The Effect of Alpha Thalassemia, HbF and HbC on Haematological Parameters of Sickle Cell Disease Patients in Ibadan, Nigeria

BACKGROUND: Sickle cell disease is a protean disease with limited data on Nigeria’s phenotypic and genetic variants. This study was conducted to provide baseline data on these variants by characterising the existing forms of sickle cell disease and correlating these with basic haematological parameters. METHODS: Adult and paediatric patients with SCD were recruited from a tertiary health centre in Nigeria. Patients were age and sex-matched with healthy controls. Blood samples were obtained for Full Blood Count, phenotyping by High-Performance Liquid Chromatography, and genotyping for alpha thalassemia by multiplex Gap-polymerase chain reaction. Data analysis was done using IBM SPSS statistics version 23. RESULTS: A total of 130 patients with sickle cell disease and 117 controls were studied. Alpha thalassemia in the study population was due to a 3.7kb deletion in the alpha-globin gene cluster at a prevalence of 45.4% in the patients and 47% in the controls. The prevalence of the various existing forms of SCD genotype was: Homozygous S without alpha gene deletion (HbSS)- 39.2%; HbSC - 10.8%; HbSS(α+1)- 35.4%; HbSS(α+2) - 6.9% and HbSF- 7.7%. In the control population, HbAA without alpha gene deletion had a prevalence of 42.7%, HbAA(α+1) was 25.6%, HbAA (α+2) was 6%, HbAS- 7.7%, HbAS (α+1) – 11.1%, HbAS (α+2) - 2.6%, HbAC – 2.6% and HbAC (α+1) – 1.7%. HbA(2) was significantly elevated in HbSS individuals with two alpha gene deletions but reduced in normal controls (HbAA) with alpha gene deletions. HbF and HbA(2) were negatively correlated with each other (r= −0.587, p < 0.001). Individuals with the HbSC genotype followed by HbSSα(+2) had the best haematological parameters. CONCLUSIONS: Haematological parameters vary with haemoglobin genotype. The C haemoglobin and homozygous alpha-thalassemia deletion had a better ameliorating effect on SCD haematological parameters than the F haemoglobin in this population. The effect of alpha thalassemia on some haematological parameters in SCD patients are reversed in normal controls.