Men with sickle cell disease experience greater sexual dysfunction when compared with men without sickle cell disease

Nitric Oxide Resistance in Priapism Associated with Sickle Cell Disease: Mechanisms, Therapeutic Challenges, and Future Directions

Patients with sickle cell disease (SCD) display priapism, a prolonged penile erection in the absence of sexual arousal. The current pharmacological treatments for SCD-associated priapism are limited and focused on acute interventions rather than prevention. Thus, there is an urgent need for new drug targets and preventive pharmacological therapies for this condition. This review focuses on the molecular mechanisms linked to the dysfunction of the NO-cyclic guanosine monophosphate (cGMP)-phosphodiesterase type 5 (PDE5) pathway implicated in SCD-associated priapism. In murine models of SCD, reduced nitric oxide (NO)-cGMP bioavailability in the corpus cavernosum is associated with elevated plasma hemoglobin levels, increased reactive oxygen species levels that inactive NO, and testosterone deficiency that leads to endothelial nitric oxide synthase downregulation. We discuss the consequences of the reduced cGMP-dependent PDE5 activity in response to these molecular changes, highlighting it as the primary pathophysiological mechanism leading to excessive corpus cavernosum relaxation, culminating in priapism. We also further discuss the impact of intravascular hemolysis on therapeutic approaches, present current pharmacological strategies targeting the NO-cGMP-PDE5 pathway in the penis, and identify potential pharmacological targets for future priapism therapies. In men with SCD and priapism, PDE5 inhibitor therapy and testosterone replacement have shown promising results. Recent preclinical research reported the beneficial effect of treatment with haptoglobin and NO donors. SIGNIFICANCE STATEMENT: This review discusses the molecular changes that reduce NO-cGMP bioavailability in the penis in SCD and highlights pharmacological targets and therapeutic strategies for the treatment of priapism, including PDE5 inhibitors, hormonal modulators, NO donors, hydroxyurea, soluble guanylate cyclase stimulators, haptoglobin, hemopexin, and antioxidants.

Heme-induced corpus cavernosum relaxation and its implications for priapism in sickle cell disease: a mechanistic insight

BACKGROUND

Patients with sickle cell disease (SCD) experience intravascular hemolysis, leading to elevated plasma heme levels. This phenomenon has been associated with increased priapism in men with SCD. The heme group can be metabolized by heme oxygenase (HO), generating carbon monoxide (CO), which is known to promote smooth muscle relaxation via soluble guanylyl cyclase (sGC)-cyclic guanosine monophosphate (cGMP). However, the effects of heme on the relaxation responses of corpus cavernosum (CC) have not been investigated.

OBJECTIVES

To evaluate the functional and biochemical effects of the heme group on mouse CC smooth muscle in vitro.

MATERIALS AND METHODS

Male C57BL/6 mice were used. CC tissues were mounted in organ baths. Measurement of cGMP in mice CC was evaluated.

RESULTS

The cumulative addition of heme concentrations promoted the relaxation of CC. HO inhibitor (1J, 100 μM) or sGC inhibitor (ODQ, 10 μM) blocked the relaxing effect of the heme group. Pre-incubation of CC with heme (100 μM) enhanced relaxation induced by acetylcholine, sodium nitroprusside, and nitrergic relaxation (electrical field stimulation), which was abolished by 1J or ODQ. The heme group increased the cGMP production in CC, which was abolished by 1J or ODQ. cGMP levels were significantly higher in CC treated with heme, and pre-incubation with compound 1J or ODQ abolished the effect of heme in raising cGMP levels.

DISCUSSION AND CONCLUSION

The HO-CO-sGC-cGMP pathway appears to play a crucial role in promoting CC relaxation. Our study provides novel insight into the role of group heme in CC relaxation and its potential contribution to priapism in SCD. Heme may serve as a pharmacological target for new therapies to prevent priapism.

Priapism in a Young Adult With Sickle Cell Disease

This article presents a case study focusing on priapism in a patient with sickle cell disease, with repeated emergency department (ED) visits and hospitalizations. The patient was successfully identified and treated by the ED nurse practitioner (NP) with aspiration of the corpus cavernosum. Priapism is a persistent penile erection that continues for an extended time. There is some argument about what that length of time is, but generally, the consensus is more than 4 hr beyond sexual stimulation or unrelated to sexual stimulation or sexual interest (Bivalacqua et al., 2022). Priapism is a fairly common but underrecognized complication of sickle cell disease. It represents a urological emergency in which timely diagnosis and appropriate treatment are vital to preserving penile tissue and sexual function. The diagnosis is made clinically with a comprehensive history, physical examination, and appropriate laboratory test values. Initial management can be conservative with hydration and analgesics or, if necessary, more invasive with needle aspiration to promote detumescence. Permanent tissue damage or erectile dysfunction can result if priapism is unrecognized, untreated, or not treated immediately. The NP plays an integral role in treating and preventing permanent damage. Patient education should focus on instructions for preventing priapism and managing episodes at home.

Evaluation of knowledge of priapism in sickle cell patients in Senegal

PURPOSE

Erectile dysfunction is a dreadful complication of priapism especially with delay in diagnosis and management. The lack of awareness of priapism as a vaso-occlusive complication of sickle cell disease (SCD) is more concerning. The objective of this study was to evaluate the burden of priapism in adult Senegalese males adults with sickle cell disease.

METHODS

A cross-sectional study was carried out amongst consecutive consenting males aged 18 years and older with SCD presenting to the in Haematology Department of the National Blood Transfusion Centre (Dakar, Senegal). All participants completed a questionnaire detailing knowledge on the definition of priapism, its association with SCD, consequences of untreated priapism and treatment options.

RESULTS

A total of 219 participants completed the questionnaire. The mean age of the respondents was 27.1 years with a range of (18-54). Of the respondents, 78.5% (n = 172) did not have any knowledge of the term "priapism". After the term was explained, 38.4% (n = 84) thought that there may be a risk of developing priapism given the diagnosis of sickle cell disease. Among the participants, 41.5% (n = 91) reported having a history of priapism. Among all patients who experienced priapism, 36.3% (n = 33) did not seek medical attention with episodes of priapism. It was found that 48.4% (n = 106) of the participants thought there may be a risk of irreversible complications associated with priapism and a corresponding proportion, 42% (n = 92) thought this risk was time dependent. 36.5% (n = 80) of patients believed priapism could lead to erectile dysfunction.

CONCLUSION

Priapism is a common complication of sickle cell disease in Senegalese adults which is not well known by sickle cell patients. The health authorities must undertake efforts to raise awareness of priapism as a complication amongst sickle cell patients.

Impact of Sickle Cell Disease on Affected Individuals in Nigeria: A Critical Review

Sickle cell disease is an autosomal recessive disorder of the beta-globin gene, with resultant deformation of the red blood cells and variable clinical outcomes. Nigeria is recognised as the country with the highest burden of sickle cell disease globally. This study aimed at critically reviewing available literature on impact of sickle cell disease in Nigeria. A literature search was carried out on four databases, and a total of 116 articles that met the inclusion criteria were included in the critical review. It was observed that majority of the studies were carried out in South-Western part of Nigeria (47.4%), whilst the North-East had the least number of studies undertaken in this area, more than a quarter of the studies (27.6%) were related to hematologic and serologic screening. Major themes that emerged from this review were morbidity and mortality; prevalence of sickle cell disease; issues relating to blood transfusion; psychosocial impact; and anatomical dysfunction in sickle cell disease. Intervention programs from both government and non-governmental organizations aimed at reducing the burden of sickle cell disease and its socio-economic impact were identified as key to strategies aimed at overcoming challenges associated with the disease. Findings from this study also revealed that education and awareness interventions were central to reducing the prevalence of sickle cell disease in this setting.

Family planning needs of young adults with sickle cell disease

Sexual and reproductive healthcare standards for adolescents and young adults with sickle cell disease (SCD) are not established. A total of 50 young adults entering adult SCD care completed a Family Planning Survey assessing sexual and reproductive health needs from March 2019 to July 2020. Clinical data were abstracted from respondents' electronic medical records. Linear and logistic regression was applied to explore associations between clinical characteristics and survey results. Few respondents (8%) wished to be pregnant in the coming year, and 46% answered yes to at least one of four needs assessment questions. Those who were not employed full time were more likely to endorse needing help with getting sickle cell trait testing for a partner (ORadj = 9.59, p-value = 0.05). Contraceptive use was associated with having an obstetrician-gynecologist (OR = 6.8, p-value = 0.01). Young adults with SCD entering adult care have diverse reproductive health needs, highlighting opportunities to provide multidisciplinary, SCD-specific reproductive healthcare.

Priapism at Diagnosis of Pediatric Chronic Myeloid Leukemia: Data Derived from a Large Cohort of Children and Teenagers and a Narrative Review on Priapism Management

Pediatric chronic myeloid leukemia (CML) is a very rare malignancy (age-related incidence 0.1/100,000) typically presenting with leucocyte counts >100,000/µL. However, clinical signs of leukostasis are observed at diagnosis in only approximately 10% of all cases and among these, priapism is infrequent. Here, we analyze data from pediatric CML registries on the occurrence of priapism heralding diagnosis of CML in 16/491 (3.2%) boys (median age 13.5 years, range 4-18) with pediatric CML. In the cohort investigated, duration of priapism resulting in a diagnosis of CML was not reported in 5 patients, and in the remaining 11 patients, occurred as stuttering priapism over 3 months (n = 1), over 6 weeks (n = 1), over 1-2 weeks (n = 2), over several days (n = 2), or 24 h (n = 1), while the remaining 4 boys reported continuous erection lasting over 11-12 h. All patients exhibited splenomegaly and massive leukocytosis (median WBC 470,000/µL, range 236,700-899,000). Interventions to treat priapism were unknown in 5 patients, and in the remaining cohort, comprised intravenous fluids ± heparin (n = 2), penile puncture (n = 5) ± injection of sympathomimetics (n = 4) ± intracavernous shunt operation (n = 1) paralleled by leukocyte-reductive measures. Management without penile puncture by leukapheresis or exchange transfusion was performed in 3 boys. In total, 7 out 15 (47%) long-term survivors (median age 20 years, range 19-25) responded to a questionnaire. All had maintained full erectile function; however, 5/7 had presented with stuttering priapism while in the remaining 2 patients priapism had lasted <12 h until intervention. At its extreme, low-flow priapism lasting for longer than 24 h may result in partial or total impotence by erectile dysfunction. This physical disability can exert a large psychological impact on patients' lives. In a narrative review fashion, we analyzed the literature on priapism in boys with CML which is by categorization stuttering or persisting as mostly painful, ischemic (low-flow) priapism. Details on the pathophysiology are discussed on the background of the different blood rheology of hyperleukocytosis in acute and chronic leukemias. In addition to the data collected, instructive case vignettes demonstrate the diagnostic and treatment approaches and the outcome of boys presenting with priapism. An algorithm for management of priapism in a stepwise fashion is presented. All approaches must be performed in parallel with cytoreductive treatment of leukostasis in CML which comprises leukapheresis and exchange transfusions ± cytotoxic chemotherapy.

Epidemiology and treatment of priapism in sickle cell disease

Ischemic priapism is a common but underrecognized morbidity affecting about 33% of adult men with sickle cell disease (SCD). The onset of priapism occurs in the prepubertal period and tends to be recurrent with increasing age. Significantly, priapism is associated with an unrecognized high burden of mental duress and sexual dysfunctions. The diagnosis of priapism is clinical. Many episodes of priapism will resolve spontaneously, but when an episode lasts longer than 4 hours, the episode is considered a urologic emergency requiring quick intervention with either corporal aspiration or shunt surgery. Only 3 randomized clinical trials (stilbesterol, ephedrine or etilefrine, and sildenafil) have been conducted for secondary priapism prevention in SCD. All 3 trials were limited with small sample sizes, selection biases, and inconclusive results after completion. The current molecular understanding of the pathobiology of priapism suggests a relative nitric oxide (NO) deficiency secondary to chronic hemolysis in SCD and associated phosphodiesterase type 5 dysregulation. We posit an increase in NO levels will restore the normal homeostatic relationship between voluntary erection and detumescence. Currently, 2 randomized phase 2 trials (1 double-blind, placebo-controlled trial and 1 open-label, single-arm intervention) are being conducted for secondary priapism prevention in men at high risk for recurrent priapism (NCT03938454 and NCT05142254). We review the epidemiology and pathobiology of priapism, along with mechanistic therapeutic approaches for secondary prevention of priapism in SCD.

Go the Distance

This overview of reproductive and sexual health care concerns for people with sickle cell disease (SCD) addresses clinical concerns that can be complex and are inherently multidisciplinary. Clinicians must be prepared to initiate reproductive health care discussions, as these intimate concerns may not be volunteered by patients. SCD is associated with delayed onset of puberty, sickle pain during menstruation, disease-specific contraceptive considerations, high-risk pregnancy, priapism, erectile dysfunction, and offspring who inherit a hemoglobinopathy trait from affected parents. Reproductive health considerations are underrecognized, undertreated, and understudied. They need attention in primary care and specialty SCD, urology, and obstetrics and gynecology clinics.

Predictors of Sex-Induced Crisis, Sexual Function and Marital Satisfaction in Women with Sickle Cell Disease

BACKGROUND

Sex-induced and orgasm-induced crisis, sexual dysfunction, and marital satisfaction among women with sickle cell disease (SCD) is under-reported.

AIM

This study assessed sexual function in women with SCD and compared sexual function in women with SCD to women without SCD.

METHODS

This was a descriptive and comparative cross-sectional survey that involved 435 women with SCD and 406 women without SCD (as controls).

OUTCOMES

This study demonstrates the predictors of sex-induced crisis, sexual function and marital satisfaction in women with sickle cell disease.

RESULTS

The prevalence of dyspareunia and marital dissatisfaction was higher in women with SCD than those without SCD. In addition, SCD was significantly associated with multiple sexual dysfunctions, with reported symptoms of sexual desire disorder (HSDD), female sexual arousal disorder (FSAD), and female sexual orgasm disorder (FSOD). Genotype, age, age at puberty, dyspareunia, and duration of infertility were the observed independent predictors of sexual dysfunction in women with SCD. Also, most (54.02%) of the SCD subjects experienced sex-induced and orgasm-induced crises. Although water intake before and after sex was reported to be beneficial in preventing sex-induced and orgasm-induced crisis in women with SCD, it was not a predictor of sexual dysfunction.

CLINICAL IMPLICATIONS

SCD patients are at risk of sex-induced and orgasm-induced crisis as well as sexual dysfunction.

STRENGTHS AND LIMITATIONS

No study has ever reported the incidence of sex-and orgasm-induced crisis and sexual dysfunction in women with SCD. Also, we used a reasonably large sample size and utilized widely acceptable validated and reproducible tools like ENRICH Marital Satisfaction (EMS) and Female Sexual Function Index (FSFI) to assess the marital satisfaction and sexual function of the studied participants. This allows for the generalization of our findings. The limitations of the present study include recall bias and the inability to document real-time occurrences of sex-and orgasm-induced crisis and the incidence of female sexual dysfunction. Furthermore, though the risk factors of sexual dysfunction as perceived by women with SCD were elicited, biological risk factors and the possible associated mechanisms were not determined in this study.

CONCLUSION

Our study shows that sex-induced and orgasm-induced crisis and sexual dysfunction are significant morbidities in women with SCD, and fluid/water intake before and after sexual activity may be beneficial.

Fertility preservation for pediatric patients with hemoglobinopathies: Multidisciplinary counseling needed to optimize outcomes

Hemoglobinopathies are autosomal recessive disorders that occur when genetic mutations negatively impact the function of hemoglobin. Common hemoglobinopathies that are clinically significant include sickle cell disease, alpha thalassemia, and beta thalassemia. Advancements in disease-modifying and curative treatments for the common hemoglobinopathies over the past thirty years have led to improvements in patient quality of life and longevity for those who are affected. However, the diseases, their treatments and cures pose infertility risks, making fertility preservation counseling and treatment an important part of the contemporary comprehensive patient care. Sickle cell disease negatively impacts both male and female infertility, primarily by testicular failure and decreased ovarian reserve, respectively. Fertility in both males and females with beta thalassemia major are negatively impacted by iron deposition due to chronic blood transfusions. Hematopoietic stem cell transplant (HSCT) is currently the only curative treatment for SCD and transfusion dependent beta thalassemia. Many of the conditioning regimens for HSCT contain chemotherapeutic agents with known gonadotoxicity and whole-body radiation. Although most clinical studies on toxicity and impact of HSCT on long-term health do not evaluate fertility, gonadal failure is common. Male fertility preservation modalities that exist prior to gonadotoxic treatment include sperm banking for pubertal males and testicular cryopreservation for pre-pubertal boys. For female patients, fertility preservation options include oocyte cryopreservation and ovarian tissue cryopreservation. Oocyte cryopreservation requires controlled ovarian hyperstimulation (COH) with ten to fourteen days of intensive monitoring and medication administration. This is feasible once the patient has undergone menarche. Follicular growth is monitored via transvaginal or transabdominal ultrasound, and hormone levels are monitored through frequent blood work. Oocytes are then harvested via a minimally invasive approach under anesthesia. Complications of COH are more common in patients with hemoglobinopathies. Ovarian hyperstimulation syndrome creates a greater risk to patients with underlying vascular, pulmonary, and renal injury, as they may be less able to tolerate fluids shifts. Thus, it is critical to monitor patients undergoing COH closely with close collaboration between the hematology team and the reproductive endocrinology team. Counseling patients and families about future fertility must take into consideration the patient's disease, treatment history, and planned treatment, acknowledging current knowledge gaps.

[Sexuality assessment of homozygous adult sickle cell patients with a history of priapism in Senegal]

OBJECTIVES

The objective of this study was to evaluate the sexuality of SS sickle cell patients with a history of priapism.

METHODS

This was a case-control study of adult SS sickle cell patients. The occurrence of priapism as well as the nature of the priapism had been investigated. The patients were subdivided into three groups: Group 1 (no priapism), Group 2 (intermittent priapism) and Group 3 (acute priapism). The patients' sexuality was studied using the IIEF-15 questionnaire.

RESULTS

We interviewed 191 SS sickle cell patients. The mean age was 27.1±7.1 years. Priapism was observed in 43.5 %. Only 77 patients were eligible for the IIEF15 questionnaire. Groups 1 and 2 performed significantly better than group 3 on erectile function (EF) and orgasmic function (OF) scores. There was no significant difference in the EF and OF scores between groups 1 and 2. No significant difference was observed between the three groups for the scores of sexual desire (SD), intercourse satisfaction (IS), and overall satisfaction (OS). The impairment of erectile function in group 2 was related to the age of the first episode of priapism and the last episode. The impairment of erectile function in group 3 was related to the duration of evolution (P<0.05).

CONCLUSION

This study shows that priapism is responsible for impaired erectile function in SS adult sickle cell patients. A program to prevent intermittent episodes of priapism should be put in place.

Fertility after Curative Therapy for Sickle Cell Disease: A Comprehensive Review to Guide Care

Curative therapy for sickle cell disease (SCD) currently requires gonadotoxic conditioning that can impair future fertility. Fertility outcomes after curative therapy are likely affected by pre-transplant ovarian reserve or semen analysis parameters that may already be abnormal from SCD-related damage or hydroxyurea treatment. Outcomes are also likely affected by the conditioning regimen. Conditioning with myeloablative busulfan and cyclophosphamide causes serious gonadotoxicity particularly among post-pubertal females. Reduced-intensity and non-myeloablative conditioning may be acutely less gonadotoxic, but more short and long-term fertility outcome data after these approaches is needed. Fertility preservation including oocyte/embryo, ovarian tissue, sperm, and experimental testicular tissue cryopreservation should be offered to patients with SCD pursing curative therapy. Regardless of HSCT outcome, longitudinal post-HSCT fertility care is required.

Psychometric Impact of Priapism on Lives of Adolescents and Adults With Sickle Cell Anemia: A Sequential Independent Mixed-Methods Design

Despite priapism being one of the most frequent complications of sickle cell anemia (SCA) in male individuals, little has been reported about the impact of priapism in this population. The authors used a sequential independent mixed-methods design, which used both international multicenter focus group discussions (n=35) and a quantitative patient-reported outcome measure (n=131) to determine the impact of priapism on men with SCA in Nigeria and the United States. The authors analyzed data from focus groups using an iterative inductive-deductive approach. Comparison of the Priapism Impact Profile data was done using the Kruskal-Wallis H test. Our result showed that priapism, across cultures, is associated with shame and embarrassment. These emotions interfere with timely clinical and family communication about priapism symptoms and complications. Participants were dissatisfied with the quality of care at emergency facilities. The quality of life and physical wellness of men with SCA-related priapism were significantly different for the 3 groups: (1) priapism condition getting better, (2) priapism condition getting worse, and (3) priapism condition remain the same (P=0.002 and P=0.019, respectively). Psychological, sexual, and physical wellbeing are all adversely affected by priapism. Evidence-based methods are necessary for adequate medical, educational, and psychological treatment for recurrent priapism.

PRIMARY STROKE PREVENTION IN CHILDREN WITH SICKLE CELL ANEMIA LIVING IN AFRICA: THE FALSE CHOICE BETWEEN PATIENT-ORIENTED RESEARCH AND HUMANITARIAN SERVICE-PART II

In the United States, primary stroke prevention in children with sickle cell anemia (SCA) is the standard of care and includes annual transcranial Doppler ultrasound to detect elevated velocities. For children with velocities ≥200 cm/sec, initial monthly blood transfusion therapy for at least a year, followed by the option of hydroxyurea therapy, results in a significant decline in the stroke rate. In Africa, no prior strategy exists for primary stroke prevention because regular blood transfusion therapy is not feasible. We completed a randomized controlled trial for primary stroke prevention using initial low- and moderate-dose hydroxyurea as an alternative to blood transfusion therapy. The trial results demonstrated equal primary stroke prevention efficacy with both doses. After the trial, we provided a state-supported stroke screening service and treatment for over 20,000 children in Kano, Nigeria. We will review the strategies implemented to conduct clinical research and provide humanitarian assistance to children with SCA in Nigeria.

Economic evaluation of regular transfusions for cerebral infarct recurrence in the Silent Cerebral Infarct Transfusion Trial

Children with preexisting silent cerebral infarcts on regular transfusion therapy had 50% lower hospitalization costs than standard care.

The incremental cost-effectiveness ratio for transfusion therapy to prevent infarct recurrence was $22 025 for every infarct prevented.

In 2020, the American Society of Hematology published evidence-based guidelines for cerebrovascular disease in individuals with sickle cell anemia (SCA). Although the guidelines were based on National Institutes of Health–sponsored randomized controlled trials, no cost-effectiveness analysis was completed for children with SCA and silent cerebral infarcts. We conducted a cost-effectiveness analysis comparing regular blood transfusion vs standard care using SIT (Silent Cerebral Infarct Transfusion) Trial participants. This analysis included a modified societal perspective with direct costs (hospitalization, emergency department visit, transfusion, outpatient care, and iron chelation) and indirect costs (special education). Direct medical costs were estimated from hospitalizations from SIT hospitals and unlinked aggregated hospital and outpatient costs from SIT sites by using the Pediatric Health Information System. Indirect costs were estimated from published literature. Effectiveness was prevention of infarct recurrence. An incremental cost-effectiveness ratio using a 3-year time horizon (mean SIT Trial participant follow-up) compared transfusion vs standard care. A total of 196 participants received transfusions (n = 90) or standard care (n = 106), with a mean age of 10.0 years. Annual hospitalization costs were reduced by 54% for transfusions vs standard care ($4929 vs $10 802), but transfusion group outpatient costs added $22 454 to $137 022 per year. Special education cost savings were $2634 over 3 years for every infarct prevented. Transfusion therapy had an incremental cost-effectiveness ratio of $22 025 per infarct prevented. Children with preexisting silent cerebral infarcts receiving blood transfusions had lower hospitalization costs but higher outpatient costs, primarily associated with the oral iron chelator deferasirox. Regular blood transfusion therapy is cost-effective for infarct recurrence in children with SCA. This trial is registered at www.clinicaltrials.gov as #NCT00072761.

Recurrent Neural Networks to Automatically Identify Rare Disease Epidemiologic Studies from PubMed

Rare diseases affect between 25 and 30 million people in the United States, and understanding their epidemiology is critical to focusing research efforts. However, little is known about the prevalence of many rare diseases. Given a lack of automated tools, current methods to identify and collect epidemiological data are managed through manual curation. To accelerate this process systematically, we developed a novel predictive model to programmatically identify epidemiologic studies on rare diseases from PubMed. A long short-term memory recurrent neural network was developed to predict whether a PubMed abstract represents an epidemiologic study. Our model performed well on our validation set (precision = 0.846, recall = 0.937, AUC = 0.967), and obtained satisfying results on the test set. This model thus shows promise to accelerate the pace of epidemiologic data curation in rare diseases and could be extended for use in other types of studies and in other disease domains.