Delta-thalassemia

Delta-thalassemia is a form of thalassemia. It is associated with HBD.^[1]

Pathophysiology

As well as alpha and beta chains being present in hemoglobin about 3% of adult hemoglobin is made of alpha and delta chains. Just as with beta thalassemia, mutations can occur which affect the ability of this gene to produce delta chains.

• A mutation that prevents formation of any delta chains is termed a delta⁰ mutation.
• One that decreases but does not eliminate production of delta chain is termed a delta⁺ mutation.

When one inherits two delta⁰ mutations, no hemoglobin A2 (alpha2,delta2) can be formed. Hematologically, however, this is innocuous because only 2-3% of normal adult hemoglobin is hemoglobin A2. The individual will have normal hematological parameters (erythrocyte count, total hemoglobin, mean corpuscular volume, red cell distribution width). Individuals who inherit only one delta thalassemia mutation gene will have a decreased hemoglobin A2, but also no hematological consequences.

One mutation is at the +69 position.^[2]

Relationship to beta thalassemia

The importance of recognizing the existence of delta thalassemia is seen best in cases where it may mask the diagnosis of beta thalassemia trait. In beta thalassemia, there is an increase in hemoglobin A2, typically in the range of 4-6% (normal is 2-3%). However, the co-existence of a delta thalassemia mutation will decrease the value of the hemoglobin A2 into the normal range, thereby obscuring the diagnosis of beta thalassemia trait.^[3] This can be important in genetic counseling, because a child who is the product of parents each of whom has beta⁰ thalassemia trait has a one in four chance of having beta thalassemia major.

References