Genome-wide association study identifies Sjögren's risk loci with functional implications in immune and glandular cells.

Sjögren's disease is a complex autoimmune disease with twelve established susceptibility loci. This genome-wide association study (GWAS) identifies ten novel genome-wide significant (GWS) regions in Sjögren's cases of European ancestry: CD247, NAB1, PTTG1-MIR146A, PRDM1-ATG5, TNFAIP3, XKR6, MAPT-CRHR1, RPTOR-CHMP6-BAIAP6, TYK2, SYNGR1. Polygenic risk scores yield predictability (AUROC = 0.71) and relative risk of 12.08. Interrogation of bioinformatics databases refine the associations, define local regulatory networks of GWS SNPs from the 95% credible set, and expand the implicated gene list to >40. Many GWS SNPs are eQTLs for genes within topologically associated domains in immune cells and/or eQTLs in the main target tissue, salivary glands.

Radiographic features in 2D imaging as predictors for justified CBCT examinations of canine-induced root resorption.

OBJECTIVES: This retrospective observational study aimed to evaluate the diagnostic accuracy of two-dimensional radiographs on canine-induced root resorption (CIRR) in lateral incisors and identify predictors of CIRR in patients with impacted maxillary canines (IMC). METHODS: Ninety-nine patients aged 9-17 years, with 156 IMCs, were included in the study. All had CBCT-volumes and two-dimensional radiographs consisting of at least one panoramic radiograph. Two radiologists jointly viewed all cases twice. First, radiographic features related to the IMC and possible CIRR were recorded from two-dimensional radiographs. Then, CIRR was determined from CBCT and according to position and extension classified as mild, moderate and severe. RESULTS: CIRRs was detected in 80% of lateral incisors (mild: 45%; moderate: 44%; severe: 11%). The sensitivity was generally low at mild and moderate cut-offs (29 and 29%), and somewhat higher for severe (50%). Corresponding specificities were 48%, 63% and 68%. Canine cusp-tip superimposing the lateral incisor's middle third and root/crown ratio >1 was positively associated with mild CIRR, with an odds ratio (OR) of 3.8 and 6.7, respectively. In addition, the root development stage was positively associated with moderate/severe CIRR when the canine root was nearly or fully developed (OR = 3.1). CONCLUSIONS: The diagnostic accuracy of two-dimensional radiographs was inadequate for detecting CIRR amongst patients referred for CBCT examinations. Based on our results, none of the suggested two-dimensional radiographic features could predict moderate/severe CIRR except for root development stage. IMC in a later stage of root development seems to be associated with a higher risk of moderate/severe CIRR.

Understanding Fatigue in Sjögren's Syndrome: Outcome Measures, Biomarkers and Possible Interventions.

Sjögren's syndrome (SS) is an autoimmune disease affecting the salivary and lacrimal glands. Symptoms range from dryness to severe extra-glandular disease involving manifestations in the skin, lungs, nervous system, and kidney. Fatigue occurs in 70% of patients, characterizing primary SS (pSS) and significantly impacting the patient's quality of life. There are some generic and specific instruments used to measure fatigue in SS. The mechanisms involved with fatigue in SS are still poorly understood, but it appears fatigue signaling pathways are more associated with cell protection and defense than with pro-inflammatory pathways. There are no established pharmacological treatment options for fatigue in pSS. So far, exercise and neuromodulation techniques have shown positive effects on fatigue in pSS. This study briefly reviews fatigue in pSS, with special attention to outcome measures, biomarkers, and possible treatment options.

Genetic and clinical basis for two distinct subtypes of primary Sjögren's syndrome.

OBJECTIVES: Clinical presentation of primary Sjögren's syndrome (pSS) varies considerably. A shortage of evidence-based objective markers hinders efficient drug development and most clinical trials have failed to reach primary endpoints. METHODS: We performed a multicentre study to identify patient subgroups based on clinical, immunological and genetic features. Targeted DNA sequencing of 1853 autoimmune-related loci was performed. After quality control, 918 patients with pSS, 1264 controls and 107 045 single nucleotide variants remained for analysis. Replication was performed in 177 patients with pSS and 7672 controls. RESULTS: We found strong signals of association with pSS in the HLA region. Principal component analysis of clinical data distinguished two patient subgroups defined by the presence of SSA/SSB antibodies. We observed an unprecedented high risk of pSS for an association in the HLA-DQA1 locus of odds ratio 6.10 (95% CI: 4.93, 7.54, P=2.2×10-62) in the SSA/SSB-positive subgroup, while absent in the antibody negative group. Three independent signals within the MHC were observed. The two most significant variants in MHC class I and II respectively, identified patients with a higher risk of hypergammaglobulinaemia, leukopenia, anaemia, purpura, major salivary gland swelling and lymphadenopathy. Replication confirmed the association with both MHC class I and II signals confined to SSA/SSB antibody positive pSS. CONCLUSION: Two subgroups of patients with pSS with distinct clinical manifestations can be defined by the presence or absence of SSA/SSB antibodies and genetic markers in the HLA locus. These subgroups should be considered in clinical follow-up, drug development and trial outcomes, for the benefit of both subgroups.

Salivary Gland Ultrasonography in Sjögren's Syndrome: A European Multicenter Reliability Exercise for the HarmonicSS Project.

Objectives: Salivary gland ultrasonography (SGUS) is increasingly applied for the management of primary Sjögren's syndrome (pSS). This study aims to: (i) compare the reliability between two SGUS scores; (ii) test the reliability among sonographers with different levels of experience. Methods: In the reliability exercise, two four-grade semi-quantitative SGUS scoring systems, namely De Vita et al. and OMERACT, were tested. The sonographers involved in work-package 7 of the HarmonicSS project from nine countries in Europe were invited to participate. Different levels of sonographers were identified on the basis of their SGUS experience and of the knowledge of the tested scores. A dedicated atlas was used as support for SGUS scoring. Results: Twenty sonographers participated in the two rounds of the reliability exercise. The intra-rater reliability for both scores was almost perfect, with a Light's kappa of 0.86 for the De Vita et al. score and 0.87 for the OMERACT score. The inter-rater reliability for the De Vita et al. and the OMERACT score was substantial with Light's Kappa of 0.75 and 0.77, respectively. Furthermore, no significant difference was noticed among sonographers with different levels of experience. Conclusion: The two tested SGUS scores are reliable for the evaluation of major salivary glands in pSS, and even less-expert sonographers could be reliable if adequately instructed.

Juvenile Sjögren's Syndrome: Clinical Characteristics With Focus on Salivary Gland Ultrasonography.

OBJECTIVE: Juvenile Sjögren's syndrome (SS) is a rare, poorly defined, and possibly underdiagnosed condition affecting children and adolescents. The aim of this study was to characterize symptoms and clinical findings of juvenile SS and to explore the clinical application of major salivary gland ultrasonography (SGUS) in patients with juvenile SS. METHODS: A cross-sectional multicenter study recruited patients with disease onset until age 18 years (n = 67). Disease characteristics were recorded, and unstimulated whole sialometry and SGUS examination of the parotid and submandibular salivary glands were performed. RESULTS: The female:male ratio was 58:9. The mean age at first symptom was 10.2 years and 12.1 years at diagnosis. Ocular and oral symptoms were noted in 42 of 67 patients (63%) and 53 of 66 patients (80%), respectively. The American-European Consensus Group or American College of Rheumatology/European League Against Rheumatism classification criteria for primary SS were fulfilled by 42 of 67 patients (63%). Pathologic SGUS findings were observed in 41 of 67 patients (61%); 26 of 41 SGUS+ patients (63%) fulfilled primary SS criteria. Salivary gland enlargements/parotitis were noted in 37 of 58 patients and were nonsignificantly associated with SGUS+ status (P = 0.066). The mean levels of saliva were 5.6 ml/15 minutes in SGUS- patients compared to 3.3 ml/15 minutes in the SGUS+ patients (P = 0.049). A total of 36 of 41 SGUS+ patients (88%) were anti-Ro/La+ compared to 14 of 26 SGUS- patients (54%) (P = 0.001). In addition, 24 of 39 SGUS+ patients (62%) were positive for rheumatoid factor (RF), whereas only 5 of 25 SGUS- patients (20%) were RF+ (P = 0.001). CONCLUSION: Juvenile SS is characterized by a large spectrum of clinical symptoms and findings. Several glandular and extraglandular parameters such as hyposalivation, swollen salivary glands, and autoantibodies are associated with pathologic SGUS findings.

Assessment of major salivary gland ultrasonography in Sjögren's syndrome. A comparison between bedside and post-examination evaluations.

OBJECTIVES: Major salivary gland ultrasonography (SGUS) is a suitable diagnostic tool in Sjögren's syndrome (SS). We aimed to determine the more representative gland, projection and format most applicable for reproducible image analysis. METHODS: One investigator performed SGUS in patients with SS. Parotid and submandibular glands were examined in longitudinal and transverse planes and evaluated bedside using a simplified scoring system (0-3). Longitudinal and transverse images and videos of all glands were stored and later evaluated/graded by three investigators, at two time-points. Agreement was calculated using intraclass correlation coefficient (ICC). RESULTS: The ICC for static image and video scoring compared to bedside evaluation ranged from 0.131 to 0.882. Average ICC for longitudinal/transverse image was 0.667/0.662, and 0.683/0.510 for longitudinal/transverse video. Interobserver reliability was good to excellent (0.81-0.94). Intraobserver reliability scores ranged from fair to excellent (0.46-0.96). The correlation between image and video evaluations of all modalities and examiners was good to excellent (0.614-0.904). The best mean ICC was found for the longitudinal projection of the left parotid gland (0.861) and the lowest mean ICC was for the transverse projection of the left submandibular gland (0.66). CONCLUSIONS: Our study indicates a trend favouring longitudinal video of the parotid gland as preferred projection, gland and storage format.

Current concepts on Sjögren's syndrome - classification criteria and biomarkers.

Sjögren's syndrome is a lymphoproliferative disease with autoimmune features characterized by mononuclear cell infiltration of exocrine glands, notably the lacrimal and salivary glands. These lymphoid infiltrations lead to dryness of the eyes (keratoconjunctivitis sicca), dryness of the mouth (xerostomia), and, frequently, dryness of other surfaces connected to exocrine glands. Sjögren's syndrome is associated with the production of autoantibodies because B-cell activation is a consistent immunoregulatory abnormality. The spectrum of the disease extends from an organ-specific autoimmune disorder to a systemic process and is also associated with an increased risk of B-cell lymphoma. Current treatments are mainly symptomatic. As a result of the diverse presentation of the syndrome, a major challenge remains to improve diagnosis and therapy. For this purpose an international set of classification criteria for primary Sjögren's syndrome has recently been developed and validated and seems well suited for enrolment in clinical trials. Salivary gland biopsies have been examined and histopathology standards have been developed, to be used in clinical trials and patient stratification. Finally, ultrasonography and saliva meet the need of non-invasive imaging and sampling methods for discovery and validation of disease biomarkers in Sjögren's syndrome.

Salivary gland ultrasound abnormalities in primary Sjögren's syndrome: consensual US-SG core items definition and reliability.

OBJECTIVES: Ultrasonography (US) is sensitive for detecting echostructural abnormalities of the major salivary glands (SGs) in primary Sjögren's syndrome (pSS). Our objectives were to define selected US-SG echostructural abnormalities in pSS, set up a preliminary atlas of these definitions and evaluate the consensual definitions reliability in both static and acquisition US-SG images. METHODS: International experts in SG US in pSS participated in consensus meetings to select and define echostructural abnormalities in pSS. The US reliability of detecting these abnormalities was assessed using a two-step method. First 12 experts used a web-based standardised form to evaluate 60 static US-SG images. Intra observer and interobserver reliabilities were expressed in κ values. Second, five experts, who participated all throughout the study, evaluated US-SG acquisition interobserver reliability in pSS patients. RESULTS: Parotid glands (PGs) and submandibular glands (SMGs) intra observer US reliability on static images was substantial (κ > 0.60) for the two main reliable items (echogenicity and homogeneity) and for the advised pSS diagnosis. PG inter observer reliability was substantial for homogeneity. SMGs interobserver reliability was moderate for homogeneity (κ = 0.46) and fair for echogenicity (κ = 0.38). On acquisition images, PGs interobserver reliability was substantial (κ = 0.62) for echogenicity and moderate (κ = 0.52) for homogeneity. The advised pSS diagnosis reliability was substantial (κ = 0.66). SMGs interobserver reliability was fair (0.20< κ ≤ 0.40) for echogenicity and homogeneity and either slight or poor for all other US core items. CONCLUSION: This work identified two most reliable US-SG items (echogenicity and homogeneity) to be used by US-SG trained experts. US-PG interobserver reliability result for echogenicity is in line with diagnosis of pSS.

Long-term follow-up in primary Sjögren's syndrome reveals differences in clinical presentation between female and male patients.

BACKGROUND: Despite men being less prone to develop autoimmune diseases, male sex has been associated with a more severe disease course in several systemic autoimmune diseases. In the present study, we aimed to investigate differences in the clinical presentation of primary Sjögren's syndrome (pSS) between the sexes and establish whether male sex is associated with a more severe form of long-term pSS. METHODS: Our study population included 967 patients with pSS (899 females and 68 males) from Scandinavian clinical centers. The mean follow-up time (years) was 8.8 ± 7.6 for women and 8.5 ± 6.2 for men (ns). Clinical data including serological and hematological parameters and glandular and extraglandular manifestations were compared between men and women. RESULTS: Male patient serology was characterized by more frequent positivity for anti-Ro/SSA and anti-La/SSB (p = 0.02), and ANA (p = 0.02). Further, men with pSS were more frequently diagnosed with interstitial lung disease (p = 0.008), lymphadenopathy (p = 0.04) and lymphoma (p = 0.007). Conversely, concomitant hypothyroidism was more common among female patients (p = 0.009). CONCLUSIONS: We observe enhanced serological responses and higher frequencies of lymphoma-related extraglandular manifestations in men with pSS. Notably, lymphoma itself was also significantly more common in men. These observations may reflect an aggravated immune activation and a more severe pathophysiological state in male patients with pSS and indicate a personalized managing of the disease due to the influence of the sex of patients with pSS.

Impaired salivary gland activity in patients with autoimmune polyendocrine syndrome type I.

Autoimmune polyendocrine syndrome type I (APS-I) is a severe disease caused by mutations in the autoimmune regulator (AIRE) gene. We hypothesized that salivary gland dysfunction could be a possible unexplored component of these patients and here aimed to investigate salivary and lachrymal symptoms in the Norwegian cohort of APS-I patients (N = 41) and the aetiology behind it. Sicca symptoms and possible corresponding underlying factors were assessed by subjective reports combined with objective measures of saliva and tear flow, serological testing, immune fluorescence microscopy, ultrasonography and searching for putative autoantibodies in the salivary glands. In addition, defensin and anti-defensin levels were analysed in patients and compared with healthy controls. Our results indicate mild salivary and/or lachrymal gland dysfunction manifesting in low saliva or tear flow in a total of 62% of APS-I patients. Serum IgG from 9 of 12 patients bound to targets in salivary gland biopsy slides, although the specificity and pattern of binding varied. There was no reactivity against known Sjögren-associated autoantigens in sera from APS-I patients using quantitative methods, but 11% were ANA positive by immunofluorescence microscopy. We identified several putative autoantigens in one patient, although none of these were verified as APS-I specific. We conclude that impaired salivary gland activity is part of the clinical picture of APS-I and our findings could indicate an autoimmune aetiology. We further show that APS-I patients have an altered antimicrobial signature in both sera and saliva, which requires further investigations.

Major Salivary Gland Ultrasonography in the Diagnosis of Sjögren's Syndrome: A Place in the Diagnostic Criteria?

Major salivary gland (SG) ultrasonography (US) represents a noninvasive, nonirradiating imaging modality for evaluation of the major SGs in the diagnosis and follow-up of primary and secondary Sjögren syndrome. Structural changes can be visualized as hyperechogenic and hypoechogenic areas, inhomogeneity, and altered echogenicity in general. The reliability of SG-US is poorly investigated, and the definition of US abnormalities varies in previously published studies. Recent studies have shown correlations between SG-US findings and focus score in the minor SGs; however further studies are needed to validate a US criterion in updated classification/diagnostic criteria.

Sjögren's syndrome patients with ectopic germinal centers present with a distinct salivary proteome.

OBJECTIVE: Clinical expression of SS shows considerable interpatient heterogeneity. Thus, the aim of this study was to assess whether individual salivary proteomic profiles provide a framework for identification of disease-phenotype-driven biomarker signatures. METHODS: Using a 187-plex capture antibody-based assay, proteomic biomarker profiles from unstimulated whole saliva were generated from a SS-cohort representing six clinically distinct disease phenotypes. Discriminant function analyses identified the most powerful biomarker signatures for correct recapitulation of each patient's status with respect to hyposalivation and histopathological features of salivary gland inflammation. In addition, gene ontology-based network analyses allowed systematic interpretation of the molecular patterns underlying these specific disease features. RESULTS: Presentation of hyposalivation was associated with significant alteration in 22 out of 119 reliably detectable biomarkers. Thereof, a 4-plex signature allowed accurate prediction of salivary gland function for >80% of the cases. With respect to histopathological features, the most distinct profiles were identified in conjunction with ectopic germinal centres. Selected from the 13 analytes relevant here, pregnancy-associated plasma protein A, thrombospondin 1 and peptide YY would recapitulate the presence or absence of tertiary lymphoid organization for 93.8% of the patients. Whereas functional annotation of alterations associated with hyposalivation identified the IL1 system as a dominant pro-inflammatory component, changes observed in context with ectopic lymphoid organization revealed specific shifts in chemotactic profiles and altered regulation of apoptotic processes. CONCLUSION: Multivariate analyses of a patient's salivary proteome could reliably recapitulate specific aspects of SS disease. Accessible and repetitively collectable, such biomarker signatures harbour great potential for patient subclassification and subsequent follow-up.

Is salivary gland ultrasonography a useful tool in Sjögren's syndrome? A systematic review.

OBJECTIVE: Ultrasonography (US) is a sensitive tool in the diagnosis of major salivary gland abnormalities in primary Sjögren's syndrome (pSS). The aim of this systematic review was to assess the metric properties of this technique. METHODS: PUBMED and EMBASE databases were searched. All publications between January 1988 and January 2013 were considered. Data were extracted from the articles meeting the inclusion criteria according to US definition of salivary gland scoring system and metric properties studied. The type and number of glands tested, study design and metric properties according to OMERACT filter (truth, discrimination, feasibility) were assessed. RESULTS: Of 167 publications identified initially with PUBMED and EMBASE, 31 met the inclusion criteria. The number of pSS patients varied among the studies from 16 to 140. The diagnosis of pSS was in line in most of the cases with the American-European Consensus Group (AECG) classification criteria for Sjögren's syndrome. The US examination was performed in suspected pSS only in studies in which the sensitivity ranged from 45.8 to 91.6% and specificity from 73 to 98.1%. There was heterogeneity in regard to the definition of US in B-mode and few studies used US in colour Doppler. Few studies reported reliability of US and sensitivity to change in pSS. CONCLUSION: US is a valuable tool for detecting salivary gland abnormalities in pSS. Its reliability has been poorly investigated and there is considerable variation in the definition of US abnormalities. Further studies are required to validate and standardize the US definition of salivary gland in pSS.

Antibodies against carbamylated proteins are present in primary Sjögren's syndrome and are associated with disease severity.

OBJECTIVES: Herein, we investigate the presence and prognostic value of autoantibodies against carbamylated proteins (anti-CarP) in the serum of patients with primary Sjögren's syndrome (pSS). PATIENTS AND METHODS: Serum levels of anti-CarP antibodies were measured in Norwegian patients with pSS (n=78) and corresponding controls (n=74) using ELISA and analysed in relation with exocrine gland function, degree of salivary gland inflammation, signs of ectopic germinal centre (GC) formation and immunological markers. For univariate comparisons, the Mann-Whitney U test and χ(2) or Fisher's exact tests were used. Correlations were assessed with Spearman's rank testing. Multivariate regression analyses were used to assess the effect of anti-CarP positivity on clinical manifestations. RESULTS: Of the patients with pSS, 27% were positive for anti-CarP IgG antibodies. Levels of anti-CarP correlated positively with total IgG, IgM, rheumatoid factor and ß2-microglobulin. Importantly, after adjusting for confounding factors, patients positive for anti-CarP had significantly higher focus score. Furthermore, positive anti-CarP status coincided with 9.2-fold higher odds of having developed GC-like structures in the minor salivary glands. As a patient group considered having worse disease outcome, individuals with ectopic GC-like structures also presented with significantly higher levels of anti-CarP antibodies. CONCLUSIONS: Presence of anti-CarP in patients with pSS is strongly associated with increased focal lymphocytic infiltration, formation of ectopic GC-like structures in minor salivary glands, and diminished salivary gland function. Even taking into consideration our relatively small cohort we believe that anti-CarP antibodies offer new possibilities for identifying patients with more active disease and at risk of developing additional comorbidity.

High fidelity between saliva proteomics and the biologic state of salivary glands defines biomarker signatures for primary Sjögren's syndrome.

OBJECTIVE: Dependence on invasive procedures for classification of patients with Sjögren's syndrome (SS) hampers timely diagnosis and suitable patient followup. The aim of this study was to recapitulate the diagnosis of SS through noninvasive means and to define the biologic state of SS patients' salivary glands. METHODS: Using a 187-plex capture antibody-based assay, salivary proteomic biomarker profiles were generated from patients with primary SS, patients with rheumatoid arthritis, and asymptomatic controls. Discriminant function analyses and Gene Ontology-based network analyses allowed data analyses with a reductionist approach and with a focus on systems biology. RESULTS: Characterized by significant changes in 61 and 55 proteins, respectively, the salivary proteome of SS patients appeared profoundly altered compared to that of individuals without SS. On this basis, 4-plex and 6-plex biomarker signatures, both including interleukin-4 (IL-4), IL-5, and clusterin, achieved accurate prediction of an individual's group membership for at least 94% of cases. Of note, all misclassified SS patients presented with ectopic germinal center-like structures. Systematic inference of biologic meaning identified SS-related protein patterns delineating B cell-dominated immune responses, macrophage differentiation, and signs of T cell chemotaxis. In addition, proteomic Multi-Analyte Profiles provided insight about proteins related to collagen, cytokine, and growth factor synthesis as well as lipid transport. CONCLUSION: The SS-related molecular landscape conveyed by saliva showed great congruence with histopathologic features found in SS and advances understanding of this disease at a molecular level. Such salivary biomarker signatures harbor great potential for improving timeliness of SS diagnosis and enabling suitable patient followup.

Diagnostic utility of major salivary gland ultrasonography in primary Sjögren's syndrome.

OBJECTIVES: To investigate major salivary gland ultrasonography (US) in relation to symptoms and findings of oral and ocular dryness, and autoimmune disease, for potential use in diagnosis and follow-up of patients with primary Sjögren's syndrome (pSS). METHODS: Patients with pSS were recruited from the Department of Rheumatology, Haukeland University Hospital. The parotid and submandibular salivary glands were examined by US using a simplified scoring system for glandular homogeneity and hypoechogenic areas. Scans were graded on a scale 0-3, grades 0-1 considered corresponding to normal/non-specific changes and grades 2-3 to pathological changes. Sicca symptoms of the mouth and eyes, salivary gland capacity, tear secretion, minor salivary gland inflammation, serum autoantibodies, and fatigue were also investigated. RESULTS: US was performed in 97 patients. Oral and ocular sicca symptoms correlated with US score and decreased saliva levels. Fatigue VAS correlated with oral sicca symptoms but was inversely correlated with age. Patients with normal/non-specific US findings tended to be older than patients with pathological US findings. US score correlated with unstimulated and stimulated salivary secretion and tear secretion. Minor salivary gland inflammation correlated with major salivary gland US findings, and lymphoid organisation, germinal centre (GC)-like structures, in the minor salivary gland tissue biopsies was seemingly related to US pathology. Serum autoantibodies against Ro/SSA and/or La/SSB were associated with US pathology. CONCLUSIONS: US findings in major salivary glands correlate with subjective and objective oral and ocular items as well as systemic autoimmune features of pSS. US represents a useful imaging tool for diagnostics and follow-up of pSS.

Sjögren's syndrome: an update on epidemiology and current insights on pathophysiology.

Primary Sjögren's syndrome (pSS) is an autoimmune chronic inflammatory disorder affecting 0.2% to 3.0% of the population, with a 9:1 female to male ratio. Features are oral and ocular dryness, local and systemic autoantibody production, and progressive focal mononuclear cell infiltration in the affected salivary and lacrimal glands. Lymphoma is the most severe complication of pSS, occurring in 4% to 5% of patients. Genetic studies identified an association with HLA and susceptibility genes in cytokine genes and genes involved in B-cell differentiation. Genetic variations may help explain why disease manifestations differ among patients and supports the hypothesis of certain distinct disease phenotypes.