Karlene P Mason

OUTBREAK OF APLASTIC CRISES IN SICKLE CELL ANAEMIA ASSOCIATED WITH PARVOVIRUS-LIKE AGENT

Since 1952, 112 children with sickle cell anaemia (SCA) in Jamaica have had an aplastic crisis. Outbreaks occurred in 1956, 1960, 1065-67, 1971-73, and 1979-80. Most cases occurred in children under 10 years of age, and an aplastic crisis in a patient over the age of 15 years is rare. There were 38 cases in 1979-80 and stored serum specimens from 28 of these were available for virus studies. Evidence for infection with a parvovirus-like agent was found in 24 of these 28 cases. Viral antigen was detected in 2 patients, both of whom demonstrated seroconversion. Seroconversion during 1980 was detected in a further 7, increasing amounts of antibody during the convalescent period were found in 5, antibody was found in 2 of 4 patients from whom only an acute phase specimen was available and the remaining 10 were antibody positive in the only convalescent phase sample available for testing. Antibody was found in 4 of 94 controls with the SS genotype (in retrospect 2 of these may have had an aplastic crisis) and in 17% of 48 controls with a normal haemoglobin (AA) genotype. The results accord with the possibility that the parvovirus-like agent is the principal cause of aplastic crisis in SCA.

The interaction of alpha-thalassemia and homozygous sickle-cell disease.

Patients with homozygous sickle-cell disease may be homozygous for alpha-thalassemia 2 (alpha-/alpha-), may be heterozygous for alpha-thalassemia 2 (alpha-/alpha alpha), or may have a normal alpha-globin-gene complement (alpha alpha/alpha alpha). We compared the clinical and hematologic features of 44 patients who had sickle-cell disease and homozygous alpha-thalassemia 2 with those of controls with the two hematologic conditions. The patients with homozygous alpha-thalassemia 2 had significantly higher red-cell counts and levels of hemoglobin and hemoglobin A2, as well as significantly lower hemoglobin F, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration, mean corpuscular volume, reticulocyte counts, irreversibly-sickled cell counts, and serum total bilirubin levels, than those with a normal alpha-globin-gene complement. Heterozygotes (alpha-/alpha alpha) had intermediate values. In the group with homozygous alpha-thalassemia 2, fewer patients had episodes of acute chest syndrome and chronic leg ulceration and more patients had splenomegaly, as compared with patients in other two subgroups. These data confirm previous suggestions that alpha-thalassemia inhibits in vivo sickling in homozygous sickle-cell disease and may be an important genetic determinant of its hematologic severity.

Comparison of Sickle Cell-β° Thalassaemia with Homozygous Sickle Cell Disease

Summary. Clinical and haematological features in 41 patients with sickle cell‐β° thalassaemia (Sβ° thalassaemia) and in 123 age‐sex matched controls with homozygous sickle cell (SS) disease were compared. Persistence of splenomegaly was more common and fetal loss less common in Sβ° thalassaemia but other clinical features were similar in the two genotypes. Total haemoglobin, Hb A2, PCV, CCV, and red cell count were significantly higher and MCV, MCH, MCHC, and ISC counts significantly lower in Sβ° thalassaemia. Proportional reticulocyte counts were significantly lower in Sβ° thalassaemia but there was no difference in absolute reticulocyte counts. Persistence of splenomegaly and low ISC counts are compatible with decreased intravascular sickling which may result from the lower mean cell haemoglobin S concentration in Sβ° thalassaemia. If beneficial effects of a low MCHC can be confirmed then a carefully monitored trial of iron deficiency in SS disease may be a logical experimental procedure.

Comparison of Haematological Features of the β0 and β+ Thalassaemia Traits in Jamaican Negroes

Haematological characteristics have been compared in 29 subjects with heterozygous β0 thalassaemia and in 33 subjects with heterozygous β+ thalassaemia, identified by the type of sickle cell‐β thalassaemia among close relatives, in a Jamaican Negro population. Total haemoglobin, MCV and MCH were significantly lower in the β0 type but the level of Hb A2 was not significantly different. Individual values for MCV, MCH and Hb A2 in the β+ type occasionally overlapped those in the normal population casting doubt on the adequacy of these criteria in identifying all cases of heterozygous β+ thalassaemia. The haematological differences are those which would be expected on theoretical grounds. The inability to confidently differentiate the two types of heterozygous β thalassaemia has implications for genetic counselling. The inability to distinguish heterozygous β+ thalassaemia from normals on any single haematological index suggests that surveys depending on estimations of Hb A2 or on MCV alone may have underestimated the prevalence of the β+ thalassaemia gene.

Effect of alpha thalassaemia on the rheology of homozygous sickle cell disease

Summary. A study of rheological determinants (plasma viscosity, whole‐blood viscosity, and erythrocyte deformability) was made in 24 matched pairs of patients with homozygous sickle cell disease, with and without homozygous α‐thalassaemia 2. Patients with coexisting α‐thalassaemia showed a significant increase in erythrocyte deformability measured as filtration of washed erythrocytes through 5 μm diameter pores and also as viscosity of whole blood at high shear rate (230 s−1) and standard haematocrit (0·45). This rheological advantage may explain the beneficial effect of α‐thalassaemia 2 on haematological parameters and clinical events in homozygous sickle cell disease.

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

Summary. 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 cell (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 β‐like globin gene complex and be in linkage disequilibrium with the βs allele

The haematology of homozygous sickle cell disease after the age of 40 years

Haematological indices have been studied in 181 patients with homozygous sickle cell (SS) disease aged 40–73 years. Cross‐sectional analyses in 5‐year age bands indicated age‐related decreases in HbF (males only), total haemoglobin and platelet counts. Longitudinal studies within individuals confirmed the downward age‐related trend in haemoglobin and platelets and also revealed a falling reticulocyte count, most significant when expressed as absolute values. Total nucleated cells also fell although the decline was significant only in females. These observations are consistent with a progressive bone marrow failure which is not explained by the commonly occurring renal impairment in older SS patients since the changes persisted in analyses confined to patients with normal creatinine levels. The mechanism of this bone marrow failure is currently unknown.

The Development of Haemoglobin A2 in Normal Negro Infants and in Sickle Cell Disease

The development of haemoglobin A2 levels from birth to 3 years has been compared in normal, β‐thalassaemia trait, sickle cell (SS) disease, and S‐β‐thalassaemia genotypes. Hb A2 levels were almost identical in normals and in children with SS disease at 1, 2 and 3 years. The most rapid increases in Hb A2 levels occurred before 6 months but levels were still rising at the end of the third year. Sickle cell‐β+ thalassaemia could be differentiated from SS disease by the higher Hb A2 levels between 6 months and 1 year. Insufficient data were available on S‐β° thalassaemia but since Hb A2 levels in this condition are generally higher than those in S‐β+ thalassaemia, differentiation from SS disease may also be possible from the age of 6 months.

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‐β+ thalassaemia, and in sickle cell‐β° thalassaemia.

Haemoglobin Variant Screening in Jamaica: Meeting Student's Request

The Jamaican Cohort Study, established by the screening of 100 000 consecutive, non-operative deliveries at the main Government maternity hospital, Kingston, Jamaica between 1973 and 1981, provided the frequency of major haemoglobin variants in that population (Serjeant et al, 1986). However, newborn samples are not optimal for the diagnosis of beta thalassaemia or hereditary persistence of fetal haemoglobin and these had to be implied by extrapolation from other genotypes. Following a recent education programme on sickle cell disease to senior students of secondary schools across the island, there was demand from the students to learn their haemoglobin genotypes. In conjunction with the Jamaican Ministry of Health and Ministry of Education, the Parish of Manchester in south central Jamaica was selected for a pilot programme which targeted the 5th and 6th forms (mostly aged 15–19 years), screening 16 636 students of 15 secondary schools in the 6 academic years from 2007/8. It was assumed that greater precision would be available in the laboratory 40 years later and would allow comparison of gene frequency with the earlier study; compliance would test the interests of students in learning their haemoglobin genotypes, and, most important of all, would provide an informed cohort where the effects of genotype knowledge could be assessed on subsequent reproductive decisions. After discussions with the school staff, Parent–Teachers Associations, and illustrated lectures on sickle cell disease and its genetics, all students were given letters for their parents outlining the objectives and the option of declining for their child to be tested. At pre-arranged times, a physician, clerical assistants and 3–4 phlebotomists visited the school, the students completed a data form providing personal details and one 5 ml EDTA sample was taken by venepuncture. The turn-round time for individuals was about 20 min; 150–250 students could be screened within 2–21⁄2 h, with most schools requiring 2–5 visits. Permanent laminated cards with haemoglobin genotype were given to all students, and counselling was offered to carriers of haemoglobin variants. Compliance with screening increased over the 6 years, from 56% to 92%, testimony to the cooperation of the teaching staff and the motivation of students. Haemoglobin bands in the position of HbS were confirmed by the slide sickling test and in the position of HbC by agar gel electrophoresis at pH 6 2. Samples with mean cell haemoglobin ≤ 26 pg and red blood cell distribution width (coefficient of variation) [RDW(CV)] < 18 0 were candidates for the beta thalassaemia trait and had estimations of HbA2 performed, which if ≥3 5% underwent direct sequencing of polymerase chain reaction-amplified b-globin DNA (Vetter et al, 1997). Samples with >8% HbF, measured by high performance liquid chromatography (HPLC), were investigated by multiplex ligation-dependent probe amplification (MLPA, MRC-Holland, Amsterdam, The Netherlands) to identify deletional hereditary persistence of fetal haemoglobin (HPFH) or by DNA sequencing of gamma globin promoter regions to identify non-deletional HPFH at the Red Cell Centre, Kings College Hospital, London. Samples with negative confirmatory tests for HbS and HbC were investigated by genomic sequence analysis of HBB, HBA1 and HBA2 (Thein & Hinton, 1991; Viprakasit et al, 2002) at the Weatherall Institute of Molecular Medicine, Oxford, UK and identified using the syllabus of haemoglobin variants (http://globin.cse.psu.edu). Haemoglobin genotypes were similar to those in the Jamaican Cohort Study (Table I), which identified SS disease in every 300 births and SC disease in every 500 births,