Mitapivat versus Placebo for Pyruvate Kinase Deficiency.

BACKGROUND: Pyruvate kinase deficiency is a rare, hereditary, chronic condition that is associated with hemolytic anemia. In a phase 2 study, mitapivat, an oral, first-in-class activator of erythrocyte pyruvate kinase, increased the hemoglobin level in patients with pyruvate kinase deficiency. METHODS: In this global, phase 3, randomized, placebo-controlled trial, we evaluated the efficacy and safety of mitapivat in adults with pyruvate kinase deficiency who were not receiving regular red-cell transfusions. The patients were assigned to receive either mitapivat (5 mg twice daily, with potential escalation to 20 or 50 mg twice daily) or placebo for 24 weeks. The primary end point was a hemoglobin response (an increase from baseline of ≥1.5 g per deciliter in the hemoglobin level) that was sustained at two or more scheduled assessments at weeks 16, 20, and 24. Secondary efficacy end points were the average change from baseline in the hemoglobin level, markers of hemolysis and hematopoiesis, and the change from baseline at week 24 in two pyruvate kinase deficiency-specific patient-reported outcome measures. RESULTS: Sixteen of the 40 patients (40%) in the mitapivat group had a hemoglobin response, as compared with none of the 40 patients in the placebo group (adjusted difference, 39.3 percentage points; 95% confidence interval, 24.1 to 54.6; two-sided P<0.001). Patients who received mitapivat had a greater response than those who received placebo with respect to each secondary end point, including the average change from baseline in the hemoglobin level. The most common adverse events were nausea (in 7 patients [18%] in the mitapivat group and 9 patients [23%] in the placebo group) and headache (in 6 patients [15%] and 13 patients [33%], respectively). Adverse events of grade 3 or higher occurred in 10 patients (25%) who received mitapivat and 5 patients (13%) who received placebo. CONCLUSIONS: In patients with pyruvate kinase deficiency, mitapivat significantly increased the hemoglobin level, decreased hemolysis, and improved patient-reported outcomes. No new safety signals were identified in the patients who received mitapivat. (Funded by Agios Pharmaceuticals; ACTIVATE ClinicalTrials.gov number, NCT03548220.).

Quality of life in childhood immune thrombocytopenia: Revision of the Kids' ITP Tools (KIT).

The Kids ITP Tools (KIT) is a health-related quality of life (HRQoL) questionnaire that evaluates quality of life in children with immune thrombocytopenia (ITP). There are three formats: Child Self-Report, Parent Proxy-Report and Parent Impact-Report. This study aimed to develop a domain structure by grouping-related questions from the questionnaire into domains that independently reflect various aspects of HRQoL. The study was conducted in two phases. Phase 1 involved an online survey distributed to experts to identify conceptual domains for the KIT. Phase 2 utilized a statistical approach to analyse responses from patients with ITP and their families. A revised KIT 2.0 was ultimately developed to aid in treatment decision-making and monitoring of ITP.

An update on pediatric ITP: differentiating primary ITP, IPD, and PID.

Immune thrombocytopenia (ITP) is the most common acquired thrombocytopenia in children and is caused by immune-mediated decreased platelet production and increased platelet destruction. In the absence of a diagnostic test, ITP must be differentiated from other thrombocytopenic disorders, including inherited platelet disorders. In addition, a diagnosis of secondary ITP due to a primary immune deficiency with immune dysregulation may not be apparent at diagnosis but can alter management and should be considered in an expanding number of clinical scenarios. The diagnostic evaluation of children with thrombocytopenia will vary based on the clinical history and laboratory features. Access to genotyping has broadened the ability to specify the etiology of thrombocytopenia, whereas increasing access to immunophenotyping, functional immunologic and platelet assays, and biochemical markers has allowed for more in-depth evaluation of patients. With this greater availability of testing, diagnostic algorithms in patients with thrombocytopenia have become complex. In this article, we highlight the diagnostic evaluation of thrombocytopenia in children with a focus on ITP, including consideration of underlying genetic and immune disorders, and use hypothetical patient cases to describe disease manifestations and strategies for treatment of pediatric ITP.

Clinically meaningful improvements in patient-reported outcomes in mitapivat-treated patients with pyruvate kinase deficiency.

Clinically meaningful benefits in the signs, symptoms, and impacts of #PKDeficiency as assessed by disease-specific patient-reported outcome measures were observed in mitapivat-treated adult patients in two phase 3 clinical trials.

HLA antibodies in fetal and neonatal alloimmune thrombocytopenia.

BACKGROUND: Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is caused by antibodies against human platelet antigens (HPA). However, in many cases that meet clinical criteria for the condition, maternal sera do not have HPA antibodies. In studies examining whether human leukocyte antigen (HLA) antibodies cause FNAIT, the results are limited and inconclusive. This study sought to examine whether clinically suspected FNAIT cases with absent maternal HPA antibodies had different HLA antibody strength and specificity compared to controls. STUDY DESIGN AND METHODS: A retrospective case-control study assessed class I HLA antibody strength and specificity in cases submitted for testing to Versiti, Wisconsin. There were 813 cases that met initial screening criteria, but written consent could only be obtained for 50. After review of medical records and expert panel review, 31 cases with clinical criteria of FNAIT and maternal HLA but not HPA antibodies were included. Each case was matched for maternal age, gestational age at delivery, parity, and race/ethnicity to two controls from unaffected pregnancies that had maternal serum HLA antibodies. RESULTS: FNAIT cases were found to have both significantly higher HLA antibody strength, measured by mean fluorescence index (MFI), and broader HLA antibody specificity at antigen epitope level, compared to matched controls (p < .001). p-values remained significant after controlling for parity and gestational age at delivery. DISCUSSION: Additional studies are needed to further examine whether the strong HLA antibodies identified in HPA-antibody-negative cases directly cause neonatal thrombocytopenia and whether prenatal treatment may be warranted in select cases to prevent recurrence.

Utilization of an ITP quality improvement pathway improves adherence to management guidelines.

Despite availability of epidemiologic studies and national guidelines for the management of newly diagnosed pediatric immune thrombocytopenia (ITP), practice variation exists among and within hematology practices. We previously described the development of an ITP pathway guiding management based on bleeding symptoms. Over an 8-year period, integration of this iterative ITP pathway into management of newly diagnosed ITP increased observation rates in children with no or mild bleeding symptoms and improved consistency of laboratory evaluation and treatment strategies without increasing adverse outcomes. This quality improvement initiative has been sustainable, acceptable to providers, and increased adherence to guidelines.

Pediatric refractory immune thrombocytopenia: A systematic review.

Pediatric immune thrombocytopenia (ITP) is an acquired disorder associated with autoimmune destruction and impairment of platelet production in children. Some children exhibit poor or transient response to ITP-directed treatments and are referred to as having refractory ITP (rITP). There is currently no consensus on the definition of rITP, nor evidence-based treatment guidelines for patients with rITP. After a survey of pediatric ITP experts demonstrated lack of consensus on pediatric rITP, we pursued a systematic review to examine the reported clinical phenotypes and treatment outcomes in pediatric rITP. The search identified 253 relevant manuscripts; following review, 11 studies proposed a definition for pediatric rITP with no consensus amongst them. Most definitions included suboptimal response to medical management, while some outlined specific platelet thresholds to define this suboptimal response. Common attributes identified in this study should be used to propose a comprehensive definition, which will facilitate outcome comparisons of future rITP studies.

Safety and Efficacy of Mitapivat in Pyruvate Kinase Deficiency.

BACKGROUND: Pyruvate kinase deficiency is caused by mutations in PKLR and leads to congenital hemolytic anemia. Mitapivat is an oral, small-molecule allosteric activator of pyruvate kinase in red cells. METHODS: In this uncontrolled, phase 2 study, we evaluated the safety and efficacy of mitapivat in 52 adults with pyruvate kinase deficiency who were not receiving red-cell transfusions. The patients were randomly assigned to receive either 50 mg or 300 mg of mitapivat twice daily for a 24-week core period; eligible patients could continue treatment in an ongoing extension phase. RESULTS: Common adverse events, including headache and insomnia, occurred at the time of drug initiation and were transient; 92% of the episodes of headache and 47% of the episodes of insomnia resolved within 7 days. The most common serious adverse events, hemolytic anemia and pharyngitis, each occurred in 2 patients (4%). A total of 26 patients (50%) had an increase of more than 1.0 g per deciliter in the hemoglobin level. Among these patients, the mean maximum increase was 3.4 g per deciliter (range, 1.1 to 5.8), and the median time until the first increase of more than 1.0 g per deciliter was 10 days (range, 7 to 187); 20 patients (77%) had an increase of more than 1.0 g per deciliter in the hemoglobin level at more than 50% of visits during the core study period, with improvement in markers of hemolysis. The response was sustained in all 19 patients remaining in the extension phase, with a median follow-up of 29 months (range, 22 to 35). Hemoglobin responses were observed only in patients who had at least one missense PKLR mutation and were associated with the red-cell pyruvate kinase protein level at baseline. CONCLUSIONS: The administration of mitapivat was associated with a rapid increase in the hemoglobin level in 50% of adults with pyruvate kinase deficiency, with a sustained response during a median follow-up of 29 months during the extension phase. Adverse effects were mainly low-grade and transient. (Funded by Agios Pharmaceuticals; ClinicalTrials.gov number, NCT02476916.).

Management of pyruvate kinase deficiency in children and adults.

Pyruvate kinase deficiency (PKD) is an autosomal-recessive enzyme defect of the glycolytic pathway that causes congenital nonspherocytic hemolytic anemia. The diagnosis and management of patients with PKD can be challenging due to difficulties in the diagnostic evaluation and the heterogeneity of clinical manifestations, ranging from fetal hydrops and symptomatic anemia requiring lifelong transfusions to fully compensated hemolysis. Current treatment approaches are supportive and include transfusions, splenectomy, and chelation. Complications, including iron overload, bilirubin gallstones, extramedullary hematopoiesis, pulmonary hypertension, and thrombosis, are related to the chronic hemolytic anemia and its current management and can occur at any age. Disease-modifying therapies in clinical development may decrease symptoms and findings associated with chronic hemolysis and avoid the complications associated with current treatment approaches. As these disease-directed therapies are approved for clinical use, clinicians will need to define the types of symptoms and findings that determine the optimal patients and timing for initiating these therapies. In this article, we highlight disease manifestations, monitoring approaches, strategies for managing complications, and novel therapies in development.

Diagnosis, monitoring, and management of pyruvate kinase deficiency in children.

Pyruvate kinase (PK) deficiency is a rare, congenital red blood cell disorder caused by a single gene defect. The spectrum of genotypes, variants, and phenotypes are broad, commonly requiring a multimodal approach including enzyme and genetic testing for accurate and reliable diagnosis. Similarly, management of primary and secondary sequelae of PK deficiency varies, mainly including supportive care with transfusions and surgical interventions to improve symptoms and quality of life. Given the risk of acute and long-term complications of PK deficiency and its treatment, regular monitoring and management of iron burden and organ dysfunction is critical. Therefore, all children and adolescents with PK deficiency should receive regular hematology care with visits at least every 6 months regardless of transfusion status. We continue to learn more about the spectrum of symptoms and complications of PK deficiency and best practice for monitoring and management through registry efforts (NCT03481738). The treatment of PK deficiency has made strides over the last few years with newer disease-modifying therapies being developed and studied, with the potential to change the course of disease in childhood and beyond.

Thrombopoietin receptor agonists and rituximab for treatment of pediatric immune thrombocytopenia: A systematic review and meta-analysis of prospective clinical trials.

BACKGROUND: Children with immune thrombocytopenia (ITP) may require second-line ITP therapies. The high remission rate in pediatric patients, need for extended-duration use of thrombopoietin receptor agonists (TPO-RAs), drug adherence, potential side effects, monitoring, and cost effectiveness are factors that should be considered in decision-making about second-line therapies. Rituximab (RTX) has been used off-label for years to treat ITP but there are limited studies about its efficacy and safety in children. To date, no studies have directly compared TPO-RAs with RTX for the treatment of childhood ITP. METHODS: This systematic review analyzed the overall platelet response, durability of treatment effect, and safety for RTX use in comparison to TPO-RAs in pediatric ITP. MEDLINE/PubMed, EMBASE, Cochrane Library, and Web of Science databases were searched through December 2020 and meta-analysis was conducted using proportions of success/failure for each intervention in the selected studies. RESULTS: The proportion of participants achieving the primary endpoint of a platelet response above 50,000 was similar for TPO-RAs (proportion = 0.71, 95% CI: 0.63-0.78) and RTX (proportion = 0.68, 95% CI: 0.53-0.82). However, considerable variation was found between the two groups with regards to the sustainability of the response and other secondary outcomes such as need for rescue and adverse events. RTX was associated with higher rates of rescue therapy. CONCLUSIONS: In this analysis of prospective pediatric ITP studies, RTX and TPO-RAs had similar rates of overall platelet response but differed in other important measures. Prospective comparative studies are needed to better characterize second-line treatments for pediatric ITP.

Characteristics and outcomes of autoimmune hemolytic anemia after pediatric allogeneic stem cell transplant.

BACKGROUND: Autoimmune hemolytic anemia (AIHA) after allogeneic hematopoietic stem cell transplant (HSCT) is a rare but complex and serious complication. Detailed descriptions of cases and management strategies are needed due to lack of prospective trials. OBJECTIVES: Describe the incidence, clinical characteristics, and management of AIHA after HSCT in a pediatric cohort. METHODS: This is a retrospective cohort study of 33 pediatric patients with AIHA after HSCT at an academic tertiary care center from 2003 to 2019. RESULTS: The overall incidence of AIHA after allogeneic HSCT was 3.8% (33/868). AIHA was significantly more common after transplant for nonmalignant versus malignant diagnoses (7.0% [26/370] vs. 1.4% [7/498], p < .0001). AIHA developed at a median of 4.7 months (range 1.0-29.7) after transplant. Sixteen of 33 patients (48.5%) required new AIHA-directed pharmacologic therapy; 17 (51.5%) were managed on their current immunosuppression and supportive care. Patients managed without additional therapy were significantly older, more likely to have a malignant diagnosis, and tended to develop AIHA at an earlier time point after transplant. Patients received a median of two red blood cell transfusions within the first 2 weeks of diagnosis and a median of one AIHA-directed medication (range one to four), most commonly corticosteroids and rituximab. CONCLUSIONS: AIHA after HSCT is rare but occurs more commonly in patients transplanted for nonmalignant diagnoses. While some pediatric patients who develop AIHA after transplant can be managed on current immunosuppression and supportive care, many require AIHA-directed therapy including second-line medications.

The pyruvate kinase (PK) to hexokinase enzyme activity ratio and erythrocyte PK protein level in the diagnosis and phenotype of PK deficiency.

Diagnosis of pyruvate kinase deficiency (PKD), the most common cause of hereditary non-spherocytic haemolytic anaemia, remains challenging in routine practice and no biomarkers for clinical severity have been characterised. This prospective study enrolled 41 patients with molecularly confirmed PKD from nine North American centres to evaluate the diagnostic sensitivity of pyruvate kinase (PK) enzyme activity and PK:hexokinase (HK) enzyme activity ratio, and evaluate the erythrocyte PK (PK-R) protein level and erythrocyte metabolites as biomarkers for clinical severity. In this population not transfused for ≥90 days before sampling, the diagnostic sensitivity of the PK enzyme assay was 90% [95% confidence interval (CI) 77-97%], whereas the PK:HK ratio sensitivity was 98% (95% CI 87-100%). There was no correlation between PK enzyme activity and clinical severity. Transfusion requirements correlated with normalised erythrocyte ATP levels (r = 0·527, P = 0·0016) and PK-R protein levels (r = -0·527, P = 0·0028). PK-R protein levels were significantly higher in the never transfused [median (range) 40·1 (9·8-73·9)%] versus ever transfused [median (range) 7·7 (0·4-15·1)%] patients (P = 0·0014). The PK:HK ratio had excellent sensitivity for PK diagnosis, superior to PKLR exon sequencing. Given that the number of PKLR variants and genotype combinations limits prognostication based on molecular findings, PK-R protein level may be a useful prognostic biomarker of disease severity and merits further study.

Refractory autoimmune cytopenias in pediatric Evans syndrome with underlying systemic immune dysregulation.

Evans syndrome is a rare but challenging disorder in children; and despite rapidly growing evidence for targetable systemic immune dysregulation driving these "idiopathic" autoimmune cytopenias, precision diagnosis and management remains sub-optimal among these patients. We analyzed retrospective clinical data for 60 pediatric ES patients followed at 3 large tertiary referral centers in the United States over a recent 6-year period and found that definable underlying systemic immune dysregulation was identified in only 42% of these patients throughout the course of clinical care. Median time from ES diagnosis to identification of the underlying systemic immune dysregulation disorder was 1.3 years (<1 month for rheumatologic disease, 2.3 years for CVID, 3.4 years for ALPS, and 7.4 years for monogenic disorders of immune regulation). Notably, a significantly higher percentage of patients in whom a definitive immune dysregulation disorder was ultimately identified required ≥3 cytopenia-directed therapies (92%) and also second- and third-line immunomodulatory agents (84%), vs those in whom no unifying immune dysregulation was diagnosed (65%, and 35%, respectively)-indicating that autoimmune cytopenias as a manifestation of systemic immune dysregulation are more treatment-refractory and severe. These data underline the importance of identifying the underlying systemic immune dysregulation and providing targeted therapy in pediatric ES.

Comorbidities and complications in adults with pyruvate kinase deficiency.

OBJECTIVES: Pyruvate kinase (PK) deficiency is caused by PKLR gene mutations, leading to defective red blood cell glycolysis and hemolytic anemia. Rates of comorbidities and complications by transfusion history and relative to the general population remain poorly quantified. METHODS: Data for patients aged ≥ 18 years with two confirmed PKLR mutations were obtained from the PK deficiency Natural History Study (NCT02053480). Frequencies of select conditions were compared with an age- and sex-matched cohort from a general insured US population without PK deficiency. RESULTS: Compared with the matched population (n = 1220), patients with PK deficiency (n = 122) had significantly higher lifetime rates of osteoporosis, liver cirrhosis, and pulmonary hypertension; splenectomy and cholecystectomy rates were also significantly higher in the 8 years before the index date. Sixty-five (53.3%) patients with PK deficiency were classified as regularly transfused, 30 (24.6%) as occasionally transfused, and 27 (22.1%) as never transfused. Regularly transfused patients were significantly more likely than never transfused patients to have had splenectomy, cholecystectomy, and/or thrombosis. Liver iron overload was reported in 62% of patients and occurred regardless of transfusion cohort. CONCLUSIONS: Even never transfused patients with PK deficiency had higher rates of select comorbidities and complications than individuals without PK deficiency.

Quality of life is an important indication for second-line treatment in children with immune thrombocytopenia.

BACKGROUND: The decision to initiate second-line treatment in children with immune thrombocytopenia (ITP) is complex and involves many different factors. METHODS: In this prospective, observational, longitudinal cohort study of 120 children from 21 centers, the factors contributing to the decision to start second-line treatments for ITP were captured. At study entry, clinicians were given a curated list of 12 potential reasons the patient required a second-line treatment. Clinicians selected all that applied and ranked the top three reasons. RESULTS: Quality of life (QOL) was the most frequently cited reason for starting a second-line therapy. Clinicians chose it as a reason to treat in 88/120 (73%) patients, as among the top three reasons in 68/120 (57%), and as the top reason in 32/120 (27%). Additional factors ranked as the top reason to start second-line treatment included severity of bleeding (22/120, 18%), frequency of bleeding (19/120, 16%), and severity of thrombocytopenia (18/120, 15%). Patients for whom QOL (p = .006) or sports participation (p = .02) were ranked reasons were more likely to have chronic ITP, whereas those for whom severity (p = .003) or frequency (p = .005) of bleeding were ranked reasons were more likely to have newly diagnosed or persistent ITP. Parental anxiety, though rarely the primary impetus for treatment, was frequently cited (70/120, 58%) as a contributing factor. CONCLUSION: Perceived QOL is the most frequently selected reason pediatric patients start second-line therapies for ITP. It is critical that studies of treatments for childhood ITP include assessments of their effects on QOL.

Pyruvate kinase deficiency in children.

BACKGROUND: Pyruvate kinase deficiency (PKD) is a rare, autosomal recessive red blood cell enzyme disorder, which leads to lifelong hemolytic anemia and associated complications from the disease and its management. METHODS: An international, multicenter registry enrolled 124 individuals younger than 18 years old with molecularly confirmed PKD from 29 centers. Retrospective and prospective clinical data were collected. RESULTS: There was a wide range in the age at diagnosis from 0 to 16 years. Presentation in the newborn period ranged from asymptomatic to neonatal jaundice to fulminant presentations of fetal distress, myocardial depression, and/or liver failure. Children <5 years old were significantly more likely to be transfused than children >12 to <18 years (53% vs. 14%, p = .0006), which correlated with the timing of splenectomy. Regular transfusions were most common in children with two severe PKLR variants. In regularly transfused children, the nadir hemoglobin goal varied considerably. Impact on quality of life was a common reason for treatment with regular blood transfusions and splenectomy. Splenectomy increased the hemoglobin and decreased transfusion burden in most children but was associated with infection or sepsis (12%) and thrombosis (1.3%) even during childhood. Complication rates were high, including iron overload (48%), perinatal complications (31%), and gallstones (20%). CONCLUSIONS: There is a high burden of disease in children with PKD, with wide practice variation in monitoring and treatment. Clinicians must recognize the spectrum of the manifestations of PKD for early diagnostic testing, close monitoring, and management to avoid serious complications in childhood.

Immune dysregulation and multisystem inflammatory syndrome in children (MIS-C) in individuals with haploinsufficiency of SOCS1.

BACKGROUND: We studied 2 unrelated patients with immune thrombocytopenia and autoimmune hemolytic anemia in the setting of acute infections. One patient developed multisystem inflammatory syndrome in children in the setting of a severe acute respiratory syndrome coronavirus 2 infection. OBJECTIVES: We sought to identify the mechanisms underlying the development of infection-driven autoimmune cytopenias. METHODS: Whole-exome sequencing was performed on both patients, and the impact of the identified variants was validated by functional assays using the patients' PBMCs. RESULTS: Each patient was found to have a unique heterozygous truncation variant in suppressor of cytokine signaling 1 (SOCS1). SOCS1 is an essential negative regulator of type I and type II IFN signaling. The patients' PBMCs showed increased levels of signal transducer and activator of transcription 1 phosphorylation and a transcriptional signature characterized by increased expression of type I and type II IFN-stimulated genes and proapoptotic genes. The enhanced IFN signature exhibited by the patients' unstimulated PBMCs parallels the hyperinflammatory state associated with multisystem inflammatory syndrome in children, suggesting the contributions of SOCS1 in regulating the inflammatory response characteristic of multisystem inflammatory syndrome in children. CONCLUSIONS: Heterozygous loss-of-function SOCS1 mutations are associated with enhanced IFN signaling and increased immune cell activation, thereby predisposing to infection-associated autoimmune cytopenias.

Fatigue in children and adolescents with immune thrombocytopenia.

Immune thrombocytopenia (ITP), an acquired autoimmune disorder of low platelets and risk of bleeding, has a substantial impact on health-related quality of life (HRQoL). Patients with ITP often report significant fatigue, although the pathophysiology of this is poorly understood. In this observational cohort of 120 children receiving second-line therapies for ITP, we assessed reports of fatigue using the Hockenberry Fatigue Scale. Children and adolescents with ITP reported a similarly high level of fatigue with 54% (29/54) of children and 62% (26/42) of adolescents reporting moderate-to-severe fatigue. There was no correlation between fatigue and age or gender. Adolescents with newly diagnosed and persistent ITP had higher mean fatigue scores than those with chronic ITP (P = 0·03). Fatigue significantly improved in children and adolescents by 1 month after starting second-line treatments, and this improvement continued to be present at 12 months after starting treatment. Fatigue scores at all time-points correlated with general HRQoL using the Kids ITP Tool, but did not correlate with bleeding symptoms, platelet count, or platelet response to treatment. Fatigue is common in children and adolescents with ITP and may benefit from ITP-directed treatment even in the absence of bleeding symptoms.

Clinical spectrum of pyruvate kinase deficiency: data from the Pyruvate Kinase Deficiency Natural History Study.

An international, multicenter registry was established to collect retrospective and prospective clinical data on patients with pyruvate kinase (PK) deficiency, the most common glycolytic defect causing congenital nonspherocytic hemolytic anemia. Medical history and laboratory and radiologic data were retrospectively collected at enrollment for 254 patients with molecularly confirmed PK deficiency. Perinatal complications were common, including anemia that required transfusions, hyperbilirubinemia, hydrops, and prematurity. Nearly all newborns were treated with phototherapy (93%), and many were treated with exchange transfusions (46%). Children age 5 years and younger were often transfused until splenectomy. Splenectomy (150 [59%] of 254 patients) was associated with a median increase in hemoglobin of 1.6 g/dL and a decreased transfusion burden in 90% of patients. Predictors of a response to splenectomy included higher presplenectomy hemoglobin (P = .007), lower indirect bilirubin (P = .005), and missense PKLR mutations (P = .0017). Postsplenectomy thrombosis was reported in 11% of patients. The most frequent complications included iron overload (48%) and gallstones (45%), but other complications such as aplastic crises, osteopenia/bone fragility, extramedullary hematopoiesis, postsplenectomy sepsis, pulmonary hypertension, and leg ulcers were not uncommon. Overall, 87 (34%) of 254 patients had both a splenectomy and cholecystectomy. In those who had a splenectomy without simultaneous cholecystectomy, 48% later required a cholecystectomy. Although the risk of complications increases with severity of anemia and a genotype-phenotype relationship was observed, complications were common in all patients with PK deficiency. Diagnostic testing for PK deficiency should be considered in patients with apparent congenital hemolytic anemia and close monitoring for iron overload, gallstones, and other complications is needed regardless of baseline hemoglobin. This trial was registered at www.clinicaltrials.gov as #NCT02053480.