Hemoglobin Variants in Hematological Disorders

Structural Variants and Disease Severity

Structural variants of HbF, such as Hb F-M-Osaka and Hb F-M-Fort Ripley, can occur due to mutations in gamma-globin genes, similar to mutations causing adult hemoglobin variants 1

HbH disease is characterized by low HbA2 levels and the presence of HbH, which consists of four beta-globin chains (β₄) formed due to the relative excess of beta chains when alpha chain production is severely reduced 2
Alpha thalassemia is a common cause of hydrops fetalis, particularly in Southeast Asian populations, where it accounts for 28-55% of non-immune hydrops fetalis cases 2
Diagnosis of HbH disease involves hemoglobin electrophoresis showing the presence of HbH, peripheral blood smear examination revealing HbH inclusion bodies 3
Parents of affected individuals can be screened by evaluating the mean cell volume (MCV), which will be <80 fL in thalassemia carriers 2

The diagnostic approach typically includes complete blood count with red cell indices 4
In cases of suspected alpha thalassemia with hydrops fetalis, DNA testing for alpha-thalassemia should be performed, especially if parental MCV is <80 fL 2
Abnormal hemoglobin variants can cause various clinical manifestations, including anemia, cyanosis, and in severe cases, hydrops fetalis and fetal demise 3, 2

The American Heart Association recommends distinguishing HbH disease from beta-thalassemia trait, as both present with microcytic anemia, but HbH disease may require transfusions to prevent complications, with a mean cell volume (MCV) of <80 fL in thalassemia carriers 5, 6

Patients with HbH disease typically maintain hemoglobin levels around 9-10 g/dL in steady state, but may experience significant drops during hemolytic crises, potentially leading to shock or renal shutdown, highlighting the need for close monitoring and management 5, 6