Sideroblastic anemia is a group of hematological disorders mainly characterized by an interference in heme synthesis. It may be due to genetic defects in heme synthesis or acquired impairment of the production of heme, ultimately leading to iron overload and anemia.
Signs and symptoms of sideroblastic anemia result primarily from the reduced hemoglobin production and iron overload. These features vary in severity and include fatigue, palpitations, pallor, dyspnea, and hepatosplenomegaly. Chronic sideroblastic anemia may also lead to acute leukaemia in about 10% of the cases.
Iron overload may also cause long-term organ damage caused by the resulting hemochromatosis.
A complete blood count in sideroblastic anemia often reveals anemia, varying from mild to severe . In sideroblastic anemia, the peripheral blood film reveals dimorphic red blood cells, with a predominantly microcytic picture. However, cases with macrocytic or normocytic pictures have also been noted . Most cases of dimorphism in sideroblastic anemia is a combination of microcytic and normocytic erythrocytes .
Bone marrow analysis by aspiration and biopsy is the gold standard investigation for sideroblastic anemia and it shows the ringed sideroblasts, observed with the Prussian blue stain, as developing red blood cells with accumulation of iron in the mitochondria forming a ring around the nucleus. Erythroid hyperplasia is also revealed in bone marrow analysis. Sideroblasts may also be seen in iron deficiency anemia after replenishing the iron stores. This may mask an underlying sideroblastic anemia . During bone marrow analysis, the megakaryocytes and myelocytes should also be analyzed in detail to exclude a potential myelodysplastic syndrome.
In cases of anemia-ataxia syndromes, a magnetic resonance imaging (MRI) of the posterior cranial fossa is required, so as to exclude intracranial causes, such as tumors and other space-occupying lesions around the cerebellum.
Treatment of sideroblastic anemia includes the removal of the causative toxins, and administration of vitamin B1, B6, or B12. Reports have revealed that acquired and hereditary forms of sideroblastic anemia respond to vitamin B6 (pyridoxine), therefore, it is recommended in all cases of sideroblastic anemia. Vitamin B12 has also been noted to effectively treat sideroblastic anemia .
If the disease is unresponsive to pyridoxine treatment, blood transfusion is opted for. Iron chelators such as deferoxamine should be used if iron overload complicates the transfusion .
Bone marrow transplant is the last option of treatment and it is indicated for patients that are unresponsive to pyridoxine treatment . It is also reserved for cases requiring frequent blood transfusions .
Prognosis is variable, and mainly depends on the particular etiology of sideroblastic anemia. Generally, reversible causes do not have a bad prognosis, as the symptoms are usually mild to moderate . Congenital sideroblastic anemia and some acquired cases are associated with significant morbidity and mortality, as are cases which are associated with myelodysplastic syndromes, cases unabated by medical intervention, and cases requiring frequent blood transfusions.
Mortality from sideroblastic anemia is mainly from hemochromatosis following leukemia or blood transfusions. Leukemia carries a worse prognostic sign, while thrombocytosis constitutes a good prognostic sign . Morbidity in congenital sideroblastic anemia encompasses neuromuscular diseases sequel to mitochondrial protein defects. These neuromuscular diseases may compromise involuntary activities such as respiration, thus, increasing morbidity significantly, and mortality as well.
Sideroblastic anemia could be acquired or inherited.
Hereditary sideroblastic anemia most commonly results from a defective X-linked recessive gene known as ALAS2. This gene is responsible for the formation of an enzyme which plays a vital role in heme synthesis. This gene is located in band 11.21 of the X chromosome. This genetic abnormality usually becomes symptomatic before the age of 30, but may remain undiagnosed till after the fourth decade of life. Other congenital forms of sideroblastic anemia are autosomal or caused by mitochondrial abnormalities. However, up to 40% of hereditary sideroblastic anemia are X-linked .
Acquired sideroblastic anemia occurs secondary to alcohol toxicity, exposure to certain toxins, substance abuse, pyridoxine deficiency, drugs such as isoniazid, cycloserine, pyrazinamide, and chloramphenicol, or as a sequela of myelodysplastic syndromes. Acquired sideroblastic anemia may also constitute a complication of some immune disorders, metabolic disorders, or malignancies.
There are, however, some cases of sideroblastic anemia with unknown causes, which are described as idiopathic.
Congenital sideroblastic anemia usually presents before the age of 30, however, some cases remain undiagnosed till after the fourth decade of life  . Hereditary sideroblastic anemia is more common among men. Acquired sideroblastic anemia occurs more commonly in the senior population with a median age of occurrence at 74 years .
Generally, there is no ethnic predilection concerning the development of sideroblastic anemia.
Sideroblasts are abnormal normoblasts with an excessive mitochondrial accumulation of iron, forming a ringed shape around the nucleus. The basis for the formation of sideroblasts is impaired heme synthesis. Congenital causes of sideroblastic anemia include an X-linked mutation of genes involved in the synthesis of heme, iron-sulfur clusters and mitochondrial proteins . The X-linked gene defect involves the δ- aminolevulinate synthase (ALAS2), the first enzyme in the heme synthesis pathway. The mitochondrial abnormality commonly affects the erythroid mitochondrial transporter SLC25A38.
Such impaired heme production leads to reduced hemoglobin production with the development of abnormally shaped hypochromic microcytic red blood cells. These cells precede the ringed sideroblasts present in the bone marrow, which is pathognomonic of sideroblastic anemia. In some cases of sideroblastic anemia, however, red blood cells could be normocytic or macrocytic. There is usually a presence of dysmorphic red blood cells.
Acquired sideroblastic anemia may be prevented with dietary modifications including the avoidance of zinc-containing supplements and alcohol. Prenatal diagnosis of sideroblastic anemia and genetic counseling have remained crucial for the successful management of congenital sideroblastic anemia. This allows for the early beginning of management of the disease and prevention of complications.
Sideroblastic anemia is a group of hematologic disorders characterized by ineffective erythropoiesis in the presence of adequate iron, leading to the accumulation of iron in the red blood cells and subsequent sideroblasts in the bone marrow . It may be caused by genetic mutations in the genes responsible for the production of enzymes involved in the synthesis of heme or mitochondrial proteins. Other causes may be external factors such as toxic ingestion, interfering with the production of these proteins.
Therefore, the presence of iron for heme synthesis in the absence of the heme synthesis apparatus renders iron unused which, in turn, accumulates in the mitochondria around the nucleus. These sideroblasts are the diagnostic feature of sideroblastic anemia .
Sideroblastic anemia usually presents with features of anemia and iron overload. Iron overload is also evident by findings of high serum ferritin, iron and transferrin saturation. However, the diagnostic investigation for sideroblastic anemia is bone marrow biopsy and aspiration which reveals the diagnostic feature of sideroblasts.
Treatment of sideroblastic anemia depends on the cause. Acquired types are managed by discontinuation of the triggers. All cases of sideroblastic anemia require treatment with B-vitamins, although some cases will require blood transfusion and bone marrow transplant.
Sideroblastic anemia is a group of blood diseases in which the part of the hemoglobin, which carries oxygen in red blood cells, is not properly formed. This condition could either be inherited or caused by external factors such as lead toxicity, alcohol overuse, drugs, and vitamin deficiencies.
It usually results in anemia, a state of reduced oxygen-carrying capacity of the blood. Another key problem with this condition is that iron, which is used to form the abnormal hemoglobin, is present in excessive amounts in the red blood cells, forming what doctors call sideroblasts, immature red blood cells with excess iron in them.
Sideroblastic anemia may be caused by genetic abnormalities in the chemicals needed for the production of the part of the hemoglobin which carries iron. These forms are inherited and can start to manifest in childhood. Other causes are due to external factors mentioned above. In a few cases, however, doctors may not be able to tell the cause.
The inherited form of this diseases occurs more frequently in men than women, and usually causes symptoms before the patient turns 30. The acquired forms occur mostly in the elderly. This disease can, however affect persons of any race.
Anemia and too much iron in the blood are key features of this disease. Anemia presents with dizziness, excessive tiredness, lightheadedness, a rapid heartbeat, fast and difficult breathing, and paleness of the eye, mouth and palms. Overtime, if the condition remains untreated, it could lead to heart disease and liver damage.
Aspiration and biopsy of the bone marrow is the standard test to confirm a diagnosis of sideroblastic anemia. The bone marrow is that part deep inside certain bones of the body, especially the long bones, where blood cells are produced. This part of the bone is reached through a biopsy needle inserted through the skin and some contents of the marrow is drawn for analysis. This analysis will reveal the presence of the sideroblasts which are defined above.
The treatment of this condition depends on the cause. If it is acquired from external factors or triggers, such factors are eliminated. However, treatment with vitamin B6 and B12 is often successful for sideroblastic anemia. In patients who fail to respond to treatment with B vitamins, blood transfusion becomes necessary. Because iron overload can be a problem from blood transfusion, drugs that clear off excess iron would also be considered.
In severe cases and in younger patients, transplanting the bone marrow may successfully treat this condition.
Avoiding alcohol, hard drugs and food items containing zinc may help to prevent sideroblastic anemia. However, in those with the genetic defects, an early diagnosis, usually at pregnancy, is advisable in families with such history. Outcome is usually bad in cases that are inherited, and not so unfavorable in cases due to external factors.