Identification of LCK mutation in a family with atypical epidermodysplasia verruciformis with T-cell defects and virus-induced squamous cell carcinoma

Case Report of Two Independent Moroccan Families with Syndromic Epidermodysplasia Verruciformis and STK4 Deficiency

Epidermodysplasia verruciformis (EV) is a rare genodermatosis caused by β-human papillomaviruses (HPV) in immunodeficient patients. EV is characterized by flat warts and pityriasis-like lesions and might be isolated or syndromic, associated with some other infectious manifestations. We report here three patients from two independent families, with syndromic EV for both of them. By whole exome sequencing, we found that the patients carry new homozygous variants in STK4, both leading to a premature stop codon. STK4 deficiency causes a combined immunodeficiency characterized by a broad infectious susceptibility to bacteria, viruses, and fungi. Auto-immune manifestations were also reported. Deep immunophenotyping revealed multiple cytopenia in the three affected patients, in particular deep CD4+ T cells deficiency. We report here the fourth and the fifth cases of the syndromic EV due to STK4 deficiency.

Synchronous Epidermodysplasia Verruciformis and Intraepithelial Lesion of the Vulva Is Caused by Coinfection With Alpha-Human Papillomavirus and Beta-Human Papillomavirus Genotypes and Facilitated by Mutations in Cell-Mediated Immunity Genes

CONTEXT.—

There have been exceedingly few reports of epidermodysplasia verruciformis (EV) or EV-like lesions in the vulva. We describe the first observation of vulvar lesions displaying synchronous EV-like histology and conventional high-grade squamous intraepithelial lesion (HSIL), a finding hitherto unreported in medical literature.

OBJECTIVES.—

To describe this novel vulvar lesion with hybrid features of HSIL and EV, attempt to confirm the hypothesis of coinfection with α and β human papillomavirus (α-HPV and β-HPV) genotypes, and describe relevant underlying genetic mutations.

DESIGN.—

Cases were retrospectively selected from our institutional archive. Detailed review of clinical information, histologic examination, and whole genome sequencing (WGS) were performed.

RESULTS.—

Five samples from 4 different patients were included. Three of 4 patients had a history of either iatrogenic immune suppression or prior immune deficiency, and all 3 featured classic HSIL and EV changes within the same lesion. One patient had no history of immune disorders, presented with EV-like changes and multinucleated atypia of the vulva, and was the sole patient without conventional HSIL. By WGS, several uniquely mappable reads pointed toward infection with multiple HPV genotypes, including both α-HPVs and β-HPVs. Mutations in genes implicated in cell-mediated immunity, such as DOCK8, CARMIL2, MST1, and others, were also found.

CONCLUSIONS.—

We provide the first description of vulvar lesions harboring simultaneous HSIL and EV features in the English-language literature, a phenomenon explained by coinfection with α-HPV and β-HPV genotypes. The finding of EV-like changes in a vulvar specimen should prompt assessment of the patient's immune status.

Identification of an inflammatory response-related gene prognostic signature and immune microenvironment for cervical cancer

Background: Cervical cancer (CC) is the fourth most common cancer among women worldwide. As part of the brisk cross-talk between the host and the tumor, prognosis can be affected through inflammatory responses or the tumor microenvironment. However, further exploration of the inflammatory response-related genes that have prognostic value, microenvironment infiltration, and chemotherapeutic therapies in CC is needed. Methods: The clinical data and mRNA expression profiles of CC patients were downloaded from a public database for this study. In the TCGA cohort, a multigene prognostic signature was constructed by least absolute shrinkage and selection operator (LASSO) and Cox analyses. CC patients from the GEO cohort were used for validation. K‒M analysis was used to compare overall survival (OS) between the high- and low-risk groups. Univariate and multivariate Cox analyses were applied to determine the independent predictors of OS. The immune cell infiltration and immune-related functional score were calculated by single-sample gene set enrichment analysis (GSEA). Immunohistochemistry was utilized to validate the protein expression of prognostic genes in CC tissues. Results: A genetic signature model associated with the inflammatory response was built by LASSO Cox regression analysis. Patients in the high-risk group had a significantly lower OS rate. The predictive ability of the prognostic genes was evaluated by means of receiver operating characteristic (ROC) curve analysis. The risk score was confirmed to be an independent predictor of OS by univariate and multivariate Cox analyses. The immune status differed between the high-risk and low-risk groups, and the cancer-related pathways were enriched in the high-risk group according to functional analysis. The risk score was significantly related to tumor stage and immune infiltration type. The expression levels of five prognostic genes (LCK, GCH1, TNFRSF9, ITGA5, and SLC7A1) were positively related to sensitivity to antitumor drugs. Additionally, the expression of prognostic genes was significantly different between CC tissues and myoma patient cervix (non-tumorous) tissues in the separate sample cohort. Conclusion: A model consisting of 5 inflammation-related genes can be used to predict prognosis and influence immune status in CC patients. Furthermore, the inhibition or enhancement of these genes may become a novel alternative therapy.

Monogenic etiologies of persistent human papillomavirus infections: A comprehensive systematic review

PURPOSE

Persistent human papillomavirus infection (PHPVI) causes cutaneous, anogenital, and mucosal warts. Cutaneous warts include common warts, Treeman syndrome, and epidermodysplasia verruciformis, among others. Although more reports of monogenic predisposition to PHPVI have been published with the development of genomic technologies, genetic testing is rarely incorporated into clinical assessments. To encourage broader molecular testing, we compiled a list of the various monogenic etiologies of PHPVI.

METHODS

We conducted a systematic literature review to determine the genetic, immunological, and clinical characteristics of patients with PHPVI.

RESULTS

The inclusion criteria were met by 261 of 40,687 articles. In 842 patients, 83 PHPVI-associated genes were identified, including 42, 6, and 35 genes with strong, moderate, and weak evidence for causality, respectively. Autosomal recessive inheritance predominated (69%). PHPVI onset age was 10.8 ± 8.6 years, with an interquartile range of 5 to 14 years. GATA2,IL2RG,DOCK8, CXCR4, TMC6, TMC8, and CIB1 are the most frequently reported PHPVI-associated genes with strong causality. Most genes (74 out of 83) belong to a catalog of 485 inborn errors of immunity-related genes, and 40 genes (54%) are represented in the nonsyndromic and syndromic combined immunodeficiency categories.

CONCLUSION

PHPVI has at least 83 monogenic etiologies and a genetic diagnosis is essential for effective management.

A partial human LCK defect causes a T cell immunodeficiency with intestinal inflammation

Lymphocyte-specific protein tyrosine kinase (LCK) is essential for T cell antigen receptor (TCR)-mediated signal transduction. Here, we report two siblings homozygous for a novel LCK variant (c.1318C>T; P440S) characterized by T cell lymphopenia with skewed memory phenotype, infant-onset recurrent infections, failure to thrive, and protracted diarrhea. The patients' T cells show residual TCR signal transduction and proliferation following anti-CD3/CD28 and phytohemagglutinin (PHA) stimulation. We demonstrate in mouse models that complete (Lck-/-) versus partial (LckP440S/P440S) loss-of-function LCK causes disease with differing phenotypes. While both Lck-/- and LckP440S/P440S mice exhibit arrested thymic T cell development and profound T cell lymphopenia, only LckP440S/P440S mice show residual T cell proliferation, cytokine production, and intestinal inflammation. Furthermore, the intestinal disease in the LckP440S/P440S mice is prevented by CD4+ T cell depletion or regulatory T cell transfer. These findings demonstrate that P440S LCK spares sufficient T cell function to allow the maturation of some conventional T cells but not regulatory T cells-leading to intestinal inflammation.

A Novel Biallelic LCK Variant Resulting in Profound T-Cell Immune Deficiency and Review of the Literature

Lymphocyte-specific protein tyrosine kinase (LCK) is an SRC-family kinase critical for initiation and propagation of T-cell antigen receptor (TCR) signaling through phosphorylation of TCR-associated CD3 chains and recruited downstream molecules. Until now, only one case of profound T-cell immune deficiency with complete LCK deficiency [1] caused by a biallelic missense mutation (c.1022T>C, p.L341P) and three cases of incomplete LCK deficiency [2] caused by a biallelic splice site mutation (c.188-2A>G) have been described. Additionally, deregulated LCK expression has been associated with genetically undefined immune deficiencies and hematological malignancies. Here, we describe the second case of complete LCK deficiency in a 6-month-old girl born to consanguineous parents presenting with profound T-cell immune deficiency. Whole exome sequencing (WES) revealed a novel pathogenic biallelic missense mutation in LCK (c.1393T>C, p.C465R), which led to the absence of LCK protein expression and phosphorylation, and a consecutive decrease in proximal TCR signaling. Loss of conventional CD4+ and CD8+ αβT-cells and homeostatic T-cell expansion was accompanied by increased γδT-cell and Treg percentages. Surface CD4 and CD8 co-receptor expression was reduced in the patient T-cells, while the heterozygous mother had impaired CD4 and CD8 surface expression to a lesser extent. We conclude that complete LCK deficiency is characterized by profound T-cell immune deficiency, reduced CD4 and CD8 surface expression, and a characteristic TCR signaling disorder. CD4 and CD8 surface expression may be of value for early detection of mono- and/or biallelic LCK deficiency.

Recent advances in cutaneous HPV infection

More than 200 types of human papillomavirus (HPV) have been reported to date and have been associated with various dermatological diseases. Among dermatological diseases, viral verrucae are the most commonly reported to be associated with HPV. Epidermodysplasia verruciformis (EV) consists of three types: typical EV is an autosomal recessive genetic disorder with TMC6/TMC8 gene mutations, atypical EV develops due to various gene mutations that cause immunodeficiency, and acquired EV develops due to acquired immunodeficiency. Generalized verrucosis differs from EV in that it involves numerous verrucous nodules (mainly on the limbs), histopathologically no blue cells as seen in EV, and infection with cutaneous α-HPVs as well as β-HPVs. HPV-induced skin malignancies include squamous cell carcinoma (SCC) caused by β-HPV (especially HPV types 5 and 8) in EV patients, organ transplant recipients, and healthy individuals, and SCC of the vulva and nail unit caused by mucosal high-risk HPV infection. Carcinogenesis of β-HPV is associated with sunlight. Mucosal high-risk HPV-associated carcinomas may also be sexually transmitted. We focused on Bowen's disease of the nail, which has been the subject of our research for a long time and has recently come to the fore in the field of dermatology.

Human genetic and immunological dissection of papillomavirus-driven diseases: new insights into their pathogenesis

Human papillomaviruses (HPVs) are responsible for cutaneous and mucosal lesions. Persistent HPV infection remains a leading cause of uterine cancer in women, but also of cutaneous squamous cell carcinoma in patients with epidermodysplasia verruciformis (EV), and of rare and devastating benign tumors, such as 'tree-man' syndrome. HPV infections are usually asymptomatic or benign in the general population. Severe manifestations in otherwise healthy subjects can attest to inherited immunodeficiencies. The human genetic dissection of these cases has identified critical components of the immune response to HPVs, including the non-redundant roles of keratinocyte-intrinsic immunity in controlling β-HPVs, and of T cell-dependent adaptive immunity for controlling all HPV types. A key role of the CD28 T-cell costimulation pathway in controlling common warts due to HPVs was recently discovered. This review summarizes the state of the art in the human genetics of HPV infection, focusing on two key affected cell types: keratinocytes and T cells.

Identification and Splicing Characterization of Novel TMC6 and TMC8 Variants Associated With Epidermodysplasia Verruciformis in Three Chinese Families

Background: Epidermodysplasia verruciformis (EV) is a rare genodermatosis characterized by abnormal susceptibility to human beta papillomavirus infections and a particular propensity to develop non-melanoma skin cancers (NMSCs). The majority of EV cases are caused by biallelic null variants in TMC6, TMC8, and CIB1. This study aimed to identify disease-causing variants in three Chinese families with EV and to elucidate their molecular pathogenesis. Methods: Genomic DNA from the probands of three EV families was analyzed by whole-exome sequencing (WES). cDNA sequencing was performed to investigate abnormal splicing of the variants. Quantitative RT-PCR (qRT-PCR) was conducted to quantify the mRNA expression of mutant TMC6 and TMC8. Results: Whole-exome sequencing identified two novel homozygous variants (c.2278-2A > G in TMC6 and c.559G > A in TMC8) in families 1 and 2, respectively. In family 3, WES revealed a recurrent and a novel compound heterozygous variant, c.559G > A and c.1389G > A, in TMC8. The c.2278-2A > G TMC6 variant led to the skipping of exon 19 and resulted in premature termination at codon 776. Subsequent qRT-PCR revealed that the aberrantly spliced transcript was partly degraded. Notably, the TMC8 c.559G > A variant created a novel acceptor splice site at c.561 and yielded three different aberrant transcripts. qRT-PCR revealed that most of the mutant transcripts were degraded via nonsense-mediated mRNA decay (NMD). Conclusion: We identified three novel disease-causing variants in TMC6 or TMC8 in three Chinese families with EV. The EV phenotypes of the three patients were due to a reduction in TMC6 or TMC8. Our findings expand the genetic causes of EV in the Chinese population.

Naturally Occurring Genetic Alterations in Proximal TCR Signaling and Implications for Cancer Immunotherapy

T cell-based immunotherapies including genetically engineered T cells, adoptive transfer of tumor-infiltrating lymphocytes, and immune checkpoint blockade highlight the impressive anti-tumor effects of T cells. These successes have provided new hope to many cancer patients with otherwise poor prognoses. However, only a fraction of patients demonstrates durable responses to these forms of therapies and many develop significant immune-mediated toxicity. These heterogeneous clinical responses suggest that underlying nuances in T cell genetics, phenotypes, and activation states likely modulate the therapeutic impact of these approaches. To better characterize known genetic variations that may impact T cell function, we 1) review the function of early T cell receptor-specific signaling mediators, 2) offer a synopsis of known mutations and genetic alterations within the associated molecules, 3) discuss the link between these mutations and human disease and 4) review therapeutic strategies under development or in clinical testing that target each of these molecules for enhancing anti-tumor T cell activity. Finally, we discuss novel engineering approaches that could be designed based on our understanding of the function of these molecules in health and disease.

Generalized Verrucosis Revealing a Life-Threatening and Unlabeled T-Cell Lymphopenia Associated With Autoimmune Hemolytic Anemia: A Case Report and Review of Literature

Primary immunodeficiencies are inherited disorders, which may be revealed in the context of autoimmune hemolytic anemia (AIHA). We report the case of a girl presenting with an enterovirus-related AIHA. Despite being in complete remission for her anemia after treatment, the initial CD4/CD8 lymphopenia dramatically worsened with time. Its sole clinical presentation was generalized verrucosis. Cellular quantitative and functional immunodeficiency was evidenced but no known molecular defect was identified despite extensive workup. This unlabeled profound naive T-lymphopenia was cured by bone marrow transplantation. No similar case was ever described in the scientific literature. Patients with AIHA and/or generalized verrucosis should be screened for primary immunodeficiency, before initiating any immunomodulatory treatment.

Human genetic dissection of papillomavirus-driven diseases: new insight into their pathogenesis

Human papillomaviruses (HPVs) infect mucosal or cutaneous stratified epithelia. There are 5 genera and more than 200 types of HPV, each with a specific tropism and virulence. HPV infections are typically asymptomatic or result in benign tumors, which may be disseminated or persistent in rare cases, but a few oncogenic HPVs can cause cancers. This review deals with the human genetic and immunological basis of interindividual clinical variability in the course of HPV infections of the skin and mucosae. Typical epidermodysplasia verruciformis (EV) is characterized by β-HPV-driven flat wart-like and pityriasis-like cutaneous lesions and non-melanoma skin cancers in patients with inborn errors of EVER1-EVER2-CIB1-dependent skin-intrinsic immunity. Atypical EV is associated with other infectious diseases in patients with inborn errors of T cells. Severe cutaneous or anogenital warts, including anogenital cancers, are also driven by certain α-, γ-, μ or ν-HPVs in patients with inborn errors of T lymphocytes and antigen-presenting cells. The genetic basis of HPV diseases at other mucosal sites, such as oral multifocal epithelial hyperplasia or juvenile recurrent respiratory papillomatosis (JRRP), remains poorly understood. The human genetic dissection of HPV-driven lesions will clarify the molecular and cellular basis of protective immunity to HPVs, and should lead to novel diagnostic, preventive, and curative approaches in patients.

Hematopoietic Stem Cell Transplantation in Primary Immunodeficiency Diseases: Current Status and Future Perspectives

Primary immunodeficiencies (PID) are disorders that for the most part result from mutations in genes involved in immune host defense and immunoregulation. These conditions are characterized by various combinations of recurrent infections, autoimmunity, lymphoproliferation, inflammatory manifestations, atopy, and malignancy. Most PID are due to genetic defects that are intrinsic to hematopoietic cells. Therefore, replacement of mutant cells by healthy donor hematopoietic stem cells (HSC) represents a rational therapeutic approach. Full or partial ablation of the recipient's marrow with chemotherapy is often used to allow stable engraftment of donor-derived HSCs, and serotherapy may be added to the conditioning regimen to reduce the risks of graft rejection and graft versus host disease (GVHD). Initially, hematopoietic stem cell transplantation (HSCT) was attempted in patients with severe combined immunodeficiency (SCID) as the only available curative treatment. It was a challenging procedure, associated with elevated rates of morbidity and mortality. Overtime, outcome of HSCT for PID has significantly improved due to availability of high-resolution HLA typing, increased use of alternative donors and new stem cell sources, development of less toxic, reduced-intensity conditioning (RIC) regimens, and cellular engineering techniques for graft manipulation. Early identification of infants affected by SCID, prior to infectious complication, through newborn screening (NBS) programs and prompt genetic diagnosis with Next Generation Sequencing (NGS) techniques, have also ameliorated the outcome of HSCT. In addition, HSCT has been applied to treat a broader range of PID, including disorders of immune dysregulation. Yet, the broad spectrum of clinical and immunological phenotypes associated with PID makes it difficult to define a universal transplant regimen. As such, integration of knowledge between immunologists and transplant specialists is necessary for the development of innovative transplant protocols and to monitor their results during follow-up. Despite the improved outcome observed after HSCT, patients with severe forms of PID still face significant challenges of short and long-term transplant-related complications. To address this issue, novel HSCT strategies are being implemented aiming to improve both survival and long-term quality of life. This article will discuss the current status and latest developments in HSCT for PID, and present data regarding approach and outcome of HSCT in recently described PID, including disorders associated with immune dysregulation.

The human CIB1-EVER1-EVER2 complex governs keratinocyte-intrinsic immunity to β-papillomaviruses

Patients with epidermodysplasia verruciformis (EV) and biallelic null mutations of TMC6 (encoding EVER1) or TMC8 (EVER2) are selectively prone to disseminated skin lesions due to keratinocyte-tropic human β-papillomaviruses (β-HPVs), which lack E5 and E8. We describe EV patients homozygous for null mutations of the CIB1 gene encoding calcium- and integrin-binding protein-1 (CIB1). CIB1 is strongly expressed in the skin and cultured keratinocytes of controls but not in those of patients. CIB1 forms a complex with EVER1 and EVER2, and CIB1 proteins are not expressed in EVER1- or EVER2-deficient cells. The known functions of EVER1 and EVER2 in human keratinocytes are not dependent on CIB1, and CIB1 deficiency does not impair keratinocyte adhesion or migration. In keratinocytes, the CIB1 protein interacts with the HPV E5 and E8 proteins encoded by α-HPV16 and γ-HPV4, respectively, suggesting that this protein acts as a restriction factor against HPVs. Collectively, these findings suggest that the disruption of CIB1-EVER1-EVER2-dependent keratinocyte-intrinsic immunity underlies the selective susceptibility to β-HPVs of EV patients.

Epidermodysplasia Verruciformis: Inborn Errors of Immunity to Human Beta-Papillomaviruses

Epidermodysplasia verruciformis (EV) is an autosomal recessive skin disorder with a phenotype conditional on human beta-papillomavirus (beta-HPV) infection. Such infections are common and asymptomatic in the general population, but in individuals with EV, they lead to the development of plane wart-like and red or brownish papules or pityriasis versicolor-like skin lesions, from childhood onwards. Most patients develop non-melanoma skin cancer (NMSC), mostly on areas of UV-exposed skin, from the twenties or thirties onwards. At least half of the cases of typical EV are caused by biallelic loss-of-function mutations of TMC6/EVER1 or TMC8/EVER2. The cellular and molecular basis of disease in TMC/EVER-deficient patients is unknown, but a defect of keratinocyte-intrinsic immunity to beta-HPV is suspected. Indeed, these patients are not susceptible to other infectious diseases and have apparently normal leukocyte development. In contrast, patients with an atypical form of EV due to inborn errors of T-cell immunity invariably develop clinical symptoms of EV in the context of other infectious diseases. The features of the typical and atypical forms of EV thus suggest that the control of beta-HPV infections requires both EVER1/EVER2-dependent keratinocyte-intrinsic immunity and T cell-dependent adaptive immunity.

Risk of Human Papillomavirus Infection in Cancer-Prone Individuals: What We Know

Human papillomavirus (HPV) infections cause a significant proportion of cancers worldwide, predominantly squamous cell carcinomas (SCC) of the mucosas and skin. High-risk HPV types are associated with SCCs of the anogenital and oropharyngeal tract. HPV oncogene activities and the biology of SCCs have been intensely studied in laboratory models and humans. What remains largely unknown are host tissue and immune-related factors that determine an individual's susceptibility to infection and/or carcinogenesis. Such susceptibility factors could serve to identify those at greatest risk and spark individually tailored HPV and SCC prevention efforts. Fanconi anemia (FA) is an inherited DNA repair disorder that is in part characterized by extreme susceptibility to SCCs. An increased prevalence of HPV has been reported in affected individuals, and molecular and functional connections between FA, SCC, and HPV were established in laboratory models. However, the presence of HPV in some human FA tumors is controversial, and the extent of the etiological connections remains to be established. Herein, we discuss cellular, immunological, and phenotypic features of FA, placed into the context of HPV pathogenesis. The goal is to highlight this orphan disease as a unique model system to uncover host genetic and molecular HPV features, as well as SCC susceptibility factors.

[What's new in clinical dermatology?]

In addition to continuous medical education, medical journals offer to dermatologists a huge variety of news that differ by their content, validity, originality and clinical relevance. I collected here various articles relative to clinical dermatology that have been published between September, 2016 and September, 2017. These papers have been chosen in the aim of reflecting such diversity. I just excluded, as far as possible, articles dealing with other issues that the reader will find further in this booklet (such as research, pediatric, instrumental, oncologic or therapeutic dermatology, or dermatology and internal medicine). Space restriction required to skip some commentaries while keeping the references to the selected papers, which the reader will be able to read carefully in its original form.

Recurrent and Sustained Viral Infections in Primary Immunodeficiencies

Viral infections are commonplace and often innocuous. Nevertheless, within the population of patients with primary immunodeficiencies (PIDDs), viral infections can be the feature that drives a diagnostic evaluation or can be the most significant morbidity for the patient. This review is focused on the viral complications of PIDDs. It will focus on respiratory viruses, the most common type of viral infection in the general population. Children and adults with an increased frequency or severity of respiratory viral infections are often referred for an immunologic evaluation. The classic teaching is to investigate humoral function in people with recurrent sinopulmonary infections, but this is often interpreted to mean recurrent bacterial infections. Recurrent or very severe viral infections may also be a harbinger of a primary immunodeficiency as well. This review will also cover persistent cutaneous viral infections, systemic infections, central nervous system infections, and gastrointestinal infections. In each case, the specific viral infections may drive a diagnostic evaluation that is specific for that type of virus. This review also discusses the management of these infections, which can become problematic in patients with PIDDs.

Re-evaluation of epidermodysplasia verruciformis: Reconciling more than 90 years of debate

Epidermodysplasia verruciformis (EV) is a rare genodermatosis characterized by abnormal susceptibility to cutaneous human beta-papillomavirus infections causing persistent flat warts or pityriasis versicolor-like lesions. This generalized verrucous skin disorder resembles generalized verrucosis, but these 2 conditions are distinguished by differences in clinical manifestation and the human papillomavirus types involved. A breakthrough in our understanding of EV was the discovery that homozygous inactivating mutations in TMC6 (EVER1) and TMC8 (EVER2) determine susceptibility to this disorder; however, they have not solved all EV cases fully. These deficiencies account for 75% of affected individuals, leaving a substantial number of patients without an underlying genetic cause. Recently, it has been revealed that mutations in additional genes (RHOH, MST-1, CORO1A, and IL-7) result in extensive human beta-papillomavirus replication and therefore manifest with an EV-like phenotype. The term "acquired EV" is used to describe an EV-like phenotype that develops in immunocompromised hosts, and the introduction of this entity further aggravates the confusion. Reevaluation of these entities is warranted. Here, we review the available data on this issue, provide up to date information on the major characteristics that differentiate between these seemingly clinically similar disorders, and highlight the different mechanisms involved in each disorder.