Globin chain biosynthesis in iron deficiency

Iron deficiency in sickle cell anaemia

Thirty-seven patients with SCD were studied: 24 were diagnosed as homozygous Hb S on the basis of their haematological findings, and alpha:non-alpha globin chain ratios were found to be balanced in all. Thirteen patients were thought to have alpha or beta thalassaemia interaction with Hb S on the basis of low MCV and MCH, family history and/or presence of Hb A on electrophoresis. Six of them had abnormal alpha:non-alpha ratio (one had a ratio of 0.72 suggestive of alpha thalassaemia, and five had ratios between 1.4 and 1.9, compatible with beta thalassaemia interaction). The remaining seven patients with microcytosis had balanced globin chain synthesis and five were found to be iron deficient. Five additional patients (3 with Hb SS and 2 with Hb S/beta thalassaemia) had lower than normal serum ferritin concentration. The analysis of case histories disclosed that peptic ulceration, recurrent epistaxis and multiple pregnancies could account for iron loss in seven patients. These findings indicate that iron deficiency may be common in SCD and should be excluded as a cause of microcytosis. Microcytosis, in the absence of conclusive family studies and/or presence of Hb A on electrophoresis, is an unreliable indicator of alpha or beta thalassaemia interaction with Hb S.

Globin chain synthesis ratios in sideroblastic anaemia

Globin synthesis ratios were measured on reticulocytes from nine patients with primary acquired sideroblastic anaemia (SA), four patients with hereditary or congenital SA, two patients with secondary acquired SA and three patients with iron deficiency (ID). Ten of the samples from patients with SA and all the samples from patients with ID had normal ratios. Samples from three patients had significantly abnormal ratios, one from a patient with SA and acquired Hb H disease (alpha/beta 0 X 26), one from a patient with secondary acquired SA (alpha/beta 0 X 88), and one from a patient who went on to develop acute myeloblastic leukaemia (alpha/beta 1 X 36). Globin synthesis was stimulated by 100 microM haem similarly in normal, SA and ID reticulocytes. Any limitation of globin synthesis in SA and ID is therefore not easily reversible by adding haem. Inhibition of haem synthesis in nonsideroblastic reticulocytes using 4 mM isonicotinic acid hydrazide for 1 h incubation affected neither total globin synthesis nor the alpha/beta ratio. These results contradict the view that decreased haem synthesis decreases globin chain synthesis and decreases the alpha/beta globin chain synthesis ratios in human reticulocytes. Previously reported findings that haem could reverse globin chain synthesis inhibition in SA were good evidence for a primary deficiency of haem synthesis in the erythroblasts of these patients. Our inability to substantiate these findings emphasizes the need for a re-evaluation of the aetiology of sideroblastic anaemia.

Bone marrow and peripheral blood globin chain biosynthesis in iron deficiency

Globin chain synthesis was studied in 13 iron-deficient patients. The mean whole-cell globin alpha/beta ratio in the peripheral blood of 11 patients was 1.05 +/- 0.06 which is similar to the value 0.99 +/- 0.08 obtained for 10 controls. The ratios obtained for stroma-free globin were not significantly different from those of whole cell preparations. In contrast, the alpha/beta ratio of bone marrow was 0.73 +/- 0.14 in 10 iron deficient patients, which is significantly lower than that of controls. Two other patients had decreased alpha/beta ratios in the peripheral blood, probably because of the presence of an alpha-thalassemia gene. These results demonstrate a reduced rate of synthesis of alpha chains relative to that of beta chains in the bone marrow of iron-deficient patients that is not demonstrable in the peripheral blood.