Influence of alpha-thalassemia trait on spleen function in sickle cell anemia patients with high HbF

Clinical and laboratory factors associated with splenic dysfunction among patients with sickle cell disease in a malaria endemic region

BACKGROUND

Although loss of splenic function is the expected natural course for individuals with sickle cell disease (SCD), factors such as high HbF and coexistence of alpha thalassemia may ameliorate this process. We evaluated factors associated with two surrogate markers of spleen dysfunction, namely Howell-Jolly bodies (HJBs) and argyrophilic inclusion (AI) red cell counts, among patients with SCD.

METHODS

Cross-sectional data of 182 patients with SCD (median age 11 y; 1-45 y) and 102 normal controls (median age 12 y; 1-32 y) were evaluated. Blood tests including full blood count, serum chemistry and high-performance liquid chromatography were performed. The HJB and AI red cell counts were performed on peripheral blood smears.

RESULTS

The percentages of HJB and AI red cells rose significantly with increasing age in the SCD group. On regression analysis, the frequency of HJB red cells associated positively with mean corpuscular hemoglobin (MCH) (β=0.289; p=0.001) and negatively with HbF (β=-0.259; p=0.002). The AI red cell counts also associated positively with MCH (β=0.321; P=0.001) and negatively with HbF (β=-0.242; p=0.020).

CONCLUSIONS

Data from this study indicate that the negative association of HbF with both markers of splenic dysfunction among our patients with SCD residing in a malaria endemic region is similar to findings elsewhere of its ameliorating effect on splenic dysfunction.

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.

Determinants of splenic preservation among patients with sickle cell disease in North-Eastern Nigeria

OBJECTIVE

In patients with sickle cell disease (SCD), the spleen commonly enlarges during early childhood, but undergoes reduction in size and fibrosis from repeated episodes of vaso-occlusion and infarction. The rate of progression of this process varies markedly among these patients. The aim of current study was to explore clinical and laboratory factors associated with the preservation of the spleen among these patients.

METHODS

Two hundred four patients with SCD (103 females; age 1-45 years) underwent abdominal ultrasonography at the University of Maiduguri Teaching Hospital, Nigeria between October 2020 and November 2021 to assess for splenic visualisation and echotexture. Steady-state clinical parameters and blood samples for full blood count, serum chemistry, high-performance liquid chromatography and malaria parasitemia were obtained from all the patients.

RESULTS

The spleen was visualised in 107 (52.4%; 95% confidence interval [CI], 46%-59%) patients with SCD on ultrasonography. While the spleen was visualised in all children less than 5 years of age, it was visualised in only 23.5% of those aged 15 years and older. Visualisation of the spleen was significantly associated with low mean corpuscular haemoglobin concentration and high haemoglobin F (HbF) in those younger than 10 years. The odds of visualisation of the spleen on ultrasonography increased by a factor of 1.17% for every 1% increase in HbF level. Only 32 (15%) patients were on regular hydroxyurea therapy. The HbF level was significantly higher among patients on hydroxyurea (median 12.7 vs. 7.4; p < 0.0001).

CONCLUSION

In patients with SCD, failure to visualise the spleen was not found in children less than 5 years old. Patients with visualised spleens had a higher level of HbF than those with non-visualised spleens. HbF was significantly associated with visualisation of the spleen before 10 years of age. Since early administration of hydroxyurea will increase HbF level, we expect that it would help to preserve the spleen.

Asplenia and spleen hypofunction

Asplenia (the congenital or acquired absence of the spleen) and hyposplenism (defective spleen function) are common causes of morbidity and mortality. The spleen is a secondary lymphoid organ that is responsible for the regulation of immune responses and blood filtration. Hence, asplenia or hyposplenism increases susceptibility to severe and invasive infections, especially those sustained by encapsulated bacteria (namely, Neisseria meningitidis, Streptococcus pneumoniae, Haemophilus influenzae type b). Asplenia is predominantly due to splenectomy for either traumatic events or oncohaematological conditions. Hyposplenism can be caused by several conditions, including haematological, infectious, autoimmune and gastrointestinal disorders. Anatomical disruption of the spleen and depletion of immune cells, especially IgM memory B cells, seem to be predominantly responsible for the clinical manifestations. Early recognition of hyposplenism and proper management of asplenia are warranted to prevent overwhelming post-splenectomy infections through vaccination and antibiotic prophylaxis. Although recommendations are available, the implementation of vaccination strategies, including more effective and immunogenic vaccines, is needed. Additionally, screening programmes for early detection of hyposplenism in high-risk patients and improvement of patient education are warranted.

Diagnosis of Sickle Cell Disease and HBB Haplotyping in the Era of Personalized Medicine: Role of Next Generation Sequencing

Hemoglobin genotype and HBB haplotype are established genetic factors that modify the clinical phenotype in sickle cell disease (SCD). Current methods of establishing these two factors are cumbersome and/or prone to errors. The throughput capability of next generation sequencing (NGS) makes it ideal for simultaneous interrogation of the many genes of interest in SCD. This study was designed to confirm the diagnosis in patients with HbSS and Sβ-thalassemia, identify any ß-thal mutations and simultaneously determine the ß^S HBB haplotype. Illumina Ampliseq custom DNA panel was used to genotype the DNA samples. Haplotyping was based on the alleles on five haplotype-specific SNPs. The patients studied included 159 HbSS patients and 68 Sβ-thal patients, previously diagnosed using high performance liquid chromatography (HPLC). There was considerable discordance between HPLC and NGS results, giving a false +ve rate of 20.5% with a sensitivity of 79% for the identification of Sβthal. Arab/India haplotype was found in 81.5% of β^S chromosomes, while the two most common, of the 13 β-thal mutations detected, were IVS-1 del25 and IVS-II-1 (G>A). NGS is very versatile and can be deployed to simultaneously screen multiple gene loci for modifying polymorphisms, to afford personalized, evidence-based counselling and early intervention.

The Genetic and Clinical Significance of Fetal Hemoglobin Expression in Sickle Cell Disease

Sickle cell disease (SCD) is phenotypically heterogeneous. One major genetic modifying factor is the patient's fetal hemoglobin (HbF) level. The latter is determined by the patient's β-globin gene cluster haplotype and cis- and trans-acting single nucleotide polymorphisms (SNPs) at other distant quantitative trait loci (QTL). The Arab/India haplotype is associated with persistently high HbF levels and also a relatively mild phenotype. This haplotype carries the Xmn1 (C/T) SNP, rs7482144, in the HBG2 locus. The major identified trans-acting QTL contain SNPs residing in the BCL11A on chromosome 2 and the HMIP locus on chromosome 6. These collectively account for 15-30% of HbF expression in different world populations and in patients with SCD or β-thalassemia. Patients with SCD in Kuwait and Eastern Saudi Arabia uniformly carry the Arab/India haplotype, but despite this, the HbF and clinical phenotypes show considerable heterogeneity. Pain episodes and avascular necrosis of the femoral head are particularly common, but severe bacterial infections, stroke, priapism, and leg ulcers are uncommon. Moreover, the HbF modifiers appear to be different; the reported BCL11A and HMIP SNPs appear to play insignificant roles. There are probably novel modifiers to be discovered in this population. This review examines the common clinical phenotypes in Kuwaiti patients with elevated HbF and the available information on HbF modifiers. The response of the patients to hydroxyurea is discussed. The presentation of patients with other sickle compound heterozygotes (Sβthal and HbSD), vis-à-vis their HbF levels, is also addressed critically.

The spectrum of splenic complications in patients with sickle cell disease in Africa: a systematic review

The majority of the global population of sickle cell disease (SCD) patients resides in Africa. Individuals with this condition are at great risk of serious infections and early mortality secondary to splenic dysfunction without preventative measures. This review investigated the spectrum of splenic complications encountered in SCD among populations in Africa. We systematically searched several databases for all articles published through March 3, 2020. We included 55 studies from 14 African countries. This review reveals the difference in frequency of splenic complications in SCD in Africa when compared with their counterparts in the United State and Europe. While several studies (n = 45) described splenomegaly with a prevalence of 12% to 73% among children, and 4% to 50% among adults with HbSS, the reported prevalence for acute splenic sequestration crisis (n = 6 studies) and hypersplenism (n = 4 studies) was <10% and <5% respectively. A total of 30 surgical splenectomy was reported across eight studies. Only two (3.7%) studies provided data on spleen function. A conflicting pattern was observed amongst studies that evaluated the relationship between splenomegaly and the presence of bacterial and malaria infections. This review reveals the paucity of studies describing the role of SCD-induced splenic dysfunction in morbidity and infection related mortality in Africa.

Insights into determinants of spleen injury in sickle cell anemia

Spleen dysfunction is central to morbidity and mortality in children with sickle cell anemia (SCA). The initiation and determinants of spleen injury, including acute splenic sequestration (ASS) have not been established. We investigated splenic function longitudinally in a cohort of 57 infants with SCA enrolled at 3 to 6 months of age and followed up to 24 months of age and explored the respective contribution of decreased red blood cell (RBC) deformability and increased RBC adhesion on splenic injury, including ASS. Spleen function was evaluated by sequential ^99mTc heated RBC spleen scintigraphy and high-throughput quantification of RBCs with Howell-Jolly bodies (HJBs). At 6 and 18 months of age, spleen filtration function was decreased in 32% and 50% of infants, respectively, whereas the median %HJB-RBCs rose significantly (from 0.3% to 0.74%). An excellent correlation was established between %HJB-RBCs and spleen scintigraphy results. RBC adhesion to laminin and endothelial cells increased with time. Adhesion to endothelial cells negatively correlated with splenic function. Irreversibly sickled cells (ISCs), used as a surrogate marker of impaired deformability, were detected at enrollment and increased significantly at 18 months. %ISCs correlated positively with %HJB-RBCs and negatively with splenic uptake, indicating a relationship between their presence in the circulation and spleen dysfunction. In the subgroup of 8 infants who subsequently experienced ASS, %ISCs at enrollment were significantly higher compared with the asymptomatic group, suggesting a major role of impaired deformability in ASS. Higher levels of %HJB-RBCs were observed after the occurrence of ASS, demonstrating its negative impact on splenic function.

The Sub-Phenotypes of Sickle Cell Disease in Kuwait

Kuwaiti patients with sickle cell disease generally have a mild phenotype, but exhibit considerable heterogeneity, in spite of high Hb F levels. We have carried out a cross-sectional study of patients with sickle cell disease in the five major hospitals in Kuwait. Details of their hemoglobin (Hb) genotypes, clinical presentations and complications are presented. The study was over a span of 3 years and involved 396 patients, made up of 351 (88.6%) Kuwaitis and 45 (11.4%) expatriates. They were aged <1 to 73 years. Hb SS (β^S/β^S) was the most common (in 246 patients, i.e. 62.1%) followed by Hb S (HBB: c.20A>T)-β-thalassemia (Hb S-β-thal) in 138 (34.8%) and 11 (2.8%) Hb S/Hb D-Punjab (HBB: c.364G>C). Hb F ranged from 1.0 to 55.0%, with a mean of 21.2 ± 9.8%. The most common presentation was vaso-occlusive crises (VOCs), with 230 (54.8%) having had at least one prior to the study with 54 (13.2%) and 74 (18.9%) having between 2-3 and >3 VOCs, respectively. Hydroxyurea (HU) was prescribed to 157 (39.6%) patients. The most common complication was gallstones in 131 (33.1%), followed by acute splenic sequestration in 26.8% and avascular necrosis of the femoral head in 21.2% patients, respectively. Stroke, priapism and leg ulcers were rare. Gallstones, splenic sequestration and osteonecrosis were significantly more common in patients aged >16 years. Patients with Hb S-β-thal were similar to those with Hb SS in their clinical profiles. The phenotypic expression of sickle cell disease in Kuwaitis is unique in many respects. The role(s) of Hb F and other genetic modifiers require further elucidation.

Influence of alpha thalassemia on clinical and laboratory parameters among nigerian children with sickle cell anemia

BACKGROUND

There is paucity of data on the influence of alpha thalassemia on the clinical and laboratory parameters among Nigerian sickle cell anemia (SCA) patients. This study aimed to determine the prevalence of alpha thalassemia and the influence of alpha thalassemia on laboratory parameters and clinical manifestations in a group of young Nigerian SCA patients.

METHODS

This was a cross-sectional retrospective study conducted on 100 patients with SCA and 63 controls. The diagnosis of SCA was confirmed by DNA studies. Alpha thalassemia genotyping was performed by multiplex gap-PCR method. Laboratory parameters including complete blood count, hemoglobin quantitation, serum lactate dehydrogenase (LDH), and bilirubin were determined with standard techniques.

RESULTS

Alpha thalassemia was found in 41 (41.0%) patients compared to 24 (38.1%) controls (P = 0.744), and all were due to the 3.7 κb α-globin gene deletions. Alpha thalassemia was associated with more frequent bone pain crisis, higher hemoglobin concentration, red blood cell count, and HbA₂ level among the patients. On the contrary, patients with alpha thalassemia had lower mean corpuscular volume, mean corpuscular hemoglobin, and white blood cell count (WBC) (P ˂ 0.05). There were 6 (6.0%) patients with leg ulcers, and none of them had alpha thalassemia, P = 0.04.

CONCLUSION

This study confirms that coexistence of alpha thalassemia with SCA significantly influences both the clinical and laboratory manifestations of young Nigerian SCA patients. The coexistence of this genetic modifier is associated with increased bone pain crisis and protects against sickle leg ulcers among the patients.

Alpha thalassemia among sickle cell anaemia patients in Kampala, Uganda

BACKGROUND

Sickle cell anaemia is prevalent in sub Saharan Africa. While α+-thalassaemia is known to modulate sickle cell anaemia, its magnitude and significance in Uganda have hitherto not been described.

OBJECTIVES

To determine the prevalence of α+thalassaemia among sickle cell anaemia patients in Mulago Hospital and to describe the clinical and laboratory findings in these patients.

METHODS

A cross sectional study was carried out on patients with sickle cell anaemia in Kampala. Dried blood spots were used to analyze for the deletional α+ thalassaemia using multiplex polymerase chain reaction.

RESULTS

Of the 142 patients with sickle cell anaemia, 110 (77.5%) had the αα+thalassaemia deletion. The gene frequency of (-α) was 0.425. Ninety one percent (100/110) of those with α+thalassaemia were heterozygous (αα/α-). Amongst the patients older than 60 months, 15 (83.3%) of those without αα+thalassaemia had significant hepatomegaly of greater than 4 cm compared to 36 (45.6%) of those with α+thalassaemia (p=0.003).

CONCLUSION

The gene frequency of (-α) of 0.425 noted in this study is higher than that reported from many places in Africa. Concurrent alpha thalassemia might be a protective trait against significant hepatomegaly in sickle cell anaemia patients more than 60 months of age at Mulago hospital.

Transcranial Doppler and brain MRI in children with sickle cell disease and high hemoglobin F levels

BACKGROUND/OBJECTIVE

While overt stroke and silent brain infarcts (SBI) are uncommon among Kuwaiti patients with sickle cell disease (SCD), there have been no previous transcranial Doppler (TCD) studies in this population. The main objective of this study is to determine TCD velocities in a group of Kuwaiti children with SCD and correlate same with brain magnetic resonance imaging (MRI) and angiography (MRA) findings.

MATERIALS AND METHODS

Forty-three steady-state, pediatric patients with SCD aged 10.1 ± 3.9 years (21 SS, 19 Sβ(0)Thal, and 3 SD) were studied. Twenty-six age-matched, normal siblings of the patients served as controls. TCD was performed using a General Electric (GE), Vivid 3 equipment and MRI/MRA with a GE Signa Excite HD 1.5 Tesla magnet. Complete blood count was with an electronic counter and Hb quantitation with cation-exchange high performance liquid chromatography (HPLC).

RESULTS

The mean time-averaged mean of the maximum velocity (TAMV) was significantly higher in the SCD group than the controls, but was normal (<170 cm/second) in all. The mean values were comparable among the SS and Sβ(0)thal groups. Five (11.1%) patients had SBI and all were between 12 and 16 years of age. There was no significant difference of TAMV in this group compared to those without infarcts. No patient showed evidence of stenosis or any other abnormalities in the circle of Willis vessels.

CONCLUSION

The mild phenotype among Kuwaiti patients with SCD is reflected in normal TCD velocities and a low prevalence of SBI in children with the disease.

Limitations of Hb F as a phenotypic modifier in sickle cell disease: study of Kuwaiti Arab patients

Sickle cell disease is characterized by phenotypic heterogeneity and many genetic modifiers have been identified with elevated Hb F being the most recognized ameliorating factor. Kuwaiti sickle cell disease patients carry the India/Arab chromosomal haplotype, which is associated with elevated Hb F (on average ~22%) on account of the Xmn1 site in the (G)γ-globin gene promoter. Most patients had either Hb SS or Hb S-β(0)-thalassemia (β(0)-thal) and there are a few Hb SD compound heterozygotes. We have carried out longitudinal clinical studies of these patients to document the pattern of morbidity, spleen function, brain and hip magnetic resonance imaging (MRI) for prevalence of silent brain infarcts and avascular necrosis of the femoral head (AVNFH), respectively. In addition, pulmonary function, SPECT (single photon emission computerized tomography) brain cerebral blood flow and response of selected patients to hydroxyurea (HU) treatment were also studied. The Hb SS and Hb S-β-thal patients have a generally mild phenotype compared to sickle cell disease in other populations and most patients do not have their first pain crisis until about the age of 4 years. Spleen function is retained till late childhood; pneumococcemia and other severe bacterial infections are rare. Overt stroke and silent brain infarcts are uncommon in childhood (~3% prevalence) although SPECT reveals cerebral blood flow deficits in ~30%. Avascular necrosis of the femoral head is, however, common with a prevalence of ~26% in children and 50% in adults. There is brisk response to HU in patients with frequent pain crises, with marked increases in Hb F levels. Patients who are compound heterozygotes for Hbs S and D-Los Angeles, have the most severe phenotype despite Hb F levels of >20% and Hb S <30%. In conclusion, although the patients have a uniformly elevated Hb F level, there are still considerable phenotypic heterogeneity and other modulating genetic factors that require further studies.

Coinheritance of α-thalassemia decreases the risk of cerebrovascular disease in a cohort of children with sickle cell anemia

The study estimated α-thalassemia (α-thal) prevalence and assessed its associations with clinical and hematological features in a random sample of Brazilian children with sickle cell anemia (208 Hb SS and 13 Hb S-β⁰-thal). α-Thalassemia genotyping was carried out by multiplex polymerase chain reaction (m-PCR) for seven alleles. Clinical and hematological data were retrieved from the 221 children's medical files. Their ages ranged from 2.5 to 10.4 years. Of the Hb SS children, 27.9% carried -α(3.7)/αα and 1.4% -α(3.7)/-α(3.7). The presence of α-thal was significantly associated with reduction in MCV, MCH, WBC values and reticulocyte counts. No significant association with blood transfusion or acute chest syndrome (ACS), was found. α-Thalassemia genotypes were strongly associated with reduction in risk for cerebrovascular disease (CVD) (conditional and abnormal transcranial Doppler or stroke; p = 0.007). The interaction of α-thal with other modulating factors should be investigated in order to define subphenotypes of the disease and to use them as clinical tools in the follow-up care of patients.

Susceptibility to invasive bacterial infections in children with sickle cell disease

Individuals with sickle cell disease (SCD) demonstrate an increased susceptibility to invasive bacterial infections (IBI). The most common organisms causing IBI are Streptococcus pneumoniae, nontyphi Salmonella species and Haemophilus influenzae type b (Hib). IBI are the most common causes of death in children below 5 years of age with SCD. Increased susceptibility to IBI is because of several factors including dysfunctional antibody production and opsonophagocytosis as well as defective splenic clearance. Early diagnosis of Hib and pneumococcal infections combined with antibiotic prophylaxis and immunization programs, could lead to significant improvements in mortality, especially in Africa.

The β‐Globin Gene Cluster Haplotypes in Sickle Cell Anemia Patients from Northeast Brazil: A Clinical and Molecular View

The beta(S)-globin haplotypes were studied in 78 sickle cell Brazilian patients from Bahia, Northeast Brazil, that has a large population of African origin. Hemoglobin (Hb) profiles were developed by high-performance liquid chromatography (HPLC), and beta(S)-globin gene haplotypes were determined by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) techniques. We identified 44 (55.0%) patients with the CAR/Ben (Central African Republic/Benin) genotype, 16 (20.0%) Ben/Ben, 13 (16.2%) CAR/CAR and seven (8.8%) with other genotypes. Analyses of the phenotypes showed clinical differences related only to Hb F levels and blood transfusion therapy; the presence of -alpha(-3.7)-thalassemia (thal) demonstrated statistical significance when associated with hematocrit (p=0.044), MCV (p=0.0007), MCH (p=0.012) and spleen sequestration events. The haplotype diversity found in the present study can be justified by information about the origin of the slave traffic period in Bahia during the 19th century. The specific characteristics described among the Bahian sickle cell patients could be confirmed by increasing the number of patients with specific genotypes and further studies of genetic markers.

Hemoglobin F concentration as a function of age in Kuwaiti sickle cell disease patients

OBJECTIVE

This study aimed to document the transition of hemoglobin (Hb) F levels from early childhood to adulthood in Kuwaiti sickle cell disease patients, investigating its relationship to sex, Hb genotype and coexistence of alpha-thalassemia trait.

SUBJECTS AND METHODS

The following parameters were extracted from the patients' records: age, sex, Hb, mean corpuscular volume, mean corpuscular Hb, red blood cell count, Hb F, Hb S, Hb A(2) and alpha-globin genotype. Hb quantitation was performed with cation exchange HPLC, while alpha-globin genotype was determined by PCR.

RESULTS

Records were available for 149 patients, made up of 94 SS and 55 Sbeta(0)thal; 83 males and 66 females, aged 3 months to 60 years (mean 10.5 +/- 1.8). The mean Hb F level in the whole population was 21.5 +/- 8.1% and was not significantly different between males and females, and SS or Sbeta(0)thal. When the age groups were analyzed, the Hb F level was highest (28.9 +/- 10.9%) in those below 5 years. Indeed, patients < or =2 years had a mean level of 31.9 +/- 13.0%. There was no significant difference in the Hb F levels in SS patients with or without coexistent alpha-thal trait.

CONCLUSIONS

Kuwaiti sickle cell disease patients below 5 years of age have close to 30% Hb F and this is probably a major reason why they usually do not present before this age, unlike patients elsewhere who present within the first year of life.

The influence of uridine diphosphate glucuronosyl transferase 1A promoter polymorphisms, beta-globin gene haplotype, co-inherited alpha-thalassemia trait and Hb F on steady-state serum bilirubin levels in sickle cell anemia

PURPOSE

Homozygosity for the (AT)7 allele of uridine diphosphate glucuronosyl transferase 1A (UGT1A1) gene polymorphism is associated with increased bilirubin levels in sickle cell anemia (SCA). In the present study, in addition to UGT1A1 promoter genotype, serum bilirubin level was related to other genetic modifiers -beta(S)-globin gene haplotype, Hb F, co-inherited alpha-thal trait, age and gender.

METHODS

The patients were randomly selected from the sickle cell clinic, Medical College of Georgia. UGT1A1 promoter polymorphisms were determined using automated sequencing. Other investigations were with standard techniques.

RESULTS

There were 67 SCA patients (41 males and 26 females), aged 2-44 yr (mean of 20.6 +/- 10.7). Ten (14.9%) patients were homozygous for the (AT)6 UGT1A1 allele, 35 (52.2%) were heterozygous for (AT)6 and (AT)7 alleles while 22 (32.8%) were homozygous for (AT)7. Serum bilirubin was significantly higher in the homozygous (AT)7 group (3.7 +/- 1.5, 3.8 +/- 2.3 and 5.6 +/- 2.4 mg/dL, respectively). It was also significantly higher in males than females and in patients aged >10 yr. There was a significant negative linear correlation (r = -0.304, P = 0.016) of serum bilirubin with Hb F. The beta-globin haplotype and co-existing alpha-thal trait did not have any significant influence on serum bilirubin levels. Patients on hydroxyurea were older, had lower Hb F, but higher mean serum bilirubin. The latter also was signifcantly higher among those with UGT1A1 (AT)7 homozygosity.

CONCLUSIONS

Apart from UGT1A1 (AT)7 homozygosity, Hb F, age and gender are the other factors that significantly influence serum bilirubin level in SCA.

Predicting clinical severity in sickle cell anaemia

The ability to predict the phenotype of an individual with sickle cell anaemia would allow a reliable prognosis and could guide therapeutic decision making. Some risk factors for individual disease complications are known but are insufficiently precise to use for prognostic purposes; predicting the global disease severity is not yet possible. Genetic association studies, which attempt to link gene polymorphisms with selected disease subphenotypes, may eventually provide useful methods of foretelling the likelihood of certain complications and allow better individualized treatment.

Silent brain infarcts in adult Kuwaiti sickle cell disease patients

Although overt stroke is a common complication of sickle cell disease (SCD), its incidence is very low in Kuwaiti patients. On the other hand, the prevalence of silent brain infarcts, which is reported to be about 17-20% in American patients, has not been documented in adult Kuwaiti patients. This is a 1-year study of consecutive, asymptomatic SCD patients seen in the hematology clinic of Mubarak Al-Kabeer Hospital. Patients with a past history of seizure or any other neurological abnormality were excluded. The patients' charts were reviewed for frequency of hospitalizations, any documented complications, and steady-state CBC. MRI was done with a 1.5-Tesla unit with super-conducting magnet. T1- and T2-weighted sagittal and axial sections and proton-density axial images were obtained in 5-mm-thick sections. Thirty-five patients were studied, made up of 25 SS and 10 Sbeta(0)Thal, aged between 17 and 44 years, with a mean age of 26.9 +/- 9.3 years. MRI findings consistent with infarcts were found in 7 (20.0%) patients-6 SS and 1 Sbeta(0)thal-with a mean age of 31.8 +/- 8.2 years, which was significantly higher (P < 0.05) than the mean age of the unaffected group (25.1 - 9.0 years). There were also no differences in the mean Hb, Hb F, or any other hematological parameter in the two groups. Among the affected 6 SS, 2 had co-existent alpha-thal trait. It is interesting that, while silent infarcts are prevalent in young American patients, it is in the older age group that they occur in Kuwaiti patients. Further studies are needed to investigate the factors modulating this heterogeneity.

Temporal sequence of splenic dysfunction in sickle cell disease

Sickle cell patients develop splenic dysfunction early in the course of their disease as shown by failure to visualize the organ on technetium-99m colloid scintigraphy. However, preliminary studies from our center have shown that, when the spleen is not demonstrable on colloid uptake, it may be visualized on technetium-99m heat-denatured RBC scintigraphy. With time, however, the spleen can no longer be visualized with both tests in many patients. We have studied 46 patients aged 2 to 16 years, which included 36 SS, 7 Sbeta(0) thal, and 3 SD. Eighteen (39.1%) had normal splenic colloid uptake (Group 1), 15 (32.6%) had partial uptake (Group 2), and 13 (28.3%) had absent uptake (Group 3). When the patients in Group 1 were compared to those in the two other groups, there was no significant difference in the mean age and Hb F values. However, the mean Hb of 10.2 g/dl in Group 1 was significantly higher than the value of 9.0 g/dl in the other two groups. In addition, 60% of the SS patients with normal uptake and 40% of those with partial or absent uptake had co-existing alpha-thal trait; the difference in this proportion is significant (chi(2) = 85, P < 0.0001). Heat-denatured RBC scintigraphy was carried out on five patients in Group 2, and the spleen was visible in all, while of 12 children in Group 3, the spleen was visible only in 4 patients. This study demonstrates that the phagocytic function of the spleen, which is tested by colloid uptake, is the first to be lost while the filtration function, tested by denatured RBC uptake, persists for much longer. This finding may have significant implications for the clinical symptomatology and therapeutic strategies of sickle cell disease.

Avascular necrosis of the hip in children with sickle cell disease and high Hb F: magnetic resonance imaging findings and influence of alpha-thalassemia trait

Avascular necrosis (AVN) of the hip is a common cause of morbidity in sickle cell disease (SCD). Its prevalence increases with age and predisposing factors include coexistent alpha-thalassemia trait, frequent vaso-occlusive crisis and a high hematocrit (Hct). SCD is relatively mild among Kuwaiti patients because of their elevated Hb F levels, but a subset exists with severe recurrent vaso-occlusive crises. We carried out a prospective magnetic resonance imaging (MRI) study of the hip in a group of patients being followed in the Pediatric Hematology clinics of Al-Mubarak and Al-Amiri Hospitals. The association of AVN with age, frequency of hospitalization, alpha-thal trait, steady-state Hb, Hct, Hb F, WBC and platelet counts was investigated. MRI was carried out with a 1.5-tesla GE unit with a super-conducting magnet. Thirty patients (19 males, 11 females) (23 SS and 7 SbetaThal) were studied. Their ages ranged from 6 to 17 years, with a mean of 9.8 +/- 3.5 years, and Hb F from 11 to 35% with a mean of 22.8 +/- 5.7%. Among the SS patients, 11 (47.8%) had coexistent alpha-thal trait (-3.7-kb deletion). A total of 8 (26.7%) patients (6 SS and 2 SbetaThal) had varying degrees of osteonecrosis of the hip. Four (36.4%) of the 11 SS patients with alpha-thal trait and 2 (16.7%) of those without alpha-thal trait had osteonecrosis. This difference is, however, not statistically significant (chi(2) = 0.3, p = 0.5). While there was also no significant difference in the mean age and hematological parameters (Hb, Hct, Hb F, WBC, platelets), the SS patients with osteonecrosis had a significantly higher number of hospitalizations for vaso-occlusive crisis in the preceding 3 years than those without osteonecrosis.

Frequency of the 677 C-->T mutation of the methylenetetrahydrofolate reductase gene among Kuwaiti sickle cell disease patients

Sickle cell disease (SCD) is relatively mild among Kuwaiti Arabs. However, an atypical subset of patients exists with frequent, severe vaso-occlusive crisis and osteonecrosis. The thermolabile variant of MTHFR, resulting from a C-->T mutation at nucleotide 677, has been shown to be associated with hyperhomocysteinemia, which is an important risk factor for premature vascular disease. We have screened an unselected group of 41 Kuwaiti SCD patients (33 SS and 8 Sbeta(0)-thal) attending the Hematology Clinic of Kuwait University Teaching Hospital for the MTHFR mutation, using a PCR-RFLP method. The patients were aged 2-41 years (mean of 12.8 +/- 8.6). One (2.4%) individual was homozygous for the mutation while 15 (36.6%) were heterozygous, giving an allele frequency of 20.7%. Twenty-one patients (14 SS and 7 Sbeta(0)-thal) were screened for osteonecrosis using MRI of the hip (spin-echo T1- and T2-weighted images). Seven (33.3%) had varying degrees of osteonecrosis, among whom the frequency of the 677 C-->T allele was 21.4%. The frequency was identical among those without osteonecrosis. Although the allele frequency is higher among our patients compared to American SS patients, our results do not suggest an association with osteonecrosis.

Th1 and Th2 cytokine profiles in sickle cell disease

We have investigated the levels of Th1 (IL-2 and IFN-gamma) and Th2 (IL-4) cytokines in the plasma and supernatants following peripheral blood mononuclear cell culture and mitogen stimulation in a group of 39 patients with sickle cell disease (SCD) made up of 29 SS, 8 Sbeta-thal and 2 Hb SD in steady state. Five SS patients were studied during 7 episodes of vaso-occlusive crisis. Twenty-four control (3 Hb AS and 21 Hb AA) were also studied; 10 were acutely ill while 14 were healthy at the time of the study. The plasma levels of IL-2 and IFN-gamma were similar in the patients and the controls. However, plasma IL-4 was significantly higher among the steady-state SS patients than in the controls. While there was no significant difference in cytokine levels following mitogen stimulation in the different groups, plasma IL-2 to IL-4 and IFN-gamma to IL-4 ratios were significantly lower among the steady-state SS patients, indicating a possible Th2 bias in our sickle cell patients and suggesting a possible mechanism to explain the predisposition of SCD patients to bacterial infections. However, SS patients with good splenic function showed a relative Th1 bias, which may be an additional explanation for the protection against bacterial infections in such patients.

Tumor necrosis factor-alpha is undetectable in the plasma of SS patients with elevated Hb F

Steady-state sickle cell disease (SCD) patients may have increased plasma levels of acute phase reactants and pro-inflammatory cytokines because of subclinical inflammation. We have estimated TNF-alpha levels in the plasma and in supernatants following peripheral blood mononuclear cell (PBMC) activation with phytohemagglutinin (PHA) in a group of Kuwaiti SCD patients using ELISA. The group consisted of 28 SS, 8 Sbeta-thal, and 2 SD patients all in steady state; 5 SS patients were studied during 7 episodes of painful crisis. The subjects were aged 2 to 16 years, with a mean of 7.3 +/- 3.5 years. The beta(S)-globin gene cluster haplotype, alpha-tha1 status, and spleen function were determined in the SS group using standard techniques. Most (82%) were homozygous for the Saudi Arabia/India haplotype and had elevated Hb F levels ranging from 15% to 35%. There were 24 controls (Hb AA or AS), of whom 14 were healthy and 10 were acutely ill at the time of the study. None of the children with SCD (either in steady state or crisis) had detectable plasma TNF-alpha, but four controls (3 acutely ill and one healthy) had levels ranging from 61.7 to 249.8 pg/mL. Following PHA stimulation most subjects responded with high levels of TNF-alpha, with the median level among the steady-state SS patients being significantly higher than that in the controls (both the acutely ill or healthy). It therefore appears that because of the mild disease among our Arab SS children, TNF-alpha is not detectable in their plasma in steady state; these children, however, had a significantly higher response than controls following PBMC activation.

Influence of alpha-thalassemia on cholelithiasis in SS patients with elevated Hb F

Chronic hemolysis, with consequent hyperbilirubinemia, predisposes SS patients to pigment gallstones. The other factors which influence the development of stones in these patients have not been identified. We have carried out a combined prospective and retrospective study of SS patients in Kuwait and specifically investigated the influence of coexistent alpha-thal trait on the prevalence of gallstones. A total of 45 patients (30 males, 15 females) with ages ranging from 1 to 16 years (mean 7.2 +/- 3.1) were studied. Most were either homozygotes for the Saudi Arabia/India haplotype (86.7%) or compound heterozygotes for this and the Benin haplotype (11.1%). They were screened for gallstones with ultrasonography. alpha-Globin genotypes were determined using a combination of PCR and allele-specific oligonucleotide hybridization techniques to identify the common alpha-thalassemia alleles in this population. Gallstones were detected in 7 (15.6%) patients (4 males, 3 females), whose mean age (10.5 +/- 5.5 years) was significantly higher than that (6.8 +/- 3.2 years) of those without stones (p < 0.01). The mean total Hb of the former (8.4 +/- 0.8 g/dl) was also significantly (p < 0.05) lower than in the latter (9.5 +/- 1.3 g/dl), while the difference in mean Hb F levels was not significant. None of the 4 alpha-thal homozygotes had gallstones while 2 of 13 heterozygotes and 5 of the 23 patients without coexistent alpha-thal had. The differences in these proportions are statistically significant (chi2 = 20.4, p < 0. 001). It therefore appears that coexistent alpha-thal decreases the chance of developing gallstones in Arab SS patients. This may be related to less hemolysis in such patients as shown by their higher mean Hb level.