Erythrocyte Disorders Mimicking Congenital Dyserythropoietic Anemia Based on Bone Marrow Pathology Exposed By Genetic Evaluation

Congenital dyserythropoietic anemias (CDAs) are a rare group of heterogeneous genetic diseases characterized by hemolysis, ineffective erythropoiesis predisposing to iron overload, and the pathologic finding of bi- and multinucleated erythroblasts in the bone marrow (BM). With the identification of causative genetic mutations over the last two decades, the current classification includes the following types with the causative gene in parenthesis: Ia (CDAN1), Ib (CDIN1); II (SEC23B); IIIa (KIF23), IIIb (RACGAP1); IV (KLF1); and XLTD (GATA1). Clinical presentation can vary widely even within the same type, ranging from mild cases of anemia to severe cases in which patients are subject to lifelong transfusion dependency.

The CDA registry (CDAR) in North America (NCT02964494) was established to allow natural history studies on patients with CDA. Participants without a genetic diagnosis are offered whole genome sequencing (WGS) for patients and parents and may elect to provide samples to the CDAR biorepository to support collaborative mechanistic studies.

Currently 169 subjects from 73 different families are enrolled in CDAR (85 patients, 84 unaffected family members). After genetic evaluation, 13 patients were found to be affected not by CDA, but rather by other causes of hereditary hemolytic anemia with secondary dyserythropoiesis.

Three patients were diagnosed with pyruvate kinase deficiency (PKD). Patient (pt) 1 had a history of chronic anemia requiring sporadic transfusions since birth and was diagnosed with CDA-II based on BM studies. WGS revealed that the patient was heterozygous for a known PKLR pathogenic variant c.1022G>C p.(Gly341Ala) and for a novel variant of uncertain significance (c.695-3C>G). PK activity assay confirmed the diagnosis of PKD and the patient is now treated with the PK activator mitapivat. Pt 2 had severe transfusion dependent anemia since birth and iron overload. The patient underwent splenectomy at the age of 4 with mild improvement of symptoms. He was diagnosed with CDA II based on BM pathology. Genetic testing was performed and he was found to be compound heterozygous for 2 pathogenic variants in PKLR: c.644dup p.(Arg216fs) and c.994_1003dup p.(Val335fs). Pt 3 had a history of anemia and jaundice since birth; she has not had frequent transfusions but was splenectomized at age 17. The patient was found to be homozygous for c.1436G>A p.(Arg510Gln), a known pathogenic variant in PKLR.

Four patients were diagnosed with HBB pathogenic variants causing frameshift and transcription of an elongated β-globin chain, i.e. unstable hemoglobinopathy. Pt 4 was first diagnosed with CDA II at 12 years of age based on BM studies performed due to chronic hemolytic anemia. After enrolling in CDAR, WES revealed heterozygous HBB p.(Lys96Asnfs*63). Pts 5, 6, and 7 are all symptomatic participants from the same family (mother and children). The mother (Pt 5) had frequent transfusion requirement, misdiagnosed in childhood as CDA IV due to BM dyserythropoiesis and the finding of high fetal hemoglobin. Her children had a similar phenotype requiring episodic transfusions initially, transitioning to scheduled transfusions by 8 y.o. WES in pt 5 revealed heterozygous HBB c.348_349delinsG (Hb Grand Junction) with follow-up HBB sequencing confirming that the children also carry the same variant.

Three more patients were diagnosed with SPTA1 variants causing RBC membrane disorders. Pt 8 was found to have homozygous c.4339-99C>T (alpha-LEPRA) and heterozygous c.4347G>T p.(Lys1449Asn) with a phenotype of hereditary spherocytosis. Pts 9 and 10 are sisters, who presented with chronic, transfusion-dependent anemia since birth. They were diagnosed with CDA-II based on binucleated erythroblasts in BM studies performed in early childhood. They had splenectomy at 5 years of age and became transfusion-independent but continued to have mild anemia and reticulocytosis. WGS performed for them and their parents revealed a novel homozygous intronic variant in SPTA1 c.5834-18A>G. Phenotypic analysis was compatible with hereditary spherocytic pyropoikilocytosis.

Hemolytic anemias with stress erythropoiesis may mimic the clinical presentation and pathologic findings of CDAs, making the phenotypic diagnosis challenging. Including genetic evaluation in the diagnostic workup of these patients can improve accuracy, timing of diagnosis, and management by specific therapy, if available.