Molecular heterogeneity of pyruvate kinase deficiency

Relative Bioavailability Studies With Mitapivat: Formulation and Food Effect Assessments in Healthy Subjects

Pyruvate kinase (PK) deficiency is a rare, hereditary, hemolytic anemia caused by mutations in the PKLR gene encoding the PK enzyme. Mitapivat (previously designated AG-348) is a first-in-class, oral, allosteric activator of PK. We report results from 5 Phase 1 trials in healthy adults to characterize and compare mitapivat pharmacokinetics across different formulations and analyze food effects on mitapivat bioavailability (Studies 1-5). Pharmacokinetic assessments were peak exposure, total exposure, time to maximum plasma concentration of mitapivat, and relative bioavailability (where appropriate). Plasma total exposure of mitapivat was similar in the fasted and fed (high-fat meal or different soft foods) states after capsule, tablet, and pediatric granule formulations. Although mitapivat administration with food reduced the rate of mitapivat absorption (delay in time to maximum plasma concentration; reduction in maximum concentration) versus dosing under fasted conditions, this was not considered clinically relevant, given the lack of effect on total mitapivat exposure. Consequently, the administration instructions for mitapivat relating to food state that "patients may take mitapivat tablets with or without food." These findings will continue to inform clinical studies and development of mitapivat in adult and pediatric patients with hemolytic anemias and may help inform healthcare professionals on mitapivat dosing/administration recommendations in clinical practice.

Mortality among US veterans with a physician-documented diagnosis of pyruvate kinase deficiency

Real-world studies of pyruvate kinase (PK) deficiency and estimates of mortality are lacking. This retrospective observational study aimed to identify patients with PK deficiency and compare their overall survival (OS) to that of a matched cohort without PK deficiency. Patients with ≥1 diagnosis code related to PK deficiency were selected from the US Veterans Health Administration (VHA) database (01/1995-07/2019); patients with a physician-documented diagnosis were included (PK deficiency cohort; index: date of first diagnosis code related to PK deficiency). Patients in the PK deficiency cohort were matched 1:5 to patients from the general VHA population (non-PK deficiency cohort; index: random visit date during match's index year). OS from index was compared between the two cohorts. Eighteen patients in the PK deficiency cohort were matched to 90 individuals in the non-PK deficiency cohort (both cohorts: mean age 57 years, 94% males; median follow-up 6.0 and 8.0 years, respectively). At follow-up, patients in the non-PK deficiency cohort had significantly longer OS than the PK deficiency cohort (median OS: 17.1 vs. 10.9 years; hazard ratio: 2.3; p = 0.0306). During their first-year post-index, 75% and 40% of the PK deficiency cohort had laboratory-confirmed anemia and iron overload, respectively. Among patients who died, cause of death was highly heterogeneous. These results highlight the increased risk of mortality and substantial clinical burden among patients with PK deficiency. While the intrinsic characteristics of the VHA database may limit the generalizability of the results, this is the first real-world study to characterize mortality in patients with PK deficiency.

Comorbidities and complications in adult and paediatric patients with pyruvate kinase deficiency: Analysis from the Peak Registry

Pyruvate kinase (PK) deficiency, a rare, congenital haemolytic anaemia caused by mutations in the PKLR gene, is associated with many clinical manifestations, but the full disease burden has yet to be characterised. The Peak Registry (NCT03481738) is an observational, longitudinal registry of adult and paediatric patients with PK deficiency. Here, we described comorbidities and complications in these patients by age at most recent visit and PKLR genotype. As of 13 May 2022, 241 patients were included in the analysis. In total, 48.3% had undergone splenectomy and 50.5% had received chelation therapy. History of iron overload (before enrolment/during follow-up) was common (52.5%), even in never-transfused patients (20.7%). Neonatal complications and symptoms included jaundice, splenomegaly and hepatomegaly, with treatment interventions required in 41.5%. Among adults, osteopenia/osteoporosis occurred in 19.0% and pulmonary hypertension in 6.7%, with median onset ages of 37, 33 and 22 years, respectively. Biliary events and bone health problems were common across PKLR genotypes. Among 11 patients who had thromboembolic events, eight had undergone prior splenectomy. Patients with PK deficiency may have many complications, which can occur early in and throughout life. Awareness of their high disease burden may help clinicians better provide appropriate monitoring and management of these patients.

Biallelic hexokinase 1 (HK1) variants causative of non-spherocytic haemolytic anaemia: A case series with emphasis on the HK1 promoter variant and literature review

The hexokinase (HK) enzyme plays a key role in red blood cell energy production. Hereditary non-spherocytic haemolytic anaemia (HNSHA) caused by HK deficiency is a rare disorder with only 12 different disease-associated variants identified. Here, we describe the clinical features and genotypes of four previously unreported patients with hexokinase 1 (HK1)-related HNSHA, yielding two novel truncating HK1 variants. The patients' phenotypes varied from mild chronic haemolytic anaemia to severe infantile-onset transfusion-dependent anaemia. Three of the patients had mild haemolytic disease caused by the common HK1 promoter c.-193A>G variant combined with an intragenic HK1 variant, emphasizing the importance of including this promoter variant in the haemolytic disease gene panels. HK activity was normal in a severely affected patient with a homozygous HK1 c.2599C>T, p.(His867Tyr) variant, but the affinity for ATP was reduced, hampering the HK function. In cases of HNSHA, kinetic studies should be considered in the functional studies of HK. We reviewed the literature of previously published patients to provide better insight into this rare disease and add to the understanding of genotype-phenotype correlation.

Pyruvate kinase deficiency and PKLR gene mutations: Insights from molecular dynamics simulation analysis

Pyruvate kinase deficiency is a rare hereditary erythrocyte enzyme disease caused by mutations in the pyruvate kinase liver and red blood cell gene. The clinical presentations of pyruvate kinase deficiency are significantly heterogeneous, ranging from just mild anemia to hemolytic crisis or even death. The proband in our study was a 2-year-old girl for severe skin and scleral icterus with progressive aggravation. We collected the family's data for further analysis. Whole exome genome sequencing of the pedigree revealed a novel compound heterozygous mutation, c.1097del (p.P366Lfs*12) and c.1493G > A (p.R498H), in the pyruvate kinase liver and red blood cell gene. Furthermore, molecular dynamics simulations were employed to uncover differences between the wild type and mutant pyruvate kinase liver and red blood cell proteins, focusing on structural stability, protein flexibility, secondary structure, and overall conformation. The combined bioinformatic tools were also utilised to assess the effects of the missense mutation on protein function. Thereafter, wild type and mutant plasmids were constructed and transfected into 293T cells, and Western blot assay was conducted to validate the impact of the mutations on the expression of pyruvate kinase liver and red blood cell protein. The data presented in our study enriches the genotype database and provides evidence for genetic counseling and molecular diagnosis of pyruvate kinase deficiency.

Diagnosis and management of pyruvate kinase deficiency: international expert guidelines

Pyruvate kinase (PK) deficiency is the most common cause of chronic congenital non-spherocytic haemolytic anaemia worldwide, with an estimated prevalence of one in 100 000 to one in 300 000 people. PK deficiency results in chronic haemolytic anaemia, with wide ranging and serious consequences affecting health, quality of life, and mortality. The goal of the International Guidelines for the Diagnosis and Management of Pyruvate Kinase Deficiency was to develop evidence-based guidelines for the clinical care of patients with PK deficiency. These clinical guidelines were developed by use of GRADE methodology and the AGREE II framework. Experts were invited after consideration of area of expertise, scholarly contributions in PK deficiency, and country of practice for global representation. The expert panel included 29 expert physicians (including adult and paediatric haematologists and other subspecialists), geneticists, laboratory specialists, nurses, a guidelines methodologist, patients with PK deficiency, and caregivers from ten countries. Five key topic areas were identified, the panel prioritised key questions, and a systematic literature search was done to generate evidence summaries that were used in the development of draft recommendations. The expert panel then met in person to finalise and vote on recommendations according to a structured consensus procedure. Agreement of greater than or equal to 67% among the expert panel was required for inclusion of a recommendation in the final guideline. The expert panel agreed on 31 total recommendations across five key topics: diagnosis and genetics, monitoring and management of chronic complications, standard management of anaemia, targeted and advanced therapies, and special populations. These new guidelines should facilitate best practices and evidence-based PK deficiency care into clinical practice.

Activation of pyruvate kinase as therapeutic option for rare hemolytic anemias: Shedding new light on an old enzyme

Novel developments in therapies for various hereditary hemolytic anemias reflect the pivotal role of pyruvate kinase (PK), a key enzyme of glycolysis, in red blood cell (RBC) health. Without PK catalyzing one of the final steps of the Embden-Meyerhof pathway, there is no net yield of adenosine triphosphate (ATP) during glycolysis, the sole source of energy production required for proper RBC function and survival. In hereditary hemolytic anemias, RBC health is compromised and therefore lifespan is shortened. Although our knowledge on glycolysis in general and PK function in particular is solid, recent advances in genetic, molecular, biochemical, and metabolic aspects of hereditary anemias have improved our understanding of these diseases. These advances provide a rationale for targeting PK as therapeutic option in hereditary hemolytic anemias other than PK deficiency. This review summarizes the knowledge, rationale, (pre)clinical trials, and future advances of PK activators for this important group of rare diseases.

Mitapivat: A Quinolone Sulfonamide to Manage Hemolytic Anemia in Adults With Pyruvate Kinase Deficiency

BACKGROUND

Pyruvate kinase (PK) deficiency is a rare enzyme-linked glycolytic defect resulting in mild-to-severe chronic persistent erythrocyte hemolysis. The disease is an autosomal recessive trait caused by mutations in the PK liver and red blood cell gene characterized by insufficient erythrocyte PK activity. PK deficiency is most diagnosed in persons of northern European descent and managed with packed red blood cell transfusions, chelation, and splenectomy with cholecystectomy. Mitapivat is the first approved therapy indicated for hemolytic anemia in adults with PK deficiency with the potential for delaying splenectomy in mild-moderate disease.

MECHANISM OF ACTION, PHARMACODYNAMICS, AND PHARMACOKINETICS

Mitapivat is a PK activator that acts by allosterically binding to the PK tetramer and increases PK activity. The red blood cell form of PK is mutated in PK deficiency, which leads to reduced adenosine triphosphate, shortened red blood cell lifespan, and chronic hemolysis. The half-life of elimination is 3-5 hours, with 73% bioavailability, 98% plasma protein binding, and a median duration of response of 7 months.

CLINICAL TRIALS

Mitapivat has been investigated through various clinical trials for different therapeutic indications. Pivotal trials that serve the primary focus throughout this article are ACTIVATE, ACTIVATE-T, and RISE. ACTIVATE is a phase 3, randomized, double-blind, placebo-controlled study that evaluated the efficacy and safety of mitapivat in adult patients who were not receiving regular blood transfusions. Contrarily, ACTIVATE-T explored the safety and efficacy of mitapivat in adults with PK deficiency who received regular blood transfusions. Both trials demonstrated favorable use of mitapivat in PK deficiency. Focusing on another indication, the ongoing RISE trial investigates the optimal dosage of mitapivat in sickle cell disease.

THERAPEUTIC ADVANCE

Mitapivat is an appropriate treatment for adults with PK deficiency requiring transfusions and may be considered for patients with symptomatic anemia who do not require transfusions and/or PK deficiency with compensated hemolysis without overt anemia.

Association of PKLR gene copy number, expression levels and enzyme activity with 2,3,7,8-TCDD exposure in individuals exposed to Agent Orange/Dioxin in Vietnam

2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) is the most toxic congener of dioxin and has serious long-term effects on the environment and human health. Pyruvate Kinase L/R (PKLR) gene expression levels and gene variants are associated with pyruvate kinase enzyme deficiency, which has been identified as the cause of several diseases linked to dioxin exposure. In this study, we estimated PKLR gene copy number and gene expression levels using real-time quantitative PCR (RT-qPCR) assays, genotyped PKLR SNP rs3020781 by Sanger sequencing, and quantified plasma pyruvate kinase enzyme activity in 100 individuals exposed to Agent Orange/Dioxin near Bien Hoa and Da Nang airfields in Vietnam and 100 healthy controls. The means of PKLR copy numbers and PKLR gene expression levels were significantly higher, while pyruvate kinase enzyme activity was significantly decreased in Agent Orange/Dioxin-exposed individuals compared to healthy controls (P < 0.0001). Positive correlations of PKLR gene copy number and gene expression with 2,3,7,8-TCDD concentrations were observed (r = 0.2, P = 0.045 and r = 0.54, P < 0.0001, respectively). In contrast, pyruvate kinase enzyme activity was inversely correlated with 2,3,7,8-TCDD concentrations (r = -0.52, P < 0.0001). PKLR gene copy number and gene expression levels were also inversely correlated with pyruvate kinase enzyme activity. Additionally, PKLR SNP rs3020781 was found to be associated with 2,3,7,8-TCDD concentrations and PKLR gene expression. In conclusion, PKLR copy number, gene expression levels, and pyruvate kinase enzyme activity are associated with 2,3,7,8-TCDD exposure in individuals living in Agent Orange/Dioxin-contaminated areas.

PYK-SubstitutionOME: an integrated database containing allosteric coupling, ligand affinity and mutational, structural, pathological, bioinformatic and computational information about pyruvate kinase isozymes

Interpreting changes in patient genomes, understanding how viruses evolve and engineering novel protein function all depend on accurately predicting the functional outcomes that arise from amino acid substitutions. To that end, the development of first-generation prediction algorithms was guided by historic experimental datasets. However, these datasets were heavily biased toward substitutions at positions that have not changed much throughout evolution (i.e. conserved). Although newer datasets include substitutions at positions that span a range of evolutionary conservation scores, these data are largely derived from assays that agglomerate multiple aspects of function. To facilitate predictions from the foundational chemical properties of proteins, large substitution databases with biochemical characterizations of function are needed. We report here a database derived from mutational, biochemical, bioinformatic, structural, pathological and computational studies of a highly studied protein family-pyruvate kinase (PYK). A centerpiece of this database is the biochemical characterization-including quantitative evaluation of allosteric regulation-of the changes that accompany substitutions at positions that sample the full conservation range observed in the PYK family. We have used these data to facilitate critical advances in the foundational studies of allosteric regulation and protein evolution and as rigorous benchmarks for testing protein predictions. We trust that the collected dataset will be useful for the broader scientific community in the further development of prediction algorithms. Database URL https://github.com/djparente/PYK-DB.

Specific correction of pyruvate kinase deficiency-causing point mutations by CRISPR/Cas9 and single-stranded oligodeoxynucleotides

Pyruvate kinase deficiency (PKD) is an autosomal recessive disorder caused by mutations in the PKLR gene. PKD-erythroid cells suffer from an energy imbalance caused by a reduction of erythroid pyruvate kinase (RPK) enzyme activity. PKD is associated with reticulocytosis, splenomegaly and iron overload, and may be life-threatening in severely affected patients. More than 300 disease-causing mutations have been identified as causing PKD. Most mutations are missense mutations, commonly present as compound heterozygous. Therefore, specific correction of these point mutations might be a promising therapy for the treatment of PKD patients. We have explored the potential of precise gene editing for the correction of different PKD-causing mutations, using a combination of single-stranded oligodeoxynucleotides (ssODN) with the CRISPR/Cas9 system. We have designed guide RNAs (gRNAs) and single-strand donor templates to target four different PKD-causing mutations in immortalized patient-derived lymphoblastic cell lines, and we have detected the precise correction in three of these mutations. The frequency of the precise gene editing is variable, while the presence of additional insertions/deletions (InDels) has also been detected. Significantly, we have identified high mutation-specificity for two of the PKD-causing mutations. Our results demonstrate the feasibility of a highly personalized gene-editing therapy to treat point mutations in cells derived from PKD patients.

Evaluation of the main regulators of systemic iron homeostasis in pyruvate kinase deficiency

Iron homeostasis and dyserythropoiesis are poorly investigated in pyruvate kinase deficiency (PKD), the most common glycolytic defect of erythrocytes. Herein, we studied the main regulators of iron balance and erythropoiesis, as soluble transferrin receptor (sTfR), hepcidin, erythroferrone (ERFE), and erythropoietin (EPO), in a cohort of 41 PKD patients, compared with 42 affected by congenital dyserythropoietic anemia type II (CDAII) and 50 with hereditary spherocytosis (HS). PKD patients showed intermediate values of hepcidin and ERFE between CDAII and HS, and clear negative correlations between log-transformed hepcidin and log-EPO (Person's r correlation coefficient =  - 0.34), log-hepcidin and log-ERFE (r =  - 0.47), and log-hepcidin and sTfR (r =  - 0.44). sTfR was significantly higher in PKD; EPO levels were similar in PKD and CDAII, both higher than in HS. Finally, genotype-phenotype correlation in PKD showed that more severe patients, carrying non-missense/non-missense genotypes, had lower hepcidin and increased ERFE, EPO, and sTFR compared with the others (missense/missense and missense/non-missense), suggesting a higher rate of ineffective erythropoiesis. We herein investigated the main regulators of systemic iron homeostasis in the largest cohort of PKD patients described so far, opening new perspectives on the molecular basis and therapeutic approaches of this disease.

FLI1 accelerates leukemogenesis through transcriptional regulation of pyruvate kinase-L/R and other glycolytic genes

In cancer cells, multiple oncogenes and tumor suppressors control glycolysis to sustain rapid proliferation. The ETS-related transcription factor Fli1 plays a critical role in the induction and progression of leukemia, yet, the underlying mechanism of this oncogenic event is still not fully understood. In this study, RNAseq analysis of FLI1-depleted human leukemic cells revealed transcriptional suppression of the PKLR gene and activation of multiple glycolytic genes, such as PKM1/2. Pharmacological inhibition of glycolysis by PKM2 inhibitor, Shikonin, significantly suppressed leukemic cell proliferation. FLI1 directly binds to the PKLR promoter, leading to the suppression of this inhibitor of glycolysis. In accordance, shRNA-mediated depletion of PKLR in leukemic HEL cells expressing high levels of FLI1 accelerated leukemia proliferation, pointing for the first time to its tumor suppressor function. PKLR knockdown also led to downregulation of the erythroid markers EPOR, HBA1, and HBA2 and suppression of erythroid differentiation. Interestingly, silencing of PKLR in HEL cells significantly increased FLI1 expression, which was associated with faster proliferation in culture. In FLI1-expressing leukemic cells, lower PKLR expression was associated with higher expression of PKM1 and PKM2, which promote aerobic glycolysis. Finally, injection of pyruvate, a known inhibitor of glycolysis, into leukemia mice significantly suppressed leukemogenesis. These results demonstrate that FLI1 promotes leukemia in part by inducing glycolysis, implicates PKLR in erythroid differentiation, and suggests that targeting glycolysis may be an attractive therapeutic strategy for cancers driven by FLI1 overexpression.

Case report: Compound heterozygosity in PKLR gene with a large exon deletion and a novel rare p.Gly536Asp variant as a cause of severe pyruvate kinase deficiency

Red cell pyruvate kinase (PK) deficiency is the most common cause of hereditary nonspherocytic hemolytic anemia and the most frequent enzyme abnormality of the glycolytic pathway. To the best of our knowledge, this is the first Korean PK deficiency study that analyzes copy number variation (CNV) using next-generation sequencing (NGS). A 7-year-old girl with jaundice was admitted for evaluation of a persistent hemolytic anemia. The proband appeared chronically ill, showing a yellowish skin color, icteric sclera, hepatomegaly, and splenomegaly on physical examination. Sequence variants and CNV generated from NGS data were estimated to determine if there was a potential genetic cause. As a result, compound heterozygosity in the PKLR gene for a large exon deletion between exon 3 and exon 9 accompanied with a novel rare p.Gly536Asp variant located on exon 10 was identified as a cause of severe PK deficiency in the proband. The PK activity of the proband had been measured at the time of day 1, 21, and 28 after receiving transfusion to indirectly assume the effect of the transfused blood, and the results were 100.9%, 73.0%, and 48.5%, compared with average of normal controls, respectively. Our report emphasizes the need to perform complete CNV analysis of NGS data and gene dosage assays such as multiplex ligation-dependent probe amplification to evaluate large deletions or duplications/insertions of the PKLR gene in patients with suspected PK deficiency.

The use of pharmacological chaperones in rare diseases caused by reduced protein stability

Rare diseases are most often caused by inherited genetic disorders that, after translation, will result in a protein with altered function. Decreased protein stability is the most frequent mechanism associated with a congenital pathogenic missense mutation and it implies the destabilization of the folded conformation in favour of unfolded or misfolded states. In the cellular context and when experimental data is available, a mutant protein with altered thermodynamic stability often also results in impaired homeostasis, with the deleterious accumulation of protein aggregates, metabolites and/or metabolic by-products. In the last decades, a significant effort has enabled the characterization of rare diseases associated to protein stability defects and triggered the development of innovative therapeutic intervention lines, say, the use of pharmacological chaperones to correct the intracellular impaired homeostasis. Here, we review the current knowledge on rare diseases caused by reduced protein stability, paying special attention to the thermodynamic aspects of the protein destabilization, also focusing on some examples where pharmacological chaperones are being tested.

Genetic Diagnosis of Pyruvate Kinase Deficiency in Undiagnosed Iranian Patients with Severe Hemolytic Anemia, using Whole Exome Sequencing

BACKGROUND

After ruling out the most common causes of severe hemolytic anemia by routine diagnostic tests, certain patients remain without a diagnosis. The aim of this study was to elucidate the genetic cause of the disease in these patients using next generation sequencing (NGS).

METHODS

Four unrelated Iranian families including six blood transfusion dependent cases and their parents were referred to us from a specialist center in Tehran. There was no previous history of anemia in the families and the parents had no abnormal hematological presentations. All probands presented severe congenital hemolytic anemia, neonatal jaundice and splenomegaly. Common causes of hemolytic anemia were ruled out prior to this investigation in these patients and they had no diagnosis. Whole exome sequencing (WES) was performed in the probands and the results were confirmed by Sanger sequencing and subsequent family studies.

RESULTS

We identified five variants in the PKLR gene, including a novel unpublished frameshift in these families. These variants were predicted as pathogenic according to the ACMG guidelines by Intervar and/or Varsome prediction tools. Subsequent family studies by Sanger sequencing supported the diagnosis of pyruvate kinase deficiency (PKD) in six affected individuals and the carrier status of disease in their parents.

CONCLUSION

These findings show that PKD is among the rare blood disorders that could remain undiagnosed or even ruled out in Iranian population without performing NGS. This could be due to pitfalls in clinical, hematological or biochemical approaches in diagnosing PKD. Furthermore, genotyping PKD patients in Iran could reveal novel mutations in the PKLR gene.

Genetic variants of PKLR are associated with acute pain in sickle cell disease

Acute pain, the most prominent complication of sickle cell disease (SCD), results from vaso-occlusion triggered by sickling of deoxygenated red blood cells (RBCs). Concentration of 2,3-diphosphoglycerate (2,3-DPG) in RBCs promotes deoxygenation by preferentially binding to the low-affinity T conformation of HbS. 2,3-DPG is an intermediate substrate in the glycolytic pathway in which pyruvate kinase (gene PKLR, protein PKR) is a rate-limiting enzyme; variants in PKLR may affect PKR activity, 2,3-DPG levels in RBCs, RBC sickling, and acute pain episodes (APEs). We performed a candidate gene association study using 2 cohorts: 242 adult SCD-HbSS patients and 977 children with SCD-HbSS or SCD-HbSβ0 thalassemia. Seven of 47 PKLR variants evaluated in the adult cohort were associated with hospitalization: intron 4, rs2071053; intron 2, rs8177970, rs116244351, rs114455416, rs12741350, rs3020781, and rs8177964. All 7 variants showed consistent effect directions in both cohorts and remained significant in weighted Fisher's meta-analyses of the adult and pediatric cohorts using P < .0071 as threshold to correct for multiple testing. Allele-specific expression analyses in an independent cohort of 52 SCD adults showed that the intronic variants are likely to influence APE by affecting expression of PKLR, although the causal variant and mechanism are not defined.

Novel Compound Heterozygous PKLR Mutation Induced Pyruvate Kinase Deficiency With Persistent Pulmonary Hypertension in a Neonate: A Case Report

Background

Pulmonary hypertension could be associated with pyruvate kinase deficiency (PKD). There are few reported cases of PPHN as the first clinical manifestation of PKD. Herein we report a rare case of PKD in which the patient exhibited persistent pulmonary hypertension in the neonate (PPHN), and genetic testing helped to rapidly identify an potential association.

Case presentation

The patient was a newborn boy who suffered from severe dyspnea, extreme anemia, skin pallor, and hypoxemia. Repeated echocardiography indicated persistent severe pulmonary hypertension with a calculated pulmonary artery pressure of 75 mmHg, and right ventricular hypertrophy. The administration of nitric oxide significantly reduced the pulmonary artery pressure. Whole-exome sequencing revealed a compound heterozygous mutation consisting of c.707T > G and c.826_827insAGGAGCATGGGG. PolyPhen_2 and MutationTaster indicated that both the c.707T > G (probability 0.999) and c.826_827insAGGAGCATGGGG (probability 0.998) mutations were disease causing. PROVEAN protein batch analysis indicated that the associated p.L236R region was deleterious (score −4.71) and damaging (SIFT prediction 0.00), and this was also the case for p.G275_V276insEEHG (deleterious score −12.00, SIFT prediction 0.00). Substantial structural changes in the transport domain of the protein were predicted using SWISS-MODEL, and indicated that both mutations led to an unstable protein structure. Thus, a novel compound heterozygous mutation of PKLR-induced PKD with PPHN was diagnosed.

Conclusion

The current study suggests that molecular genetic screening is useful for identifying PPHN, particularly in children with metabolic disorders. In patients exhibiting unexplained hyperbilirubinemia combined with severe pulmonary hypertension, PKD might be a potential possible alternative explanation. Genetic screening is helpful for identifying genetic causes of pulmonary hypertension, especially in patients with PPHN. This report expands the mutation spectrum of the PKLR gene, and contributes to the genotype-phenotype map of PKD.

Concomitant Hereditary Spherocytosis and Pyruvate Kinase Deficiency in a Spanish Family with Chronic Hemolytic Anemia: Contribution of Laser Ektacytometry to Clinical Diagnosis

Background: Hereditary spherocytosis (HS) and pyruvate kinase deficiency (PKD) are the most common causes of hereditary chronic hemolytic anemia. Here, we describe clinical and genetic characteristics of a Spanish family with concomitant β-spectrin (SPTB) c.647G>A variant and pyruvate kinase (PKLR) c.1706G>A variant. Methods: A family of 11 members was studied. Hematological investigation, hemolysis tests, and specific red cell studies were performed in all family members, according to conventional procedures. An ektacytometric study was performed using the osmoscan module of the Lorca ektacytometer (MaxSis. RR Mechatronics). The presence of the SPTB and PKLR variants was confirmed by t-NGS. Results: The t-NGS genetic characterization of the 11 family members showed the presence of a heterozygous mutation for the β-spectrin (SPTB; c.647G>A) in seven members with HS, three of them co-inherited the PKLR variant c.1706G>A. In the remaining four members, no gene mutation was found. Ektacytometry allowed a clear diagnostic orientation of HS, independently from the PKLR variant. Conclusions: This family study allows concluding that the SPTB mutation, (c.647G>A) previously described as likely pathogenic (LP), should be classified as pathogenic (P), according to the recommendations for pathogenicity of the American College of Medical Genetics and the Association for Molecular Pathology. In addition, after 6 years of clinical follow-up of the patients with HS, it can be inferred that the chronic hemolytic anemia may be attributable to the SPTB mutation only, without influence of the concomitant PKLR. Moreover, only the family members with the SPTB mutation exhibited an ektacytometric profile characteristic of HS.

A novel homozygous missense variant p.D339N in the PKLR gene correlates with pyruvate kinase deficiency in a Pakistani family: a case report

Background

Pyruvate kinase deficiency is an exceptionally rare autosomal recessive Mendelian disorder caused by bi-allelic pathogenic variants in the PKLR gene. It is mainly characterized by chronic nonspherocytic hemolytic anemia though other symptoms such as splenomegaly, hepatomegaly, pallor, fatigue, iron overload, shortness of breath, hyperbilirubinemia, and gallstones might also prevail.

Case presentation

We present here a novel genetic defect in the PKLR gene that correlates with pyruvate kinase deficiency phenotype in a consanguineous family from North-Western Pakistan. The family included three affected individuals who were all born to consanguineous parents. The proband, a 13-year-old female of Pashtun ethnicity, showed chronic nonautoimmune hemolytic anemia since birth, extremely low hemoglobin (7.6 g/dL) and pyruvate kinase (12.4 U/g Hb) levels, splenomegaly, and hepatomegaly. Bone marrow aspirate showed a markedly decreased myeloid to erythroid ratio and hypercellular marrow particles due to hyperplasia of the erythroid elements. Molecular characterization of the proband’s genomic DNA uncovered a likely pathogenic homozygous missense variant p.[D339N] in exon 7 of the PKLR gene. In-depth in silico analysis and familial cosegregation implies p.[D339N] as the likely cause of pyruvate kinase deficiency in this family. Further in vitro or in vivo studies are required to validate the impact of p.[D339N] on protein structure and/or stability, and to determine its role in the disease pathophysiology.

Conclusions

In summary, these findings suggest a novel genetic defect in the PKLR gene as a likely cause of pyruvate kinase deficiency, thus further expanding the mutational landscape of this rare Mendelian disorder.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13256-022-03292-z.

Novel PKLR missense mutation (A300P) causing pyruvate kinase deficiency in an Omani Kindred-PK deficiency masquerading as congenital dyserythropoietic anemia

We report herein a child with transfusion-dependent chronic anemia, the cause of which was difficult to establish because of his transfusion dependency. The clinical and laboratory features suggested a chronic nonspherocytic hemolytic anemia (CNSHA) with bone marrow features suggestive of congenital dyserythropoietic anemia (CDA). DNA studies, however, revealed the underlying condition to be due to a novel mutation in the PKLR gene responsible for pyruvate kinase deficiency (PKD). Molecular investigations by a targeted next-generation sequencing (t-NGS) using a custom panel of 71 genes involved in the red blood cell (RBC) disorders revealed that the patient was homozygous for a novel missense mutation c.898G>C, p.Ala300Pro, whereas both his parents were heterozygous for the same mutation.

Mitapivat, a novel pyruvate kinase activator, for the treatment of hereditary hemolytic anemias

Mitapivat (AG-348) is a novel, first-in-class oral small molecule allosteric activator of the pyruvate kinase enzyme. Mitapivat has been shown to significantly upregulate both wild-type and numerous mutant forms of erythrocyte pyruvate kinase (PKR), increasing adenosine triphosphate (ATP) production and reducing levels of 2,3-diphosphoglycerate. Given this mechanism, mitapivat has been evaluated in clinical trials in a wide range of hereditary hemolytic anemias, including pyruvate kinase deficiency (PKD), sickle cell disease, and the thalassemias. The clinical development of mitapivat in adults with PKD is nearly complete, with the completion of two successful phase III clinical trials demonstrating its safety and efficacy. Given these findings, mitapivat has the potential to be the first approved therapeutic for PKD. Mitapivat has additionally been evaluated in a phase II trial of patients with alpha- and beta-thalassemia and a phase I trial of patients with sickle cell disease, with findings suggesting safety and efficacy in these more common hereditary anemias. Following these successful early-phase trials, two phase III trials of mitapivat in thalassemia and a phase II/III trial of mitapivat in sickle cell disease are beginning worldwide. Promising preclinical studies have additionally been done evaluating mitapivat in hereditary spherocytosis, suggesting potential efficacy in erythrocyte membranopathies as well. With convenient oral dosing and a safety profile comparable with placebo in adults with PKD, mitapivat is a promising new therapeutic for several hereditary hemolytic anemias, including those without any currently US Food and Drug Administration (FDA) or European Medicines Agency (EMA)-approved drug therapies. This review discusses the preclinical studies, pharmacology, and clinical trials of mitapivat.

Screening tools for hereditary hemolytic anemia: new concepts and strategies

INTRODUCTION

Hereditary hemolytic anemias are a group of rare and heterogeneous disorders due to abnormalities in structure, metabolism, and transport functions of erythrocytes; they may overlap in clinical and hematological features making differential diagnosis difficult, particularly in mild and atypical forms.

AREAS COVERED

In the present review, the main tools currently adopted in routine hematologic investigation for the diagnosis of hereditary hemolytic anemias are described, together with the new diagnostic approaches that are being to be developed in the next future. Available recommendations in this field together with a systematic review through MEDLINE, EMBASE, and PubMED for publications in English from 2000 to 2020 in regards to diagnostic aspects of hereditary hemolytic anemias have been considered.

EXPERT OPINION

The recent development of specific molecules and treatments for hereditary hemolytic anemias and the increased interest in translational research raised the attention on differential diagnosis and the demand for novel diagnostic assays and devices. Automatic blood cell analyzers, omic-approaches including NGS technologies, and development of new automated tools based on artificial neural networks definitely represent the future strategies in this field.

A Proposed Concept for Defective Mitophagy Leading to Late Stage Ineffective Erythropoiesis in Pyruvate Kinase Deficiency

Pyruvate kinase deficiency (PKD) is a rare congenital hemolytic anemia caused by mutations in the PKLR gene. Here, we review pathophysiological aspects of PKD, focusing on the interplay between pyruvate kinase (PK)-activity and reticulocyte maturation in the light of ferroptosis, an iron-dependent process of regulated cell death, and in particular its key player glutathione peroxidase 4 (GPX4). GPX4 plays an important role in mitophagy, the key step of peripheral reticulocyte maturation and GPX4 deficiency in reticulocytes results in a failure to fully mature. Mitophagy depends on lipid oxidation, which is under physiological conditions controlled by GPX4. Lack of GPX4 leads to uncontrolled auto-oxidation, which will disrupt autophagosome maturation and thereby perturb mitophagy. Based on our review, we propose a model for disturbed red cell maturation in PKD. A relative GPX4 deficiency occurs due to glutathione (GSH) depletion, as cytosolic L-glutamine is preferentially used in the form of α-ketoglutarate as fuel for the tricarboxylic acid (TCA) cycle at the expense of GSH production. The relative GPX4 deficiency will perturb mitophagy and, subsequently, results in failure of reticulocyte maturation, which can be defined as late stage ineffective erythropoiesis. Our hypothesis provides a starting point for future research into new therapeutic possibilities, which have the ability to correct the oxidative imbalance due to lack of GPX4.