Congenital dyserythropoietic anemia type III
Description, Causes and Risk Factors:
Abbreviation: CDA III.
Congenital dyserythropoietic anemia type III is a group of very rare disorders characterized by similar bone marrow morphology. The clinical picture is characterized by hemolytic anemia and dramatic bone marrow changes dominated by active erythropoiesis with giant multlnucleate erythroblasts.
The genetic cause of Congenital dyserythropoietic anemia type has not been identified. It likely results from mutations in a gene located on the long arm of chromosome 15 at a position designated 15q21-q25. Researchers continue to search for the specific gene associated with this form of the condition. Preliminary results indicate genetic and phenotypic similarities between an American and a Swedish family, both with an autosomally dominant inherited form of CDA-III. It is possible that the genetic lesion is identical in these families, but the different phenotypes and modes of inheritance reported among some other cases of CDA-III are probably the results of other genetic lesions.
At present, the function of the gene responsible for the Swedish variant of Congenital dyserythropoietic anemia type III (CDAN3) is unknown and it is an important goal to characterize and clone this gene in order to study its function.
Nonfamilial Congenital dyserythropoietic anemia typeIII is the rarest type of the CDAs, with less than 20 well-documented cases. They are probably the results of other genetic lesions. Researchers observed CDA III-like giant erythroblasts in multiple myeloma and there are some doubts whether patients in whom Congenital dyserythropoietic anemia typeIII was detected on examination for malignant lymphoma
truly had congenital anemia.
In several families, CDA III appears to have an autosomal dominant pattern of inheritance. Autosomal dominant inheritance means that one copy of the altered gene in each cell is sufficient to cause the disorder. In these families, affected individuals often have a parent and other relatives with the condition.
The signs and symptoms of Congenital dyserythropoietic anemia type III tend to be milder than those of the other types. Most affected individuals do not have hepatosplenomegaly, and iron does not build up in tissues and organs. In adulthood, abnormalities of a specialized tissue at the back of the eye (the retina) can cause vision impairment. Some people with CDA III also have a blood disorder known as monoclonal gammopathy, which can lead to a cancer of white blood cells (multiple myeloma).
The main laboratory finding is a mild macrocytic anemia, which makes it possible for most patients to reach longevity. Bone marrow examination by light microscopy reveals multinucleated large erythroid precursors and other dyserythropoietic features. The reported ultrastructural studies demonstrate various dysplastic features in the erythroblasts, such as multinuclearity, intranuclear clefts, iron-loaded mitochondria, and intracytoplasmic autophagic vacuoles and myelin figures.
EM studies would be an important tool in diagnosis of Congenital dyserythropoietic anemia typeIII particularly during investigations of anemia of obscure etiology in aged person in which the diagnosis first seem to be improbable. In addition, analysis of ultrastructural findings in new cases of CDA III may be of help for understanding of pathogenesis and for its further classification.
Usually, no special treatment is needed. The patient should be seen by a specialist of Pediatrics or Internal Medicine in suitable intervals, and also by an ophthalmologist since changes endangering the vision may develop. Treatment usually consists of frequent blood transfusions and chelation therapy. Potential cures include bone marrow transplantation and gene therapy.
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