 1, we outlined the disease characteristics, course, treatment and understanding of the pathophysiology of juvenile idiopathic arthritis (JIA) associated uveitis (further referred as ‘JIA-associated uveitis’) according to the current state of knowledge. Up to one third of the patients with the most common categories (oligoarticular and polyarticular rheumatoid factor negative) JIA will develop uveitis, usually within 4 years after arthritis onset. Likewise, JIA is the most common systemic association in children with uveitis. Despite this strong association and the discovery of various clinical and molecular markers linked to uveitis, it remains challenging to predict the development of uveitis in advance. This is further complicated by the typical insidious disease course of the characteristic chronic anterior uveitis. This asymptomatic clinical ‘prelude’ is not noticed by affected children until irreversible damage has occurred and accordingly demands careful and intensive ophthalmological screening to detect uveitis at an early stage. In this chapter, we propose several unmet research needs to cover critical gaps in the understanding of JIA-associated uveitis; For example, JIA as well as non-infectious uveitis are considered to be driven by T helper-1 and T helper-17 cells, but the mechanisms (if any) that simultaneously link these cell subsets to inflammatory reactions to both joints and eyes remains poorly understood. Aqueous humour (AqH) provides an excellent tissue to study the molecular perturbations near the primary side of inflammation. Recent genome-wide association studies (GWAS) in the uveitis-prone categories of JIA or in cohorts of non-infectious uveitis patients have identified several risk loci significantly associated with these multifactorial diseases, thus, we postulate that the use of GWAS may enable detailed genetic interrogation of uveitis susceptibility in JIA. Finally, studies on the visual prognosis or the Quality of Life (QoL) related to JIA-associated uveitis have been limited to investigations during childhood, but, evidently there is also need for studies on these important clinical parameters in patients with longstanding disease that have entered adulthood. Bearing in mind the need for clinical, genetic and molecular biomarkers to predict the occurrence of uveitis in JIA and to understand its disease mechanism, and the need for studies on clinical parameters and QoL in adulthood, in this thesis, we studied the ocular micro-environment, assessed the genetic susceptibility, and investigated clinical and laboratory parameters in patients with JIA-associated uveitis. In addition, we investigated the prognosis and QoL of young adults with JIA-associated uveitis.

Clinical predictors for uveitis in JIA
In chapter 2 our main aim was to study inflammatory parameters at arthritis onset as possible predictors for the development of uveitis in JIA. Inflammatory parameters and demographic and clinical factors were studied in 147 JIA patients with and 211 JIA patients without uveitis. Erythrocyte Sedimentation Rate (ESR) was more elevated in the uveitis group compared to the non-uveitis group. We could also confirm the established risk factors for uveitis in JIA: lower age of JIA onset, and anti-nuclear antibody (ANA) positivity. To test the clinical relevance of the newly found predictor ESR, we designed a model, taking into account the already established predictors (ANA, age of arthritis onset, and JIA-subtype) and compared the uveitis risk in different situations (Figure 1 in chapter 2). In conclusion, we found increased ESR at JIA onset to be predictive for uveitis occurrence in JIA. ESR is already routinely tested in patients at JIA onset, so its use as a biomarker can easily be implemented in daily practice. 

Genetic susceptibility in JIA-associated uveitis
In chapter 3 we conducted a GWAS to compare the frequencies of single nucleotide polymorphisms (SNPs) in 192 JIA patients with uveitis and 330 JIA patients without uveitis using extended ophthalmological follow-up data. Patients in two independent cohorts from the Netherlands, Germany, Belgium and Switzerland were genotyped followed by (major histocompatibility complex, genome-wide) SNP imputation and collectively investigated by mega-analysis. We identified the amino acid serine at position 11 (serine-11) encoded by the human leukocyte antigen (HLA)-DRB1 gene associated to uveitis in JIA. The serine-11 amino acid resides in ‘the YST-motif’ in the bottom of the peptide binding groove of HLA-DR. This motif is comprised of tyrosine (Y) at position 10, serine (S) at position 11, and threonine (T) at position 12. Consequently, all three amino acids were in perfect linkage disequilibrium and confer identical risk to the development of uveitis in JIA. To explore the biological relevance of the associated variation in the HLA-DRB1 locus, we investigated whether the associated motif would influence the peptide binding preferences of HLA-DR. To this end, we in silico predicted the binding affinities of all 15-mer overlapping peptides from selected proteins found in iris tissues (n~150) to 13 common HLA-DRβ1 allotypes. This revealed that the binding affinities of HLA-DRB1 alleles that encode the YST-motif were distinct from alleles that did not encode this motif. Intriguingly, the serine-11 signal in uveitis was found to be female specific. In fact, only 1 female uveitis patient (1%) did not carry the allele encoding serine-11 (Table 1). Strikingly, this female appeared to suffer from peripheral multifocal choroiditis, without anterior segment inflammation, thus did not suffer from the characteristic (chronic anterior) uveitis phenotype linked to oligoarticular JIA. In conclusion we found the YST-motif in the HLA-DRB1 gene to be a genetically distinct, female specific feature of JIA-associated uveitis compared to non-uveitis JIA. This association indicates potential involvement of antigen presentation by HLA-DRβ1 in the development of uveitis in JIA. 

Ocular fluid analysis in childhood uveitis
In order to better understand the disease mechanism that distinguish chronic anterior uveitis in JIA from other forms of childhood uveitis, we measured a panel of 51 soluble mediators in AqH (n=73) and paired serum (n=66) samples by multiplex immunoassay (chapter 4). In detail, we compared the soluble mediators of 21 children with JIA-associated uveitis, 15 with chronic anterior uveitis without arthritis (termed ‘CAU’), 29 children suffering from noninfectious idiopathic uveitis, and 8 children with non-inflammatory conditions were used as unaffected controls. After correcting for disease activity and treatment, the levels of interleukin-29 (IL-29)/interferon-λ1 (IFNλ1) were specifically decreased in AqH from JIA-associated uveitis patients compared to idiopathic uveitis. No other mediators could distinguish JIA-associated uveitis from other forms of uveitis by univariate analysis. The area under the receiver operating characteristic (ROC) curve of 0.954 revealed that IL-29/IFNλ1 could perfectly differentiate JIA-associated uveitis from idiopathic uveitis. Likewise, using a cut-off of value of 22.7 pg/mL for IL-29/IFNλ1, JIA-associated uveitis could be relatively well distinguished (AUC 0.771) from chronic anterior uveitis without arthritis (CAU). Considering multiple mediator profiles, JIA-associated uveitis patients showed additional subtle disease specific changes in AqH (profiles) compared to the other groups investigated (Figure 3 in chapter 4). IL-29/IFNλ1 could not be detected in the serum samples. In conclusion, IL-29/IFNλ1 was found to be an intra-ocular biomarker for JIA-associated uveitis, suggesting that IL-29/IFNλ1 signaling might be a specific and important biomarker in JIA-associated uveitis. 

Quality of Life in adults with JIA
In chapter 5 we studied the impact of uveitis on the QoL of adolescent JIA patients, by analyzing their scores of three validated QoL questionnaires. Scores of 31 JIA-associated uveitis and 51 JIA without uveitis patients were compared. The vision-related QoL in JIA was lower in uveitis patients, despite ‘good visual acuity’ according to the criteria of the world health organization (WHO) and standardization of uveitis nomenclature (SUN) international working group.1,2 According to these combined criteria, a patient with a bilateral best corrected visual acuity (BCVA) of 20/50 or worse is considered as visually impaired or legally blind (BCVA of 20/200 or worse and/or a visual field of 10˚ or less). Although, the general QoL scores did not differ between uveitis and non-uveitis JIA patients, the use of systemic immunomodulatory treatment (IMT) did negatively influence general QoL scores in JIA patients. In conclusion, vision related QoL scores were lower in uveitis patients compared to non-uveitis JIA patients. The use of systemic IMT decreased general QoL scores in all JIA patients. 

Prognosis of JIA-associated uveitis in adulthood 
Chapter 6 describes a retrospective multicenter cohort study, outlining uveitis activity, complications and visual prognosis of 67 young adult patients with exclusively (childhood onset) uveitis and JIA. Since treatment strategies drastically changed in the early nineties with the advent of Methotrexate (MTX) and later anti-TNFα therapy (around the year 2000), and the ophthalmologic screening protocols for JIA were also introduced during that time, we compared patients with uveitis onset before and after 1990. Disease characteristics were studied at three fixed time-points; at the age of 18, 22 and 30 years. We found that the binocular visual outcome in adulthood is fairly good, but up to 30% of the JIA-associated uveitis patients developed severe visual impairment or blindness of at least one eye. Also, many patients needed ongoing treatment, had persisting uveitis activity and needed surgery during adulthood. Furthermore, more patients used systemic IMT when diagnosed with uveitis after 1990 compared to those diagnosed before 1990. In conclusion, bilateral visual outcome of JIA-associated uveitis in adulthood is fairly good, but about one third of all adult JIA-associated uveitis patients developed one visually impaired or blind eye. Also, a fair amount of the patients had ongoing uveitis activity or needed treatment during adulthood as well as surgical interventions. 

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