Jeffrey's insights: Jeffrey Modell Foundation's global genetic sequencing pilot program to identify specific primary immunodeficiency defects to optimize disease management and treatment

Transitions of Care in Patients With Inborn Errors of Immunity

Inborn errors of immunity (IEI) are a group of inherited conditions caused by damaged monogenic variants that result in impairment and/or dysregulation within the immune system. IEI are typically diagnosed in infancy or early childhood, with clinical presentations that include increased susceptibility to infections, immune dysregulation, autoinflammation, bone marrow failure, and/or malignancy. Historically, transitions of care experienced by patients with IEI have not been well described in the literature. However, with treatment advances extending the long-term survival of patients, this has become a primary area of research. It is crucial to establish guidelines and recommendations specific to the transition of patients with IEI. Transitions may include patients who naturally progress from pediatric to adult care, from inpatient to outpatient settings, or from their established health care team to a new team (ie, moving from one geographic area to another). This narrative review summarizes the current data on transitions of care and describes the health care challenges and patient-related barriers impacting transitions of care. Frameworks with practical guidance on how health care practitioners can better manage care transitions faced by patients with IEI are presented.

Current genetic diagnostics in inborn errors of immunity

New technologies in genetic diagnostics have revolutionized the understanding and management of rare diseases. This review highlights the significant advances and latest developments in genetic diagnostics in inborn errors of immunity (IEI), which encompass a diverse group of disorders characterized by defects in the immune system, leading to increased susceptibility to infections, autoimmunity, autoinflammatory diseases, allergies, and malignancies. Various diagnostic approaches, including targeted gene sequencing panels, whole exome sequencing, whole genome sequencing, RNA sequencing, or proteomics, have enabled the identification of causative genetic variants of rare diseases. These technologies not only facilitated the accurate diagnosis of IEI but also provided valuable insights into the underlying molecular mechanisms. Emerging technologies, currently mainly used in research, such as optical genome mapping, single cell sequencing or the application of artificial intelligence will allow even more insights in the aetiology of hereditary immune defects in the near future. The integration of genetic diagnostics into clinical practice significantly impacts patient care. Genetic testing enables early diagnosis, facilitating timely interventions and personalized treatment strategies. Additionally, establishing a genetic diagnosis is necessary for genetic counselling and prognostic assessments. Identifying specific genetic variants associated with inborn errors of immunity also paved the way for the development of targeted therapies and novel therapeutic approaches. This review emphasizes the challenges related with genetic diagnosis of rare diseases and provides future directions, specifically focusing on IEI. Despite the tremendous progress achieved over the last years, several obstacles remain or have become even more important due to the increasing amount of genetic data produced for each patient. This includes, first and foremost, the interpretation of variants of unknown significance (VUS) in known IEI genes and of variants in genes of unknown significance (GUS). Although genetic diagnostics have significantly contributed to the understanding and management of IEI and other rare diseases, further research, exchange between experts from different clinical disciplines, data integration and the establishment of comprehensive guidelines are crucial to tackle the remaining challenges and maximize the potential of genetic diagnostics in the field of rare diseases, such as IEI.

A score-based method of immune status evaluation for healthy individuals with complete blood cell counts

BACKGROUND

With the COVID-19 outbreak, an increasing number of individuals are concerned about their health, particularly their immune status. However, as of now, there is no available algorithm that effectively assesses the immune status of normal, healthy individuals. In response to this, a new score-based method is proposed that utilizes complete blood cell counts (CBC) to provide early warning of disease risks, such as COVID-19.

METHODS

First, data on immune-related CBC measurements from 16,715 healthy individuals were collected. Then, a three-platform model was developed to normalize the data, and a Gaussian mixture model was optimized with expectation maximization (EM-GMM) to cluster the immune status of healthy individuals. Based on the results, Random Forest (RF), Light Gradient Boosting Machine (LightGBM) and Extreme Gradient Boosting (XGBoost) were used to determine the correlation of each CBC index with the immune status. Consequently, a weighted sum model was constructed to calculate a continuous immunity score, enabling the evaluation of immune status.

RESULTS

The results demonstrated a significant negative correlation between the immunity score and the age of healthy individuals, thereby validating the effectiveness of the proposed method. In addition, a nonlinear polynomial regression model was developed to depict this trend. By comparing an individual's immune status with the reference value corresponding to their age, their immune status can be evaluated.

CONCLUSION

In summary, this study has established a novel model for evaluating the immune status of healthy individuals, providing a good approach for early detection of abnormal immune status in healthy individuals. It is helpful in early warning of the risk of infectious diseases and of significant importance.

Cernunnos deficiency: Further delineation in 5 Egyptian patients

Cernunnos deficiency is a rare genetic disorder characterized by immunodeficiency, microcephaly, growth retardation, bird-like facies, sensitivity to ionizing radiation, few autoimmune manifestations, premature aging of hematopoietic stem cells at an early age, and occasional myeloproliferative disease. Herein we present five Egyptian Cernunnos patients from 3 different families. We describe the patients' clinical phenotypes, their immunological profile as well as genetic results. Sequence analysis revealed three different mutations in the NHEJ1 gene: a nonsense variant c.532C > T; p.(Arg178Ter), an intronic variant c.178-1G > A and a frameshift insertion variant c.233dup; p.(Asn78LysfsTer14). In conclusion, Cernunnos deficiency can have a wide range of clinical features. The characteristic immune profile including a decrease in recent thymic emigrants and naive T cells, markedly elevated memory T cells together with normal to high IgM, and a decrease in IgG and IgA. This immune profile is highly suggestive of Cernunnos deficiency in T-B-NK + SCID patients especially surviving for older ages.

Evaluation and pilot testing of a multidisciplinary model of care to mainstream genomic testing for paediatric inborn errors of immunity

Molecular diagnosis of paediatric inborn errors of immunity (IEI) influences management decisions and alters clinical outcomes, through early use of targeted and curative therapies. The increasing demand for genetic services has resulted in growing waitlists and delayed access to vital genomic testing. To address this issue, the Queensland Paediatric Immunology and Allergy Service, Australia, developed and evaluated a mainstreaming model of care to support point-of-care genomic testing for paediatric IEI. Key features of the model of care included a genetic counsellor embedded in the department, state-wide multidisciplinary team meetings, and variant prioritisation meetings to review whole exome sequencing (WES) data. Of the 62 children presented at the MDT, 43 proceeded to WES, of which nine (21%) received a confirmed molecular diagnosis. Changes to treatment and management were reported for all children with a positive result, including curative hematopoietic stem cell transplantation (n = 4). Four children were also referred for further investigations of variants of uncertain significance or additional testing due to ongoing suspicion of genetic cause after negative result. Demonstrating engagement with the model of care, 45% of the patients were from regional areas and on average, 14 healthcare providers attended the state-wide multidisciplinary team meetings. Parents demonstrated understanding of the implications of testing, reported minimal decisional regret post-test, and identified benefits to genomic testing. Overall, our program demonstrated the feasibility of a mainstreaming model of care for paediatric IEI, improved access to genomic testing, facilitated treatment decision-making, and was acceptable to parents and clinicians alike.

Epidemiology of combined immunodeficiencies affecting cellular and humoral immunity- a multicentric retrospective cohort study from the Arabian Peninsula

AIMS

To understand the characteristics of combined immunodeficiency disorders that affect cellular and humoral immunity (CID) in the Arabian Peninsula.

METHODS

Retrospective study of 236 patients with CID from the region were enrolled from 2004 to 2022.

RESULTS

236 patients were included with a majority being profound CID. Among patients with a family history of CID, the ages at onset and diagnosis, and the delay in diagnosis were lower compared to those with no family history of CID, but this did not affect time to transplant. HSCT was performed for 51.27% of the patients with median time from diagnosis to HSCT of 6.36 months. On multivariate analysis, patients who underwent early transplant had increased odds of having CD3 count ≤1000 cell/μl, diagnosed by screening or erythroderma.

CONCLUSION

There is a delay in diagnosis and treatment of CID in our region. Establishing newborn screening programs and HSCT units in our region are the urgent need.

A National Multicenter Study of Leptin and Leptin Receptor Deficiency and Systematic Review

CONTEXT

Homozygous leptin (LEP) and leptin receptor (LEPR) variants lead to childhood-onset obesity.

OBJECTIVE

To present new cases with LEP and LEPR deficiency, report the long-term follow-up of previously described patients, and to define, based on all reported cases in literature, genotype-phenotype relationships.

METHODS

Our cohort included 18 patients (LEP = 11, LEPR = 7), 8 of whom had been previously reported. A systematic literature review was conducted in July 2022. Forty-two of 47 studies on LEP/LEPR were selected.

RESULTS

Of 10 new cases, 2 novel pathogenic variants were identified in LEP (c.16delC) and LEPR (c.40 + 5G > C). Eleven patients with LEP deficiency received metreleptin, 4 of whom had been treated for over 20 years. One patient developed loss of efficacy associated with neutralizing antibody development. Of 152 patients, including 134 cases from the literature review in addition to our cases, frameshift variants were the most common (48%) in LEP and missense variants (35%) in LEPR. Patients with LEP deficiency were diagnosed at a younger age [3 (9) vs 7 (13) years, P = .02] and had a higher median body mass index (BMI) SD score [3.1 (2) vs 2.8 (1) kg/m2, P = 0.02], which was more closely associated with frameshift variants (P = .02). Patients with LEP deficiency were more likely to have hyperinsulinemia (P = .02).

CONCLUSION

Frameshift variants were more common in patients with LEP deficiency whereas missense variants were more common in LEPR deficiency. Patients with LEP deficiency were identified at younger ages, had higher BMI SD scores, and had higher rates of hyperinsulinemia than patients with LEPR deficiency. Eleven patients benefitted from long-term metreleptin, with 1 losing efficacy due to neutralizing antibodies.

Genetic Testing in Egyptian Patients with Inborn Errors of Immunity: a Single-Center Experience

BACKGROUND

Inborn errors of immunity (IEI) are a group of heterogeneous disorders with geographic and ethnic diversities. Although IEI are common in Egypt, genetic diagnosis is limited due to financial restrictions. This study aims to characterize the genetic spectrum of IEI patients in Egypt and highlights the adaptation of the molecular diagnostic methods to a resource-limited setting.

METHODS

Genetic material from 504 patients was studied, and proper diagnosis was achieved in 282 patients from 246 families. Mutational analysis was done by Sanger sequencing, next-generation sequencing (NGS) targeting customized genes panels, and whole-exome sequencing (WES) according to the patients' phenotypes and availability of genetic testing.

RESULTS

A total of 194 variants involving 72 different genes were detected with RAG1/2 genes being the most encountered followed by DOCK8, CYBA, LRBA, NCF1, and JAK3. Autosomal recessive (AR) inheritance was detected in 233/282 patients (82.6%), X-linked (XL) recessive inheritance in 32/282 patients (11.3%), and autosomal dominant (AD) inheritance in 18/282 patients (6.4%), reflecting the impact of consanguineous marriages on the prevalence of different modes of inheritance and the distribution of the various IEI disorders.

CONCLUSION

The study showed that a combination of Sanger sequencing in selected patients associated with targeted NGS or WES in other patients is an effective diagnostic strategy for IEI diagnosis in countries with limited diagnostic resources. Molecular testing can be used to validate other nonexpensive laboratory techniques that help to reach definitive diagnosis and help in genetic counseling and taking proper therapeutic decisions including stem cell transplantation or gene therapy.

Global Expansion of Jeffrey's Insights: Jeffrey Modell Foundation's Genetic Sequencing Program for Primary Immunodeficiency

Genetic disorders that impair the immune system, known as Primary Immunodeficiencies (PI), include over 450 single-gene inborn errors of immunity. Timely and appropriate diagnosis and treatment is vital to quality of life (QOL) and sometimes survival, as patients are susceptible to frequent, persistent, severe, and sometimes life-threatening infections or autoimmunity. Suspected PI patients that do not have a genetic diagnosis often endure a prolonged, onerous, inefficient, and expensive experience, known as a diagnostic odyssey. The resulting diagnostic delay prohibits proper disease management and treatment, causing unnecessary distress and diminished QOL. Next-generation sequencing (NGS) offers relief from the distress of the diagnostic odyssey, but because of cost and barriers to access, it is regularly unobtainable. The Jeffrey Modell Foundation (JMF) introduced "Jeffrey's Insights", a no-charge genetic sequencing pilot program, in January 2019 for patients within the Jeffrey Modell Centers Network (JMCN) with an underlying PI, but no genetic diagnosis. Building on the success of the pilot program, JMF expanded it globally to more than 400 Centers in the JMCN in early 2020. The most current version of Invitae's PI Panel available was used for this program. All participating clinicians were invited to complete a brief questionnaire assessing prior impediments to access and post-sequencing alterations in disease management and treatment. A total of 1,398 patients were tested, with 20.3% receiving a molecular diagnosis and many more receiving helpful diagnostic leads. Results obtained from genetic sequencing led to an alteration of clinical diagnosis, disease management, treatment, and genetic counseling in 39%, 38%, 35%, and 53% of patients, respectively. The global expansion of this program further underscores the crucial need for NGS for PI, along with its efficiency and potential cost savings. The results of this program to date further define rationale for the availability of comprehensive diagnostic NGS for patients with PI when requisitioned by an expert immunologist.

Druggable monogenic immune defects hidden in diverse medical specialties: Focus on overlap syndromes

In the last two decades two new paradigms changed our way of perceiving primary immunodeficiencies: An increasing number of immune defects are more associated with inflammatory or autoimmune features rather than with infections. Some primary immune defects are due to hyperactive pathways that can be targeted by specific inhibitors, providing innovative precision treatments that can change the natural history of diseases. In this article we review some of these “druggable” inborn errors of immunity and describe how they can be suspected and diagnosed in diverse pediatric and adult medicine specialties. Since the availability of precision treatments can dramatically impact the course of these diseases, preventing the development of organ damage, it is crucial to widen the awareness of these conditions and to provide practical hints for a prompt detection and cure.

Growth in diagnosis and treatment of primary immunodeficiency within the global Jeffrey Modell Centers Network

BACKGROUND

Primary immunodeficiencies (PI), which include more than 450 single-gene inborn errors of immunity and may affect up to 1% of the population, are genetic disorders that impair the immune system. If not properly identified and treated, individuals with PI are subject to serious, prolonged, and sometimes life-threatening infections or autoimmunity. Despite advancements, awareness of PI remains a critical issue for physicians and the public alike, as this leads to the enhanced and expedited management of these conditions. To address this critical issue, the Jeffrey Modell Foundation (JMF) formed a global network of specialized centers. The goal of this endeavor was to raise awareness of PI to better identify, diagnose, and treat patients, reducing associated mortality and morbidity and improving quality of life (QOL). For more than two decades, the Jeffrey Modell Centers Network (JMCN) has served as the foundation upon which these goals have been pursued. The JMCN currently includes 909 Expert Physicians at 400 institutions, in 316 cities, and 86 countries spanning six continents.

METHODS

A survey was developed by JMF for members of the JMCN, following the most recent Classification of PI from the IUIS Expert Committee, to periodically describe the patient population, including treatment modalities and demographics. Physician-reported data from 2021 was compared to that from 2018 and 2013. Physicians in the JMCN also reported on select outcomes of their PI patients one year prior to and one year following diagnosis.

RESULTS

A total of 300 JMF Physician Surveys from 681 physicians were included in this analysis. This is a 75% physician response rate. From 2013 to 2021, there was a 96.3% increase in patients followed in the US and an 86.1% increase globally. During the same period, patients identified with a specific PI defect increased by 46.6% in the US and 47.9% globally. Patients receiving IgG and HSCT increased by 110% and 201% respectfully since 2013. Early diagnosis led to reported decreased morbidity and mortality and reduced calculated healthcare costs.

CONCLUSIONS

This global analysis of physician-reported data on patients with PI demonstrates an increase in both diagnosed and treated patients. This substantial increase from within the JMCN is a testament to its impact. In addition to building an extensive global patient database, the expanding JMCN serves as a unique and critical resource, providing the infrastructure for earliest diagnosis, optimized treatments, and implementation of standard-of-care and best practices. The JMCN provides a critical platform that facilitates the education of physicians and patients, awareness initiatives, and research advances, through collaboration and connectivity, ultimately resulting in improved outcomes and QOL for patients with PI. The JMCN has steadily and substantially grown for more than two decades and continues to substantively impact the field of Immunology globally.

Consensus Middle East and North Africa Registry on Inborn Errors of Immunity

Background

Inborn errors of immunity (IEIs) are a heterogeneous group of genetic defects of immunity, which cause high rates of morbidity and mortality mainly among children due to infectious and non-infectious complications. The IEI burden has been critically underestimated in countries from middle- and low-income regions and the majority of patients with IEI in these regions lack a molecular diagnosis.

Methods

We analyzed the clinical, immunologic, and genetic data of IEI patients from 22 countries in the Middle East and North Africa (MENA) region. The data was collected from national registries and diverse databases such as the Asian Pacific Society for Immunodeficiencies (APSID) registry, African Society for Immunodeficiencies (ASID) registry, Jeffrey Modell Foundation (JMF) registry, J Project centers, and International Consortium on Immune Deficiency (ICID) centers.

Results

We identified 17,120 patients with IEI, among which females represented 39.4%. Parental consanguinity was present in 60.5% of cases and 27.3% of the patients were from families with a confirmed previous family history of IEI. The median age of patients at the onset of disease was 36 months and the median delay in diagnosis was 41 months. The rate of registered IEI patients ranges between 0.02 and 7.58 per 100,000 population, and the lowest rates were in countries with the highest rates of disability-adjusted life years (DALY) and death rates for children. Predominantly antibody deficiencies were the most frequent IEI entities diagnosed in 41.2% of the cohort. Among 5871 patients genetically evaluated, the diagnostic yield was 83% with the majority (65.2%) having autosomal recessive defects. The mortality rate was the highest in patients with non-syndromic combined immunodeficiency (51.7%, median age: 3.5 years) and particularly in patients with mutations in specific genes associated with this phenotype (RFXANK, RAG1, and IL2RG).

Conclusions

This comprehensive registry highlights the importance of a detailed investigation of IEI patients in the MENA region. The high yield of genetic diagnosis of IEI in this region has important implications for prevention, prognosis, treatment, and resource allocation.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10875-021-01053-z.

Clinical Utility of Whole Exome Sequencing and Targeted Panels for the Identification of Inborn Errors of Immunity in a Resource-Constrained Setting

Primary immunodeficiency disorders (PIDs) are inborn errors of immunity (IEI) that cause immune system impairment. To date, more than 400 single-gene IEI have been well defined. The advent of next generation sequencing (NGS) technologies has improved clinical diagnosis and allowed for discovery of novel genes and variants associated with IEI. Molecular diagnosis provides clear clinical benefits for patients by altering management, enabling access to certain treatments and facilitates genetic counselling. Here we report on an 8-year experience using two different NGS technologies, namely research-based WES and targeted gene panels, in patients with suspected IEI in the South African healthcare system. A total of 52 patients' had WES only, 26 had a targeted gene panel only, and 2 had both panel and WES. Overall, a molecular diagnosis was achieved in 30% (24/80) of patients. Clinical management was significantly altered in 67% of patients following molecular results. All 24 families with a molecular diagnosis received more accurate genetic counselling and family cascade testing. Results highlight the clinical value of expanded genetic testing in IEI and its relevance to understanding the genetic and clinical spectrum of the IEI-related disorders in Africa. Detection rates under 40% illustrate the complexity and heterogeneity of these disorders, especially in an African population, thus highlighting the need for expanded genomic testing and research to further elucidate this.

Dysregulatory processes of the cellular link of the immune system in the dynamics of common variable immunodeficiency

Common variable immunodeficiency (CVID) is a variant of primary immunodeficiency in which inhibition of antibody production is formed due to disorders of intercellular interaction affecting cellular elements of both innate and adaptive immune responses. A feature of CVID is the late start and variability of clinical minifestation. These arguments determine the purpose of the study: to identify the dynamics of changes in the cellular parameters of the adaptive and innate immune response depending on the duration and severity of the infectious manifestation of CVID. In this regard, a retrospective analysis of medical histories and dynamic observation of fifteen patients with CVID were carried out. Selection of specific parameters of cellular indices of factors of innate resistance and adaptive immunity was carried out on the basis of systemic-functional approach of immunodiagnostics. It is shown that in patients with CVID -mediated hypogammaglobulinemia and infectious phenotype of clinical manifestation, enhancement of quantitative and functional potentials of T-link effector cells of adaptive immunity is recorded against the background of reduction of number of regulatory T-helpers. With a more severe clinical course of the disease, the number of CD3+HLA DR + limphocytes is lower than with a more favorable version, there is a tendency to decrease the number of these cells, as well as the number of peripheral Treg with an increase in the length of the disease. Cellular components of innate immunity are characterized by a decrease in neutrophil activity, inhibition of antigen-presenting monocyte activity, the number and cytotoxicity of natural killers. At the same time, the tendency to decrease the cytolytic potential of NK with an increase in the length of illness and statistically significant differences depending on the severity of the manifestation of the infectious phenotype of CVID was recorded. The obtained results determine the importance of evaluating the cellular link of the immune system in patients with CVID, including as a prognostic criterion for the severity of the course.

Immunity and Genetics at the Revolving Doors of Diagnostics in Primary Immunodeficiencies

Primary immunodeficiencies (PIDs) are a large and growing group of disorders commonly associated with recurrent infections. However, nowadays, we know that PIDs often carry with them consequences related to organ or hematologic autoimmunity, autoinflammation, and lymphoproliferation in addition to simple susceptibility to pathogens. Alongside this conceptual development, there has been technical advancement, given by the new but already established diagnostic possibilities offered by new genetic testing (e.g., next-generation sequencing). Nevertheless, there is also the need to understand the large number of gene variants detected with these powerful methods. That means advancing beyond genetic results and resorting to the clinical phenotype and to immunological or alternative molecular tests that allow us to prove the causative role of a genetic variant of uncertain significance and/or better define the underlying pathophysiological mechanism. Furthermore, because of the rapid availability of results, laboratory immunoassays are still critical to diagnosing many PIDs, even in screening settings. Fundamental is the integration between different specialties and the development of multidisciplinary and flexible diagnostic workflows. This paper aims to tell these evolving aspects of immunodeficiencies, which are summarized in five key messages, through introducing and exemplifying five clinical cases, focusing on diseases that could benefit targeted therapy.

Pulmonary Manifestations of Immunodeficiency and Immunosuppressive Diseases Other than Human Immunodeficiency Virus

Immune deficiencies may alter normal lung function and protective mechanisms, resulting in a myriad of pulmonary manifestations. Primary immunodeficiencies involve multiple branches of the immune system, and defects may predispose to recurrent upper and lower respiratory infections by common pathogens; opportunistic infections; and autoimmune, inflammatory, and malignant processes that may result in interstitial pneumonias. Secondary immunodeficiencies may result from neoplasms or their treatment, organ transplant and immunosuppression, and from autoimmune diseases and their treatments. Primary and secondary immunodeficiencies and their pulmonary manifestations may be difficult to diagnose and treat. A multidisciplinary approach to evaluation is essential.

Characterization of Infants with Idiopathic Transient and Persistent T Cell Lymphopenia Identified by Newborn Screening-a Single-Center Experience in New York State

PURPOSE

Newborn screening (NBS) quantifies T cell receptor excision circles (TREC) and identifies infants with T cell lymphopenia (TCL). This study elucidates the demographics, laboratory characteristics, genetics, and clinical outcomes following live viral vaccine administration of term infants with transient or persistent idiopathic TCL.

METHODS

A single-center retrospective analysis was performed from September 2010 through June 2018. Laboratory variables were compared with Mann-Whitney tests. Correlations between initial TREC levels and T cell counts were determined by Spearman tests.

RESULTS

Twenty-two transient and 21 persistent TCL infants were identified. Males comprised 68% of the transient and 52% of the persistent TCL cohorts. Whites comprised 23% of the transient and 29% of the persistent cohorts. Median initial TREC levels did not differ (66 vs. 60 TRECs/μL of blood, P = 0.58). The transient cohort had higher median initial CD3⁺ (2135 vs. 1169 cells/μL, P < 0.001), CD4⁺ (1460 vs. 866 cells/μL, P < 0.001), and CD8⁺ (538 vs. 277 cells/μL, P < 0.001) counts. The median age of resolution for the transient cohort was 38 days. Genetic testing revealed 2 genes of interest which warrant further study and several variants of uncertain significance in immunology-related genes in the persistent cohort. 19 transient and 14 persistent subjects received the initial rotavirus and/or MMRV immunization. No adverse reactions to live viral vaccines were reported in either cohort.

CONCLUSION

Transient and persistent TCL infants differ by demographic, laboratory, and clinical characteristics. Select transient and persistent TCL patients may safely receive live attenuated viral vaccines, but larger confirmatory studies are needed.