Primary Acquired Red Cell Hypoplasia Associated With a Clonal Chromosomal Abnormality and Disturbed Erythroid Proliferation

A 43-yr-old male patient with primary acquired red cell hypoplasia was studied over a course of 5 yr. Repeated bone marrow examinations showed marrow replacement by an abnormal cell clone characterized by deletion of most of the long arm of a B group chromosome (Bq-). Chromosomes of blood lymphocytes and skin fibroblasts were normal. ⁵⁵Fe labeling of bone marrow metaphases demonstrated the abnormal chromosome in developing erythroid cells, and it was considered to be present in the common erythroid-myeloid precursor stem cell and its derivatives. Studies of bone marrow cell proliferation using ³H-thymidine autoradiography combined with DNA cytochemistry demonstrated a specific breakdown of erythroid differentiation at the stage of the early polychromatic normoblast. It is suggested that red cell hypoplasia was a function of the abnormal clone that replaced normal erythropoietic stem cells of the bone marrow, but proved to be defective in the metabolism required for red cell production. Such replacement of normal bone marrow tissue, presumably associated with the somatically acquired cytogenetic change, is regarded as a neoplastic though nonmalignant development. The patient died from complications of influenzal pneumonia without evidence of tumor or leukemia.