Sideroblastic Anemia: Characteristics, Causes and Therapy

atypical, called sideroblasts, in the medulla and hypochromic erythrocytes in the peripheral blood.

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The clinical forms can be different in etiology and pathogenesis: there are, in fact, acquired and congenital sideroblastic anemias.

Sideroblastic anemia recognizes various causes. In some cases, the alteration of hematopoiesis that is at the basis of this pathology may depend on a deficiency of vitamin B6 or its altered metabolism due to the effect of drugs or toxic substances. Other times, sideroblastic anemia is a consequence of blocks or alterations of the heme biosynthetic pathway.

In addition to the finding of sideroblasts, the common characteristic of these pathologies is the alteration of the normal values ​​of the erythrocyte count (generally present, but not always) refractory to therapy. As for other forms of anemia, this situation is substantially superimposed on a pathological reduction hemoglobin (Hb) below reference levels.

of these abnormal nucleated erythroblasts it is possible to find granules of non-hemoglobin iron in the form of ferritin. In fact, in sideroblastic anemia, hemoglobin (Hb) is unable to incorporate iron into the protoporphyrin inside the red blood cells, therefore the mineral accumulates inside the developing erythroblasts.

The forms of sideroblastic anemia are usually also:

• Hypochromic, i.e. they are associated with a lower hemoglobin concentration than normal values, for age and sex;
• Microcytes, that is, the erythrocytes are smaller than normal.

In summary:

• In sideroblastic anemias, the body has the necessary iron, but is unable to incorporate it into the hemoglobin molecule, therefore:
  • In peripheral blood: hypochromic erythrocytes;
  • In the bone marrow, site of erythropoiesis: sideroblasts, that is atypical erythroblasts that have iron granules in an amorphous state (not hemoglobin, in the form of ferritin) in their cytoplasm due to a defect in the synthesis of heme.
• Sidereblastic anemias can be hereditary or acquired. There are also idiopathic forms, in which it is not possible to identify a certain cause.
• Sideroblastic anemia is often related to microcythemia and / or hypochromia. The reduction in hemoglobin, associated with that of red blood cells in the bloodstream, leads to symptoms that characterize anemia.

contained within the red blood cells, specialized in the transport of oxygen from the lungs to all organs and tissues of the body. The prosthetic heme group represents the heart that binds oxygen inside the molecule and its formation involves a series of steps that end with the insertion of an iron atom inside a molecule called protoporphyrin (PP).

In both acquired and congenital sideroblastic anemia, heme synthesis is impaired due to the inability to incorporate iron into protoporphyrin, leading to the formation of ring sideroblasts (erythroblasts with perinuclear mitochondria with iron deposits).

Acquired Sideroblastic Anemia

Acquired sideroblastic anemia is frequently associated with myelodysplastic syndrome, but can also be secondary to the intake of drugs that interfere with heme metabolism (eg chloramphenicol, cycloserine, isoniazid, linezolide and pyrazinamide) or toxic substances (including ethanol and lead ).

Acquired sideroblastic anemias can also be an expression of:

• Deficiency of pyridoxine (vitamin B6) and copper;
• Neoplastic or other disease (e.g. rheumatoid arthritis).

Acquired sideroblastic anemia is characterized by:

• Reduced production of reticulocytes;
• Intramedullary death of red blood cells;
• Erythroid hyperplasia in the bone marrow.

Hereditary Sideroblastic Anemia

Hereditary sideroblastic anemia (or X-linked sideroblastic anemia) is a congenital form that most commonly results from a point mutation in the gene encoding the ALA-synthase enzyme (ALAS2). This "gene aberration interferes with the synthesis of heme: the enzymatic reaction modulated by" ALAS2 is a limiting step in the entire production process of the prosthetic heme group contained in "hemoglobin. The gene mutation of ALAS2 is transmitted as a trait linked to the chromosome X.

Pyridoxine is an essential cofactor for this enzyme, therefore some patients may respond to pharmacological doses of vitamin B6.

Typically, in hereditary sideroblastic anemia, the red blood cells are microcytic and hypochromic.

Hereditary forms of sideroblastic anemia can be caused by numerous other mutations (X-linked, autosomal and mitochondrial) of the genes involved in heme synthesis.

);

Pallor of the skin and mucous membranes (especially accentuated on the face);

Fragility of nails and hair;

Headache;

Dizziness.

Other signs and symptoms that may develop or become evident as sideroblastic anemia worsens include:

• Feeling cold or numb in the hands or feet
• Shortness of breath;
• Palpitations;
• Chest pain.

or with a high amplitude of red blood cell volume distribution, especially in the presence of a concomitant increase in serum iron levels, serum ferritin and transferrin saturation. Mean corpuscular volume (MCV) can be low, normal or high.