CHARACTERIZATION OF THE BETA GLOBIN GENE AMONG SICKLE CELL ANAEMIA PATIENTS IN ZARIA

Abstract

Introduction/Background: Sickle Cell Anaemia (SCA) is a genetic disorder. The disability is lifelong and is of Public Health importance. The diversity in clinical and laboratory presentations may be due to additional genetic differences and environmental factors. The genetic factors may be in the β-globin gene itself, the β-globin gene cluster or elsewhere in the genome.
Aim and Objectives: This study aims to characterize the β-globin gene for additional mutations associated with the Sickle Cell mutation. The study is to also determine the Haematological and Clinical features and to determine any relationships between these and the β-globin gene characteristics.
Materials and Methods: This was a cross-sectional descriptive study utilizing questionnaires, physical examination, blood and buccal swab specimens. Fifty-one adult SCA patients participated. Full Blood Count and β-globin gene DNA Sequencing were carried out. The DNA sequences were compared with a Genbank Reference β-globin gene (NC_000011.9) using Basic Local Alignment Search Tool (BLAST) and variations noted. Data generated were analyzed using SPSS Version 17.0.
Results: There were 40 (78.43%) and 11 (21.57%) females and males respectively. Most of the Participants 21 (41.18%) were diagnosed between the ages of 1 and 5 years. Only 3 (5.88%) gave a history of Consanguinity. The mean pain episodes and hospital admissions in the last one year were 3.67±3.34 and 0.78±1.22 with 95% CIs of (2.73, 4.61) and (0.44, 1.13) respectively. Majority of the Participants 26 (51%) had less than 3 pain episodes in the last one year. Also, most of them 46 (90.20%) had less than 3 Hospital admissions in the last one year. The mean number of total blood transfusions, top up blood transfusions and exchange blood transfusions were 0.59±1.28, 0.43±1.01 and 0.16±0.58 with 95% CIs of (0.23, 0.95), (0.15, 0.71) and (0.00, 0.32) respectively. The frequency distribution of the BMI was normal weight 33 (64.71%), underweight 13 (25.49%) and overweight 5 (9.80%). The mean systolic and diastolic blood pressures were 107.84±11.27mmHg and 65.57±8.80mmHg with 95% CIs of (104.67, 111.01) and (63.10, 68.04) respectively. There were no musculoskeletal abnormalities in 44 (86.27%) but 3 (5.88%) had left femoral AVN, 2 (3.92%) had right femoral AVN, 1 (1.96%) bilateral femoral AVN and 1 (1.96%) gnathopathy. None of the participants had leg ulcers, palpable hepatomegaly or splenomegaly. The mean PCV, WBC, Platelet count, MCV, MCH, MCHC, and Reticulocyte counts were 22.72±3.41% with 95% CI of (21.76, 23.68), 10.53±2.72 x 109/l with 95% CI of (9.77, 11.30), 471.98±141.92 x 109/l with 95% CI of (432.06, 511.90), 86.02±7.74 fl with 95% CI of (83.84, 88.20), 31.28±3.94 pg with 95% CI of (30.17, 32.38), 35.83±2.06 g/dl with 95% CI of (35.25, 36.41) and 9.17±2.93 % with 95% CI of (8.34, 9.99) respectively.


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All the participants had some form of β-Globin gene variations in varying combinations with a mean of 8.61±11.30 per person, 95% CI (5.43, 11.78). Specific types of variations were substitutions 63, insertions 111 and deletions 54 occuring in various combinations and frequencies. The mean number of substitutions, insertions and deletions were 2.39±3.23, 3.61±7.66 and 2.60±2.46 with 95% CIs of (1.48, 3.30), (1.45, 5.76) and (1.92, 3.30) respectively. The G>C substitution had a frequency of 53 (43.44%) followed by A>C 21 (17.21%), T>C 18 (14.75%) and A>G 9 (7.38%). The most frequently deleted nucleotide was A 61 (45.86%) followed by T 33 (24.81%), C 21 (15.79%) and G 18 (13.53%). Cytosine was inserted 51 times (40.80%), A 31 (24.80%), G 27 (21.60%) and T 16 (12.80%).
The most frequent insertion of more than one nucleotide was AT 4 (15.38%) followed by CA and CT 3 (11.54%) each. While the GA, GG, TC and TG insertions occurred twice (7.69%) each, the AAG, CCTCC, CG, GC, GGAC, GGC, GT and TT insertions had a frequency of 1 (3.85%) each.
There was a weakly positive but statistically significant relationship between WBC count and number of deletions (r=0.319, n=51, p=.022). Also, the relationship between body weights and number of substitutions was weakly positive but significant (r=0.348, n=51, p=.012). Fisher’s Exact Test (FET) returned significant associations between Gender and Deletions (p=0.037; FET) on one hand and insertions and MCH levels (p=0.041; FET) on the other. All other analyses were not statistically significant.
Conclusion: There are additional β-globin gene variations in SCA patients in Zaria. Most of the clinical and haematological features of these patients are however not associated with the characteristics of these variations.