BAND 3CEINGE (Gly796Arg) Mutation Causes Dehydrated Hereditary Stomatocytosis (DHS) with Dyserythropoietic Phenotype

Stomatocytosis is an inherited autosomal dominant hemolytic anemia and includes overhydrated hereditary stomatocytosis (OHS), dehydrated hereditary stomatocytosis (DHS), hereditary cryohydrocytosis (CHC) and familial pseudohyperkalemia (FP).
Here, we report a novel variant of hereditary stomatocytosis  due to a de-novo band 3 mutation due to G>A transition at nucleotide 2500 in exon 17 (p. G796R, band3^CEINGE) associated with dyserythropoietic phenotype. This 43-years-old Caucasian female (II-2) with unrelated parents was admitted to our hospital for mild anemia evaluation. The patient was in good health until 7 years when she frequently experienced asthenia. Anemia was first recognized at the age of eighth years with presence of jaundice and hyperchromic urine, but she had never received blood transfusions.
We observed a mild hypochromic macrocytic anemia with a hemoglobin level of  11.5 g/dL, a mean cell volume (MCV) of  110 fL, and a mean hemoglobin concentration (MCH) of 36.1 pg, the reticulocyte count was 64 x 10³/µL. There was a typical hemolytic features:  high levels of indirect bilirubin (3.48 mg/dL) and lactate dehydrogenase ( 567 U/l, v.n. 240- 480 U/l ) with negativity at direct and indirect Coomb’s test .
Spleen was enlarged and ultrasonography detected 15 cm of longitudinal size. She was cholecystectomized at the age of 14 years because of numerous symptomatic small stones. Serum iron, soluble transferrin receptor, serum ferritin and transferrin saturation levels were all increased, while the transferrin was in the normal range.
Other blood tests including osmotic fragility with incubated and fresh erythrocytes, serum electrolytes, B12 and folate levels, erythrocyte enzyme levels, EMA test and Pink test were normal.
Peripheral blood smear showed anisopoikilocytosis with rare stomatocytes and no spherocytes. Bone marrow aspirate showed remarkable dyserythropoiesis with increased number of erythroblasts and binucleate erythroblasts, basophilic erythroblasts with alterations, irregular nuclei maturation, intererythroblastic bridges and erythroblasts with basophilic stippling.  She received  since the age of 14 yrs a diagnosis for congenital dyserythropoietic anemia type I.
Patients red cells showed (i) increase Na⁺ content and decrease K⁺ content; (ii) reduced Na-K pump activity and (iii) increased Na-H exchange, NKCC cotransport and KCC cotransport activities. We then functionally characterized band 3 CEINGE in Xenopus oocytes, showing that the mutated band 3 is converted from anion exchanger (Cl^-, HCO₃^-) function to unregulated cation pathway for Na⁺ and K⁺. The mutated band 3 was also associated with increased tyrosine phosphorylation pattern of some red cell membrane proteins.
During erythropoiesis band 3 protein is the last cytoskeletal protein to appear, thus the dyserythropoietic phenotype may be related to a possible role of the mutated band 3 in perturbation of cytoskeleton assembly in the late stage of erythropoiesis, allowing us to conclude for a new variant of stomatocytosis with dyserythropoietic phenotype.