Homozygous beta-thalassemia without anemia

Area of Science:

• Genetics
• Hematology
• Molecular Biology

Background:

• Beta-thalassemia is a group of inherited blood disorders characterized by reduced or absent synthesis of beta-globin chains.
• Typically, homozygous beta-thalassemia leads to severe anemia requiring regular blood transfusions.

Observation:

• A 37-year-old man with Guyanese ancestry presented with homozygous beta-thalassemia but lacked anemia and physical stigmata.
• His hematological values showed a low mean corpuscular volume (61 fL) and mean corpuscular hemoglobin (18.9 pg), but a high hematocrit (41-45.8%).
• Notably, his hemoglobin F (HbF) was 45% with a high G gamma:A gamma ratio (3:1) and heterogeneous distribution in erythrocytes.

Findings:

• Genetic analysis revealed homozygosity for the Senegal beta-globin haplotype (IX) and specific mutations: a -158 C-to-T substitution and a -29 A-to-G promoter mutation.
• The beta/alpha globin chain synthesis ratio was 0.25, and the (beta + gamma)/alpha ratio was 0.55.
• These genetic findings, particularly the high HbF and high G gamma expression linked to the specific haplotype and mutations, correlate with the ameliorated clinical presentation.

Implications:

• This case highlights how specific genetic modifiers, such as high HbF production due to linked mutations, can significantly ameliorate the severity of homozygous beta-thalassemia.
• Understanding these genetic factors is crucial for predicting disease severity and potentially developing novel therapeutic strategies for beta-thalassemia.