The development of haematological changes in homozygous sickle cell disease: a cohort study from birth to 6 years

Acute splenic sequestration in HbSS: observations from the Jamaican birth cohort

OBJECTIVE

To document the prevalence, clinical features, haematology and outcome of acute splenic sequestration (ASS) in homozygous sickle cell disease (HbSS).

STUDY DESIGN

A cohort study from birth.

SETTING

The Medical Research Council Laboratories at the University of the West Indies, Kingston, Jamaica.

PATIENTS

311 cases of HbSS detected during the screening of 100 000 deliveries at the main government maternity hospital between 1973 and 1981.

INTERVENTIONS

Long-term follow-up and free patient care focusing on ASS.

MAIN OUTCOME MEASURE

Acute splenic sequestration.

RESULTS

There were 183 episodes of ASS in 105 patients representing 35% of the cohort. The median age for first event was 1.07 years. During ASS, median values for haemoglobin fell by 32 g/dL, reticulocytes increased by 8% and total nucleated cells increased by 10.5%. ASS recurred in 47 (45%) patients. Conservative therapy in 133 episodes of 85 patients was associated with five deaths and splenectomy in 20 patients with 50 episodes had no deaths. Symptoms were generally non-specific but acute chest syndrome occurred in 17, and blood cultures revealed coagulase negative staphylococci in 5. The ASS case fatality rate was 3.6% and may be higher if autopsy evidence of ASS is included. There was no seasonal pattern but higher levels of fetal haemoglobin predicted patients less prone to ASS and its later occurrence.

CONCLUSIONS

ASS remains an important cause of morbidity and mortality in HbSS in developing societies. ASS appears to be a non-specific response to many possible risk factors including coagulase negative staphylococci.

Correctly Establishing and Interpreting Oxygenation Status in Sickle Cell Disease

BACKGROUND

As hypoxemia and hypoxia are central elements of disease pathophysiology and disease-related morbidity and mortality in individuals affected by sickle cell disease (SCD), clinical management aims to optimize oxygenation.

CONTENT

Hypoxemia is primarily screened for with pulse oximetry. However, in SCD pulse oximetry can inaccurately reflect arterial saturation, posing the risk of undetected (occult) hypoxemia. Solely relying on pulse oximetry might therefore lead to misdiagnosis or mismanagement, with devastating effects on tissue oxygenation. The interpretation of oxygenation status is multifaceted, and "oxygen saturation" is often used as an umbrella term to refer to distinctly different measured quantities-estimated oxygen saturation (O2Sat), hemoglobin oxygen saturation (SO2) by either pulse oximetry or co-oximetry, and fractional oxyhemoglobin (FO2Hb). While in many clinical situations this ambiguous use is of little consequence, O2Sat, SO2, and FO2Hb cannot be used interchangeably in the setting of SCD, as dyshemoglobins, anemia, cardiopulmonary comorbidities, concomitant medications, and frequent transfusions need to be accounted for. This article describes the parameters that determine blood and tissue oxygen concentration, discusses laboratory method performance characteristics and the correct interpretation of currently available clinical laboratory testing, and reviews the literature on noninvasive vs invasive oxygenation measurements in SCD.

SUMMARY

By correctly establishing and interpreting oxygenation parameters, clinical and laboratory teams can ensure high-quality, equitable healthcare, counteracting systemic exacerbations of health disparities frequently experienced by individuals with SCD.

Phenotypic variation in sickle cell disease: the role of beta globin haplotype, alpha thalassaemia and fetal haemoglobin in HbSS

INTRODUCTION

The haematological and clinical feature vary markedly between the different genotypes of sickle cell disease. Even within the single genotype of homozygous sickle cell disease (HbSS), there is marked variability which is presumed to result from interacting genetic and environmental factors.

AREAS COVERED

The classification of the different genotypes of sickle cell disease with approximate prevalence at birth in different communities and some of the major clinical and haematological differences. This assessment includes three potential genetic factors influencing haematology and clinical outcome in HbSS, the beta globin haplotype, alpha thalassaemia and persistence of fetal haemoglobin (HbF).

EXPERT OPINION

The author is a clinician with experience of sickle cell disease primarily in Jamaica but also in Greece, Uganda, Saudi Arabia and India. It is therefore necessarily an account of clinical data and does not address current debates on molecular mechanisms. Most data derive from Jamaica where efforts have been made to reduce any symptomatic bias by long term follow-up of patients all over the island and further reduced by a cohort study based on newborn screening which has been in operation for over 48 years.

Homozygous sickle cell disease in Central India & Jamaica: A comparison of newborn cohorts

Background & objectives:

Homozygous sickle cell (SS) disease in Central India runs a more severe clinical course than reports from other areas of India. The current study was undertaken to compare the disease in Central India (Nagpur) with that in Jamaica, both populations defined by newborn screening.

Methods:

The Nagpur cohort included infants born to sickling-positive mothers from May 2008 to 2012, examined by high-pressure liquid chromatography and DNA analysis. The Jamaican cohort screened 100,000 consecutive non-operative deliveries between June 1973 and December 1981, analyzed by haemoglobin (Hb) electrophoresis and confirmed by family studies and compatible HbA₂ levels.

Results:

In Nagpur, 103 SS patients were detected, but only 78 (76%) were followed up. In Jamaica, 311 cases were followed from birth and compliance with follow up remained 100 per cent up to 45 years. In the Nagpur cohort all had the Asian haplotype, and 82 per cent of Jamaicans had at least one Benin chromosome; none had the Asian haplotype. Compared to Jamaica, Nagpur patients had higher foetal Hb, less alpha-thalassaemia, later development of splenomegaly and less dactylitis. There were also high admission rates for febrile illness and marked anaemia. Invasive pneumococcal disease occurred in 10 per cent of Jamaicans but was not seen in Nagpur.

Interpretation & conclusions:

There were many differences between the disease in Nagpur, Central India and the African form observed in Jamaica. The causes of severe anaemia in Nagpur require further study, and reticulocyte counts may be recommended as a routine parameter in the management of SS disease. The role of pneumococcal prophylaxis needs to be determined in Nagpur patients. Future studies in India must avoid high default rates.

Pregnancy outcome in homozygous sickle cell disease: observations from the Jamaican Birth Cohort

OBJECTIVE

To document pregnancy outcome in homozygous sickle cell (SS) disease and in age-matched controls with a normal haemoglobin genotype followed from birth for up to 45 years.

METHODS

A total of 100 000 consecutive non-operative deliveries screened for sickle cell disease at the main Government maternity hospital in Kingston, Jamaica between 1973 and 1981 detected 311 (149 female) babies with SS disease who were matched by age and gender with 250 (129 female) controls with an AA haemoglobin phenotype. These individuals have been followed from birth with prospective assessment of menarche and detailed documentation of all pregnancies.

RESULTS

There were 177 pregnancies in 71 SS patients and 226 pregnancies in 74 AA controls. Mothers with SS disease had more spontaneous abortions (adjusted relative risk [aRR] 3.2, 95% CI 1.6-6.1), fewer live births (aRR 0.7, 95% CI 0.6-0.9) and their offspring were more likely to have a gestational age <37 weeks (aRR 2.1, 95% CI 1.1-3.7) and low birthweight <2.5 kg (aRR 3.0, 95% CI 1.6-5.3). They were more prone to acute chest syndrome (aRR 13.7, 95% CI 4.1-45.5), urinary tract infection (aRR 12.8, 95% CI 1.3-125.9), pre-eclampsia/eclampsia (aRR 3.1, 95% CI 1.1-8.8), retained placenta (aRR 10.1, 95% CI 1.1-90.3), sepsis (Fisher's Exact test 0.04) and pregnancy-related deaths (Fisher's Exact test 0.02). Four of five deaths were attributable to acute chest syndrome. There was no genotypic difference in pregnancy-induced hypertension or postpartum haemorrhage.

CONCLUSION

Pregnancy in SS disease carries risks for both mother and child. The variable characteristics of pregnancy-related deaths complicate their prevention.

TWEETABLE ABSTRACT

Pregnancy in SS disease compared with controls showed increased abortions and stillbirths, fewer live births and maternal deaths in 7% patients.

Not all red cells sickle the same: Contributions of the reticulocyte to disease pathology in sickle cell anemia

Sickle cell anemia (SCA) is associated with morbidity and early death. While the switch from fetal to sickle hemoglobin during the first months of life results in hemolytic anemia with reticulocytosis, the role of the reticulocyte in the pathophysiology and prognosis of SCA is not well-defined. Reticulocytes have unique cytoskeletal and membrane components that allow them to be distinguished from mature sickle erythrocytes in the circulation. Reticulocytes in patients with SCA are less dense than more mature and 'sickled' erythrocytes, and have increased adhesive properties. The circulating reticulocyte number in peripheral blood may assist in predicting disease severity in SCA; characterization of patient-specific reticulocyte properties during infancy and childhood may assist in predicting therapeutic response to therapies. Here, we review the biological and clinical data regarding reticulocytes and their potential impact on SCA pathophysiology and disease severity.

Hematological parameters in Ghanaian sickle cell disease patients

BACKGROUND

Effective treatment and management of sickle cell disease (SCD) has been a challenge in Africa over the years. Hematological parameters are very useful profiles in the effective management of the disease. However, there is scarcity of studies on the hematological parameters of SCD in Ghana. This study aimed at determining hematological parameters among SCD patients with vaso-occlusion, those in the steady state as well as healthy controls at a teaching hospital in Ghana.

METHODOLOGY

This was a cross-sectional study involving a total of 628 subjects, including 148 HbAA controls, 208 HbSS patients in steady state, 82 HbSC patients in steady state, 156 HbSS patients in vaso-occlusive crises (VOC), and 34 HbSC patients in VOC. Venous blood sample was collected from all study participants. A full blood count was done within 2 hours of collection, and hemoglobin (Hb) concentration, packed cell volume, red blood cell (RBC) concentration, mean corpuscular Hb, mean cell volume, mean corpuscular Hb concentration, and white blood cells (WBC) and platelet (PLT) counts were recorded.

RESULTS

WBC and PLT counts were significantly higher in both female and male patients with SCD, compared with their healthy counterparts (P<0.05). The level of WBC was, however, significantly higher in patients with HbSS VOC among the SCD patients (P<0.001). Levels of Hb, RBC, and hematocrit were significantly higher in the controls (P<0.001). There was no significant difference in mean cell Hb among male patients with SCD (P=0.274) and female patients with SCD (P=0.5410).

CONCLUSION

The SCD patients had lower Hb and RBC than the controls; however, higher PLT and WBC are noted in various status of SCD, possibly reflecting spleen effect in these patients. Further studies are needed to confirm these findings.

Realizing effectiveness across continents with hydroxyurea: Enrollment and baseline characteristics of the multicenter REACH study in Sub-Saharan Africa

Despite its well-described safety and efficacy in the treatment of sickle cell anemia (SCA) in high-income settings, hydroxyurea remains largely unavailable in sub-Saharan Africa, where more than 75% of annual SCA births occur and many comorbidities exist. Realizing Effectiveness Across Continents with Hydroxyurea (REACH, ClinicalTrials.gov NCT01966731) is a prospective, Phase I/II open-label trial of hydroxyurea designed to evaluate the feasibility, safety, and benefits of hydroxyurea treatment for children with SCA in four sub-Saharan African countries. Following comprehensive training of local research teams, REACH was approved by local Ethics Committees and achieved full enrollment ahead of projections with 635 participants enrolled over a 30-month period, despite half of families living >12 km from their clinical site. At enrollment, study participants (age 5.4 ± 2.4 years) had substantial morbidity, including a history of vaso-occlusive pain (98%), transfusion (68%), malaria (85%), and stroke (6%). Significant differences in laboratory characteristics were noted across sites, with lower hemoglobin concentrations (P < .01) in Angola (7.2 ± 1.0 g/dL) and the DRC (7.0 ± 0.9 g/dL) compared to Kenya (7.4 ± 1.1 g/dL) and Uganda (7.5 ± 1.1 g/dL). Analysis of known genetic modifiers of SCA demonstrated a high frequency of α-thalassemia (58.4% with at least a single α-globin gene deletion) and G6PD deficiency (19.7% of males and 2.4% of females) across sites. The CAR β-globin haplotype was present in 99% of participants. The full enrollment to REACH confirms the feasibility of conducting high-quality SCA research in Africa; this study will provide vital information to guide safe and effective dosing of hydroxyurea for children with SCA living in Africa.

An age dependent response to hydroxyurea in pediatric sickle cell anemia patients with alpha thalassemia trait

Hydroxyurea (HU) is a key drug therapy for individuals with sickle cell anemia (SCA), yet its clinical and hematologic responses can be variable. Various studies have reported the role of α-thalassemia as one of the most prevalent heritable traits that may modify HU response. We provide data from 62 pediatric and adolescent patients with SCA, 26 with co-inherited α-thalassemia trait. Our data suggest that altered hematologic and clinical responses to HU therapy are noted in adolescent SCA individuals with co-inherited α-thalassemia trait. Adolescent patients who co-inherited α-thalassemia trait had a greater reduction in vaso-occlusive episodes compared to those without α-thalassemia, despite a less robust fetal hemoglobin induction as well as a lower maximum HU dose. This clinical improvement was associated with a lower MCH and higher RBC count. Responses to HU in younger SCA children (ages 5-11years) with co-inherited α-thalassemia trait, compared to those without α-thalassemia trait, did not show any difference in number vaso-occlusive episodes, fetal hemoglobin induction and change in MCH and RBC count.

Variability of Iron Load in Patients of Sickle Cell Anaemia (HbSS): A study from Eastern India

INTRODUCTION

Sickle Cell Anaemia (SCA) is one of the commonest haemoglobinopathies due to a point mutation (A→T) of the β-globin gene. Out of five haplotypes, the Arab-Indian haplotype present in India is one of the least severe phenotype and least studied also. It is characterized by lifelong haemolytic anaemia requiring red cell transfusion leading to iron overload. In contrast, there is very high incidence of deficiency of iron, folic acid and vitamin B12.

AIM

Our objective was to access the Iron status of SCA patients and to find its correlation with various parameters like red cell transfusion, haemolysis and serum hepcidin.

MATERIALS AND METHODS

This was a cross-sectional study conducted on 208 patients for a period of five years. Complete Blood Count (CBC), iron profile, haemolytic parameters and transfusion requirement were studied and data compared with 52 healthy controls.

RESULTS

Few patients (9.6%) revealed significant iron overload (Serum ferritin > 1000 ng/ml). In majority (80.8%) it was either normal or border line raised (300 to 1000 ng/ml) or iron deficiency was noted in a small fraction (9.6%). Frequency of transfusion is the principal factor which positively correlated with level of iron load (p<0.001) while parameters of haemolysis and serum hepcidin level play an insignificant role in this context (p= 0.0634).

CONCLUSION

This study supports the notion that the presentation of SCA patients in India is of "Viscosity - Vaso-Occlusive Crisis (VOC) phenotype" with high incidence of VOC, low haemolytic rate and transfusion requirement. Iron deficiency may be present in SCA patients requiring Iron supplementation. We suggest further studies to establish the role of hepcidin, ferroportin and other factors that control iron absorption in these patients.

Effect of Age on Blood Rheology in Sickle Cell Anaemia and Sickle Cell Haemoglobin C Disease: A Cross-Sectional Study

OBJECTIVES

Blood rheology plays a key role in the pathophysiology of sickle cell anaemia (SS) and sickle cell haemoglobin C disease (SC), but its evolution over the lifespan is unknown.

MATERIALS AND METHODS

Blood viscosity, red blood cell (RBC) deformability and aggregation, foetal haemoglobin (HbF) and haematocrit were measured in 114 healthy individuals (AA), 267 SS (161 children + 106 adults) and 138 SC (74 children + 64 adults) patients.

RESULTS

Our results showed that 1) RBC deformability is at its maximal value during the early years of life in SS and SC populations, mainly because HbF level is also at its peak, 2) during childhood and adulthood, hydroxycarbamide treatment, HbF level and gender modulated RBC deformability in SS patients, independently of age, 3) blood viscosity is higher in older SS and SC patients compared to younger ones and 4) haematocrit decreases as SS patients age.

CONCLUSION

The hemorheological changes detected in older patients could play a role in the progressive development of several chronic disorders in sickle cell disease, whose prevalence increases with age. Retarding these age-related haemorheological impairments, by using suitable drugs, may minimize the risks of vaso-occlusive events and chronic disorders.

Red blood cell complement receptor one level varies with Knops blood group, α(+)thalassaemia and age among Kenyan children

Both the invasion of red blood cells (RBCs) by Plasmodium falciparum parasites and the sequestration of parasite-infected RBCs in the microvasculature are mediated in part by complement receptor one (CR1). RBC surface CR1 level can vary between individuals by more than 20-fold and may be associated with the risk of severe malaria. The factors that influence RBC CR1 level variation are poorly understood, particularly in African populations. We studied 3535 child residents of a malaria-endemic region of coastal Kenya and report, for the first time, that the CR1 Knops blood group alleles Sl2 and McC(b), and homozygous HbSS are positively associated with RBC CR1 level. Sickle cell trait and ABO blood group did not influence RBC CR1 level. We also confirm the previous observation that α(+)thalassaemia is associated with reduced RBC CR1 level, possibly due to small RBC volume, and that age-related changes in RBC CR1 expression occur throughout childhood. RBC CR1 level in malaria-endemic African populations is a complex phenotype influenced by multiple factors that should be taken into account in the design and interpretation of future studies on CR1 and malaria susceptibility.

Early Reticulocytosis and Anemia Are Associated with Abnormal and Conditional Transcranial Doppler Velocities in Children with Sickle Cell Anemia

OBJECTIVE

To improve prediction of sickle cell anemia severity at an early age, we evaluated whether absolute reticulocyte count (ARC) or hemoglobin (Hb) levels during early infancy (2-6 months of age) in patients with sickle cell anemia predict the risk of later developing an abnormal (abTCD) or conditional (cdTCD) Transcranial Doppler (TCD).

STUDY DESIGN

We used chart review to identify 121 consecutive patients who underwent TCD screening and had steady state ARC and Hb levels recorded between 2 and 6 months of age. Cox regression analysis was used to determine the relationship between ARC, Hb levels, and risk of developing cdTCD/abTCD over time.

RESULTS

Mean ARC in early infancy was highest and mean Hb lowest in those children with abTCDs and cdTCDs. Cox regression analysis revealed that those subjects with an ARC ≥200 K/μL in early infancy had nearly 3 times the risk of having an abTCD/cdTCD than the group with an ARC <200 K/μL, and patients with a Hb <8.5 g/dL had 2.7 times the risk of having an abTCD/cdTCD.

CONCLUSIONS

These data suggest that both elevated ARC and low baseline Hb during early infancy are associated with an increased risk of developing a cdTCD or abTCD later in childhood.

Iron Deficiency Anaemia among Pre-School Children with Sickle Cell Anaemia: Still a Rare Diagnosis?

Background

The frequent need for blood transfusion in children with SCA creates the impression that IDA is rare in this class of children.

Objectives

The objective of the study is to determine the prevalence of IDA in a population of under-five children with SCA in Lagos, Nigeria.

Methodology

Serum iron, total iron binding capacity, transferrin saturation and serum ferritin were assayed in 97 under-five children with SCAand 97 age/sex matched controls.

The diagnosis of IDA was established based on the following criteria: haemoglobin <11.0 g/dl plus two or more of the following: MCV <70fl, transferrin saturation (Ts) <16% or serum ferritin (SF) <25ng/dL

Results

Overall prevalence of IDA was significantly higher among AA controls. In the younger age group, the prevalence of IDA was significantly higher among HbAA controls while in the older age group the odds of having IDA was three times higher among HbSS subjects but the difference was not statistically significant. Two of the three SCA children with IDA have history of previous blood transfusion.

Conclusion

IDA is uncommon in pre-school aged children with SCA. A multi-centre study is necessary to yield large number of transfused subjects to examine the effects of blood transfusion on prevalence of IDA.

The natural history of sickle cell disease

The term sickle cell disease embraces a group of genetic conditions in which pathology results from the inheritance of the sickle cell gene either homozygously or as a double heterozygote with another interacting gene. The spectrum of resulting conditions is therefore influenced by the geography of individual hemoglobin genes, but in most populations, the commonest genotype at birth is homozygous sickle cell (SS) disease. Because this genotype generally manifests a greater mortality, the relative proportion of sickle cell genotypes is influenced by age as well as the geographical distribution of individual genes.

Increased reticulocytosis during infancy is associated with increased hospitalizations in sickle cell anemia patients during the first three years of life

Objective

Among older children with sickle cell anemia, leukocyte counts, hemoglobin, and reticulocytosis have previously been suggested as disease severity markers. Here we explored whether these blood parameters may be useful to predict early childhood disease severity when tested in early infancy, defined as postnatal ages 60–180 days.

Study Design

Data from fifty-nine subjects who were followed at Children’s National Medical Center’s Sickle Cell Program for at least three years was retrospectively analyzed. Comparisons were made between white blood cell counts, hemoglobin and reticulocyte levels measured at ages 60–180 days and the clinical course of sickle cell anemia during infancy and childhood.

Results

A majority of subjects had demonstrable anemia with increased reticulocytosis. Only increased absolute reticulocyte levels during early infancy were associated with a significant increase in hospitalization during the first three years of life. Higher absolute reticulocyte counts were also associated with a markedly shorter time to first hospitalizations and a four-fold higher cumulative frequency of clinical manifestations over the first three years of life. No significant increase in white blood cell counts was identified among the infant subjects.

Conclusions

These data suggest that during early infancy, increased reticulocytosis among asymptomatic SCA subjects is associated with increased severity of disease in childhood.

An observational study of children with sickle cell disease in Kilifi, Kenya

Globally, sickle cell disease (SCD) has its highest prevalence and worst prognosis in sub-Saharan Africa. Nevertheless, relatively few studies describe the clinical characteristics of children with SCD in this region. We conducted a prospective observational study of children with SCD attending a specialist out-patient clinic in Kilifi, Kenya. A total of 124 children (median age 6·3 years) were included in the study. Splenomegaly was present in 41 (33%) subjects and hepatomegaly in 25 (20%), both being common in all age groups. A positive malaria slide was found at 6% of clinic visits. The mean haemoglobin concentration was 73 g/l, compared to 107 g/l in non-SCD controls (P < 0·001). Liver function tests were elevated; plasma bilirubin concentrations were 46 μmol/l and aspartate aminotransferase was 124 iu/l. Forty-eight (39%) children were admitted to hospital and two died. Children with SCD in Kilifi have a similar degree of anaemia and liver function derangement to patients living in developed countries, but splenomegaly persists into later childhood. The prevalence of malaria was lower than expected given the prevalence in the local community. This study provides valuable data regarding the clinical characteristics of children living with SCD in a rural setting in East Africa.

Iron overload in an African American woman with SS hemoglobinopathy and a promoter mutation in the X-linked erythroid-specific 5-aminolevulinate synthase (ALAS2) gene

We report the case of an African American woman with sickle cell anemia and iron overload incompletely explained by erythrocyte transfusion who is heterozygous for a promoter mutation in the X-linked erythroid-specific 5-aminolevulinate synthase gene (ALAS2): a C to G transversion at nucleotide -206 from the transcription start site, as defined by primer extension (-258 from the start ATG). This mutation has previously been associated with sideroblastic anemia and iron overload in members of a Welsh kinship. No coding region mutation of HFE, FPN1, TFR2, HAMP, or HJV genes was detected. The mother of the proband has mild, chronic anemia and is also heterozygous for the same proximal promoter region mutation of ALAS2. However, she has no evidence of iron overload. We conclude that an ALAS2 promoter region mutation could partly account for iron overload in the present proband, and that this or other ALAS2 mutations could explain the occurrence of iron overload in other whites or blacks with or without anemia. The occurrence of anemia and iron overload may be discordant in women heterozygous for ALAS2 mutations.

Are there clinical phenotypes of homozygous sickle cell disease?

The distribution of clinical features was examined in subjects with homozygous sickle cell (SS) disease in the Jamaican Cohort Study to determine whether there is evidence of distinct clustering of symptoms or clinical phenotypes. A twofold model yielded groups that could be interpreted as painful crisis or leg ulcer phenotypes and 78% of patients were classified with 95% confidence into one of these. The painful crisis phenotype also manifested higher frequencies of dactylitis, meningitis/septicaemia, acute chest syndrome and stroke. Attempts to define a three-group model were less convincing although 43% of patients could be allocated with 95% confidence. The three-group model essentially divided subjects with the leg ulcer phenotype into subgroups with higher and lower frequencies of painful crisis, dactylitis, meningitis/septicaemia and acute chest syndrome. In the three-group model, the painful crisis phenotype had lower total haemoglobin, fetal haemoglobin, mean cell volume and higher reticulocytes but there was no apparent influence of alpha thalassaemia or beta globin haplotype. Both environmental and genetic factors are likely to contribute to most manifestations of SS disease and the evidence for different clinical phenotypes suggests that a search for associated genetic polymorphisms may provide insights into the mechanisms of clinical variability in SS disease.

Alpha Thalassemia is associated with decreased risk of abnormal transcranial Doppler ultrasonography in children with sickle cell anemia

PURPOSE

Cerebrovascular complications of sickle cell disease (SCD) are common, but the risk factors remain unclear. The multicenter Stroke Prevention Trial in Sickle Cell Anemia (STOP) provided an opportunity to examine alpha thalassemia-2 as a modifying risk factor, using abnormal transcranial Doppler ultrasonography (TCD) as a surrogate marker for cerebrovascular disease. The authors hypothesized that children with abnormal TCD are less likely to have alpha thalassemia-2, and an increased hemoglobin level accounts for this protective effect.

METHODS

A retrospective study was conducted of children with SCD who had both alpha gene and TCD data from STOP: 128 with TCD of at least 200 cm/s (abnormal TCD) and 172 with TCD less than 170 cm/s (normal TCD).

RESULTS

Alpha thalassemia-2 was more frequent in the normal TCD group compared with the abnormal TCD group. The odds ratio for normal TCD and alpha thalassemia-2 was 4.1. Adjusting for either hemoglobin level or red cell size (mean corpuscular volume) reduced the odds ratio only slightly. Age, normal TCD, and alpha thalassemia-2 had significant statistical interaction, so that alpha thalassemia-2 was not related to TCD for age 10 years or older.

CONCLUSIONS

The frequency of alpha thalassemia-2 was significantly higher in children with normal TCD. Speculation on mechanisms of effect includes improved erythrocyte deformability, reduced red cell adhesion, and reduced nitric oxide scavenging in alpha thalassemia-2. The association of alpha thalassemia-2 and normal TCD adds to the evidence on the protective effects of alpha thalassemia-2 in SCD and highlights the contribution of epistatic factors.

Chronic leg ulceration in homozygous sickle cell disease: the role of venous incompetence

Chronic leg ulceration is a common cause of morbidity in Jamaican patients with homozygous sickle cell (SS) disease. Ulcers heal more rapidly on bed rest and deteriorate on prolonged standing, suggesting a role of venous hypertension in their persistence. This hypothesis has been tested by Doppler detection of venous competence in SS patients and in matched controls with a normal haemoglobin (AA) genotype in the Jamaican Cohort Study. Venous incompetence was significantly more frequent in SS disease [137/183 (75%)] than in non-pregnant AA controls [53/137 (39%)]. Past or present ulceration occurred in 78 (43%) SS patients, with a highly significant association between leg ulceration and venous incompetence in the same leg (P < 0.001). Prominence and/or varicosities of the veins and spontaneous leg ulcers were more common among patients with multiple sites of incompetence. The association of venous incompetence with chronic leg ulceration identifies a further pathological mechanism contributing to the morbidity of SS disease. The cause of venous incompetence is unknown but the sluggish circulation associated with dependency, turbidity and impaired linear flow at venous valves, hypoxia-induced sickling, the rheological effects of high white cell counts, and activation of components of the coagulation system may all contribute. Venous hypertension in SS patients with leg ulceration suggests that firm elastic supportive dressings might promote healing of chronic leg ulcers.

Survival estimates for patients with homozygous sickle-cell disease in Jamaica: a clinic-based population study

BACKGROUND

Information about life expectancy of patients with homozygous sickle-cell disease is needed for research and patient counselling. Our aim was to study two Jamaican populations, one clinic-based and one birth cohort and, by careful consideration of data quality and statistical analysis, to identify ways to increase the chances of obtaining valid and generalisable results.

METHODS

We investigated the survival experience of 3301 patients with homozygous sickle-cell disease attending the Jamaican sickle-cell clinic between Jan 1, 1987, and Dec 31, 1996. We applied and assessed a simulation technique for incorporating early life mortality using a birth cohort, and analysed the precision of this technique. Kaplan-Meier survival estimates are produced.

FINDINGS

290 of the 3301 patients died. Median survival calculated with the excess mortality rate simulation data was 53 years (95% CI 49.3-57.0) for men and 58.5 (55.1-67.5) for women.

INTERPRETATION

Our simulation technique, with realistic assumptions based on empirical evidence, offers a new estimate of median survival for patients with homozygous sickle-cell disease. We present the precision of these survival estimates, which introduces an important level of uncertainty. The inherent biases of clinically ascertained populations of patients, and the assumptions underlying analysis techniques are crucial features of survival studies in sickle-cell disease, and can modify summary statistics substantially.

Factors associated with lowered intelligence in homozygous sickle cell disease

The intelligence quotient (IQ) of 60 patients with homozygous sickle cell (SS) disease and 60 age and sex matched controls with a normal haemoglobin (AA) genotype aged 15-18 years, followed up in a cohort study from birth, was assessed by the Wechsler intelligence scales for children or for adults. IQ appeared to be normally distributed in both genotypes but mean values in SS disease were 5.6 points (95% confidence interval (CI) 1.0 to 10.2) lower than in AA controls (p = 0.016). The difference occurred in both verbal (5.5 points, p = 0.017) and performance (5.0 points, p = 0.044) subscales of the IQ score and the IQ defect in SS disease was associated with a significantly lower attention factor score (p = 0.005) but not with other factor scores. The genotype difference in IQ was not accounted for by differences in parental occupational level, school absenteeism, or school drop out, or reported activity level. In SS disease, IQ was not related to mean steady state haemoglobin, fetal haemoglobin, or mean cell haemoglobin concentration, or clinical severity as judged by the frequency of painful crises, hospital admission, or sick visits. IQ, at age 15-18 years, correlated with the patients' height at all ages from 1 to 10 years (partial correlations increasing from 0.14 (p = 0.15) at age 1 to 0.27 (p = 0.004) at age 10). Adjusting for height reduced the mean genotype difference in IQ to 5.5 (95% CI 0.6 to 10.3) points at age 1 and to 2.6 points (95% CI to -2.3, 7.5) at age 10. Prepubertal height therefore accounted for much of the genotype difference in IQ. It is speculated that early factors, possible nutritional, contribute to both impaired growth and mental development in sickle cell disease.

Pitfalls in newborn hemoglobinopathy screening: failure to detect beta(+)-thalassemia

Although universal newborn screening can reliably identify all infants with sickle cell hemoglobinopathies, the initial screening result must not be considered the definitive diagnosis. We describe 23 infants whose screening phenotype was FS or FC but whose true phenotype included hemoglobin A, establishing a definitive diagnosis of hemoglobin S or hemoglobin C in combination with beta(+)-thalassemia. Higher than expected hemoglobin concentrations or lower than expected mean erythrocyte volumes should suggest concurrent beta(+)-thalassemia.

Screening for ophthalmic manifestations of sickle cell disease in the United Kingdom

There are marked variations in the manifestations of sickle disease in different populations. The ocular complications of this condition amongst the Afro-Caribbeans living in the United Kingdom have not previously been reported. We present the preliminary results of an ophthalmic screening programme at King's College Hospital, London. One hundred eyes of 50 patients with sickle cell disease were assessed. Full ocular examination was performed including fundus fluorescein angiography. We have looked at the haematological and clinical profile of the patients involved as well as the number of days spent in hospital during the year preceding the eye examination. The incidence of grade II retinopathy was found to be significantly higher than grade I in SC disease. This concurs with the results of the Jamaican screening and confirms that these patients are at higher risk of visual impairment than those with SS disease. Our results also agree with the Jamaican experience which suggest that visual morbidity is mostly due to complications of proliferative sickle retinopathy (PSR). However, the findings in patients without proliferative changes are different; in particular, angioid streaks leading to disciforms are an important cause of visual loss in Jamaica, but were not seen in any of the 98 eyes examined in this study. No correlation was found between the grade of retinopathy and age, sex, systemic complications and various haematological parameters except for the percentage of haemoglobin F, which was significantly higher in patients with grade I (7.6) compared with grade II (4.2) retinopathy (p = 0.0127).

New classification of peripheral retinal vascular changes in sickle cell disease

The systemic complications of homozygous sickle cell disease (SS) are more severe than in sickle cell haemoglobin C (SC) disease, and yet visual loss due to proliferative retinopathy is more common in the latter. This anomaly is unexplained. It is believed that proliferative disease occurs in response to closure of the peripheral retinal vasculature, yet a systematic longitudinal survey of the peripheral retinal vascular bed has not been undertaken. In the Jamaica Sickle Cohort study all subjects are scheduled to receive annual ocular examination and fluorescein angiography. The results have now been analysed in subjects with SS and SC disease using a new classification system based on a comparison of the peripheral retinal vascular bed with that recorded in the cohort with normal haemoglobin (AA) genotype. The vascular patterns could be classified as qualitatively normal (type I) or abnormal (type II). An abnormal vascular pattern was identified more commonly with age, in a significantly larger proportion of subjects with SC than SS disease, and was associated with the development of proliferative disease. In order to establish the dynamics of change, the angiograms were analysed in the 18 subjects (24 eyes) who developed proliferative disease. It is shown that a qualitatively normal vascular pattern may be retained despite loss of capillary bed and posterior displacement of the vascular border. A border which is qualitatively abnormal does not revert to normal, and once abnormal, continuous evolution may occur before development of proliferative lesions. The peripheral border of the retinal vasculature was too peripheral to photographed in 13 of the 24 eyes before it becoming qualitatively abnormal. It is concluded that a normal border, if posterior, results from gradual modification of the capillary bed and indicates low risk of proliferative disease. A qualitatively abnormal vascular border occurs as a radical alteration of retinal perfusion in subjects in whom little modification of the vascular bed occurred before the event, and signals risk of proliferative disease. This classification system is useful in identifying the likelihood of threat to vision in young Jamaicans with sickle cell disease, and the higher frequency of proliferative retinopathy in SC can be explained by the higher prevalence of a qualitatively abnormal peripheral retinal vasculature.

Peripheral retinal vasculature in normal Jamaican children

A prospective study of the peripheral retinal vasculature in a Jamaican cohort of subjects with sickle cell disease has been in progress over a period of 12 years using fluorescein angiography. Various vascular patterns were identified but their significance was unclear since no comparable records were available in subjects of a similar age with normal (AA) haemoglobin genotype. Fluorescein retinal angioscopy and angiography have been performed in 76 haemoglobin AA controls participating in the cohort study. The peripheral retinal capillary bed could be seen and photographed in a limited portion of the temporal peripheral fundus in a majority of this group, and there was considerable variation in the vascular pattern which could be characterised. These observations allow deviations from normal to be identified in the retinal vasculature in subjects with sickle cell disease.

Human parvovirus infection in homozygous sickle cell disease

We studied the epidemiology of human parvovirus B19 infection in 308 children with homozygous sickle cell (SS) disease and 239 controls with a normal haemoglobin (AA) genotype followed from birth in a cohort study. Annual serum samples identified the time and frequency of B19 infection, which did not differ between SS and AA children, about 40% of each group developing specific IgG by age 15. B19 infection followed an epidemic pattern similar to that observed for aplastic crises; accounted for all 91 aplastic crises that occurred; and was found in an additional 23 SS patients, of whom 10 showed mild haematological changes and 13 no changes. The magnitude or duration of IgG response did not differ between these groups. No patient had 2 attacks of aplasia and no patient nor control had 2 attacks of B19 infection. Following B19 infection, serial specific IgG concentrations remained high after 5 years in only 45% of SS patients, although the rarity of recurrent aplasia suggests lifelong immunity. B19 infection accounts for most if not all aplastic crises in SS disease, but at least 20% of infections do not result in aplasia. An effective vaccine against B19 might make an important contribution to the management of sickle cell disease.

Neurocognitive aspects of pediatric sickle cell disease

Studies pertaining to the neurocognitive functioning and learning of children in whom sickle cell disease is diagnosed are reviewed, and findings suggest diffuse neurocognitive deficits, with much variability across subjects. A hypothesis is presented about the cumulative nature of such deficits in children who have not sustained cerebral vascular accidents. Important methodological shortcomings in the literature are identified and recommendations are made for future neurocognitive research with children in whom sickle cell disease has been diagnosed. Studies pertaining to the psychosocial development of these children are also reviewed, and it is concluded that behavioral problems, low self-esteem, and disturbances of body image are frequently characteristic of these children. Recommendations are made including early special education and psychosocial intervention programs for children with sickle cell disease.

Stroke in a cohort of patients with homozygous sickle cell disease

Strokes occurred in 17 of 310 children with homozygous sickle cell disease who were followed from birth, representing an incidence of 7.8% by the age of 14 years. Two children had subarachnoid hemorrhage, one having resolution of symptoms after aneurysm surgery and another dying of a presumed second hemorrhage 14 days later. The remaining 15 strokes were presumed to be cerebral infarction, although autopsy, angiographic, or computed tomographic evidence was available in only 8 children. There were 6 deaths, 2 in the acute event and 4 after recurrence, which occurred in 6 (46%) of 13 patients who survived the initial episode. There were 10 recurrent episodes at a median interval of 9 months after the initial event. Steady-state hematologic data revealed significantly higher leukocyte counts than in control subjects without strokes at age 1 year and in the last study preceding the stroke. The initial stroke coincided with an acutely lowered hemoglobin value in 5 patients (3 aplastic crises, 1 acute splenic sequestration, 1 probable pulmonary sequestration) and with painful crises in another 7 patients. We conclude that a high leukocyte count and an acute decrease of hemoglobin are risk factors for stroke in patients with homozygous sickle cell disease.

Cardiac abnormalities in children with sickle cell anemia

The cardiac status of 64 children (ages 0.2 to 18 yr) with sickle cell anemia documented by hemoglobin electrophoresis was evaluated by echocardiography. Left atrial, left ventricular and aortic root dimensions were significantly increased in over 60 percent of these children at all ages compared to values for 99 normal black (non-SCA) control subjects. Left ventricular wall thickness was increased in only 20 percent of older children with sickle cell anemia. Estimated LV mass/m2 and left ventricular cardiac index were increased compared to control subjects (p less than 0.001). Left heart abnormalities expressed as a single composite function, derived from multivariate regression analysis, correlated well with severity of anemia expressed as grams of hemoglobin (r = -0.52, p = less than 0.001) and with percentage of hemoglobin S (r = 0.51, p less than 0.001), but not to the same extent with age. Echocardiographically assessed left ventricular function at rest was comparable to that of control subjects. These data suggest that the major cardiac abnormalities in children are related to the volume overload effects of chronic anemia, and that in this age group, there is no evidence for a distinct "sickle cell cardiomyopathy" or cardiac dysfunction.

The influence of fetal hemoglobin on the clinical expression of sickle cell anemia

The variable levels of HbF in sickle cell anemia reflect the heterogeneous genetic mix of the beta s-gene-cluster haplotypes and coinheritance of alpha-thalassemia-2 in American SS patients. Clinical severity is less when the level of HbF reaches 20% or 1.2 g/dl or more. The coinheritance of alpha-thalassemia-2 not only increases the intracellular red cell water but modifies the HbF level in accordance with the beta-cluster haplotype. In general, the SS patient with at least one Senegalese haplotype who does not have a CAR haplotype in trans, has a significantly greater probability of maintaining HbF above 20%. This is in part related to the genetic control of the G gamma HbF locus. Such a patient is protected from arteriolar vasculopathy and subsequent major organ destruction. Much of this but perhaps not all of the better health of patients with a Senegalese haplotype can be attributed to the elevation of G gamma HbF. The coinheritance of alpha-thalassemia-2 further decreases the risk of major morbidity of the soft tissues but increases the risk of avascular necrosis of the bony skeleton. Although these heterozygous Senegal patients are healthier, eventually most, in time, will show the deleterious effect of HbS as retinopathy and avascular necrosis usually beginning after age 30 and sickle nephropathy after age 40. Because of the age-specific effect, the onset of the sickle vasculopathy is delayed by nearly 20 years in the Sen/Ben patient with increased G gamma HbF as compared to those with a CAR haplotype or the homozygous Benin. Lifetime elevation of HbF above 20% modifies the severity of disease expression and provides relative protection to the patient with sickle cell anemia.

Gall stones in Jamaican children with homozygous sickle cell disease

Gall stones were detected by ultrasonography in 30 of 226 (13%) children with homozygous sickle cell disease aged 5-13 years participating in a cohort study from birth. Children with gall stones had significantly lower total haemoglobin and fetal haemoglobin and higher bilirubin concentrations, but further analysis showed that the apparent effects of haemoglobin and fetal haemoglobin concentration were secondary to their relationship with bilirubin concentrations. Abdominal pain crises were significantly associated with gall stones but both factors appeared to reflect an increased clinical severity and were probably not causally related. No patients had symptoms specific of gall stones and an association with abdominal pain crisis should not, of itself, be considered an indication for surgery.

Endoscopic and gastric acid studies in homozygous sickle cell disease and upper abdominal pain

Upper endoscopic and gastric acid output studies were done in 51 patients with homozygous sickle cell (SS) disease and recurrent epigastric pain. Twenty (39%) had abnormalities in the upper gastrointestinal tract including 18 (35%) with peptic ulcers. Mean basal and maximum acid output were similar in patients with and without duodenal ulcer (DU). Because DU in SS disease does not appear to be associated with high acid outputs observed in other populations, it may reflect reduced mucosal resistance, possibly resulting from ischaemia. This hypothesis was supported by the significantly lower fetal haemoglobin level among SS-DU patients.

Sickle cell retinopathy in Jamaican children: further observations from a cohort study

Serial retinal examinations were performed in children aged 5 years and older and fluorescein angiography/angioscopy in children 6 years and older participating in a cohort study of sickle cell disease. There were 1229 patient years of observation among 389 children aged 5-13 years. Peripheral retinal vessel closure was present in approximately 50% of children with SS and SC genotypes at age 6 years and increased to affect 90% of children by age 12 years. A matched pair analysis, comparing groups with minimal and complete closure, indicated that complete closure was associated with significantly lower total haemoglobin and fetal haemoglobin levels and significantly lower weight in SS disease, whereas in SC disease the risk factors appeared to be high mean cell volume and low platelet count. Proliferative retinopathy was rare, occurring only once in an 8-year-old boy with SC disease, despite 592 patient years of observation in children over this age.

Cardiac performance in children with homozygous sickle cell disease

Cardiac function was evaluated in 24 children from a Jamaican sickle cell cohort study. Ten patients with sickle cell disease underwent echocardiographic studies on their eighth birthday. The results were compared with 14 age- and sex-matched control children born within hours of the index patients. Left ventricular dimension index (systolic 2.89 +/- 0.31 versus 2.33 +/- 0.42 cm and diastolic 4.70 +/- 0.35 versus 3.64 +/- 0.48 cm, p = 0.001), diastolic volume (79.4 +/- 17.1 versus 60.8 +/- 7.8 ml, p = 0.01), left ventricular mass index (116.3 +/- 3.4 versus 74.3 +/- 15.2 g/m2, p = 0.001) and cardiac index (5.51 +/- 1.32 versus 3.38 +/- 0.85 liters/min per m2 p = 0.001) were significantly increased in patients with sickle cell disease compared with values in control subjects. However, there was no statistically significant difference between the two groups for ejection fraction, velocity of circumferential fiber shortening, percent fractional shortening, systolic time intervals, wall stress and ratio of wall stress-systolic volume. Although two mean ratios of wall stress-systolic volume index were lower in children with sickle cell disease as compared with control subjects (4.0 +/- 0.7 versus 5.4 +/- 1.7, p = 0.02 and 5.9 +/- 1.2 versus 8.3 +/- 2.5, p = 0.005, respectively), the range of ratios remained within normal limits (3.4 to 5.8 in children with sickle cell disease versus 2.8 to 9.5 in controls and 4.2 to 8.3 versus 3.8 to 12.5, respectively). Furthermore, only body surface area predicted group status independent of other variables (p = 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Nutrition and sickle cell disease

The role of protein and calorie deficiency in sickle cell disease remains poorly defined. While such features as growth retardation, impaired immune function, and delayed menarche do suggest a relationship between sickle cell disease and undernutrition, measurement of more direct nutritional parameters in these patients have yielded mixed results. Anthropometric measurements such as skinfold thickness are subnormal in many but not all reports. Serum protein levels are normal, but low values for serum lipids have been reported. Finally, one small study shows an improvement in both growth parameters and clinical course following caloric supplementation. A variety of micronutrient deficiencies have been suggested in sickle cell disease. Numerous case reports describing an exacerbation of the chronic anemia that was reversed by folic acid therapy led to routine folate supplementation. More recent studies have shown, however, that clinically significant folic acid deficiency occurs only in a small minority of sickle cell patients. Clearly, more work is necessary to define the cost/benefit ratio of routine folic acid supplementation. Pharmacological amounts of vitamin B6 and certain of its derivatives possess in vitro antisickling activities. Nevertheless, a small clinical trial failed to demonstrate any consistent hematologic effects of B6 supplementation. Several reports indicate that vitamin E levels are low in sickle erythrocytes. Since these abnormal red cells both generate excessive oxidation products and are more sensitive to oxidant stress, and because oxidants appear to play a role in ISC formation, vitamin E deficiency could well be linked to ISC formation and hemolysis. Small clinical trials, however, have again failed to produce a clear hematological response in sickle cell anemia. The role of zinc in sickle cell disease has received considerable attention. Though studies are generally small, most do support a relationship between sickle cell disease and zinc deficiency. Etiologic associations between zinc deficiency and such complications of sickle cell disease as poor ulcer healing, growth retardation, delays in sexual development, immune deficiencies, and high ISC counts have all been suggested. Most of these studies need further corroboration. Iron deficiency is now known to be a relatively common occurrence in sickle cell anemia, especially in children and pregnant women. The theoretical benefits of concomitant iron deficiency and sickle cell anemia remain to be proven in a controlled clinical trial.(ABSTRACT TRUNCATED AT 400 WORDS)

Haemoglobin gene frequencies in the Jamaican population: a study in 100,000 newborns

The gene frequencies of abnormal haemoglobins have been determined in a group of 100,000 Jamaican newborns screened over a period of 8 1/2 years. The population is predominantly of West African origin and the survey represents approximately one quarter of all island deliveries within the period of the study. The common beta globin chain abnormalities beta s and beta c occurred with gene frequencies of 0.055 and 0.019 respectively; beta thalassaemia was relatively rare. In contrast, alpha thalassaemia was quite common, occurring with a gene frequency of 0.183. In addition to these common abnormalities, the frequencies of 256 rare abnormal haemoglobins are described. This survey thus represents a complete and accurate documentation of the alpha and beta globin variants that occur in the Jamaican population.

Recurrent infections in sickle cell disease: haematological and immune studies

Some haematological and immunological indices were compared in 19 children with sickle cell disease and a history of recurrent infections and in 16 children with sickle cell disease without any known infections. The recurrent infection group had significantly greater pitted red cell counts and greater absolute monocyte counts. No differences were apparent in routine haematological indices, foetal haemoglobin, immunoglobulin, or complement levels between the groups. The interpretation of these results is discussed.

Clinical presentation of homozygous sickle cell disease

The pattern of initial clinical symptoms and signs developing in a representative sample of 305 children with homozygous sickle cell (SS) disease diagnosed at birth was analyzed. Specific symptoms were present by age 6 months in 6% of the group, and had developed by the first to eighth birthdays in 32%, 61%, 78%, 86%, 90%, 92%, 94%, and 96%, respectively. Inclusion of nonspecific symptoms in the analysis led to earlier recognition by a mean of 3 months in the first year and by a mean of approximately 1 year between the ages of 2 and 4 years. Dactylitis was the most common initial symptom, noted in 40% of the group overall and in 50% in the first 2 years. Painful crisis was the first symptom in more than one fourth of the patients and was the most frequent symptom after the age of 2 years. Acute splenic sequestration led to presentation in one-fifth of the group overall and in one third of patients younger than 2 years. The most common nonspecific symptom was pneumonia. There was a significant trend of earlier presentation in children with low fetal hemoglobin levels. The age at presentation did not appear to be affected by alpha-thalassemia status.

Haematological change in sickle cell-haemoglobin C disease and in sickle cell-beta thalassaemia: a cohort study from birth

The haematological changes in early years following neonatal diagnosis have been observed in representative groups of children with sickle cell-haemoglobin C (SC) disease, sickle cell-beta(+) thalassaemia, and in sickle cell-beta(0) thalassaemia. Most haematological indices in SC disease were intermediate between previously published values in SS disease and in AA controls, generally being closer to values in normal children. Exceptions were microcytosis which may be genetically determined and a striking elevation of mean cell haemoglobin concentration from age 2 months to 4 years. The combination of a raised MCHC and a lowered MCV is unusual and may be characteristic of SC disease. Features in sickle cell-beta thalassaemia generally differed according to the type of beta thalassaemia gene. Sickle cell-beta(0) thalassaemia had lower levels of haemoglobin, MCHC, red cell count, MCV, and higher reticulocytes, most differences being significant before 1 year. No differences between S beta(0) thalassaemia and S beta(+) thalassaemia were apparent in HbF levels (which resembled those in SS disease) or in HbA2 levels (which exceeded those in SS disease by 1 year of age).

The haematology of steady state homozygous sickle cell disease: frequency distributions, variation with age and sex, longitudinal observations

The steady state haematological characteristics observed in 1071 patients with homozygous sickle cell (SS) disease aged 5-66 years are presented. Cross sectional studies indicated that HbA2 levels were consistently higher in males but no age related change was apparent. Fetal haemoglobin levels were consistently higher in females and fell significantly in males between the 5-9 and 10-14 year age groups. Total haemoglobin was significantly higher in females before age 15 and higher in males after 20 years, a dramatic age related rise occurring in males between the 10-14 and 25-29 year age groups, and a fall in patients aged 40 years and over. The mean cell volume was consistently greater in females after 15 years and a marked age related rise occurred in both sexes between the 5-9 and 25-29 year age groups. Counts of irreversibly sickled cells were consistently higher in males. Reticulocytes fell significantly with age, while platelets and total bilirubin fell significantly after the age of 15 years. Longitudinal studies confirmed the increase in total haemoglobin levels in males over the ages 10-14 years, and a significant fall in males after the age of 30 years. Such studies also confirmed the fall in HbF in males aged 5-14 years, the increase in MCV in both sexes aged 5-29 years, and the fall in platelet counts in both sexes over the age of 20 years. These observations provide 'normal' values for patients seen elsewhere and also contribute to an understanding of factors determining the haemoglobin indices in SS disease.

G gamma beta+ hereditary persistence of fetal hemoglobin: cosmid cloning and identification of a specific mutation 5' to the G gamma gene

Hereditary persistence of fetal hemoglobin (HPFH) is a benign condition in which the normal shutoff of fetal hemoglobin (Hb F) production fails to occur. In the G gamma beta+ type of HPFH, erythrocytes of adult heterozygotes contain approximately equal to 20% Hb F, which is almost exclusively of the G gamma-globin variety, without increased levels of gamma-globin chains from the nearby A gamma-globin gene. Unlike some forms of HPFH, no major deletions in the globin gene cluster have been found by genomic blotting in the G gamma beta+ variety. We report here a family with this condition, from which cosmid clones of the beta-globin gene cluster from the G gamma beta+ HPFH allele have been obtained. Sequencing around the fetal genes has identified a point mutation 202 base pairs 5' to the G gamma-globin gene that is present in genomic DNA of 3/3 unrelated individuals with G gamma beta+ HPFH but in none of more than 100 non-HPFH individuals. Although the mutation could represent a tightly linked polymorphism, its location in a region suggested by recent data to be important in tissue-specific control of gene expression suggests the possibility that the -202 mutation accounts for the phenotype. The sequence created resembles elements of other eukaryotic promoters known to be important for efficient transcription.

A trial of folate supplementation in children with homozygous sickle cell disease

A double blind controlled trial of supplementation with folic acid has been performed in 117 children with homozygous sickle cell (SS) disease aged 6 months to 4 years over a 1 year period. No megaloblastic change was observed in either group. At the end of the study period the folate supplemented group showed no significant differences in haemoglobin, growth characteristics, or in the proportion of children affected by major or minor infections, acute splenic sequestration, dactylitis or episodes of bone or abdominal pain. However, the folate supplemented group showed a significantly lower mean cell volume and the placebo group contained a significant excess of children experiencing multiple episodes of dactylitis. The results are compatible with mild folate deficiency in some patients in the placebo group but the absence of striking effects on haematology or growth suggest that the policy of regular folate supplementation in children with SS disease should be critically reviewed.

Post-natal decline of fetal haemoglobin in homozygous sickle cell disease: relationship to parenteral Hb F levels

The decline of fetal haemoglobin (Hb F) from birth to 6 years has been compared in a cohort of 266 Jamaican children with homozygous sickle cel (SS) disease and in 243 matched controls with a normal haemoglobin (AA) genotype. Hb F levels were significantly higher in the SS cases from 1 month onward but, unlike the normal controls, no sex difference was apparent. The Hb F levels in SS disease were significantly correlated with parental Hb F levels, suggesting that genetic factors regulating adult Hb F levels are active at earlier stages in development. Furthermore, some of these genetic determinants of Hb F production may be linked to the beta-like globin gene complex and be in linkage disequilibrium with the beta s allele.