The many faces of sickle cell disease in children: complications in the appendicular skeleton.

Sickle cell disease (SCD) is a hereditary red cell disorder with clinical manifestations secondary to sickling or crescent-shaped distortion of the red blood cells. Musculoskeletal complications of SCD are often the main causes for acute and chronic morbidities in children with manifestations including osteomyelitis, osteoporosis and osteonecrosis. This article aims to familiarise the paediatric radiologist with appendicular skeletal complications of SCD in the paediatric population and their imaging appearance.

What is the role of chest X-ray imaging in the acute management of children with sickle cell disease?

Children with sickle cell disease (SCD) frequently present to hospital acutely unwell and are often exposed to diagnostic chest X-rays (CXRs). Little evidence exists to determine when CXRs are clinically useful. Using electronic hospital records, we audited CXR use in children aged 0-18 who presented to hospital over the past 10 years in both an inpatient and emergency department setting. From a total of 915 first CXRs, only 28·2% of CXRs (n = 258) had clinically significant findings that altered management or final diagnosis. Of these abnormalities, consolidation represented 52·3%, effusion 8·9%, cardiomegaly 8·4% and sickle cell-related bone changes 6·3%. Indications for CXR of respiratory distress (OR = 3·74, 95% CI 2·28-6·13), hypoxia (OR = 1·86, 95% CI 1·50-2·31) and cough (OR = 1·64, 95% CI 1·33-2·02), were more likely to have significant CXR findings. Patients who had higher peak fever (38·4°C vs. 37·4°C, P = 0·001), higher peak CRP (156·4 vs. 46·1, P < 0·001) and higher WCC (20·2 vs. 13·6, P < 0·001) were more likely to have clinically significant abnormalities on CXR. We found a decision tool using either hypoxia, cough, respiratory distress, T > 38°C, CRP > 50 or WCC > 15 × 109 /l as indications for CXR, to have a sensitivity of 88% (with 95% CI 0·78-0·95) and specificity of 46% (95% CI 0·43-0·50) for clinically significant findings.

Protecting vulnerable patients with inherited anaemias from unnecessary death during the COVID-19 pandemic.

With the developing COVID-19 pandemic, patients with inherited anaemias require specific advice regarding isolation and changes to usual treatment schedules. The National Haemoglobinopathy Panel (NHP) has issued guidance on the care of patients with sickle cell disease, thalassaemia, Diamond Blackfan anaemia (DBA), congenital dyserythropoietic anaemia (CDA), sideroblastic anaemia, pyruvate kinase deficiency and other red cell enzyme and membrane disorders. Cascading of accurate information for clinicians and patients is paramount to preventing adverse outcomes, such as patients who are at increased risk of fulminant bacterial infection due to their condition or its treatment erroneously self-isolating if their fever is mistakenly attributed to a viral cause, delaying potentially life-saving antibiotic therapy. Outpatient visits should be minimised for most patients, however some, such as first transcranial dopplers for children with sickle cell anaemia should not be delayed as known risk of stroke will outweigh the unknown risk from COVID-19 infection. Blood transfusion programmes should be continued, but specific changes to usual clinical pathways can be instituted to reduce risk of patient exposure to COVID-19, as well as contingency planning for possible reductions in blood available for transfusions. Bone marrow transplants for these disorders should be postponed until further notice. With the current lack of evidence on the risk and complications of COVID-19 infection in these patients, national data collection is ongoing to record outcomes and eventually to identify predictors of disease severity, particularly important if further waves of infection travel through the population.

Antenatal screening for haemoglobinopathies: current status, barriers and ethics.

Sickle cell disease (SCD) and thalassaemia are genetic disorders that are caused by errors in the genes for haemoglobin and are some of the most common significant genetic disorders in the world, resulting in significant morbidity and mortality. Great disparities exist in the outcome of these conditions between resource- rich and resource-poor nations. Antenatal screening for these disorders aims to provide couples with information about their reproductive risk and enable them to make informed reproductive choices; ultimately reducing the likelihood of children being born with these conditions. This review provides an overview of the current status of antenatal, pre-marital and population screening of SCD and thalassaemia in countries with both high-and low prevalence of these conditions, methods of screening in use, and discusses some of the pitfalls, ethical issues and controversies surrounding antenatal screening. It also discusses outcomes of some screening programmes and recognises the need for the establishment of antenatal screening in areas where their prevalence is highest; namely sub-Saharan Africa and India.

Effectiveness of hydroxycarbamide in children with sickle cell disease - Analysis of dose-response metrics in a large birth cohort in a tertiary sickle cell centre.

BACKGROUND: Despite the well-established efficacy of hydroxycarbamide in the management of sickle cell disease (SCD), the paucity of real-world clinical data limits the establishment of a practical dosing strategy. The aim of this study was to analyse the dose-response metrics of hydroxycarbamide associated with the minimum effective dose protocol - specifically, between dose groups and differing degrees of myelosuppression. DESIGN/METHODS: A retrospective cohort study was conducted on 93 patients who were initiated on hydroxycarbamide between 2005 and 2017 at a tertiary haemoglobinopathy centre in London, UK. The burden of acute SCD-related complications was defined by the annualised rates of emergency department attendances and hospital admissions. Secondary outcomes included haematological, biochemical, liver, renal and transcranial Doppler velocity status. Comparisons were performed upon stratification via dose (<20 mg/kg/day, 20-24 mg/kg/day and ≥25 mg/kg/day) and sustained absolute neutrophil count (ANC) values (ANC <4 × 109 /L and ANC ≥4 × 109 /L). RESULTS: Clinical outcomes were not predicted by dose or ANC values. Whilst laboratory indices between dose groups were also non-statistically significant, patients maintained on ANC <4 × 109 /L were shown to achieve superior responses in haemoglobin, haemoglobin F, absolute reticulocyte count and liver function. Toxicities occurred idiosyncratically, with minimal reports of transient neutropaenia and thrombocytopaenia. CONCLUSIONS: Objective clinical responses may be achievable without intensive dose escalation. Our finding that greater myelosuppression is associated with greater improvements in laboratory markers of clinical benefit is consistent with prior clinical trials, but ongoing effectiveness studies are needed to determine whether these benefits can be reliably demonstrated in routine clinical practice using different dosing protocols.

Not being heard: barriers to high quality unplanned hospital care during young people's transition to adult services - evidence from 'this sickle cell life' research.

BACKGROUND: Young people's experiences of healthcare as they move into adult services can have a major impact on their health, and the transition period for young people with sickle cell disease (SCD) needs improvement. In this study, we explore how young people with SCD experience healthcare during this period of transition. METHODS: We conducted a co-produced longitudinal qualitative study, including 80 interviews in 2016-2017 with young people with SCD aged 13-21 (mean age 16.6) across two cities in England. We recruited 48 participants (30 female, 18 male): 27 interviews were one-off, and 53 were repeated 2-3 times over approximately 18 months. We used an inductive analytical approach, combining elements of Grounded Theory and thematic analysis. RESULTS: Participants reported significant problems with the care they received in A&E during painful episodes, and in hospital wards as inpatients during unplanned healthcare. They experienced delays in being given pain relief and their basic care needs were not always met. Participants said that non-specialist healthcare staff did not seem to know enough about SCD and when they tried to work with staff to improve care, staff often seemed not prepared to listen to them or act on what they said. Participants said they felt out of place in adult wards and uncomfortable with the differences in adult compared with paediatric wards. Because of their experiences, they tried to avoid being admitted to hospital, attempting to manage their painful episodes at home and accessing unplanned hospital care only as a last resort. By contrast, they did not report having problems within SCD specialist services during planned, routine care. CONCLUSIONS: Our study underscores the need for improvements to make services youth-friendly and youth-responsive, including training staff in SCD-specific care, compassionate care and communication skills that will help them elicit and act on young people's voices to ensure they are involved in shaping their own healthcare. If young people are prevented from using transition skills (self-management, self-advocacy), or treated by staff who they worry do not have enough medical competency in their condition, they may well lose their trust in services, potentially compromising their own health.

How I manage sickle cell patients with high transcranial doppler results.

Stroke is one of the most severe complications to affect children with sickle cell anaemia (SCA). Transcranial doppler (TCD) is an accurate and non-invasive method to determine stroke risk. Randomised controlled trials have demonstrated the efficacy of chronic transfusion therapy in stroke prevention based on risk stratification determined by TCD velocities. This has led to the regular use of TCD monitoring for children with SCA in order to determine stroke risk. Significant resource allocation is necessary to facilitate training, quality assurance and failsafe arrangements for non-attenders. In a subgroup of patients, chronic transfusions for primary stroke prevention can be replaced by hydroxycarbamide therapy, provided careful monitoring is undertaken; including repeat TCD studies at frequent intervals. The authors propose an evidence-based algorithm for the management of abnormal TCD velocities and discuss the role of this test in other clinical contexts, such as in Haemoglobin SC disease.

Associations between environmental factors and hospital admissions for sickle cell disease.

Sickle cell disease is an increasing global health burden. This inherited disease is characterized by a remarkable phenotypic heterogeneity, which can only partly be explained by genetic factors. Environmental factors are likely to play an important role but studies of their impact on disease severity are limited and their results are often inconsistent. This study investigated associations between a range of environmental factors and hospital admissions of young patients with sickle cell disease in London and in Paris between 2008 and 2012. Specific analyses were conducted for subgroups of patients with different genotypes and for the main reasons for admissions. Generalized additive models and distributed lag non-linear models were used to assess the magnitude of the associations and to calculate relative risks. Some environmental factors significantly influence the numbers of hospital admissions of children with sickle cell disease, although the associations identified are complicated. Our study suggests that meteorological factors are more likely to be associated with hospital admissions for sickle cell disease than air pollutants. It confirms previous reports of risks associated with wind speed (risk ratio: 1.06/standard deviation; 95% confidence interval: 1.00-1.12) and also with rainfall (1.06/standard deviation; 95% confidence interval: 1.01-1.12). Maximum atmospheric pressure was found to be a protective factor (0.93/standard deviation; 95% confidence interval: 0.88-0.99). Weak or no associations were found with temperature. Divergent associations were identified for different genotypes or reasons for admissions, which could partly explain the lack of consistency in earlier studies. Advice to patients with sickle cell disease usually includes avoiding a range of environmental conditions that are believed to trigger acute complications, including extreme temperatures and high altitudes. Scientific evidence to support such advice is limited and sometimes confusing. This study shows that environmental factors do explain some of the variations in rates of admission to hospital with acute symptoms in sickle cell disease, but the associations are complex, and likely to be specific to different environments and the individual's exposure to them. Furthermore, this study highlights the need for prospective studies with large numbers of patients and standardized protocols across Europe.

The risk of hemophagocytic lymphohistiocytosis in Hermansky-Pudlak syndrome type 2.

Genetic disorders of lymphocyte cytotoxicity predispose patients to hemophagocytic lymphohistiocytosis (HLH). Reduced lymphocyte cytotoxicity has been demonstrated in Hermansky-Pudlak syndrome type 2 (HPS2), but only a single patient was reported who developed HLH. Because that patient also carried a potentially contributing heterozygous RAB27A mutation, the risk for HLH in HPS2 remains unclear. We analyzed susceptibility to HLH in the pearl mouse model of HPS2. After infection with lymphocytic choriomeningitis virus, pearl mice developed all key features of HLH, linked to impaired virus control caused by a moderate defect in CTL cytotoxicity in vivo. However, in contrast to perforin-deficient mice, the disease was transient, and all mice fully recovered and controlled the infection. An additional heterozygous Rab27a mutation did not aggravate the cytotoxicity defect or disease parameters. In the largest survey of 22 HPS2 patients covering 234 patient years, we identified only 1 additional patient with HLH and 2 with incomplete transient HLH-like episodes, although cytotoxicity or degranulation was impaired in all 16 patients tested. HPS2 confers a risk for HLH that is lower than in Griscelli or Chediak-Higashi syndrome, probably because of a milder defect in cytotoxicity. Preemptive hematopoietic stem cell transplantation does not appear justified in HPS2.

Impairment of neutrophil oxidative burst in children with sickle cell disease is associated with heme oxygenase-1.

Sickle cell disease is a risk factor for invasive bacterial infections, and splenic dysfunction is believed to be the main underlying cause. We have previously shown that the liberation of heme in acute hemolysis can induce heme oxygenase-1 during granulopoiesis, impairing the ability of developing neutrophils to mount a bactericidal oxidative burst, and increasing susceptibility to bacterial infection. We hypothesized that this may also occur with the chronic hemolysis of sickle cell disease, potentially contributing to susceptibility to infections. We found that neutrophil oxidative burst activity was significantly lower in treatment-naïve children with sickle cell disease compared to age-, gender- and ethnicity-matched controls, whilst degranulation was similar. The defect in neutrophil oxidative burst was quantitatively related to both systemic heme oxygenase-1 activity (assessed by carboxyhemoglobin concentration) and neutrophil mobilization. A distinct population of heme oxygenase-1-expressing cells was present in the bone marrow of children with sickle cell disease, but not in healthy children, with a surface marker profile consistent with neutrophil progenitors (CD49d(Hi) CD24(Lo) CD15(Int) CD16(Int) CD11b(+/-)). Incubation of promyelocytic HL-60 cells with the heme oxygenase-1 substrate and inducer, hemin, demonstrated that heme oxygenase-1 induction during neutrophilic differentiation could reduce oxidative burst capacity. These findings indicate that impairment of neutrophil oxidative burst activity in sickle cell disease is associated with hemolysis and heme oxygenase-1 expression. Neutrophil dysfunction might contribute to risk of infection in sickle cell disease, and measurement of neutrophil oxidative burst might be used to identify patients at greatest risk of infection, who might benefit from enhanced prophylaxis.

Disruption of AP3B1 by a chromosome 5 inversion: a new disease mechanism in Hermansky-Pudlak syndrome type 2.

BACKGROUND: Hermansky-Pudlak syndrome 2 (HPS2; OMIM #608233) is a rare, autosomal recessive disorder caused by loss-of-function genetic variations affecting AP3B1, which encodes the ß3A subunit of the adaptor-related protein complex 3 (AP3). Phenotypic characteristics include reduced pigmentation, absent platelet dense granule secretion, neutropenia and reduced cytotoxic T lymphocyte (CTL) and natural killer (NK) cell function. To date HPS2 has been associated with non-synonymous, stop-gain or deletion-insertion nucleotide variations within the coding region of AP3B1. CASE PRESENTATION: We describe a consanguineous female infant with reduced pigmentation, neutropenia and recurrent infections. Platelets displayed reduced aggregation and absent ATP secretion in response to collagen and ADP, indicating a platelet dense granule defect. There was increased basal surface expression of CD107a (lysosome-associated membrane protein 1(LAMP-1)) on NK cells and CTLs from the study subject and a smaller increase in the percentage of CD107a positive cells after stimulation compared to most healthy controls. Immunoblotting of protein extracts from EBV-transformed lymphoblasts from the index case showed absent expression of full-length AP-3 ß3A subunit protein, confirming a phenotypic diagnosis of HPS2.The index case displayed a homozygous pericentric inv(5)(p15.1q14.1), which was also detected as a heterozygous defect in both parents of the index case. No loss of genetic material was demonstrated by microarray comparative genome hybridisation at 60kb resolution. Fluorescence in-situ hybridisation using the 189.6kb probe RP11-422I12, which maps to 5q14.1, demonstrated dual hybridisation to both 5q14.1 and 5p15.1 regions of the inverted Chr5. The RP11-422I12 probe maps from intron 1 to intron 16 of AP3B1, thus localising the 5q inversion breakpoint to within AP3B1. The probe RP11-211K15, which corresponds to an intergenic region on 5p also showed dual hybridisation, enabling localisation of the 5p inversion breakpoint. CONCLUSION: This case report extends the phenotypic description of the very rare disorder HPS2. Our demonstration of a homozygous Chr5 inversion predicted to disrupt AP3B1 gene provides a novel pathogenic mechanism for this disorder.

Sickle cell disease: embedding patient participation into an international conference can transform the role of lived experience.

BACKGROUND: Sickle cell disease (SCD) is an inherited chronic life-threatening disorder with increasing prevalence in Europe. People living with SCD in Europe mainly belong to vulnerable minorities, have a lower level of health education and suffer from isolation compared to those living with other chronic conditions. As a result, SCD patients are much less likely to partner in the design of research related to their condition and are limited in their ability to influence the research agenda. Aiming to increase the influence of patient voice in the development of SCD-related research, we set out to develop patient centered actions in the frame of International Scientific Conferences in collaboration with the ERN-EuroBloodNet, Oxford Blood Group, Annual Sickle Cell Disease and Thalassaemia Conference (ASCAT), the European Hematology Association and the British Society of Hematology. RESULTS: Two events were organized: a one-day research prioritization workshop and a series of education sessions based on topics chosen by SCD patients and their families. Methodology and outcomes were analyzed in terms of influence on scientific, medical and patient communities. CONCLUSION: The ERN-EuroBloodNet workshops with patients at annual ASCAT conferences have provided an opportunity to enhance patient experience and empowerment in SCD in Europe, producing benefits for patients, caregivers, patient associations and health professionals. Future work should focus on delivering the research questions identified at this workshop and the opportunities to share information for patient education.

Structural connectivity mediates the relationship between blood oxygenation and cognitive function in sickle cell anemia.

In sickle cell disease, the relative importance of reduced hemoglobin (Hb) and peripheral oxygen saturation on brain structure remains uncertain. We applied graph-theoretical analysis to diffusion magnetic resonance imaging data to investigate the effect of structural brain connectivity on cognitive function, alongside the presence or absence, number, and volume of silent cerebral infarction. In patients, we investigated the relationships between network properties, blood oxygenation, and cognition (working memory and processing speed indices). Based on streamline counts and fractional anisotropy, we identified a subnetwork with weakened connectivity in 92 patients with sickle cell disease (91 homozygous for HbS [HbSS], 1 heterozygote with HbSß0 thalassemia; 49 males; aged 8.0 to 38.8 y), compared with 54 control subjects (22 males; aged 6.7 to 30.6 y). Multiple regression analyses showed a significant effect of Hb on full-network edge density (P < .05) and of peripheral oxygen saturation on streamline-weighted subnetwork efficiency (P < .01). There were effects of fractional anisotropy-weighted full-network and subnetwork efficiency on working memory index (both P < .05), and of streamline-weighted subnetwork efficiency on processing speed index (P = .05). However, there were no effects of presence, number or volume of silent cerebral infarcts. Streamline-weighted efficiency was progressively lower with lower oxygen saturation, with a downstream effect on the processing speed index. In path analysis, indirect relationships between blood oxygenation and cognition, mediated by network properties, were better supported than direct alternatives, with an indirect relationship between low oxygen saturation and processing speed index in patients, mediated by structural connectivity efficiency in a subnetwork of the brain differing from control subjects. Our findings are consistent with the notion that cognitive impairment is primarily mediated by hypoxic-ischemic effects on normal-appearing white matter and highlight the utility of network-based methods in providing biomarkers of cognitive dysfunction in patients with sickle cell disease.

How I manage neonatal thrombocytopenia.

Although neonatal thrombocytopenia (platelet count < 150×10(9) /l) is a common finding in hospital practice, a careful clinical history and examination of the blood film is often sufficient to establish the diagnosis and guide management without the need for further investigations. In preterm neonates, early-onset thrombocytopenia (<72h) is usually secondary to antenatal causes, has a characteristic pattern and resolves without complications or the need for treatment. By contrast, late-onset thrombocytopenia in preterm neonates (>72h) is nearly always due to post-natally acquired bacterial infection and/or necrotizing enterocolitis, which rapidly leads to severe thrombocytopenia (platelet count<50×10(9) /l). Thrombocytopenia is much less common in term neonates and the most important cause is neonatal alloimmune thrombocytopenia (NAIT), which confers a high risk of perinatal intracranial haemorrhage and long-term neurological disability. Prompt diagnosis and transfusion of human platelet antigen-compatible platelets is key to the successful management of NAIT. Recent studies suggest that more than half of neonates with severe thrombocytopenia receive platelet transfusion(s) based on consensus national or local guidelines despite little evidence of benefit. The most pressing problem in management of neonatal thrombocytopenia is identification of safe, effective platelet transfusion therapy and controlled trials are urgently needed.

Individual Watershed Areas in Sickle Cell Anemia: An Arterial Spin Labeling Study.

Previous studies have pointed to a role for regional cerebral hemodynamic stress in neurological complications in patients with sickle cell anemia (SCA), with watershed regions identified as particularly at risk of ischemic tissue injury. Using single- and multi-inflow time (TI) arterial spin labeling sequences (ASL) in 94 patients with SCA and 42 controls, the present study sought to investigate cerebral blood flow (CBF) and bolus arrival times (BAT) across gray matter, white matter with early arrival times, and in individual watershed areas (iWSAs). In iWSAs, associations between hemodynamic parameters, lesion burden, white matter integrity, and general cognitive performance were also explored. In patients, increases in CBF and reductions in BAT were observed in association with reduced arterial oxygen content across gray matter and white matter with early arrival times using both sequences (all p < 0.001, d = -1.55--2.21). Across iWSAs, there was a discrepancy between sequences, with estimates based on the single-TI sequence indicating higher CBF in association with reduced arterial oxygen content in SCA patients, and estimates based on the multi-TI sequence indicating no significant between-group differences or associations with arterial oxygen content. Lesion burden was similar between white matter with early arrival times and iWSAs in both patients and controls, and using both sequences, only trend-level associations between iWSA CBF and iWSA lesion burden were observed in patients. Further, using the multi-TI sequence in patients, increased iWSA CBF was associated with reduced iWSA microstructural tissue integrity and slower processing speed. Taken together, the results highlight the need for researchers to consider BAT when estimating CBF using single-TI sequences. Moreover, the findings demonstrate the feasibility of multi-TI ASL for objective delineation of iWSAs and for detection of regional hemodynamic stress that is associated with reduced microstructural tissue integrity and slower processing speed. This technique may hold promise for future studies and treatment trials.