An algorithm-based approach to ascertain patients with rare diseases in electronic health records using hypereosinophilic syndrome as an example

PURPOSE

Improved hypereosinophilic syndrome (HES) ascertainment in electronic health record (EHR) databases may improve disease understanding and management. An algorithm to ascertain and characterize this rare condition was therefore developed and validated.

METHODS

Using the UK clinical practice research datalink (CPRD)-Aurum database linked to the hospital episode statistics database (Admitted Patient Care data) from Jan 2012 to June 2019, this cross-sectional study ascertained patients with a specific HES code (index). Patients with HES were matched (age, sex and index date) 1:29 with a non-HES cohort. An algorithm was developed by identifying pre-defined variables differing between cohorts; model-fitting using Firth logistic regression and statistical determination of the top-five performing models; and internal validation using Leave-One-Out Cross Validation. Final model sensitivity and specificity were determined at an 80% probability threshold.

RESULTS

The HES and non-HES cohorts included 88 and 2552 patients, respectively; 270 models with four variables each (treatment used for HES, asthma code, white blood cell condition code, and blood eosinophil count [BEC] code) plus age and sex variables were tested. Of the top five models, the sensitivity model performed best (sensitivity, 69% [95% CI: 59%, 79%]; specificity, >99%). The strongest predictors of HES versus non-HES cases (odds >1000 times greater) were an ICD-10 code for white blood cell disorders and a BEC ≥1500 cells/μL in the 24 months pre-index.

CONCLUSIONS

Using a combination of medical codes, prescribed treatments data and laboratory results, the algorithm can help ascertain patients with HES from EHR databases; this approach may be useful for other rare diseases.

The increasing incidence and prevalence of hypereosinophilic syndrome in the United Kingdom

Introduction

Data on the burden of hypereosinophilic syndrome (HES) are limited. This study investigated the incidence and prevalence of HES using real‐world data from patients in the United Kingdom.

Methods

Primary care data from the Clinical Practice Research Datalink were analyzed. The patients of interest were identified using medical codes specific for HES. Annual incidence rates and prevalence were estimated for the years 2010–2018 (inclusive) using patients observed for a minimum period of one year.

Results

Between 2010 and 2018, 93 patients were identified with HES. During the study period the incidence of HES ranged from less than 0.04, 95% confidence interval (CI) (0.01–0.07) to 0.17, 95% CI (0.10–0.26) per 100,000 person‐years and the prevalence ranged from 0.15, 95% CI (0.10–0.25) to 0.89, 95% CI (0.74–1.09) cases per 100,000 persons. Sensitivity analyses varying the minimum observation period required to identify HES patients gave similar results.

Conclusion

These results provide estimates of the burden of HES in the United Kingdom and indicate that whilst HES is a very rare disease, there is evidence that is increasingly being recorded in UK primary care.

The severity of FIP1L1–PDGFRA-positive chronic eosinophilic leukaemia is associated with polymorphic variation at the IL5RA locus

We have investigated the hypothesis that constitutional genetic variation in IL-5 signalling may be associated with the development or severity of FIP1L1-PDGFRA-positive chronic eosinophilic leukaemia (CEL) in humans. We genotyped six single-nucleotide polymorphisms (SNP) within or close to the IL5RA or IL5 genes in 82 patients with FIP1L1-PDGFRA-positive CEL plus, as controls, healthy individuals (n=100), patients with FIP1L1-PDGFRA-negative eosinophilia (n=100) or patients with chronic myeloid leukaemia (CML) (n=100). We found no association between SNP allele frequency between FIP1L1-PDGFRA-positive and control cases. However, for FIP1L1-PDGFRA cases, we found an association between the genotype at rs4054760, an SNP in the 5'-UTR of IL5RA and peripheral blood eosinophil count (P=0.026) as well as the presence or absence of tissue infiltration (P=0.032). Although these associations fell below the level of significance once corrected for multiple testing, no such association was seen in FIP1L1-PDGFRA-negative cases and no difference in allele frequencies for rs4054760 was seen in control populations across Europe. Furthermore, in an analysis of 112 patients with CML, IL5RA expression was strongly related to rs4054760 genotype (P<0.001). These data suggest that the variations in IL5RA expression are linked to constitutional IL5RA genotype and severity of FIP1L1-PDGFRA disease.

Hypereosinophilic syndromes

Hypereosinophilic syndromes (HES) constitute a rare and heterogeneous group of disorders, defined as persistent and marked blood eosinophilia (> 1.5 × 10⁹/L for more than six consecutive months) associated with evidence of eosinophil-induced organ damage, where other causes of hypereosinophilia such as allergic, parasitic, and malignant disorders have been excluded. Prevalence is unknown. HES occur most frequently in young to middle-aged patients, but may concern any age group. Male predominance (4–9:1 ratio) has been reported in historic series but this is likely to reflect the quasi-exclusive male distribution of a sporadic hematopoietic stem cell mutation found in a recently characterized disease variant. Target-organ damage mediated by eosinophils is highly variable among patients, with involvement of skin, heart, lungs, and central and peripheral nervous systems in more than 50% of cases. Other frequently observed complications include hepato- and/or splenomegaly, eosinophilic gastroenteritis, and coagulation disorders. Recent advances in underlying pathogenesis have established that hypereosinophilia may be due either to primitive involvement of myeloid cells, essentially due to occurrence of an interstitial chromosomal deletion on 4q12 leading to creation of the FIP1L1-PDGFRA fusion gene (F/P⁺ variant), or to increased interleukin (IL)-5 production by a clonally expanded T cell population (lymphocytic variant), most frequently characterized by a CD3^-CD4⁺ phenotype. Diagnosis of HES relies on observation of persistent and marked hypereosinophilia responsible for target-organ damage, and exclusion of underlying causes of hypereosinophilia, including allergic and parasitic disorders, solid and hematological malignancies, Churg-Strauss disease, and HTLV infection. Once these criteria are fulfilled, further testing for eventual pathogenic classification is warranted using appropriate cytogenetic and functional approaches. Therapeutic management should be adjusted to disease severity and eventual detection of pathogenic variants. For F/P⁺ patients, imatinib has undisputedly become first line therapy. For others, corticosteroids are generally administered initially, followed by agents such as hydroxycarbamide, interferon-alpha, and imatinib, for corticosteroid-resistant cases, as well as for corticosteroid-sparing purposes. Recent data suggest that mepolizumab, an anti-IL-5 antibody, is an effective corticosteroid-sparing agent for F/P-negative patients. Prognosis has improved significantly since definition of HES, and currently depends on development of irreversible heart failure, as well as eventual malignant transformation of myeloid or lymphoid cells.

A multicenter analysis of the FIP1L1-αPDGFR fusion gene in Japanese idiopathic hypereosinophilic syndrome: an aberrant splicing skipping the αPDGFR exon 12

To study the clinical characteristics of hypereosionophilic syndrome and chronic eosinophilic leukemia (HES/CEL) in Japan, the clinical data of 29 HES/CEL patients throughout the country were surveyed. Moreover, the involvement of the FIP1L1-alphaPDGFR fusion gene resulting from a cryptic del (4)(q12q12) was examined in 24 cases. The FIP1L1-alphaPDGFR messenger RNA (mRNA) was detected in three patients (13% of patients fulfilled WHO criteria and 17% of Chusid criteria). One had a novel fusion transcript, which skipped the exon 12 of alphaPDGFR. The transcript appears to be generated by a splicing mechanism that is different from the previously reported splicing patterns. In silico analysis, the exon skipping was not related to a disruption of the exonic splicing enhancers within the exon but strongly associated with the loss of the vast majority of the FIP1L intron 8a where intronic splicing enhancers were accumulated. Unexpectedly, pseudo-chimera DNA fragments with some shared characteristic features were occasionally generated from healthy control samples by reverse transcriptase polymerase chain reaction (RT-PCR). Considering the relatively low incidence of the FIP1L1-alphaPDGFR transcript positive case, extreme care must therefore be taken when making a diagnosis using RT-PCR before imatinib therapy.

FIP1L1-PDGFRA positive chronic eosinophilic leukemia in Tunisian patients

Hypereosinophilic syndromes (HES) are a heterogenous group of rare disorders characterized by sustained and otherwise unexplained overproduction of eosinophils with organ involvement and consecutive dysfunction. Detection of the FIP1L1-PDGFRA fusion gene or the corresponding cryptic 4q12 deletion in HES supports the diagnosis of chronic eosinophilic leukemia (CEL) and provides a molecular explanation for the pathogenesis of this disorder. We screened seven Tunisian patients fulfilling the WHO criteria of HES for the presence of the FIP1L1-PDGFRA fusion gene using nested reverse transcription polymerase chain reaction on peripheral blood samples. Four of the seven patients were positive for this fusion gene. Sequence analysis revealed a substantial heterogeneity of the fusion transcripts due to the involvement of several FIP1L1 exons. All patients were male. The median age at diagnosis was 24 years (range, 18-50); one patient had a history of hypereosinophilia of more than 10 years. Two patients had clinically important and symptomatic eosinophilic endomyocardial disease with thrombotic events. Splenomegaly was constant in FIP1L1-PDGFRA positive CEL but not in the other HES patients (only 1/3).

Acute coronary syndrome associated with hypereosinophilia

Patients with hypereosinophilia often present with symptoms and signs of other systemic disease.We present the case of a 30-year-old man who had hypereosinophilia presenting as acute coronary syndrome, while having normal coronaries. The history, clinical examination and laboratory investigations were consistent with a diagnosis of tropical eosinophilia, which responded promptly to diethyl carbamazine.

Idiopathic hypereosinophilic syndrome in children: report of a 7-year-old boy with FIP1L1-PDGFRA rearrangement

Idiopathic hypereosinophilic syndrome (HES) in children is a very rare disorder; certain clinical differences with adult HES have been described, with no pediatric case with the imatinib-responsive FIP1L1-PDGFRA fusion gene reported to date. The authors describe the clinical course of three children with HES in whom FIP1L1-PDGFRA fusion gene was studied and report the first child with this rearrangement.

Recent advances in the diagnosis and treatment of hypereosinophilic syndromes

Hypereosinophilic syndromes (HES) are a heterogeneous group of disorders characterized by marked peripheral blood and tissue eosinophilia resulting in end organ damage. Recent advances in molecular biology and immunology have led to the identification of a number of distinct subtypes of HES with differing epidemiology, pathogenesis, and prognosis. The ability to distinguish between these HES subtypes combined with the availability of new treatment modalities, including tyrosine kinase inhibitors and monoclonal antibodies, that target specific molecules involved in disease pathogenesis have dramatically altered the approach to the diagnosis and treatment of HES.

[Orphan lung diseases: from curiosity to concern]

As their name implies, orphan diseases are rare, often poorly studied diseases. Patients with orphan diseases are often deprived of adequate diagnosis and treatment. To promote a comprehensive study of orphan pulmonary diseases, we established a network of pulmonologists, allowing us to collect and study several series of patients. Based on the examples of lymphangioleiomyomatosis and idiopathic eosinophilic pneumonia, we emphasize the value of a global approach to orphan diseases within the context of a medical specialty.

Strongyloidiasis in Sfax (Tunisia): a survey over 13 years period

A retrospective study of strongyloidiasis cases was carried out in Sfax University (Tunisia), between 1989 and June 2001. Diagnosis was done by direct stool examination, concentration methods, Baermann larval extraction and fecal culture. Strongyloidiasis was diagnosed in 27 patients of whom 77% were males living in rural areas under low socioeconomic level. Mean age of patients was 47 years (8 to 85 years). Hypereosinophilia was present in 75 % of cases, and 7 patients were treated by systemic corticosteroids. So, it is important to detect this parasite by repeated parasitological stool examinations, particularly before a long corticosteroid treatment.

Hypereosinophilic syndrome with pulmonary and cardiac involvement in a patient with asthma

Idiopathic hypereosinophilic syndrome is characterized by prolonged eosinophilia without an identifiable underlying cause and multiple-organ dysfunction, most frequently involving the heart, the central or peripheral nervous system and the lungs. We describe a case in which a patient with asthma who had idiopathic hypereosinophilic syndrome with pulmonary involvement presented with symptoms of pulmonary embolism and left ventricular thrombus.

[Incidence and differential diagnosis of chronic eosinophilic leukemia]

The diagnosis of chronic eosinophilic leukemia (CEL) is based on the evidence of an autonomous, clonal proliferation of eosinophilic precursors and the exclusion of other myeloid neoplasms with eosinophilia. Histopathological evaluations of bone marrow are rare, and reliable data on the frequency of CEL do not yet exist. A total of 100 cases characterized by eosinophilia >/=1.5x10(9)/l blood for more than 6 months were evaluated. In 87 cases, the eosinophilia turned out to be secondary and a reactive genesis was likely, but not proven in 3 further cases. Idiopathic hypereosinophilic syndrome was diagnosed in three cases. The diagnosis CEL was considered in four out of a total of seven cases with a myeloid neoplasia and all four disorders showed an abnormal karyotype. However, only one of them could be classified as CEL. We conclude that CEL is a rare disease concerning only a minority of cases with chronic eosinophilia.

[The heart and the eosinophil]

The beneficial effects of polynuclear eosinophils (PE) are well known. However, under certain circumstances, PE can be harmful. The heart is a prime target for PE toxicity which is due to release of basic proteins by eosinophils including major basic protein, cationic protein, and peroxidase. The most common manifestation of PE toxicity is chronic parietal endocarditis (CPE) which regroups two entities: Loeffler's fibroplastic endocarditis and Davies' endomyocardial fibrosis. Loeffler's fibroplastic endocarditis occurs mainly in temperate climates. Patients present high, persistent eosinophil levels similar to those observed in essential hypereosinophilic syndrome (EHS) or Chusid syndrome. Davies' endomyocardial fibrosis occurs in tropical countries where eosinophilic helminthiasis are endemic. The incidence of eosinophilic myocarditis (EM) is low but probably underestimated. EM can be observed in any case involving PE and has been described in many cases of drug-induced atopy, in Churg and Strauss syndrome, and in EHS. The most common cause of death is short-term occurrence of cardiogenic shock or dilated hypokinetic cardiomyopathy. Some patients have been successfully treated by early, intensive corticosteroid therapy and/or heart transplantation. The nosological classification of EM and CPE remains controversial. The two disorders may form a continuum with CPE as the second phase. Other authors have suggested that EM and CPE result from the action of PE on two distinct targets, i.e. endothelial cells for EM and myocytes for CPE. In the future, it may be possible to identify subjects with a predisposition to PE-induced heart disease by studying of genes coding for interleukins (IL-5, IL-4, IL-3) and GM-CSF in the 5q31-q33 region of chromosome 5.