Effects of alpha thalassaemia and haemoglobin F (HbF) level on the clinical severity of sickle-cell anaemia

Genetic Variation and Sickle Cell Disease Severity: A Systematic Review and Meta-Analysis

Importance

Sickle cell disease (SCD) is a monogenic disorder, yet clinical outcomes are influenced by additional genetic factors. Despite decades of research, the genetics of SCD remain poorly understood.

Objective

To assess all reported genetic modifiers of SCD, evaluate the design of associated studies, and provide guidelines for future analyses according to modern genetic study recommendations.

Data Sources

PubMed, Web of Science, and Scopus were searched through May 16, 2023, identifying 5290 publications.

Study Selection

At least 2 reviewers identified 571 original, peer-reviewed English-language publications reporting genetic modifiers of human SCD phenotypes, wherein the outcome was not treatment response, and the comparison was not between SCD subtypes or including healthy controls.

Data Extraction and Synthesis

Data relevant to all genetic modifiers of SCD were extracted, evaluated, and presented following STREGA and PRISMA guidelines. Weighted z score meta-analyses and pathway analyses were conducted.

Main Outcomes and Measures

Outcomes were aggregated into 25 categories, grouped as acute complications, chronic conditions, hematologic parameters or biomarkers, and general or mixed measures of SCD severity.

Results

The 571 included studies reported on 29 670 unique individuals (50% ≤ 18 years of age) from 43 countries. Of the 17 757 extracted results (4890 significant) in 1552 genes, 3675 results met the study criteria for meta-analysis: reported phenotype and genotype, association size and direction, variability measure, sample size, and statistical test. Only 173 results for 62 associations could be cross-study combined. The remaining associations could not be aggregated because they were only reported once or methods (eg, study design, reporting practice) and genotype or phenotype definitions were insufficiently harmonized. Gene variants regulating fetal hemoglobin and α-thalassemia (important markers for SCD severity) were frequently identified: 19 single-nucleotide variants in BCL11A, HBS1L-MYB, and HBG2 were significantly associated with fetal hemoglobin (absolute value of Z = 4.00 to 20.66; P = 8.63 × 10-95 to 6.19 × 10-5), and α-thalassemia deletions were significantly associated with increased hemoglobin level and reduced risk of albuminuria, abnormal transcranial Doppler velocity, and stroke (absolute value of Z = 3.43 to 5.16; P = 2.42 × 10-7 to 6.00 × 10-4). However, other associations remain unconfirmed. Pathway analyses of significant genes highlighted the importance of cellular adhesion, inflammation, oxidative and toxic stress, and blood vessel regulation in SCD (23 of the top 25 Gene Ontology pathways involve these processes) and suggested future research areas.

Conclusions and Relevance

The findings of this comprehensive systematic review and meta-analysis of all published genetic modifiers of SCD indicated that implementation of standardized phenotypes, statistical methods, and reporting practices should accelerate discovery and validation of genetic modifiers and development of clinically actionable genetic profiles.

Hemoglobin SS Nigerian Woman First Diagnosed at the Age of 52 years with Manifestation Mimicking Tuberculosis of the Spine

Sickle cell anemia (SCA) is an inherited disorder of hemoglobin due to the presence of abnormal hemoglobin in a homozygous state. Manifestation is usually in infancy or early childhood due to gradual decrease in hemoglobin F level as age advances. Diagnosis in middle age is unusual. We present a woman who was diagnosed of SCA for the first time at middle age. The aim was to bring to the knowledge of physicians that patients with SCA can also present late so high index of suspicion is required to make diagnosis. A 52-year-old woman presented to orthopedic clinic with complaints of generalized bone pain and low back pain. There was no history of trauma prior to the onset of the pain. There was no associated fever, weight loss, loss of appetite, nor weakness of the lower limbs. X-ray of the spine done showed wedge collapse of the 12^th thoracic and first lumbar vertebrae with posterior angulation of the thoracolumbar junction giving dorsal kyphosis. Her mode of presentation raised a suspicion of tuberculosis of the spine to rule out multiple myeloma. However, investigations for tuberculosis and multiple myeloma were all negative. This necessitated the investigation for SCA and the diagnosis was confirmed. The diagnosis of SCA is usually made in infancy or early childhood. High index of suspicion is required to make the diagnosis at middle age.

Foetal haemoglobin, erythrocytes containing foetal haemoglobin, and hematological features in congolese patients with sickle cell anaemia

High HbF levels and F cells are correlated with reduced morbidity and mortality in sickle cell disease (SCD). This paper was designed to determine the HbF and F cells levels in Congolese sickle cell anemia (SCA) patients in order to determine their impact on the expression of SCD. Population and Method. HbF levels were measured in 89 SCA patients (mean age 11.4 yrs) using a standard HPLC method. F cell quantitation was done in a second group of SCA patients (n = 42, mean age 8.9 yrs) and compared with a control group (n = 47, mean age 5 yrs). F cells were quantified by a cytofluorometric system (MoAb-HbF—FITC; cut off at 0.5%). Results. The mean value of HbF was 7.2% ± 5.0 with heterogeneous distribution, most patients (76%) having HbF < 8%. Mean values of F-cells in SCA patients and control group were 5.4% ± 7.6 (median: 2.19%; range 0,0–30,3%) and 0.5% ± 1.6 (median 0.0, range 0–5.18), respectively. SCA patients with F cells >4.5% developed less painful crisis and had higher percentage of reticulocytes. Conclusion. Congolese SCA patients displayed low levels of HbF and F-cells that contribute to the severity of SCD.

Hematological profile of sickle cell disease from South Gujarat, India

The aim of this study was to determine hematological profile of sickle cell disease (SCD) from Surat, South Gujarat, India. This prospective cross-sectional study was conducted in the Department of Pediatrics and Sickle Cell Anemia Laboratory, Faculty of Pathology, Government Medical College, Surat, India, between July 2009 and December 2010. Patients included in this study were in their steady state for a long period of time without any symptoms related to SCD or other diseases which could affect the hematological parameters. Venous blood of all patients was collected in ethylenediaminetetraacetic acid and hematological indices were measured. Thirty-three subjects homozygous in all were studied for their hematological parameters for sickle cell anemia. Moderate to severe anemia, low mean cell volume and high foetal hemoglobin dominate the hematological profile of SCD children.

Sickle cell disease patients in eastern province of Saudi Arabia suffer less severe acute chest syndrome than patients with African haplotypes

BACKGROUND AND OBJECTIVES

Genetic studies suggest that the sickle cell mutation has arisen on at least four separate occasions in Africa and as a fifth independent mutation in the Eastern Province of Saudi Arabia or India. The pathophysiology of sickle cell disease (SCD) is essentially similar in these different areas although the frequency and severity of complications may vary between areas. The aim of this study was to evaluate the prevalence and outcome of acute chest syndrome (ACS) in SCD patients from Eastern province of Saudi Arabia in comparison with patients with African haplotypes.

MATERIALS AND METHODS

This was a retrospective study involving 317 SCD patients who were two years or older, admitted to King Fahad Hospital Hofuf between January-May 2003 for different etiologies. Twenty six patients presented with different causes of ACS; 11 patients presented with different pathologies other than ACS, but had past history of ACS; 280 patients presented with different pathologies and never presented with ACS. Clinical features, CBC, Hb-electrophoresis, G6PD activity, cultures, chest X-ray, arterial oxygen saturation, blood transfusion rates and outcome were studied. Univariate and multiple regression analysis were carried out to evaluate influence on ACS. Comparison between SCD patients with ACS from this study and from Eastern province of Saudi Arabia to patients with African haplotypes were carried out, using data reported in the literature.

RESULTS

During the period of this study, 37 patients with new or previous episodes of ACS were studied (accounting for 11.67% of admitted SCD patients). Most of the patients with ACS had only one episode, but five patients (13.51%) had had episodes or more. One patient died giving an in-hospital mortality rate of 1/26 (3.85%). Comparison of recurrence of ACS and mortality between SCD patients in Eastern province of Saudi Arabia to that of patients with African haplotype showed that recurrence is significantly lower (P<0.025) in patients from Eastern province compared to patients with African haplotype, mortality also is lower but not statistically significant.

CONCLUSION

Acute chest syndrome in SCD patients in Eastern province of Saudi Arabia is relatively uncommon, but causes significant morbidity and mortality. Its prevalence and recurrence is low if compared to that of patients with African haplotypes.

Asociación de hemoglobinopatía S y alfatalasemia. Análisis de 45 casos

BACKGROUND AND OBJECTIVE

Hemoglobin S (HbS) alpha-thalassemia together with ss-thalassemia and hemoglobins C, E and D are named common hemoglobinopathies. In this study, we analyzed the frequency of the association between alpha-thalassemia and HbS and its phenotypic expression.

PATIENTS AND METHOD

Since January 1995 to March 2003 we studied 83 cases of HbS, which were diagnosed by electrophoretic and chromatographic criteria. The molecular study was carried out by Southern blot with the restriction enzymes Bam HI and Bgl II and a (1.5 Kb Pst) and z (1.8 Kb Sac Y) probes.

RESULTS

45 cases (54.2%) had a-thalassemia (36 -alpha3,7/aa; 1-alpha4,2/alphaalpha; 6 -alpha3,7/-alpha3,7; 1-alpha4,2/-alpha4,2); 36 had not alpha-thalassemia and in two cases there were a triplication of a genes. The patients with HbS heterozygote associated with alpha-thalassemia showed a percentage of HbS (p < 0.0001), CMV (p = 0.004), MCH (p = 0.002) and MCHC (p = 0.02) significantly lower than the cases of HbS without this association. However, no differences between both groups were found with regard to the rest of parameters analyzed (Hb p = 0.56; PVC p = 0.84; RDW p = 0.06; Reticulocytes p = 0.26; HbF p = 0.76; HbA2 p = 0.13). In the cases with a severe form of disease (HbS homozygote; HbS/Hb C; HbS/beta-thalassemia), patients with alpha-thalassemia had a number of leukocytes that was significantly lower than that of patients without alpha-thalassemia (p = 0.034).

CONCLUSION

An association between HbS and alpha-thalassemia was common (> 50%). Screening for this association is of great interest because the clinical expression in the cases of HbS homozigote will be modulated. This association must be suspected in cases of homozygous HbS in which levels of HbS are lower than expected.

"Race", ethnicity and haemoglobin disorders

The new genetics has brought forth concerns that such developments as screening for genetic diseases will accentuate the oppression of minority ethnic groups [Bradby (1996) Genetics and racism. In The Troubled Helix: social and psychological aspects of the new human genetics, ed. T. Marteau and M. Richards, pp. 295-316. Cambridge University Press, Cambridge]. Haemoglobin disorders primarily affect minority ethnic groups in the U.K. but have been the subject of protest regarding lack of services as much as the unwelcome advent of them. This paper examines various conceptions of "race", from biological reductionism, through notions of ethnicity, racialized groups, sociological conceptions of "race", political and analytical uses of the term "Black" and so-called "new ethnicities" such as situational and plastic ethnicity in order to examine the consequences of these competing conceptions of race for a social analysis of sickle cell anaemia and beta-thalassaemia. The paper concludes that any group of people associated with the haemoglobin disorders are subject both to constraints upon their actions and opportunities for re-interpreting their social world. In conclusion it is proposed that no nomenclature classifies the phenomenon unproblematically. The notion of race as a political construct [Goldberg (1993) Racist Culture: Philosophy and the Politics of Meaning. Blackwell, Oxford] is used to suggest that attempts to construct all-embracing definitions themselves signal the potential abuses which may be attendant upon programmatic or mechanistic conceptions of the relationship between race and haemoglobin disorders.