Elizabeth Oluwatimilehin ABODUNRIN2024-05-152024-05-152022-12M.Schttps://repository.lcu.edu.ng/handle/123456789/80This study aimed at assessing the level of Foetal Haemoglobin (HbF) in among Sickle Cell Patients in the Ibadan, determined the occurrence of the SNP(rs66650371) responsible for elevated HbF levels and investigated the relationship between the SNP type, HbF level and SCA severity in the SCD patients. Relationship between foetal haemoglobin and SCD is poorly studied. Hence, this study provides the data needed for future research on HbF variants among SCD patients and its severity. This is a cross-sectional hospital based study, blood samples were collected from the university college hospital and Adeoyo state hospital in Ibadan respectively. The socio-demographic information and SCD severity was evaluated from 260 SCD patients, based on the frequency of significant painful episodes, blood transfusion, acute chest symptoms and leg ulcers in the past one year. HbF and haematocrit levels were determined. Amplification Refractory-Mutation System (ARMS) PCR was performed to determine the 3-bp deletion in the HBS1L-MYb gene. The mean HbF levels of 260 patients is 4.9% ± 2.4, about 50% of the population had low HbF level, patients with elevated levels of HbF had increased PCV counts, reduced vaso-occlusive crises in a year, reduced acute chest syndromes and reduced leg ulcer. The allelic frequency of the rs66650371 is three percent. rs66650371 SNP was associated with elevated level of HbF and reduced disease severity, The study demonstrated the beneficial effect of the rs66650371 SNP in Nigerian patients. Facilities for early and regular quantification of foetal haemoglobin should be made available in Sickle cell Clinics and Hospitals. Keywords – Foetal Haemoglobin, Sickle Cell Disease (SCD), ARMS-PCR, rs66650371, SNP, vaso-occlusive, allelic frequency Word Count – 260enThesis