Why is electrophoresis normal in alpha thalassemia - kasava

[ArchivalUser]

Anyone can clear my confusion? Thanx

[ArchivalUser]

I can copy/paste this q from MKSAP 14 to be able to explain your q.

A 20-year-old woman is evaluated for excessive fatigue. The remainder of the medical history and physical examination are noncontributory.

Laboratory studies include a hemoglobin of 10 g/dL (100 g/L), a mean corpuscular volume of 60 fL, and a red blood cell count of 5.5 million cells/μL (5.5 × 1012/L). The leukocyte and platelet counts and results of hemoglobin electrophoresis are normal. The peripheral blood smear is shown (Figure 13).

Which of the following is the most likely composition of her α-gene alleles?

A (α,––) /(α,α
B (α,––) /(α,––)
C (––,––) /(––,α
D (––,––) /(––,––)
(Correct Answer = B)
Key Points

* Patients with the α-thalassemia trait have a two-gene defect ([α,--]/[α,--]) in the α-globin gene chain of chromosome 16.
* Patients who have α-thalassemia trait have mild microcytic anemia with prominent target cells on peripheral blood smear.

This patient has the α-thalassemia trait as demonstrated by a two-gene defect ([α,––]/[α,––]). Chromosome 16 normally contains two copies of an α gene. The α-thalassemias occur when there are defects in transcription or translation of any of the four α-globin genes. A two-gene defect leads to mild microcytic anemia with prominent target cells as shown in this patient's peripheral blood smear; the hemoglobin electrophoretic pattern is normal in these patients. Additionally, patients with thalassemia typically have preserved or increased red blood cell counts compared with patients with iron deficiency, who have a reduced red blood cell count.

A single gene defect is clinically silent, and in these patients, there is a normal complete blood count. Patients with a three-gene defect have hemoglobin H disease associated with severe microcytic anemia caused by hemoglobin H, which is composed of tetramers of β genes. A four-gene defect is not compatible with life and results in hydrops fetalis.

[ArchivalUser]

Thanx for reply.

Does that mean the hemoglobin electrophoresis can not separate hemoglobin H as one variant ? ( For example in B thal hemog A2 and Hemog F increase and the electrophoresis can identify the increase in those hemoglobins.In Alpha thal the hemoglobin H will increase and why not the electrophoresis show the increase in hemoglobin H ?)

[ArchivalUser]

@Kasava

I believe that trait and silent carrier would have normal electrophoresis since they do not produce hemoglobin H, they produce defective variant of Heme A