The spleen in the sickling disorders: an update

Partial Splenic Embolization in Paediatric Sickle Cell Disease Patients with Hypersplenism

PURPOSE

To assess the safety and efficacy of partial splenic embolization (PSE) to reduce the need of transfusions and improve hematologic parameters in patients with hypersplenism and sickle cell disease (SCD).

MATERIAL AND METHODS

This prospective study includes 35 homozygous hemoglobin S patients with SCD and hypersplenism who underwent PSE from 2015 until 2021 in Kinshasa. Patients were evaluated, before and after PSE (1, 3 and 6 months), using clinical, laboratory and ultrasonographic methods. PSE was performed with the administration of gelatin sponge particles embolizing 60-70% of the splenic parenchyma.

RESULTS

The mean age was 10 (± 4) years and (21/35, 60%) were male. After PSE Leucocytes decreased at 3 months (16 692.94 vs 13 582.86, p = 0.02) and at six months Erythrocytes increased 2 004 000 vs. 2 804 142 (p < 0.001), Platelets increased (168 147 vs. 308 445, p < 0.001) and Hemoglobin increased (5.05 g/dL vs. 6.31 g/dL, p < 0.001) There was a significant dicrease in the need of transfusions from 6 (2-20) before PSE to 0.06 (0-1) after PSE (p < 0.001). The most frequent complication was splenic rupture (4/35, 11.4%), seen only and in all patients with hypoechogenic nodules at baseline.

CONCLUSION

PSE is a safe procedure in patients with SCD and hypersplenism, that do not have hypoechogenic nodules in the spleen. PSE improves the hematological parameters and reduces the frequency of blood transfusions.

Incidence and risk factors for osteonecrosis of the femoral head in five hundred and ten sickle cell disease paediatric patients

PURPOSE

Osteonecrosis of the femoral head (ONFH) is a degenerative and progressive disorder that mainly affects people with sickle cell disease (SCD). Herein, we aimed to search for a better understanding of markers that can act as risk factors for ONFH in patients with SCD.

METHODS

We conducted a retrospective study including 510 SCD patients followed over 23 years. Patients were divided into the ONFH group and the no-ONHF control group. Univariate and multivariate logistic regression analyses were performed to identify risk factors.

RESULTS

Among 510 SCD patients, 41(8%) were diagnosed with ONFH at a mean age of 167 months ± 64 (72-288). The cumulative incidence of ONHF increased from 2.3% at ten years to 18.3% at 20 years of age. The radiological grade 3 ONHF was predominant. No significant differences in sex, age at diagnosis of SCD, and Hb genotype were found between groups. The patient age and the time since diagnosis of SCD were statistically higher in patients with ONHF in univariate and multivariate analysis. ONHF was also associated with higher creatinine level (p = 0.001) lower LDH level (p = 0.006), and higher number of vaso-occlusive crisis (VOC)/patient/year (p < 0.001). The cumulative incidence of ONHF in patients having more than 3 VOC/year was significantly higher (43% versus 18.9% at 20 years, p < 0.001). In addition, infections, gallstones, growth delay, delayed initiation of hydroxyurea, and a higher transfusion rate were significantly associated with ONFH.

CONCLUSION

These findings confirm that ONFH is closely related to the age, severity, and duration of SCD. Better management of this disease prevents acute and chronic complications, and early screening of the ONFH as soon as the first signs of the severity of the disease are detected provides a better functional prognosis.

In silico and in vitro study of the adhesion dynamics of erythrophagocytosis in sickle cell disease

Erythrophagocytosis occurring in the spleen is a critical process for removing senescent and diseased red blood cells (RBCs) from the microcirculation. Although some progress has been made in understanding how the biological signaling pathways mediate the phagocytic processes, the role of the biophysical interaction between RBCs and macrophages, particularly under pathological conditions such as sickle cell disease, has not been adequately studied. Here, we combine computational simulations with microfluidic experiments to quantify RBC-macrophage adhesion dynamics under flow conditions comparable to those in the red pulp of the spleen. We also investigate the RBC-macrophage interaction under normoxic and hypoxic conditions. First, we calibrate key model parameters in the adhesion model using microfluidic experiments for normal and sickle RBCs under normoxia and hypoxia. We then study the adhesion dynamics between the RBC and the macrophage. Our simulation illustrates three typical adhesion states, each characterized by a distinct dynamic motion of the RBCs, namely firm adhesion, flipping adhesion, and no adhesion (either due to no contact with macrophages or detachment from the macrophages). We also track the number of bonds formed when RBCs and macrophages are in contact, as well as the contact area between the two interacting cells, providing mechanistic explanations for the three adhesion states observed in the simulations and microfluidic experiments. Furthermore, we quantify, for the first time to our knowledge, the adhesive forces between RBCs (normal and sickle) and macrophages under different oxygenated conditions. Our results show that the adhesive forces between normal cells and macrophages under normoxia are in the range of 33-58 pN and 53-92 pN for sickle cells under normoxia and 155-170 pN for sickle cells under hypoxia. Taken together, our microfluidic and simulation results improve our understanding of the biophysical interaction between RBCs and macrophages in sickle cell disease and provide a solid foundation for investigating the filtration function of the splenic macrophages under physiological and pathological conditions.

Attitudes and practices of unmarried adults towards sickle cell disease: emergent factors from a cross sectional study in Nigeria's capital

INTRODUCTION

Sickle cell disease is a genetic autosomal blood disorder that causes red blood cells to turn rigid and crescent shaped. The condition ultimately results to several complications leading to organ damage. This study aimed at assessing attitudes and practices of unmarried adults towards sickle cell disease.

METHODS

A cross sectional study was undertaken in the Nigerian Federal Capital Territory. Data were collected using a well-structured questionnaire. Descriptive and inferential statistics were undertaken.

RESULTS

Male and female participants were of a similar proportion as represented by 52% and 48%. The overall mean score for attitude towards sickle disease was 6.60 ± 2.583 (range; 0-11). A higher attitude score was observed among female participants (p = 0.012), older participants reported a better attitude towards sickle cell disease (p < 0.001), and level of education also influenced perception towards the disease (p < 0.001). Three-quarters of the participants (73.4%) supported the need for contextual legislation to prohibit marriage between two sickle cell carriers. More than one-tenth of the sample (14.4%) indicated that they would marry someone with sickle cell disease irrespective of their own genotype. Whilst two-thirds of the study participants (67.1%) indicated that they would prioritise sickle cell screening in their relationships, a third of them (33.3%) expressed a contrary standpoint.

CONCLUSION

Findings emanating from this research can guide Government and other critical Stakeholders in developing contextual policies and practices that will reduce the burden of sickle cell disorder.

Hematopoietic cell transplantation for sickle cell disease: updates and future directions

Excellent outcomes in hematopoietic cell transplantation (HCT) from HLA-identical siblings, improvements in conditioning regimens, novel graft-versus-host disease prophylaxis, and the availability of alternative donors have all contributed to the increased applicability and acceptability of HCT for sickle cell disease (SCD). In young children with symptomatic SCD with an available HLA-identical related donor, HCT should be carefully considered. HCT from alternative donors is typically undertaken only in patients with severe symptoms, causing or likely to cause organ damage, and in the context of clinical trials. Patients undergoing HCT for SCD require careful counseling and preparation. They require careful monitoring of unique organ toxicities and complications during HCT. Patients must be prospectively followed for a prolonged time to determine the long-term outcomes and late effects of HCT for SCD. Thus, there is a need for a universal, longitudinal clinical registry to follow patients after HCT for SCD in conjunction with individuals who do not receive HCT to compare outcomes. Antibody-based conditioning and ex-vivo umbilical cord blood expansion are likely to improve the availability and acceptability of HCT. In addition, new disease-modifying drugs and the emerging option of the autologous transplantation of gene-modified hematopoietic progenitor cells are likely to expand the available therapeutic options and make decision-making by patients, physicians, and caregivers even more complicated. Future efforts must also focus on determining the impact of socioeconomic status on access to and outcomes of HCT and the long-term impact of HCT on patients, families, and society.

Imaging of Acute Abdominal Pain in the Pediatric Population

Acute abdominal pain is a common complaint in pediatrics. Although age and location of pain can help focus differential diagnosis, imaging plays an essential role in clinical evaluation. In this review, we discuss the optimal imaging approach to pediatric patients with acute abdominal pain and important imaging findings in the most common causes of abdominal pain in the pediatric population. [Pediatr Ann. 2020;49(9):e380-e388.].

Prevalence and predictive factors of splenic sequestration crisis among 423 pediatric patients with sickle cell disease in Tunisia

This study was aimed to identify the predictors of splenic sequestration crisis (SSC) among pediatric patients with sickle cell disease (SCD). This prognosis study was carried out in the pediatric immuno-hematology unit, over 20 years (1998 to 2017), enrolling patients with SCD. The cox model was used in multivariate analysis. Among 423 patients with SCD (240 S/S phenotype, 128 S/B0, 30 S/B+, 14 S/O arab and 11 S/C), 150(35.4%) had at least one episode of SSC. The average age of patients at the first episode was 48.3 months ± 32.4(2-168). Recurrence of SSC was observed in 117 patients (78%). Spleen size ≥3 cm at baseline was the strongest predictor of SSC occurrence (HR = 7.27, CI: 4.01-13.20, p = 0.05) and recurrence (HR = 6.37, CI: 1,46-27.83, p = 0.01). Pallor revealing the disease, age at onset of symptoms <24 months and reticulocytosis ≥300,000/mm³ increased the risk of SSC. Pain crisis revealing the disease as well as neutrophilia was associated with a lower risk of SSC. In conclusion, this study confirmed the high prevalence of SSC in SCD and the high frequency of recurrence after a first episode. The SSC occurrence and recurrence were intimately linked to the presence of splenomegaly, chronic pallor revealing the disease as well as reticulocytosis.

The mouse Char10 locus regulates severity of pyruvate kinase deficiency and susceptibility to malaria

Pyruvate kinase (PKLR) deficiency protects mice and humans against blood-stage malaria. Although mouse strain AcB62 carries a malaria-protective Pklr^I90N genetic mutation, it is phenotypically susceptible to blood stage malaria induced by infection with Plasmodium chabaudi AS, suggesting a genetic modifier of the Pklr^I90N protective effect. Linkage analysis in a F2 cross between AcB62 (Pklr^I90N) and another PK deficient strain CBA/Pk (Pklr^G338D) maps this modifier (designated Char10) to chromosome 9 (LOD = 10.8, 95% Bayesian CI = 50.7–75Mb). To study the mechanistic basis of the Char10 effect, we generated an incipient congenic line (Char10C) that harbors the Char10 chromosome 9 segment from AcB62 fixed on the genetic background of CBA/Pk. The Char10 effect is shown to be highly penetrant as the Char10C line recapitulates the AcB62 phenotype, displaying high parasitemia following P. chabaudi infection, compared to CBA/Pk. Char10C mice also display a reduction in anemia phenotypes associated with the Pklr^G338D mutation including decreased splenomegaly, decreased circulating reticulocytes, increased density of mature erythrocytes, increased hematocrit, as well as decreased iron overload in kidney and liver and decreased serum iron. Erythroid lineage analyses indicate that the number of total TER119⁺ cells as well as the numbers of the different CD71⁺/CD44⁺ erythroblast sub-populations were all found to be lower in Char10C spleen compared to CBA/Pk. Char10C mice also displayed lower number of CFU-E per spleen compared to CBA/Pk. Taken together, these results indicate that the Char10 locus modulates the severity of pyruvate kinase deficiency by regulating erythroid responses in the presence of PK-deficiency associated haemolytic anemia.

Spleen histology in children with sickle cell disease and hereditary spherocytosis: hints on the disease pathophysiology

Hereditary spherocytosis (HS) and sickle cell disease (SCD) are associated with splenomegaly and spleen dysfunction in pediatric patients. Scant data exist on possible correlations between spleen morphology and function in HS and SCD. This study aimed to assess the histologic and morphometric features of HS and SCD spleens, to get possible correlations with disease pathophysiology. In a large series of spleens from SCD, HS, and control patients, the following parameters were considered: (i) macroscopic features, (ii) lymphoid follicle (LF) density, (iii) presence of perifollicular marginal zones, (iv) presence of Gamna-Gandy bodies, (v) density of CD8-positive sinusoids, (vi) density of CD34-positive microvessels, (vii) presence/distribution of fibrosis and smooth muscle actin (SMA)-positive myoid cells, and (viii) density of CD68-positive macrophages. SCD and HS spleens had similar macroscopic features. SCD spleens had lower LF density and fewer marginal zones than did HS spleens and controls. SCD also showed lower CD8-positive sinusoid density, increased CD34-positive microvessel density and SMA-positive myoid cells, and higher prevalence of fibrosis and Gamna-Gandy bodies. HS had lower LF and CD8-positive sinusoid density than did controls. No significant differences were noted in red pulp macrophages. By multivariate analysis, most HS spleens clustered with controls, whereas SCD grouped separately. A multiparametric score could predict the degree of spleen changes irrespective of the underlying disease. In conclusion, SCD spleens display greater histologic effacement than HS, and SCD-related changes suggest impaired function due to vascular damage. These observations may contribute to guide the clinical management of patients.

Expected Sonographic Appearance of the Spleen in Children and Young Adults With Sickle Cell Disease: An Update

OBJECTIVES

To update the imaging literature regarding spleen appearances in young patients with sickle cell disease (SCD).

METHODS

We conducted a retrospective study and included 112 patients age 0 to 21 years with SCD who had at least 1 abdominal sonogram at our institution between 1999 and 2011. Radiologic findings were compared between risk groups by χ(2) analysis. Findings were correlated with other imaging modalities when available.

RESULTS

In our cohort, 35.7% of patients had autosplenectomy, and 8.0% had undergone surgical splenectomy. Only 5.0% of individuals age 0 to 5 years had autosplenectomy. In those who had not undergone surgical splenectomy or autosplenectomy, 76.2% had echogenic spleens, heterogeneous-appearing spleens, or both, and patients with the homozygous sickle cell anemia (HbSS) genotype were more likely to have an abnormal spleen echo texture. Patients treated with transfusions had echogenic spleens and had a higher frequency of splenic regeneration nodules. Most patients (80%) with splenomegaly did not require surgical splenectomy after 5.7 years of follow-up.

CONCLUSIONS

Twenty years ago, children with HbSS SCD were expected to have autosplenectomy by age 5 years. There have been changes in the radiologic appearance of the spleen in patients with SDC, likely due to improved supportive care and the use of acute and chronic transfusion therapy. We found that autosplenectomy is rare by age 5 years, and during childhood and adolescence, the spleen typically appears echogenic, heterogeneous, or both, depending on disease severity.

Phenotypic differences of CD4(+) T cells in response to red blood cell immunization in transfused sickle cell disease patients

Alloimmunization against red blood cells (RBCs) is the main immunological risk associated with transfusion in patients with sickle cell disease (SCD). However, about 50-70% of SCD patients never get immunized despite frequent transfusion. In murine models, CD4(+) T cells play a key role in RBC alloimmunization. We therefore explored and compared the CD4(+) T-cell phenotypes and functions between a group of SCD patients (n = 11) who never became immunized despite a high transfusion regimen and a group of SCD patients (n = 10) who had become immunized (at least against Kidd antigen b) after a low transfusion regimen. We studied markers of CD4(+) T-cell function, including TLR, that directly control lymphocyte function, and their spontaneous cytokine production. We also tested responders for the cytokine profile in response to Kidd antigen b peptides. Low TLR2/TLR3 expression and, unexpectedly, strong expression of CD40 on CD4(+) T cells were associated with the nonresponder status, whereas spontaneous expression of IL-10 by CD4(+) T cells and weak Tbet expression were associated with the responder status. A Th17 profile was predominant in responders when stimulated by Jb(k) . These findings implicate CD4(+) T cells in alloimmunization in humans and suggest that they may be exploited to differentiate responders from nonresponders.

The current state of imaging pediatric hemoglobinopathies

The hemoglobinopathies are a group of genetic disorders with a broad spectrum of clinical manifestations and radiologic findings. The imaging of pediatric hemoglobinopathies, which is influenced by concomitant hemosiderosis and the sequela of chelation therapy, has evolved over the years along with ever-improving technology. This article reviews and illustrates the most common radiographic and cross-sectional imaging findings of the 2 best known and clinically relevant hemoglobinopathies in pediatric patients, sickle cell disease and β-thalassemia.

Current sickle cell disease management practices in Nigeria

BACKGROUND

Although Nigeria has the highest burden of sickle cell disease (SCD) worldwide, there is still variable and poor utilisation of standard-of-care practices for SCD patients in the country.

METHODS

This was a questionnaire survey of doctors in some dedicated SCD clinics in Nigeria in order to document the facilities available and common management practices.

RESULTS

There were responses from 18 clinics based in 11 institutions. The number of patients being followed in each centre ranged from 15 to approximately 11 000. All clinics provided malaria prophylaxis and folic acid routinely to their patients. Only eight clinics prescribe penicillin prophylaxis. Eight prescribe hydroxyurea to patients who can afford it when indicated. All of the centres except three have electronic cell counters, but all had access to haemoglobin electrophoresis. Three had high-performance liquid chromatography machines installed but none was being routinely used. One institution had a functioning molecular biology laboratory. There is no official newborn screening programme in the country. All had access to microbiology and chemistry laboratories. Nine institutions had CT, six had MRI and three had transcranial Doppler facilities.

CONCLUSION

The care available for SCD in Nigeria is still suboptimal and there is an urgent need for concerted effort to tackle the problem, but to make a significant impact on the burden of the disease would require more focus at the primary care level. Some steps to achieving this are outlined.

Clonal structure ofStaphylococcus aureuscolonizing children with sickle cell anaemia and healthy controls

Children with sickle cell anaemia (SCA) might carry hospital-associated bacterial lineages due to frequent hospital stays and antibiotic treatments. In this study we comparedStaphylococcus aureusfrom SCA patients (n = 73) and healthy children (n = 143) in a cross-sectional study in Gabon.S. aureuscarriage did not differ between children with SCA (n = 34, 46·6%) and controls matched for age, residence and sex (n = 67, 46·9%). Both groups shared similarS. aureusgenotypes. This finding points towards a transmission ofS. aureusbetween both groups in the community. We conclude that resistance rates from population-based studies with healthy participants could therefore also be used to guide treatment and prophylaxis of endogenous infections in children with SCA despite a different selection pressure.

Splenic morphological changes are accompanied by altered baseline immunity in a mouse model of sickle-cell disease

Although functional asplenia from infarctions may be a major contributor to increased infectious mortality in sickle-cell disease (SCD), this relationship has not been fully defined. We used the transgenic Berkeley SCD mouse to define blood and splenic immunophenotypic differences in this model compared with C57BL/6 and hemizygous controls. In the serum of SCD mice, we found increased IgG2a and suppressed IgM, IgG2b, and IgA levels. Serum IL-6 levels in SCD mice were elevated, whereas IL-1α, CXCL10, and CCL5 levels were decreased. The blood of SCD mice had higher white blood cell counts, with an increased percentage of lymphocytes and decreases in other leukocytes. Immunophenotyping of lymphocytes revealed higher percentages of CD8(+) and T-regulatory cells and lower percentages of B cells. SCD mouse spleens exhibited histological disorganization, with reduction of defined lymphoid follicles and expansion of red pulp, a greater than fourfold increase in splenic mononuclear cells, marked expansion of the nucleated red blood cell fraction, and B-cell and CD8(+) T-cell lymphopenia. Within the splenic B-cell population, there was a significant decrease in B-1a B cells, with a corresponding decrease in IgA secreting plasma cells in the gut. Confocal microscopy of spleens demonstrated complete disruption of the normal lymphofollicular structure in the white pulp of SCD mice without distinct B, T, and marginal zones. Our findings suggest that altered SCD splenic morphological characteristics result in an impaired systemic immune response.

Carriage of encapsulated bacteria in Gabonese children with sickle cell anaemia

Sickle cell anaemia (SCA) is a haemoglobin disorder that alters the deformability of erythrocytes through abnormal polymerization of haemoglobin. Children with SCA have an increased risk of infections with encapsulated bacteria. To guide the antibiotic prophylaxis and vaccinations in children with SCA in Gabon, we characterized Streptococcus pneumoniae, Staphylococcus aureus and Haemophilus influenzae from children with and without SCA. We performed a cross-sectional study and compared nasal and pharyngeal S. pneumoniae, Staph. aureus and H. influenzae isolates from SCA children (n = 73) with comparators matched for age, residence and sex (n = 143) in a matched-comparison analysis. The resistance pattern and capsular type were identified for each isolate. The total carriage rate for S. pneumoniae, Staph. aureus and H. influenzae was 13.8%, 46.7% and 12.5%, respectively, and did not differ between groups (p >0.05). The mean number of days under antibiotic treatment in the past year was higher in children with SCA than in controls (penicillin: 70.1 vs 0.1 days, p 0.00002). The total non-susceptibility rate was 30% for oral and parenteral (meningitis) penicillin in S. pneumoniae, resistance rates were 1.6% for oxacillin in Staph. aureus and 14.8% for ampicillin in H. influenzae. Susceptibility to antibiotic agents and distribution of capsular types did not differ significantly between both groups. In conclusion, carriage and resistance rates are similar in children with and without SCA. Our data provide the basis to guide empiric therapy of invasive diseases caused by S. pneumoniae, Staph. aureus and H. influenza in children in Gabon.

Abdominal ultrasound with scintigraphic and clinical correlates in infants with sickle cell anemia: baseline data from the BABY HUG trial

OBJECTIVE

The purpose of this study is to perform and evaluate baseline abdominal ultrasound in infants with sickle cell anemia who participated in the BABY HUG multiinstitutional randomized placebo-controlled trial of hydroxyurea therapy and to examine the potential relationships among ultrasound results and clinical, nuclear medicine, and laboratory data.

SUBJECTS AND METHODS

After local institutional review board approval and with informed guardian consent, 116 girls and 87 boys (age range, 7.5-18 months) with sickle cell anemia underwent standardized abdominal sonography at 14 institutions. Imaging was centrally reviewed by one radiologist who assessed and measured the spleen, kidneys, gallbladder, and common bile duct. Baseline physical assessment of spleen size, serum alanine aminotransferase and bilirubin levels, (99m)Tc sulfur colloid liver-spleen scans, and (99m)Tc diethylenetriaminepentaacetic acid clearance glomerular filtration rates (GFRs) were obtained. Analysis of variance and the Student test were performed to compare sonographic findings to published results in healthy children and to clinical and laboratory findings.

RESULTS

The mean (± SD) spleen volume (108 ± 47 mL) was significantly greater than published normal control values (30 ± 14 mL; p < 0.0001). There was no correlation between spleen volume and function assessed by liver-spleen scan. The mean GFR (125 ± 34 mL/min/1.73 m(2)) was elevated compared with control GFRs (92 ± 18 mL/min/1.73 m(2)). Renal volumes (right kidney, 29 ± 8 mL; left kidney, 31 ± 9 mL) were significantly greater than control volumes (right kidney, 27 ± 3 mL; left kidney, 27 ± 3 mL; p < 0.0001) and were positively correlated with GFR (p = 0.0009). Five percent of patients had sonographic biliary abnormalities (sludge, n = 6; dilated common bile duct, n = 2; and cholelithiasis and thickened gallbladder wall, n = 1 each). There was no correlation between biliary sonographic findings and laboratory results.

CONCLUSION

In infants with sickle cell anemia, sonographic spleen volume does not reflect function, but increased renal volume correlates with GFR and is consistent with hyperfiltration. Sonographic biliary abnormalities can occur early in life, while remaining clinically silent.

Robust erythrophagocytosis leads to macrophage apoptosis via a hemin-mediated redox imbalance: role in hemolytic disorders

MP from the RES are responsible for the clearance of senescent RBC. Although the frequency of senescent RBC is low under steady-state conditions, it increases dramatically during hemolytic disorders, resulting in enhanced erythrophagocytosis. As erythrophagocytosis has been involved in MP dysfunction and as certain hemolytic disorders associate to MP apoptosis, a possible link between erythrophagocytosis and the viability of phagocytes was investigated herein. To mimic hemolytic disorders, two distinct in vitro models, artificially oxidized RBC and DSRBC, were chosen to study the erythrophagocytosis impact on the viability of J774A.1 MP. Although CRBC were weakly phagocytosed and did not affect MP viability significantly, erythrophagocytosis of oxidized RBC and DSRBC was robust and resulted in a sharp decrease of MP viability via apoptosis. Under these conditions, Hb-derived HE was shown to be involved in the induction of apoptosis. Moreover, oxidized RBC, DSRBC, and HE generated ROS species, which were responsible for the apoptosis of MP. Furthermore, HO-1, strongly induced in response to treatment with oxidized RBC, DSRBC, or HE, was shown to protect MP partially against apoptosis, suggesting that robust erythro-phagocytosis may exceed the detoxification capabilities of MP. Taken together, these results suggest that enhanced erythrophagocytosis associated to hemolytic disorders leads to MP apoptosis in vitro and may have critical implications for the control of malaria infection and for the exacerbated susceptibility to bacterial infections during hemolytic disorders.

Sickle cell disease resulting from uniparental disomy in a child who inherited sickle cell trait

Sickle cell disease (SCD) is a classic example of a disorder with recessive Mendelian inheritance, in which each parent contributes one mutant allele to an affected offspring. However, there are exceptions to that rule. We describe here the first reported case of conversion of inherited sickle cell trait to SCD by uniparental disomy (UPD) resulting in mosaicism for SS and AS erythrocytes. A 14-year-old boy presented with splenomegaly and hemolysis. Although his father has sickle cell trait, his mother has no abnormal hemoglobin (Hb). DNA sequencing, performed to rule out Hb S/β-thalassemia, detected homozygous Hb SS. Further studies revealed mosaic UPD of the β-globin locus, more SS erythroid progenitors than AS, but a reverse ratio of erythrocytes resulting from the survival advantage of AS erythrocytes. This report exemplifies non-Mendelian genetics wherein a patient who inherited sickle cell trait has mild SCD resulting from postzygotic mitotic recombination leading to UPD.

Hemoglobin disorders and endothelial cell interactions

Endothelial damage and inflammation make a significant contribution to the pathophysiology of sickle cell disease (SCD) and the beta-thalassemia syndromes. Endothelial dysfunction and ensuing vasculopathy are implicated in pulmonary hypertension in the hemoglobinopathies and endothelial activation and endothelial-blood cell adhesion, accompanied by inflammatory processes and oxidative stress, are imperative to the vaso-occlusive process in SCD. Herein, we discuss the role that the endothelium plays in all of these processes and the effect that genetic modifiers and hydroxyurea therapy may have upon endothelial interactions. Therapies targeting the endothelium and endothelial interactions may represent a promising approach for treating these diseases.