Characterization of the Severe Phenotype of Pyruvate Kinase Deficiency
Authors: Al-Samkari Hanny , van Beers Eduard J. , Morton D Holmes , Barcellini Wilma , Eber Stefan W. , Glader Bertil , Yaish Hassan M. , Chonat Satheesh , Kuo Kevin H. M. , Kollmar Nina , Despotovic Jenny M. , Pospisilova Dagmar , Knoll Christine M. , Kwiatkowski Janet L. , Pastore Yves D. , Thompson Alexis A. , Wlodarski Marcin W. , Ravindranath Yaddanapudi , Rothman Jennifer A. , Wang Heng , Holzhauer Suzanne , Breakey Vicky R. , Verhovsek Madeleine M. , Kunz Joachim B. , Sheth Sujit , Sharma Mukta , Rose Melissa J. , Bradeen Heather , McNaull Melissa A. , Addonizio Kathryn , Al-Sayegh Hasan , London Wendy B. , Grace Rachael F. 
Published: February 2020

Background: Pyruvate kinase deficiency (PKD) is the most common cause of chronic hereditary non-spherocytic hemolytic anemia. The spectrum of disease in PKD is broad, ranging from an incidentally discovered mild anemia to a severe transfusion-dependent anemia. Splenectomy partially ameliorates the anemia and reduces the transfusion burden in the majority of patients. Because hemoglobin poorly correlates with symptoms in PKD, transfusion requirements are typically used clinically to classify disease severity with those who are regularly transfused despite splenectomy recognized as the most severely affected subgroup.
Aim: To compare demographics, complications, and laboratory results between the most severely-affected PKD patients (those that are splenectomized and regularly transfused) with non-regularly transfused splenectomized PKD patients.
Methods: After ethics committee approval, patients were enrolled on the PKD Natural History Study, a prospective 30 site international study. All patients had molecularly confirmed PKD. Only splenectomized patients were included in the analysis. Transfusion frequency was observed over a 3-year period. Patients were divided into two groups based on transfusion frequency: the severe phenotype group was defined as those who receive regular transfusions (≥6 discrete red cell transfusion episodes per year) and the control group did not receive regular transfusions. Phenotype stability over the 3-year period was also assessed.
Results: 154 splenectomized patients with PKD were included: 30 patients in the severe PKD phenotype group and 124 patients in the comparison PKD group. Results of the analysis comparing the two groups are described in the Table. Severely affected patients were more likely to be female (77% versus 51%, p=0.013), older at the time of splenectomy (median age: 5 versus 3.6, p=0.011), have iron overload (93% vs. 51%, p&lt;0.0001), have received chelation therapy (90% vs. 42%, p&lt;0.0001), and had more lifetime transfusions (median: 77 versus 15, p&lt;0.0001). Rates of other PKD complications including pulmonary hypertension, extramedullary hematopoiesis, liver cirrhosis, endocrinopathy, and bone fracture appear similar between the two groups. Laboratory values, including hemoglobin, total bilirubin, normalized PK enzyme activity, and median absolute reticulocyte count appear similar between the two groups. The underlying genetic mutation patterns (missense mutations versus non-missense mutations) were also similar between the groups. Phenotype stability over time was highly variable: of the patients with a severe phenotype at enrollment, 62% had a severe phenotype during the first follow-up year and 39% had a severe phenotype at the second follow-up year.
Conclusions: Patients with PKD who are regularly transfused despite splenectomy appeared to have similar rates of PKD-associated complications (except for iron overload) and similar relevant laboratory values and genotypes when compared to those who are not regularly transfused after splenectomy. The similarity observed between severe phenotype patients and comparison patients with PKD may result from a protective effect of transfusion (e.g. reduction of bone fractures and extramedullary hematopoiesis) or could suggest transfusion-dependence is an artificial signifier of disease severity, reflective of provider practices and patient symptoms rather than an actual distinct phenotype. Transfusion requirements in severe PKD appear to fluctuate significantly over time.

Disclosures
Al-Samkari: Dova: Consultancy, Research Funding; Agios: Consultancy, Research Funding; Moderna: Consultancy. van Beers:RR Mechatronics: Research Funding; Agios Pharmaceuticals, Inc.: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Research Funding; Pfizer: Research Funding. Barcellini:Agios: Consultancy, Other: Advisory board; Apellis: Consultancy; Incyte: Consultancy, Other: Advisory board; Bioverativ: Consultancy, Other: Advisory board; Novartis: Research Funding, Speakers Bureau; Alexion: Consultancy, Research Funding, Speakers Bureau. Eber:Agios Pharmaceuticals, Inc.: Consultancy. Glader:Agios Pharmaceuticals, Inc: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Chonat:Alexion: Other: advisory board; Agios Pharmaceuticals, Inc.: Other: advisory board. Kuo:Pfizer: Consultancy; Novartis: Consultancy, Honoraria; Celgene: Consultancy; Agios: Consultancy; Alexion: Consultancy, Honoraria; Apellis: Consultancy; Bioverativ: Other: Data Safety Monitoring Board; Bluebird Bio: Consultancy. Despotovic:Dova: Honoraria; Novartis: Research Funding; Amgen: Research Funding. Kwiatkowski:Celgene: Consultancy; Terumo: Research Funding; Apopharma: Research Funding; bluebird bio, Inc.: Consultancy, Research Funding; Agios: Consultancy; Imara: Consultancy; Novartis: Research Funding. Thompson:Baxalta: Research Funding; Novartis: Consultancy, Research Funding; bluebird bio, Inc.: Consultancy, Research Funding; Celgene: Consultancy, Research Funding. Ravindranath:Agios Pharmaceuticals, Inc.: Other: I am site PI on several Agios-sponsored studies, Research Funding. Rothman:Pfizer: Consultancy, Honoraria, Research Funding; Novartis: Honoraria, Research Funding; Agios: Honoraria, Research Funding. Verhovsek:Sickle Cell Awareness Group of Ontario: Membership on an entity's Board of Directors or advisory committees; Sickle Cell Disease Association of Canada: Membership on an entity's Board of Directors or advisory committees, Research Funding; Canadian Haemoglobinopathy Association: Membership on an entity's Board of Directors or advisory committees; Vertex: Consultancy. Kunz:Novartis: Membership on an entity's Board of Directors or advisory committees. Sheth:CRSPR/Vertex: Other: Clinical Trial Steering committee; Apopharma: Other: Clinical trial DSMB; Celgene: Consultancy. London:United Therapeutics: Consultancy; ArQule, Inc: Consultancy. Grace:Novartis: Research Funding; Agios Pharmaceuticals, Inc: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding.