|Year : 2019 | Volume
| Issue : 2 | Page : 118-122
The effect of the coinheritance of Glucose-6-phosphate dehydrogenase deficiency on the severity of sickle cell disease
Foluke Atinuke Fasola1, Florence Olamide Fowodu2, Wuraola Adebola Shokunbi1, Taiwo Rachel Kotila1
1 Department of Haematology, College of Medicine, University of Ibadan, Ibadan, Nigeria
2 Department of Haematology, University College Hospital, Ibadan, Nigeria
|Date of Web Publication||10-Jun-2019|
Dr. Taiwo Rachel Kotila
Department of Haematology, University College Hospital, Ibadan
Source of Support: None, Conflict of Interest: None
Background: Sickle cell disease (SCD) and glucose-6-phosphate dehydrogenase (G6PD) deficiency are inherited disorders associated with chronic haemolysis. Therefore, coinheritance of both disorders could worsen haemolysis in the former and compound a haemolytic crisis. This study compared clinical and laboratory features of deficient and non-deficient SCD patients and the G6PD activities of SCD patients and apparently healthy controls. Materials and Methods: This is a case–control study of 175 SCD patients and 166 non-SCD controls. G6PD assay was carried out on haemolysate from washed red cells. The G6PD activity was measured by spectrophotometry. Results: The mean age of patients and controls was 27.3 ± 9.4 and 35.9 ± 9.7 years, respectively, with 75 (46.2%) and 87 (52.4%) being males, respectively. G6PD activity was similar in cases and controls (6.7 ± 3.3 vs. 6.9 ± 3.0 IU/gHb), respectively (P = 0.6). The prevalence of G6PD deficiency was higher in patients than controls (28.6% vs. 22.3%, P = 0.18), and SCD patients were twice more likely to have enzyme activities below 3.0 IU/gHb. No significant difference was observed in the clinical parameters between deficient and non-deficient patients. Deficient patients were more likely to have lower haematocrit (22.8 ± 3.9% vs. 24.5 ± 5%, P = 0.04) and non-significantly higher bilirubin and reticulocyte counts. Furthermore, in patients, severe deficiency resulted in higher bilirubin than in those with mild deficiency (60.5 vs. 21.7 IU/L, P < 0.001). G6PD activity correlated positively with haematocrit (r = 0.91, P = 0.01) and mean corpuscular haemoglobin concentration (r = 0.17, P = 0.02). Conclusions: Coinheritance of both disorders could worsen haemolysis in SCD patients, and care should, therefore, be taken in the choice of drugs in deficient SCD patients.
Keywords: Balanced polymorphism, epidemiology, haemolytic anaemia, sex-linked disorders
|How to cite this article:|
Fasola FA, Fowodu FO, Shokunbi WA, Kotila TR. The effect of the coinheritance of Glucose-6-phosphate dehydrogenase deficiency on the severity of sickle cell disease. Niger Postgrad Med J 2019;26:118-22
|How to cite this URL:|
Fasola FA, Fowodu FO, Shokunbi WA, Kotila TR. The effect of the coinheritance of Glucose-6-phosphate dehydrogenase deficiency on the severity of sickle cell disease. Niger Postgrad Med J [serial online] 2019 [cited 2019 Jun 18];26:118-22. Available from: http://www.npmj.org/text.asp?2019/26/2/118/259915
| Introduction|| |
Sickle cell disease (SCD) and glucose-6-phosphate dehydrogenase (G6PD) deficiency are inherited chronic haemolytic anaemias prevalent in Nigeria. While SCD is inherited as an autosomal recessive disorder, G6PD deficiency is inherited as a sex-linked disorder. The high incidence of G6PD deficiency has been reported in some areas of the world where sickle cell gene is most prevalent., The deficiency is the most common human enzyme deficiency affecting an estimate of 400 million people worldwide. Affected individuals may exhibit chronic haemolytic anaemia as a result of infection, exposure to certain medications or chemicals. Similarly, too in SCD, haemolysis is often triggered by infections, especially malaria parasitaemia. Although the severe forms of G6PD deficiency rarely occur in Nigeria, patients with the deficiency are also infrequently hospitalised. This is in contrast to SCD in which recurrent haemolysis often requires blood transfusion and hospitalisation.
The coexistence of G6PD deficiency and SCD could have a significant impact on the clinical manifestations of the latter, and this has led to studies regarding the possible relationships between these two disorders. In some studies, a positive association has been found between the disorders., It was suggested that G6PD deficiency might confer an advantage on patients with SCD, thus prolonging survival., It has also been postulated that the coinheritance of G6PD deficiency could exacerbate haemolysis, thus increasing the severity of SCD. This study assesses the effect of the coinheritance of G6PD with SCD and its influence on some clinical and laboratory parameters of the disorder.
| Materials and Methods|| |
Ethical approval for the study was obtained from the UI/UCH Ethics Committee on May 24, 2012, with protocol number UI/EC/11/0271 assigned to the study. All participants gave an informed consent. The study was carried out between June and November 2012.
Selection of cases and controls
This is a case–control study carried out on 175 consecutive HbS patients presenting in the steady state. The inclusion criteria include SCD patients aged between 18 and 65 years who have no evidence of infection, have not had any crises in the past 1 month and have not had blood transfusion at least 3 months prior to the study. The controls were 166 apparently healthy volunteers with no history of SCD and were matched by age group and gender as the patient and were selected from the hospital workforce.
This was calculated based on the following assumptions:
- Type I error (α) rate of 5%
- Type II error (β) rate of 80%
- Previous estimate of prevalence of G6PD deficiency in SCD of 16%
- Previous estimate of prevalence of G6PD deficiency in the community of 24%
- Difference in the estimate between cases and controls (δ) 24%–16% =8%
- N = Zα2 pq/δ2.
P = 16%
q = 1–16
= (1.96)2 × 0.16 × 0.84/(0.08) 2
Five millilitres of venous blood was obtained from all participants after an informed consent was obtained, 3 ml was put into a specimen bottle containing sodium ethylenediamine tetra-acetic acid (EDTA) crystals and 2 ml was put into a second bottle with lithium heparin anticoagulant. The bottle containing lithium heparin anticoagulant and blood was covered with black carbon paper during transportation for bilirubin analysis. The specimen in the EDTA bottle was analysed within 24 h at room temperature for G6PD activity by spectrophotometry method according to International Committee for Standardization in Haematology (ICSH). The specimen in the lithium heparin bottle was centrifuged, and plasma was separated for bilirubin estimation within 6 h of collection using the diazo method.
G6PD assay was carried out on haemolysate prepared by mixing 9 volume of lysing solution (2.7 mmol/L EDTA, pH 7.0 and 0.7 mmol/L 2-mercaptoethanol) to 1 volume of washed red cell suspension. The assay was conducted within 1 h of the freshly prepared haemolysate. The G6PD activity was calculated from the change in the absorbance at 340 nm over a period of 5 min by following the rate of production of NADPH which has a peak of ultraviolet light absorption at 340 nm. The absorbance of the blank was also measured. The control samples were assayed at the same time as the test samples.
The results of G6PD activity were expressed per gHb according to the ICSH recommendation. The enzyme activity was expressed in international units, one unit of G6PD being the quantity of enzyme which reduces 1 μmol of NADP per minute. The normal range for G6PD activity in this study is 4.6–10 IUg/Hb at 30°C.
Other investigations carried out were reticulocyte count and complete blood count from the specimen in the EDTA bottle, and these were done by automation.
Data management and statistical analysis
Demographic and clinical data were obtained through an interviewer-administered questionnaire. Data were analysed using the Statistical Package for the Social Sciences (SPSS) version 16 (IBM Inc., New York, USA). Frequency tables and descriptive statistics were used to summarise the data. Quantitative data were compared between cases and controls and between G6PD deficient and non-deficient participants using two-sample t-test. Categorical data were compared between the groups using Chi-squared test. The correlation of G6PD activity with the haematological parameters was computed by Pearson's correlation coefficient. The level of significance was set at 5%.
| Results|| |
The SCD patients and controls were aged 18–59 years, with a mean of 27.3 ± 9.4 and 35.9 ± 9.7 years, respectively. The SCD patients consisted of 75 (46.2%) males and 100 (53.8%) females, whereas the controls consisted of 87 (52.4%) males and 79 (47.6%) females (P > 0.05). The mean G6PD activity was not significantly different between cases and controls (6.7 ± 3.3 vs. 6.9 ± 3.0 IU/gHb, respectively, P = 0.6).
The prevalence of G6PD deficiency was higher in SCD patients than controls (28.6% vs. 22.3%, respectively, χ2 = 1.77, P = 0.18). The prevalence was also higher in male and female patients than male and female controls, respectively [Table 1]. The severity of G6PD deficiency was more pronounced in SCD patients than controls. SCD patients were twice more likely to have enzyme activities below 3.0 IU/gHb than controls [Figure 1]. Furthermore, G6PD-deficient patients had the higher levels of absolute reticulocyte counts and the different fractions of bilirubin than G6PD-deficient HbA controls [Table 2]. There was no statistically significant difference in the clinical parameters between G6PD-deficient SCD and G6PD non-deficient SCD patients [Table 3]. Although the absolute reticulocyte count in G6PD-deficient SCD was not significantly different from non-deficient SCD (5.9 ± 2.9 × 106/l vs. 4.6 ± 2.0 × 106/l respectively, P = 0.27), the deficient patients had a significantly lower haematocrit (24.5% vs. 22.8%, P = 0.04). Furthermore, the total bilirubin and its various fractions were significantly higher in severely deficient sickle cell disease patients than mildly deficient patients' [Table 4].
|Table 1: Prevalence of glucose-6-phosphate dehydrogenase deficiency in sickle cell disease patients and healthy controls by gender|
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|Figure 1: Comparison of severity of glucose-6-phosphate dehydrogenase deficiency between sickle cell disease patients and controls|
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|Table 2: Laboratory parameters showing evidence of more severe haemolysis in glucose-6-phosphate dehydrogenase-deficient HbS patients than HbA controls|
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|Table 3: Comparison of clinical and laboratory indices of glucose-6-phosphate dehydrogenase deficient and non-deficient sickle cell disease patients|
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|Table 4: Comparison of bilirubin levels of mildly and severely deficient sickle cell disease patients|
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The correlation of G6PD activity with the haematological parameters showed that the haematocrit (r = 0.91, P = 0.01) and mean corpuscular haemoglobin concentration (r = 0.17, P = 0.02) positively correlated with G6PD activity.
| Discussion|| |
This study showed that the prevalence of G6PD deficiency was higher in SCD patients than apparently healthy controls even though the G6PD activity was similar for both the groups. Furthermore, the severe form of the deficiency was more pronounced in the SCD patients. In addition, the various fractions of bilirubin and absolute reticulocyte counts were higher in patients compared to controls and also in deficient patients compared to non-deficient patients. This would suggest the likelihood of G6PD deficiency worsening the haemolysis in SCD.
Many studies have found similarity in the prevalence of G6PD deficiency in sickle cell anaemia patients and community controls.,, All these studies have also noted that the coinheritance of G6PD with sickle cell anaemia did not affect the clinical severity of the disease.,, Neither did it confer any biological advantage on the disorder. Similar to our findings, Diop et al. found a higher prevalence of G6PD deficiency in SCD patients compared to their HbA counterpart in Senegal. It is interesting to note that the prevalence of G6PD deficiency and the sickle cell trait are similar in both communities with a higher prevalence of G6PD deficiency in the SCD populations. Similarities in the prevalence of sickle cell trait and G6PD deficiency in a community may possibly predict the prevalence of the latter in SCD.
The finding of a higher prevalence of G6PD deficiency in SCD patients in our study contrasted with the that of Bienzle et al. who found a lower prevalence, though both studies were done in the same community. However, the observation of a lower haematocrit and higher reticulocyte count in deficient patients compared to non-deficient patients was common to both studies. The differences in prevalence could be due to patient selection; Bienzle et al. included only male paediatric patients and excluded patients with sickle cell thalassaemia, whereas our study was conducted in adult patients of both genders and did not exclude patients with thalassaemia. In our study, the G6PD assay was done at the same time on the control in determining the prevalence, but Bienzle et al. compared the prevalence in the patient with what was previously known in the community. It should be noted that the prevalence in our control group is similar to what is the known prevalence in the community. The high prevalence of G6PD noted in both female patients and controls (24.5% and 21.5%, respectively) is in sharp contrast to the previous findings of 4.6% by Ademowo and Falusi. This could be partly because female heterozygotes (carriers) were not separated from homozygote females in our study in comparison to previous studies., It should be noted that 4.5% of our participants were severely deficient, whereas 25.7% were mildly deficient. Molecular studies would have been useful in delineating heterozygotes from hemizygotes and homozygotes.
Comparing the clinical and laboratory profile of SCD patients with G6PD deficiency and SCD patients with normal G6PD activity showed no statistical difference between the two groups in most parameters except in the haematocrit. The frequency of blood transfusion, hospital admissions and sizes of the liver and spleen did not differ significantly. However, severely deficient patients had significantly higher bilirubin than patients with mild deficiency, and this difference was noted in all the bilirubin fractions. A combination of the two disorders might, therefore, lead to more severe haemolysis in patients with SCD when exposed to subliminal haemolysis-triggering condition such as infections and culprit drugs. Malarial infections and antimalarial drugs are mostly encountered triggers in our environment. Benkerrou et al. observed lower steady-state haemoglobin and higher reticulocyte count in under 5-year-old G6PD-deficient SCA as seen in our study. In contrast to our finding of similar blood transfusion rates for both deficient and non-deficient HbS patients, Benkerrou et al. reported a higher frequency of blood transfusion. This is in addition to the reporting of three times higher acute anaemic event rates in the G6PD-deficient SCA, the effect of which decreased after 2 years of age. It is, therefore, possible that the coinheritance of the two disorders could result in higher mortality in childhood as a result of frequent anaemic crises. However, this will be at variance with the observation that G6PD deficiency increases with age., When the two problems coexist, particular care should, therefore, be exercised in the administration of drugs such as antimalarials known to trigger hemolysis in patients with G6PD deficiency.
A pitfall of this study is failure to differentiate heterozygotes from hemizygotes and homozygotes, and other causes of haemolysis such as liver pathology were not excluded in the participants.
| Conclusions|| |
G6PD deficiency may have a subtle effect on the severity of hemolysis and also worsen the degree of anaemia in SCD when the two disorders coexist. Therefore, selective decision should be taken in patients in whom the two conditions coexist in the choice of drug and in the treatment of infections.
We are grateful to Prof. OG Ademowo of the Institute of Advanced Medical Research and Training, College of Medicine, University of Ibadan, for his assistance in sourcing for G6P.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3], [Table 4]