Peripheral marginalisation of endoplasmic reticulum membranes in cultured erythroblasts of congenital dyserythropoietic anaemia type II

Congenital dyserythropoietic anaemia type II (CDAII, MIM 224100) is an autosomal recessive disorder of the bone marrow resulting in ineffective erythropoiesis. A characteristic diagnostic ultrastructural feature is a peripherally located ‘double membrane’ in late-stage erythroblasts. Both a patient study1 and a culture of erythroblasts of CDAII using plasma clot technique2 reported dyserythropoiesis at the early and late stages of erythroid maturation. Using electron microscopy of cultured erythroblast from two patients with molecularly confirmed CDAII enabled us to follow the increasing peripheral location of the strands of endoplasmic reticulum (ER) between days 9 and 14. Our electron micrographs have shown the development of double membrane in CDAII in cultured erythroblasts and its origin from the ER. Two consenting patients with CDA II (F1P1-age 11 years and F4P1-age 17 years) from two unrelated families were recruited from the large Vaish/Agrawal community in North India for this study. The diagnosis of CDA II was based on their clinical picture and laboratory tests results (figure 1). Both patients were confirmed to have biallelic mutations in SEC23B (both were homozygous for the Y462C mutation).3 Peripheral blood (10 mL) anticoagulated in EDTA was collected from both patients with CDAII and one gender matched normal blood donor. Their CD34+ cells were isolated from the peripheral blood mononuclear cells by positive selection using the mini MACS kit (Miltenyi, Surrey, UK) within 12–16 h of collection. The number of CD34+ at the start of each culture was 6×105 cells (F1P1), 7.6×105 cells (F4P1) and 1×105 cells (normal control). Cells were seeded at 1×105/mL in static …