Haemoglobin Ottawa, sickle cell trait and vaso-occlusive crises

Area of Science:

• Hematology
• Genetics
• Molecular Biology

Background:

• Sickle cell trait (HbAS) typically presents with mild or no symptoms.
• Vaso-occlusive crises (VOCs) are a hallmark of sickle cell disease, but their severity can vary.
• The influence of co-inherited hemoglobin variants on HbAS phenotype is not fully understood.

Purpose of the Study:

• To investigate the genetic basis of variable VOC severity in a family with sickle cell trait.
• To identify potential contributing factors to severe vaso-occlusive crises in individuals with HbAS.
• To characterize the role of the Hb Ottawa variant in modulating sickle cell trait phenotype.

Main Methods:

• Agarose gel electrophoresis under alkaline conditions to analyze hemoglobin types.
• Sanger sequencing to detect specific gene mutations, including the c.46G>C mutation for Hb Ottawa.
• Clinical correlation of genotypic findings with patient phenotypes, specifically VOC severity.

Main Results:

• The index patient with severe VOCs had HbAS and was homozygous for the Hb Ottawa variant.
• The father with mild VOCs had HbAS and was heterozygous for Hb Ottawa.
• The mother, asymptomatic, was heterozygous for Hb Ottawa but did not have HbS.
• Siblings with Hb Ottawa (without HbS) were asymptomatic, suggesting HbS is required for VOCs.

Conclusions:

• Hb Ottawa, an alpha-globin variant, contributes to the severity of vaso-occlusive crises in individuals with sickle cell trait (HbAS).
• The combination of HbS and Hb Ottawa can lead to a more severe phenotype than HbAS alone.
• This study highlights the importance of considering co-inherited hemoglobin variants in understanding sickle cell disease pathophysiology.