Evolution of genome diagnostics in epidermolysis bullosa: Unveiling the power of next-generation sequencing

BACKGROUND

Genome diagnostics is considered gold standard diagnostics for epidermolysis bullosa (EB), a phenotypically and genetically heterogeneous group of rare disorders characterized by blistering and wounding of mucocutaneous tissues. EB is caused by pathogenic variants in genes encoding proteins of the dermo-epidermal junction. Accurate genetic diagnosis of EB is crucial for prognostication, counselling and precision-medicine. Genome diagnostics for EB started in 1991 with the introduction of Sanger sequencing (SS), analysing one gene at a time. In 2013, SS was superseded by next-generation sequencing (NGS), that allow for high-throughput sequencing of multiple genes in parallel. Several studies have shown a beneficial role for NGS in EB diagnostics, but its true benefit has not been quantified.

OBJECTIVES

To determine the benefit of NGS in EB by systematically evaluating the performance of different genome diagnostics used over time based on robust data from the Dutch EB Registry.

METHODS

The diagnostic performances of SS and NGS were systematically evaluated in a retrospective observational study including all index cases with a clinical diagnosis of EB in whom genome diagnostics was performed between 01 January 1994 and 01 January 2022 (n = 308), registered at the Dutch EB Expertise Centre.

RESULTS

Over time, a genetic diagnosis was made in 289/308 (94%) EB cases. The diagnostic yield increased from 89% (SS) to 95% (NGS). Most importantly, NGS significantly reduced diagnostic turnaround time (39 days vs. 211 days, p < 0.001). The likelihood of detecting variants of uncertain significance and additional findings increased from 5% and 1% (SS) to 22% and 13% (NGS) respectively.

CONCLUSIONS

Our study quantifies the benefit of NGS-based methods and demonstrate they have had a major impact on EB diagnostics through an increased diagnostic yield and a dramatically decreased turnaround time (39 days). Although our diagnostic yield is high (95%), further improvement of genome diagnostics is urgently needed to provide a genetic diagnosis in all EB patients.

Patients suffering from dystrophic epidermolysis bullosa are prone to developing autoantibodies against skin proteins: A longitudinal confirmational study

Epidermolysis bullosa (EB) is a heritable skin blistering disease caused by variants in genes coding for proteins that secure cell-cell adhesion and attachment of the epidermis to the dermis. Interestingly, several proteins involved in inherited EB are also associated with autoimmune blistering diseases (AIBD). In this study, we present a long-term follow-up of 15 patients suffering from recessive dystrophic or junctional EB. From these patients, 62 sera were analysed for the presence of autoantibodies associated with AIBD. We show that patients suffering from recessive dystrophic EB (RDEB) are more susceptible to developing autoantibodies against skin proteins than patients suffering from junctional EB (70% vs. 20%, respectively). Interestingly, no correlation with age was observed. Most patients showed reactivity to Type XVII collagen/linear IgA bullous dermatosis autoantigen (n = 5; 33%), followed by BP230 (n = 4; 27%), Type VII collagen (n = 4; 27%) and laminin-332 (n = 1; 7%). The pathogenicity of these autoantibodies remains a subject for future experiments.

[Eosinophilic dermatoses]

Eosinophilic dermatoses are a heterogeneous group of rare diseases that histopathologically display the defining pattern of an eosinophil-rich dermal infiltrate. In these eosinophilic dermatoses, a histopathologic pattern called flame figures, which result from degranulation of eosinophils in the tissue, can be observed. Although eosinophil granulocytes can also be detected in other dermatoses such as atopic dermatitis, urticaria, prurigo and bullous pemphigoid, the eosinophil-rich infiltrate is decisive for classic eosinophilic dermatoses. Accordingly, eosinophilic dermatoses include hypereosinophilic syndrome, eosinophilic fasciitis, granuloma faciale, pustular sterile eosinophilia, and angiolymphoid hyperplasia with eosinophilia. These eosinophilic dermatoses display clinical different patterns and are discussed in this article, as well as the interesting eosinophils and novel therapeutic options.

[Skin-coloured vulvar papules]

We report a 43-year-old woman with asymptomatic vulvar papules. Histopathology showed ducts with luminal differentiation and eosinophil debris with a tadpole shape. Based on these findings, the diagnosis vulvar syringoma was made. Syringoma are benign eccrine sweat gland tumour mostly located on lower eyelids and cheeks. Vulvar syringoma are rare.

IgE autoantibodies in serum and skin of non-bullous and bullous pemphigoid patients

BACKGROUND

Non-bullous pemphigoid (NBP) is a pemphigoid variant which frequently resembles other pruritic skin diseases. In contrast with bullous pemphigoid (BP), blisters are absent. In BP, previous studies showed that IgE autoantibodies may be involved in its pathogenesis. IgE-activated mast cells, basophils and eosinophils may participate in BP by inducing pruritus and possibly blister formation, although the differential role of IgE in NBP compared with BP has not yet been described.

OBJECTIVE

To assess IgE in serum and skin of NBP and BP patients.

METHODS

We examined total IgE and pemphigoid-specific IgE in the serum of 68 NBP and 50 BP patients by enzyme-linked immunosorbent assay (ELISA). Sera of 25 pemphigus patients and 25 elderly patients with pruritus were included as controls. Skin biopsies of 14 NBP and 14 BP patients with the highest IgE titres to NC16A were stained for IgE by immunofluorescence techniques.

RESULTS

Total IgE was elevated in 63% of NBP and 60% of BP patients, and in 20% of pemphigus controls, as well as 60% of elderly controls. IgE ELISAs were more frequently positive in BP than in NBP (NC16A 18% vs. 9%, P = 0.139; BP230 34% vs. 22%, P = 0.149). IgE ELISAs for NC16A and BP230 were positive in 8% and 20% of elderly controls, respectively, while all pemphigus controls were negative. Two of 28 biopsies (7%; one NBP, one BP) showed linear IgE along the basement membrane zone, while in most biopsies (71% NBP; 86% BP) IgE was bound to dermal cells.

CONCLUSION

Since IgE was present in the serum and skin of both NBP and BP patients, this supports IgE-dependent mechanisms common to both diseases, such as pruritus. However, it remains to be elucidated whether IgE contributes to blister formation in BP.

Keratinocyte footprint assay discriminates antilaminin-332 pemphigoid from all other forms of pemphigoid diseases

Background

Antilaminin‐332 mucous membrane pemphigoid is a chronic severe pemphigoid disease characterized by autoantibodies to laminin‐332. At present no commercial assay is available to demonstrate antilaminin‐332 antibodies, and diagnosis relies on in‐house techniques with limited sensitivities.

Objectives

In order to move, keratinocytes cultured in vitro secrete laminin‐332 to attach to the culture dish. In that way, they leave behind a unique footprint trail of laminin‐332. We aimed to develop a sensitive and specific laboratory assay to determine antilaminin‐332 autoantibodies in patient serum based on binding of patient IgG to these unique footprints.

Methods

Normal human keratinocytes were grown on glass coverslips and incubated with patient or control serum for 1 h. The binding of IgG was then investigated by immunofluorescence. After validating the test for its ability to identify antilaminin‐332 autoantibodies it was converted into a daily available test based on binding of IgG to dried coverslips that can be stored frozen. The staining patterns of sera from patients with antilaminin‐332 pemphigoid were then compared with those of sera from patients with other autoimmune bullous diseases and normal human sera.

Results

IgG of all antilaminin‐332 pemphigoid sera (n = 16) bound to laminin‐332 footprints, while all normal human controls (n = 55) were negative. From the sera of patients with other diseases (n = 72) four sera tested positive. The footprint assay was also positive for sera that were negative by salt‐split skin analysis, demonstrating that it is a very sensitive technique.

Conclusions

The keratinocyte footprint assay is a fast and specific assay to confirm or rule out the presence of antilaminin‐332 autoantibodies.

What's already known about this topic?

Antilaminin‐332 mucous membrane pemphigoid is a severe form of pemphigoid, and patients may have an increased risk of malignancies.

The diagnosis of antilaminin‐332 mucous membrane pemphigoid is complicated by the lack of specific commercial tests for antilaminin‐332 antibodies and can be confirmed only in specialized laboratories.

Keratinocytes in culture need laminin‐332 for adhesion and migration and therefore deposit it on the bottom of the culture dish.

What does this study add?

The keratinocyte footprint assay detects antilaminin‐332 autoantibodies in patient serum using the native laminin‐332 produced by cultured keratinocytes.

What is the translational message?

The keratinocyte footprint assay is a fast and specific assay to confirm or rule out the presence of antilaminin‐332 autoantibodies.

Linked Comment: https://doi.org/10.1111/bjd.18372.

https://doi.org/10.1111/bjd.18761 available online

Pemphigoid variants affecting the skin

Pemphigoid diseases are autoimmune subepidermal blistering diseases affecting the skin and mucous membranes, which are caused by autoantibodies targeting structural hemidesmosomal proteins or hemidesmosome-associated proteins. Variants of pemphigoid can be differentiated based on targeted antigens and clinical aspects. In this review, we will discuss pemphigoid variants that predominantly affect the skin, and provide clinicians with clues to diagnosis.

Laboratory diagnosis of paraneoplastic pemphigus

BACKGROUND

Paraneoplastic pemphigus (PNP) is a multiorgan disease characterized by antibodies against plakins, desmogleins and the α2-macroglobulin-like-1 (A2ML1) protein, in association with an underlying neoplasm. Accurate diagnosis relies on the demonstration of these autoantibodies in serum.

OBJECTIVES

To evaluate the value of different laboratory techniques in the serological diagnosis of PNP.

METHODS

We performed immunoblotting, envoplakin (EP) enzyme-linked immunosorbent assay (ELISA), indirect immunofluorescence (IIF) on rat bladder, radioactive immunoprecipitation and a nonradioactive combined immunoprecipitation-immunoblot assay. Additional assays included BP180 ELISA and BP230 ELISA. We included the sera of 19 patients with PNP and 40 control subjects.

RESULTS

The sensitivities were 63% for anti-EP ELISA, 74% for rat bladder IIF, 89% for immunoblotting, 95% for radioactive immunoprecipitation and 100% for nonradioactive immunoprecipitation. Specificities ranged from 86% to 100%. The BP180 and BP230 ELISAs had low sensitivity and specificity for PNP. The combination of rat bladder IIF and immunoblot showed 100% sensitivity and specificity. The analysis of sequential PNP sera showed that antibody titres may decrease over time, possibly resulting in negative outcomes for EP ELISA and rat bladder IIF studies.

CONCLUSIONS

The detection of autoantibodies against EP and periplakin, or A2ML1 by immunoprecipitation is most sensitive for PNP. The combination of rat bladder IIF and immunoblotting is equally sensitive and highly specific, and represents an alternative valuable and relatively easy approach for the serological diagnosis of PNP.

Low sensitivity of type VII collagen enzyme-linked immunosorbent assay in epidermolysis bullosa acquisita: serration pattern analysis on skin biopsy is required for diagnosis

BACKGROUND

The type VII collagen (coll VII) enzyme-linked immunosorbent assay (ELISA) has been reported to have high sensitivity (> 93%) and specificity (> 96%) for diagnosing epidermolysis bullosa acquisita (EBA) in patients who are seropositive on indirect immunofluorescence on salt-split skin (SSS).

OBJECTIVES

To investigate the added value of the coll VII ELISA in the laboratory diagnosis of SSS-positive and SSS-negative EBA and to correlate the ELISA index with disease episode.

METHODS

The coll VII ELISA was performed on banked sera of 28 patients with EBA: 15 SSS positive and 13 SSS negative. Sera from healthy blood donors (n = 17) and patients with other autoimmune blistering diseases (n = 29) served as controls. In four patients, the ELISA index was measured longitudinally. Serration pattern analysis by direct immunofluorescence has been prospectively performed since 2000 in 19 patients.

RESULTS

The sensitivity in the SSS-positive group was 80% whereas it was 23% in the SSS-negative group. In the prospective EBA subset it was 45%. The sensitivity of u-serration pattern analysis on skin biopsy was 89%. Ten (53%) of these cases were seronegative with both ELISA and SSS, and would have been missed by serum analysis alone. Of the 46 control sera, one serum tested positive (specificity 97·8%). The coll VII ELISA correlated with disease activity over time in individual patients.

CONCLUSIONS

The coll VII ELISA has limited added value in SSS-negative EBA cases. The ELISA test is valuable in differentiating EBA from antilaminin-332 mucous membrane pemphigoid and anti-p200 pemphigoid and in its ability to monitor patients with EBA serologically. U-serration pattern analysis on immunofluorescence skin biopsy is the gold standard for the diagnosis of EBA.

Why you should ask your patients about their fishing hobbies

Patients who use immunosuppressive agents, in particular medication that blocks tumour necrosis factor-a, are at risk for mycobacterial infections. Besides the typical Mycobacterium tuberculosis infection, a lso a typical mycobacterial disease may occur. Here we demonstrate two patients with such atypical mycobacterial infection due to swimming and fishing water contact. We propose that patients, before starting with immunosuppressive therapy, are counselled about risk factors for mycobacterial disease.

Vascular endothelial growth factor: the link between cardiovascular risk factors and microalbuminuria?

BACKGROUND

Microalbuminuria, i.e. slightly elevated urinary albumin excretion, is associated with increased cardiovascular risk factors and cardiovascular morbidity in the general population. Microalbuminuria has been proposed to indicate increased endothelial permeability. Unknown are the mechanisms underlying this increased vascular permeability. Vascular endothelial growth factor (VEGF), also known as vascular permeability factor, increases endothelial permeability. We hypothesised that plasma VEGF levels may be associated with microalbuminuria in a large sample of the general population.

METHODS

Out of a large sample of the general population, we studied 189 control subjects (urinary albumin excretion (UAE): 0-30 mg/24 h) and 194 microalbuminuric subjects (UAE: 30-300 mg/24 h), matched for age, sex and the presence of ischemia on the electrocardiogram.

RESULTS

Subjects with microalbuminuria had significant higher plasma levels of VEGF (p<0.05). The correlation between plasma levels of VEGF and systolic and diastolic blood pressure, cholesterol, glucose, diabetes and body mass index were statistically significant. Using logistic regression analysis, microalbuminuria was significantly associated with VEGF (odds ratio 1.62; 95% confidence interval: 1.15-2.27; p<0.01). This association was dependent on cardiovascular risk factors.

CONCLUSION

This study suggests a relation between increased plasma VEGF levels and subsequent occurrence of microalbuminuria.

The importance of microalbuminuria as a cardiovascular risk indicator: A review

The present review describes the knowledge of microalbuminuria as a cardiovascular risk indicator. Microalbuminuria is usually defined as a urinary albumin excretion rate of 30 to 300 mg in a 24 h urine collection, or as a urinary albumin excretion rate of 20 to 200 mg/min in a timed overnight urine collection, although microalbuminuria was demonstrated to be a predictor for cardiovascular events at levels below these conventional cut-off values. More than one consecutive urine collection is preferred given the high day to day variability of urinary albumin excretion. Microalbuminuria is frequently present and a known cardiovascular risk indicator in diabetic populations. Also, in hypertensive and general populations, microalbuminuria is common and has been associated with an adverse atherogenic risk profile and a higher prevalence of cardiovascular disease. Moreover, evidence strongly suggests that microalbuminuria is also an independent predictor of cardiovascular disease in these populations. However, more prospective studies are needed to elucidate fully the value of microalbuminuria as a cardiovascular risk indicator in hypertensive and general populations. Generalized endothelial dysfunction has been hypothesized to be the underlying factor for microalbuminuria on one hand and the underlying factor for increased cardiovascular risk on the other. In this respect, the loss of the glycosaminoglycan heparin sulphate might be an important pathophysiological mechanism. This hypothesis needs further clarification, especially in nondiabetic populations.