Rapid detection and prenatal diagnosis of beta-thalassaemia: studies in Indian and Cypriot populations in the UK

Distribution of beta-thalassemia mutations in the Indian population referred to a diagnostic center

Hemoglobinopathies are the most commonly inherited genetic disorders in India. Population screening has identified certain communities in India with high risk of beta-thalassemia, the prevalence of carrier status in some being as high as 17%. Over a period of 6 years we have conducted DNA analysis on 1,233 carriers of 23 beta-thalassemia mutations and Hb E, using the amplification refractory mutation system. The studies included analyses of five common mutations for Asian Indians, namely IVS-I-5 (G-->C), 619 bp deletion, IVS-I-1 (G-->T), and the frameshifts at codons 8/9 (+G) and 41/42 (-TTCT). The occurrence of these was seen in 1,066 (86.45%) of the carriers referred to us, the percentage of mutations varying between 5.03-42.58%. We found codon 15 (TGG-->TAG) in 47 (3.81%) samples which was also considered a common mutation in the Indian population. Rare beta-thalassemia mutations were found in 87 (7.06%) individuals. We have designed five new primers and modified four primers for nine rare mutations. These were seen in nine (0.73%) samples. The beta-thalassemia anomaly in 33 (2.68%) carriers remained uncharacterized. State-wide and community-wide distribution patterns of mutations indicated that IVS-I-5 (G-->C) is the most common beta-thalassemia allele in the Indian population. Sindhis settled in Gujrat, and Maharashtra and Lohanas from Gujrat showed a prevalence of the 619 bp deletion mutation in 49.2 and 45.5% carriers, respectively. High frequency of the IVS-I-1 (G-->T) mutation was also found in Sindhis (25.5%), Punjabi Hindus (34.7%), and Lohanas (31.2%). These studies of mutation patterns in different communities have helped us in the quick identification of beta-thalassemia mutations for prenatal diagnosis.

The mutation associated with Hb Peterborough [beta111(G13)Val-->Phe] originated from Southern Italy

Hb Peterborough [beta111(G13)Val-->Phe], an unstable hemoglobin variant with low oxygen affinity, was first described in two patients of Italian origin. This paper reports the first observation of this variant in Campania, Southern Italy, in two unrelated patients suffering from mild anemia. The variant was separated from Hb A by cation exchange chromatography on a high performance liquid chromatographic system with an automated procedure that might be useful for diagnostic purposes. The amino acid replacement, Val-Phe at [beta111, was assessed by tandem electrospray mass spectrometry analysis, and the corresponding DNA mutation was established as G-->T at the first position of codon 111 (GTC-TTC) by polymerase chain reaction amplification techniques. A family study showed that the two original carriers of Hb Peterborough were members of the same family as the proband examined in this study. This finding, and the presence of a second unrelated family carrying Hb Peterborough in Campania, strongly suggests that the DNA mutation associated with this variant originated in Southern Italy.

Molecular studies of beta-thalassemia heterozygotes with raised Hb F levels

Hb F levels in beta-thalassemia heterozygotes are usually less than 2%, but amongst 1,059 patients studied, 73 (7%) had Hb F levels above 2.5% (2.6-14.0%). To investigate factors that may influence the increase of Hb F levels in these heterozygotes, we characterized the beta-thalassemia mutations and their chromosomal background, gamma-globin gene promoter variations, and alpha-globin genotypes. All 73 beta-thalassemia heterozygotes carried beta-thalassemia point mutations previously observed in the Greek population; gene mapping excluded b gene cluster deletions; only two cases had an additional gamma-globin gene (gammagammagamma/gammagamma). Five alpha-globin genes (alphaalphaalpha/alphaalpha) were detected in 17/73 cases (23%) as compared to a carrier rate of 1.76% in the general population. Molecular, hematological, and biosynthetic findings in these compound heterozygotes indicated that the raised Hb F levels were caused by cell selection due to ineffective erythropoiesis. In the remaining 56 simple beta-thalassemia heterozygotes, 11 beta-thalassemia mutations were observed, each on the expected haplotype(s), and analysis of the gamma gene promoters revealed three known polymorphisms (in linkage disequilibrium), with minimal influence on gamma-globin levels. However, the overall distribution of beta-thalassemia mutations in the 56 simple beta-thalassemia heterozygotes was significantly different (P<0.0002) compared to that in 986 simple beta-thalassemia heterozygotes with <2.5% Hb F, implicating an association between beta-thalassemia mutations and moderately increased Hb F levels, most notably codon 39 (C-->T), IVS-II-1 (G-->A), codon 6 (-A), and codon 8 (-AA), which accounted for 41/56 (73%) cases with >2.5% Hb F. In the remaining 15/56 (27%) cases, no common underlying globin genotypes could explain the raised Hb F levels. Overall, this study indicates that the control of Hb F levels in beta-thalassemia heterozygotes is heterogeneous and multi-factorial.

Long-term effect of prospective detection of high genetic risk on couples' reproductive life: data for thalassaemia

Prospective risk detection with availability of prenatal diagnosis is the best service currently available for couples at high genetic risk Here we describe the long term effect of this service on the reproductive life of 102 couples at risk of thalassaemia, whose risk was detected prospectively by carrier screening, who made use of prenatal diagnosis, and where the woman is now over 40. Overall outcome for couples is described in terms of number of favourable versus unfavourable pregnancy outcomes. (A favourable pregnancy outcome = unaffected livebirth, or affected livebirth resulting from informed parental choice.) The 102 couples had a total of 356 pregnancies, including 302 viable pregnancies, and 88% achieved a family unburdened by thalassaemia. 68% of viable pregnancies had a favourable outcome, but only 43% of couples had only favourable outcomes, and 26% lost two or more viable wanted pregnancies. When early losses are included 58% of pregnancies had a favourable outcome, but only 30% of couples had only favourable outcomes, and 41% lost two or more pregnancies. Even with the best available service, at risk couples remain victims of chance, and a significant minority experience great difficulty in obtaining even one healthy child. Research is needed on approaches that may allow couples better control of reproductive outcomes.

Determination of beta-globin gene cluster haplotypes and prevalence of alpha-thalassemia in sickle cell anemia patients in Venezuela

Sickle cell anemia and alpha-thalassemia have a heterogeneous distribution in Venezuela with a high frequency in the coastal area (sea level) and few cases in the mountains. Most of our population is an ethnic admixture of Europeans (Spaniards colonists), Africans (slaves), and Amerindians. The purpose of our study was to determine the origin of the beta(s) globin haplotype, age and survival dependency, and the admixture among the different African groups in our population. The alpha(3.7) globin gene deletion status was also studied and found in a very high frequency. DNA from peripheral blood of 191 non-related patients (81 with HbS homozygous and 15 patients compound heterozygous for HbS, HbC, HbD with beta-thalassemia, and 95 with sickle cell trait) were studied. The beta(s) chromosome was linked 51% to the Benin Haplotype, 29.5% with the CAR, 12.5% to the Senegal, and 2.5% to the Cameroon. We did not find any significant difference between the haplotype distribution among adults and children and among sickle cell patients and traits. Only 8.6% of the patients have homozygosity for the Benin haplotype. These results show a very high frequency of admixture in our African origin population.

Geographic and ethnic distribution of beta-thalassemia mutations in Uttar Pradesh, India

We have studied the geographic and ethnic distribution of mutations in 376 subjects who were carriers of beta-thalassemia, and identified the mutations in 365 chromosomes. The majority of the beta-thalassemia carriers were of Uttar Pradesh (India) origin. Their pattern of mutations differed from the other states of India and from those families who had migrated from Pakistan. The frequency of the IVS-I-5 (G-->C) and 619 bp deletion mutations were 64.3 and 2.5%, respectively, among families originating from Uttar Pradesh, compared to a prevalence of 37.5 and 27.5%, respectively in the population of Pakistani immigrants. Of the 10 common Asian Indian mutations, only eight were observed in subjects studied from different parts of India. By use of the amplification refractory mutation system along with DNA sequencing techniques, the mutations were successfully identified in 97.1% of subjects, while 11 cases (2.9%) still remain to be characterized by single strand conformation polymorphism and sequencing analyses. The application of this knowledge has facilitated the successful implementation of the program of genetic counseling and prenatal diagnosis of beta-thalassemia, thus helping to avoid the birth of an affected child in India.

Beta-thalassaemia in Cubans: novel allele increases the genetic diversity at the HBB locus in the Caribbean

In order to establish the molecular basis of beta-thalassaemia in Cubans, a total of 75 unrelated individuals, with beta-thalassaemia major (7), Hb S-beta-thalassaemia (28), Hb C-beta-thalassaemia (1), and beta-thalassaemia trait (39) yielding 82 beta-thalassaemia alleles, were analyzed. Seventeen different point mutations were identified accounting for 93% of the beta-thalassaemia alleles studied, revealing a high genetic heterogeneity at the HBB locus in this population. The more prevalent mutations, namely, CD 39 (C --> T) (30.5%), -29 (A --> G) (13.4%), IVS-I-110 (G --> A) (8.5%), and IVS-II-1 (G --> A) (8.5%), reflect the Mediterranean and African predominant ancestry of the extant Cuban population. We also report the identification of a novel allele, IVS-I-108 (T --> C), that possibly activates a cryptic branch site, in a beta-thalassaemia carrier with no other molecular defect within the beta-globin gene and its proximal promoter. This study shows that prenatal diagnosis of beta-thalassaemia should be feasible in about 60% of at-risk pregnancies by direct detection of selected point mutations. However, due to the wide spectrum of mutations, and in order to offer fully informative prenatal diagnosis to more than 87% of at-risk couples, the screening for beta-thalassaemia mutations in Cubans should be performed by using a general point mutation detection method, such as DGGE (denaturing gradient gel electrophoresis).

Thalassaemia in Sri Lanka: implications for the future health burden of Asian populations. Sri Lanka Thalassaemia Study Group

BACKGROUND

Thalassaemias pose an increasing problem for the Indian subcontinent and many Asian countries. We analysed the different types of thalassaemia in the Sri Lankan population, surveyed gene frequencies in schoolchildren, and estimated the burden of disease and requirements for its control.

METHODS

We analysed blood samples from patients attending clinics in nine hospitals and defined the different types of beta thalassaemia by high-performance liquid chromatography (HPLC) and DNA analysis. The range of mutations was obtained by analysis of beta-globin genes. Capillary blood was obtained from schoolchildren from different parts of the island and analysed by HPLC to provide an approximate assessment of the carrier frequency of beta thalassaemia and haemoglobin E (HbE). To estimate the frequency of alpha thalassaemia the alpha-globin genotypes were also analysed when it was possible.

FINDINGS

Blood samples were obtained from 703 patients with beta thalassaemia and from 1600 schoolchildren. The thalassaemia mutations were unevenly spread. Although 23 different beta-thalassaemia mutations were found, three accounted for the thalassaemia phenotype in about 70% of the patients, most whom are homozygotes or compound heterozygotes for IVS1-5 (G-->C) or IVS1-1 (G-->A). The third common mutation, codon 26 (G-->A), which produces HbE, interacts with one or other of these mutations to produce HbE/beta thalassaemia; this comprises 13.0-30.9% of cases in the main centres. Samples from 472 patients were analysed to determine the alpha-globin genotype. Overall, 15.5% patients were carriers for deletion forms of alpha+ thalassaemia. Average gene frequencies showed that there will be more than 2000 patients requiring treatment at any one time, in the future, of whom those with HbE/beta thalassaemia will account for about 40%.

INTERPRETATION

In Sri Lanka, interactions of the two common beta-thalassaemia alleles will nearly always result in a transfusion-dependent disorder. However, about 40% of patients will have HbE/beta thalassaemia, which has a variable course. The management of these disorders could require about 5% of the total health budget. We need to learn more about the natural history and appropriate management of HbE/beta thalassaemia if resources are to be used effectively.

Informed choice in genetic screening for thalassaemia during pregnancy: audit from a national confidential inquiry

OBJECTIVE

National audit of informed choice in antenatal screening for thalassaemia.

DESIGN

Audit from the UK Confidential Enquiry into Counselling for Genetic Disorders.

SETTING

Thalassaemia module of the UK Confidential Enquiry into Counselling for Genetic Disorders.

SUBJECTS

138 of 156 couples who had had a pregnancy affected by a major beta thalassaemia from 1990 to 1994.

MAIN OUTCOME MEASURES

How and when genetic risk was identified for each couple, and whether and when prenatal diagnosis was offered.

RESULTS

Risk was detected by screening before or during the first pregnancy in 49% (68/138) of couples and by diagnosis of an affected child in 28% (38/138) of couples. Prenatal diagnosis was offered in 69% (274/400) of pregnancies, ranging from 94% (122/130) for British Cypriots to 54% (80/149) for British Pakistanis and from 90% in the south east of England to 39% in the West Midlands. Uptake of prenatal diagnosis was 80% (216/274), ranging from 98% (117/120) among British Cypriots in either the first or second trimester to 73% (35/48) among British Pakistanis in the first trimester and 39% (11/28) in the second trimester. A demonstrable service failure occurred in 28% (110/400) of pregnancies, including 110 of 126 where prenatal diagnosis was not offered and 48 of 93 that ended with an affected liveborn infant.

CONCLUSION

Although antenatal screening and counselling for haemoglobin disorders are standard practices in the United Kingdom, they are delivered inadequately and inequitably. An explicit national policy is needed, aiming to make prenatal diagnosis in the first trimester available to all couples and including ongoing national audit.

Jamaican Sbeta+-thalassaemia: mutations and haematology

The sickling disorders are a common cause of morbidity and mortality in Jamaica. Sickle cell beta+-thalassaemia is the fourth commonest form, occurring in one in every 3000 births. This is a heterogeneous condition, producing HbS, HbF and HbA2 with variable amounts of HbA, depending on the mutation and, within a defined population, only a few beta-thalassaemia mutations occur at high frequency. This study establishes the frequency of beta-thalassaemia mutations in Sbeta+-thalassaemia patients in Jamaica. In addition, comparison of the haematological phenotypes is possible by looking at the 'average steady-state haematology' of the different mutational groups. Blood samples from 132 unrelated Sbeta+-thalassaemia patients attending the MRC Sickle Cell Unit at the University of the West Indies were analysed by amplification refractory mutation system (ARMS) polymerase chain reaction (PCR) or sequencing to determine the nature and frequencies of the underlying beta-thalassaemia mutations. Ten mutations were identified, four of which accounted for 93% of patients studied. These were -29(A --> G) in 71 (54%), -88(C --> T) in 27 (20%), polyA(T --> C) in 17 (13%) and IVS1-5(G --> C) in nine (7%). The six remaining mutations found at low frequency were C24(T --> A) in two patients and one each of IVS2-848(C --> A), -90(C --> T), IVS1-5(G --> T), IVS1-5(G --> A) and IVS1-6 (T --> C). In one individual, no mutation was found. The three commonest mutations were all associated with haemoglobin levels of greater than 10 g/dl, whereas IVS1-5 (G --> C) had a more severe haematological phenotype. The predominance of -29(A --> G) and -88(C --> T) is in keeping with other studies on populations of African origin. IVS1-5(G --> C) is found chiefly in Indian populations, and all affected families acknowledged Indian ancestry, reflecting the prominent Indian community in Jamaica.

Molecular, haematological and clinical studies of the -101 C --> T substitution of the beta-globin gene promoter in 25 beta-thalassaemia intermedia patients and 45 heterozygotes

We report the clinical, haematological, biosynthetic and molecular data of 25 double heterozygote beta-thalassaemia intermedia patients and 45 beta-thalassaemia heterozygotes with the C --> T substitution at nucleotide position -101 from the Cap site, in the distal CACCC box of the beta-globin gene promoter. This mutation is considered the most common amongst the silent beta-thalassaemia mutations in Mediterranean populations. Of the 25 compound heterozygotes for the beta -101 C --> T and common severe beta-thalassaemia mutations, all but one had mild thalassaemia intermedia preserving haemoglobin levels around 9.5 g/dl and haemoglobin F levels < 25%. The only transfused patient was characterized to have an additional alpha-globin gene. Strict assessment of haematological and biosynthetic findings in the heterozygotes for the beta -101 C --> T mutation (excluding six cases with an alpha-globin gene defect) demonstrated that less than half of them had completely normal (silent) haematology; the remainder had either high haemoglobin A2 values (in the range of 3.7-5.1%) and/or low red cells indices and/or raised haemoglobin F values. The alpha/non-alpha-globin chain synthesis ratios were generally raised, with mean 1.44 (1.07-2.10). Amongst the parents of the compound heterozygotes, who were not selected for molecular analysis following haematological screening, half of the cases were completely silent. Interaction with severe beta-thalassaemia mutations always resulted in the clinical phenotype of mild non-transfusion-dependent thalassaemia intermedia.

Bone age progression during five years of substitutive therapy for the induction of puberty in thalassemic girls--effects on height and sitting height

It is known that in thalassemic patients there is a disproportion between lower and upper segments whose causes have not yet been identified. We evaluated whether the administration of estrogens to induce puberty in hypogonadic thalassemic girls caused an inappropriate acceleration of bone maturation and whether this had a negative influence on final and sitting height.

MATERIALS AND METHODS

Twelve thalassemic patients with spontaneous puberty (Group A) and seven patients with hypogonadism (Group B) were studied. The mutations of the beta gene were identified by DNA analysis. We took into account four observations, ranging from the onset of spontaneous puberty in group A or the start of substitutive therapy in group B, to 5 years later. At each observation we considered: chronological age (CA), bone age (BA), height (Ht) expressed in cm and as standard deviation score (HtSDS) calculated with respect to CA (HtSDSCA) and BA (HtSDSBA), growth spurt, sitting height, expressed as SDS (SH-SDS), and height gain (HG). The delta BA and delta CA were calculated between the first and the final observation values to evaluate the bone age acceleration (delta BA/delta CA).

RESULTS

No acceleration of BA was noted. delta BA/delta CA was 0.98 +/- 0.1 in group A and 0.89 +/- 0.1 in group B (p > 0.05). All patients in group B had the most severe form (beta degree/beta degree) of thalassemia. During the final observation, SH-SDS was -1.43 +/- 1.2 and -2.9 +/- 0.6 in group A and B respectively (p < 0.002), while no difference between the two groups for HtSDSCA and HtSDSBA was observed. HG was greater in group A than in group B (17.7 +/- 5.4 cm vs 10.8 +/- 5.2 cm) (p < 0.002), such as the spurt 8.6 +/- 1.4 cm (group A) and 6.1 +/- 2.6 cm (group B) (p < 0.05).

CONCLUSIONS

Girls with hypogonadism did not show an inappropriate acceleration of BA, as they reached near final height similar to girls with spontaneous puberty. The auxological parameters showed a more severe body disproportion with the prevalence of the lower segment in the hypogonadic girls. This could be explained by a higher degree of bone marrow hyperplasia related to the most severe form of thalassemia and a higher blood consumption. As a consequence, damage at the vertebral level might determine an inability of the bone tissue to respond to estrogens. We suggest beginning estrogen therapy earlier in order to obtain better truncal growth.

Hb Rainier [beta145(HC2)Tyr-->Cys] in Italy. Characterization of the amino acid substitution and the DNA mutation

A high oxygen affinity hemoglobin variant was identified in a 53-year-old male patient from Napoli (Italy), suffering from pulmonary thromboembolism and polycythemia. A detailed structural characterization of the variant hemoglobin was carried out, both at the protein and DNA levels, by a combination of DNA sequencing and allele-specific amplification techniques with mass spectrometric procedures. The amino acid substitution was found to be Tyr-->Cys, and the corresponding DNA mutation was identified as A-->G at the second position of codon 145 of the beta chain. These variations indicated the presence of Hb Rainier. Haplotype analysis of DNA polymorphisms showed that the beta-globin gene from Hb Rainier was associated with haplotype II. Moreover, structural analyses provided direct identification of an intramolecular disulphide bridge joining the newly inserted beta145Cys with beta93Cys. This is the first report of the occurrence of Hb Rainier in Italy.

Molecular, haematological and clinical studies of a silent beta-gene C-->G mutation at 6 bp 3' to the termination codon (+1480 C-->G) in twelve Greek families

We report the clinical, haematological, biosynthetic and molecular data of 12 beta-thalassaemia intermedia patients and their heterozygous parents, all of whom carried a rare C-->G mutation at nucleotide position 6 3' to the termination codon (term. cd +6 C-->G) in the 3' untranslated region (3' UTR) of the beta-globin gene (+1480 C-->G). This mutation has been reported previously in a single beta-thalassaemia intermedia patient of Greek origin. The 12 patients of the present study had the clinical phenotype of mild non-transfusion-dependent thalassaemia intermedia, preserving haemoglobin levels around 9 g/dl and haemoglobin F levels <25%. All were compound heterozygotes for the +1480 C-->G mutation and common severe beta-thalassaemia mutations. The haematological parameters of heterozygotes with this mutation were within the normal range with the exception of a slightly raised alpha/non-alpha-globin chain synthesis (1.2-1.9). mRNA analysis demonstrated a 20-34% reduction in mRNA levels associated with the +1480 C-->G mutation compared to normal beta-globin alleles. These findings confirm that the C-->G mutation at position 6 3' to the termination codon is a mild beta-thalassaemia mutation causing slight reduction in beta-globin mRNA levels and beta-globin chain synthesis. It becomes clinically relevant when co-inherited with a severe beta-thalassaemia mutation in trans.

A multidisciplinary approach for improving services in primary care: randomised controlled trial of screening for haemoglobin disorders

OBJECTIVE

To investigate the feasibility of improving screening for carriers of haemoglobin disorders in general practice by using a nurse facilitator to work with primary care teams and the relevant haematology laboratories; to identify problems in communication between all those involved in delivering the service, and to implement solutions.

DESIGN

Two year, practice based randomised controlled trial.

SETTING

North London area where 29% of residents and 43% of births are in ethnic groups at risk for haemoglobin disorders.

SUBJECTS

26 of the 93 practices using the services of the area's haematology laboratory agreed to take part and were randomly divided into control and intervention practices.

MAIN OUTCOME MEASURE

Change in number of requests for screening tests for haemoglobin disorders made by control and intervention practices in baseline and intervention years.

RESULTS

The number of screening tests requested varied from 0-150 in the 93 practices in the baseline year. Study practices tended to have made a moderate number of requests (10-50) during this period. During the intervention year intervention practices made 292 more requests (99% increase) and control practices made 74 fewer requests (23% decrease; P=0.001 for difference in median change). Four practices, three of which were singlehanded, accounted for 75% of the increase. The number of requests from intervention practices, adjusted for baseline requests, was 3.2 times higher than control practices (P<0.0001).

CONCLUSION

General practitioners and practice nurses are willing to undertake a new genetic screening service (or expand an existing one) if they are persuaded that it benefits the health of a significant proportion of their practice population. They need appropriate tools (for example, information materials for carriers and groups at risk), and the laboratory must be sensitive to their needs. Preconceptional carrier screening and counselling need to be coupled with antenatal screening.

An alpha-thalassemic hemoglobinopathy: homozygosity for the HB Agrinio alpha 2-globin chain variant

This report describes the first case of homozygosity for the Hb Agrinio [alpha 29(B10)Leu-->Pro] alpha 2-globin gene variant (codon 29, CTG-->CCG) in a Greek patient. At 12 months of age, the proband presented with a marked hypochromic, microcytic anemia, a very low level of Hb H (< 2.5%), rare Hb H inclusions, and a balanced alpha/non-alpha biosynthesis ratio. The mother had hematological findings and globin biosynthesis consistent with heterozygous beta-thalassemia, but paradoxically, red cell morphology demonstrated very rare Hb H inclusions. The father had mild microcytosis and hypochromia. Analysis of alpha- and beta-globin genotypes demonstrated that the patient was homozygous for the highly unstable Hb Agrinio variant, caused by a T-->C mutation in codon 29 of the alpha 2-globin gene. At the age of 13 years, the proband had a clinical phenotype compatible with mild thalassemia intermedia with moderate anemia (Hb 7-8 g/dL), normal growth and development, slight splenomegaly, and minimal bone changes, while Hb H and inclusion bodies were not detected.

Beta-thalassaemia intermedia: is it possible consistently to predict phenotype from genotype?

Eighty-seven patients with beta thalassaemia of intermediate severity were investigated in our Unit to determine whether it is possible to consistently predict phenotypic severity from genotypic factors. The subjects were from the following ethnic backgrounds: Asian Indian (35.1%), Middle Eastern (24.3%), Mediterranean (21.6%), Northern European (14.9%) and South-East Asian/Chinese (4.1%). There was a wide spectrum of phenotypic severity; 49 had mild disease, 22 moderate and 16 severe disease. 22/87 patients had inherited only a single copy of a beta-thalassaemia allele, of whom 11 had also co-inherited triplicated alpha genes (alpha alpha alpha/alpha alpha or alpha alpha alpha/alpha alpha alpha) and seven had dominantly inherited beta thalassaemia. In four of the heterozygotes no explanation was found for the thalassaemia-intermedia phenotype. 65/87 patients were homozygous or compound heterozygous for 26 mutations (40 genotypes) which ranged from very mild beta+ to beta0 thalassaemia alleles. All patients with two mild or very mild beta+ thalassaemia alleles had mild to moderate disease. Although concurrent inheritance of extra alpha genes with heterozygous beta thalassaemia results in thalassaemia intermedia, the disease is mild. Co-inheritance of alpha thalassaemia as a modulating factor was not evident in this cohort of patients. Presence of the in-cis Xmn I-Ggamma site was a modulating factor but insufficient to explain the high fetal haemoglobin levels encountered. In conclusion, apart from the two categories of triplicated alpha genes with heterozygous beta thalassaemia and inheritance of mild beta+ thalassaemia alleles, it was not possible to consistently predict phenotype from alpha and beta genotypes alone, due to the influence of modulating factors, some implicated (such as inheritance of HPFH determinants) and others as yet unidentified.

Prenatal diagnosis of beta-thalassemia among Indians using denaturing gradient gel electrophoresis

We have offered first trimester prenatal diagnosis to 55 couples at risk for beta-thalassemia, originating from various parts of India, using polymerase chain reaction and denaturing gradient gel electrophoresis. Apart from the six common mutations, codon 30 (CAG-->CAA), Cap site +1 (A-->C), as well as three uncharacterized mutations were seen among the parents. In the majority of cases, the diagnosis was possible by scanning only one fragment (B) where most of the Indian mutations are situated. In 18 out of 55 cases, framework analysis could also have been used to offer prenatal diagnosis without characterizing the beta-thalassemia mutations. In the two cases where the mutations were uncharacterized, prenatal diagnosis was done only on the basis of the anomalous denaturing gradient gel electrophoresis patterns seen in the parents and in previously affected children. This is the first attempt of prenatal analysis using denaturing gradient gel electrophoresis in the extremely diverse Indian population where the profile of mutations has not yet been fully elucidated.

A significant beta-thalassemia heterogeneity in the United Arab Emirates

The Dubai Thalassemia Center has identified 35 different beta-thalassemia mutations in 570 chromosomes from the United Arab Emirates population using gene amplification, hybridization with specific labeled oligonucleotide probes, sequencing of amplified DNA, restriction enzymes, and amplification refractory mutation system techniques. This large number of mutations which represent 21% of the total beta-mutations discovered worldwide reflects the heterogenous nature of the population living in the United Arab Emirates (1). We found that 50% of our beta-thalassemia patients have a concomitant alpha-thalassemia; namely the -alpha 3.7 kb deletion. Co-inheritance of alpha-thalassemia especially in the form of two alpha-globin gene deletions have an ameliorating effect on the phenotype presentation of our beta-thalassemia. Nine patients (one homozygote and eight compound heterozygotes) were identified with Hb Monroe (IVS-I,-1 (G-->C)), a thalassemic hemoglobin characterized by an Arg-->Thr substitution in codon 30 of the beta-globin gene. In addition, one of the patients was a compound heterozygote for Hb Tacoma [IVS-I, +1 (G-->C)]; a point mutation affecting the third nucleotide of codon 30 (G-->C) causing an Arg-->Ser replacement.

Longitudinal monitoring of bone mineral density in thalassemic patients. Genetic structure and osteoporosis

The changes in bone mineral density (BMD) measured by single photon absorptiometry (SPA) using two observations conducted over a period of 2 years were examined in 54 thalassemic subjects [30 F(A) and 24 M(B)] with a chronological age ranging from 2.6 to 22.6 years and in 27 sex- and age-matched controls (C). Each category (A, B and C) was divided into three groups according to pubertal signs: pre-pubertal subjects (A1, B1 and C1); peri-pubertal subjects (A2, B2 and C2) and pubertal subjects from the first observation (A3, B3 and C3). Furthermore, each group of patients was divided into sub-groups on the basis of haematological phenotypes, those with a more severe form were called beta0/beta0 while those with other forms were called "others". The most significant findings were the following: the presence of a more severe reduction of the bone mineral density in patients with the beta0/beta0 phenotype than in patients with the "others" phenotype; patients with hypogonadism corresponded to the beta0/beta0 phenotype, while those with spontaneous puberty corresponded to the "others" phenotype. In conclusion, since puberty and the degree of bone mineral density are related to the haematological phenotype, puberty (spontaneous or induced) positively influences the bone mineral density only at the start of puberty, while subsequently, the degree of osteoporosis is the expression of widespread and chronic systemic damage due to the haematological phenotype.

Relationship between the severity of beta-thalassaemia syndromes and the number of alleviating mutations

Thalassaemia intermedia, defined as homozygous beta-thalassaemia in which patients are not transfusion-dependent, covers a wide range of clinical severity. It may arise because one or more genetic factors ameliorate the otherwise severe phenotype of thalassaemia major. Exactly which and how many such mutations are necessary to produce a thalassaemia intermedia phenotype is incompletely understood, although such information would be useful both clinically and for prenatal diagnosis. We examined DNA from 28 patients with thalassaemia intermedia resident in London and 28 matched patients with thalassaemia major, for 3 types of genetic modifying factors, namely; mild beta-thalassaemia mutations, the upstream XmnI G-gamma globin gene polymorphism, and alpha-globin gene deletions. The results show that the number of alleviating mutations present has a large influence on the phenotype of patients with homozygous beta-thalassaemias. A single alleviating mutation was present in 56% of thalassaemia intermedia subjects compared with 26% of thalassaemia major subjects. Two alleviating mutations were present in 33% of thalassaemia intermedia subjects compared with 1 thalassaemia major subject. No patients with thalassaemia major had 3 alleviating mutations, in contrast to 11% of those with thalassaemia intermedia. Although the findings did not account for the full range of phenotypic variation, such information is of potential value both in the clinical management and the prenatal diagnosis of homozygous beta-thalassaemia.

Compound heterozygosity for Hb Lepore-Boston and Hb Neapolis (Dhonburi) [beta 126(H4)Val-->Gly] in a patient from Naples, Italy

The simultaneous presence of two hemoglobin variants has been detected in a 14-month-old patient affected by thalassemia intermedia. The two variants were characterized by a combination of allele-specific amplification methods and mass spectrometric procedures carried out on isolated globins. These were identified as Hb Lepore-Boston and Hb Neapolis (also known as Hb Dhonburi) or beta 126 (H4)Val-->Gly. Hb Lepore-Boston is the most common hybrid variant detected in Campania and several cases of Hb Neapolis which causes a mild hypochromic microcytic anemia have been identified in this region in the last few years. This is the first report of a double heterozygosity involving Hb Lepore-Boston and Hb Neapolis.

Haemoglobinopathies

The inherited haemoglobinopathies are a heterogeneous group of recessive disorders that include the thalassaemias and sickle cell disease. Nearly a thousand mutant alleles have now been characterized. The mutations are regionally specific and in most cases the geographical and ethnic distributions have been determined providing the foundation for a programme of control through screening, genetic counselling and prenatal diagnosis. The main requirements for methodologies providing molecular diagnosis are speed, cost, convenience and the ability to test for multiple mutations simultaneously. For beta-thalassaemia mutations the procedures that meet these requirements are the amplification refractory mutation system and the reverse dot-blot hybridization system. For alpha-thalassaemia the technique of gap PCR is useful for targeting specific deletion mutations but Southern blotting remains the standard diagnostic test.

Detection of eight beta-thalassemia mutations using a DNA enzyme immunoassay

We describe the use of a polymerase chain reaction-based method followed by a DNA enzyme immunoassay for the simultaneous detection of the eight most common beta-thalassemia mutations in the Mediterranean population. The method is specific, sensitive, and easily applicable in routine clinical laboratories for the molecular diagnosis of beta-thalassemia patients and at risk couples.

Prenatal diagnosis of hemoglobinopathies in Turkey: Hacettepe experience

Prenatal diagnosis of hemoglobinopathies was performed in 250 fetuses at risk for hemoglobinopathies. The main diagnostic procedures were in vitro hemoglobin synthesis analysis in fetal blood and analysis of DNA obtained from chorionic villus samples. Sixty-six percent of the fetuses were at risk for beta thalassemia major and 28% for sickle cell anemia. Beta thalassemia mutations were heterogenous, and 51 fetuses examined by the DNA technique were found to be at risk for at least 20 different combinations.

Rapid diagnosis of beta-thalassaemia by mutagenically separated polymerase chain reaction (MS-PCR) and its application to prenatal diagnosis

We have developed a rapid and simple PCR-based method which is modified from the mutagenically separated polymerase chain reaction (MS-PCR) to detect the molecular defects of beta-thalassaemia. We can use this technique to amplify normal and mutant alleles of the beta-globin gene in the same reaction tube, using different-sized allele-specific primers. This mutagenesis separates the amplification reactions of alleles performed in the same tube. Subsequent gel electrophoresis shows at least one of the two allelic products at the same locus or at least two of the several allelic products at different loci. Therefore, in addition to simple handling, MS-PCR provides a within-assay quality control for the exclusion of false negative results. The five most common mutations of beta-thalassaemia and haemoglobin E which occur in the Taiwanese population were tested, and 14 prenatal samples were checked with accurate results. This method is simple, rapid and accurate, and can be used routinely in prenatal diagnosis. The principle used here can also be applied to other genetic diseases.

Beta-thalassaemia unlinked to the beta-globin gene interacts with sickle-cell trait in a Portuguese family

An autosomally transmitted hypochromic microcytic mild anaemia with elevated haemoglobin (Hb) A2 and globin chain imbalance has been observed in a three-generation family of Portuguese origin. Extensive DNA analysis of the beta-globin gene cluster, including the complete sequencing of the beta-globin gene and flanking regions, failed to reveal any genetic alteration. The co-segregation of sickle-cell trait in this family enabled us to postulate a defective erythroid trans-acting factor was playing a role in the down-regulation of both beta A- and beta S-globin genes. Among the transcription factors that could possibly have caused the reported phenotype, NF-E2 is unlikely to be implicated, whereas Nrf1 and Nrf2 cannot be ruled out. Thus, this family carries a novel beta-thalassaemia autosomal determinant unlinked to the beta-globin gene. This observation reinforces the notion of the haemoglobinopathies as single gene disorders under polygenic regulation.

Genetic interactions in thalassemia intermedia: analysis of beta-mutations, alpha-genotype, gamma-promoters, and beta-LCR hypersensitive sites 2 and 4 in Italian patients

In order to verify the genetic factors influencing the clinical expression of beta-thalassemia we have studied 292 Italian patients, 165 with thalassemia intermedia and 127 with thalassemia major. The beta-globin gene mutations were defined in all cases. The number of alpha-globin genes and the integrity of specific control regions of the beta-globin cluster--gamma promoters and beta-Locus Control Region (beta-LCR)--were studied in selected cases. Homozygosity for mild mutations (group I) accounts for 24% of the intermedia patients and it is not represented among major patients. Forty-four percent of intermedia patients had combinations of mild/severe (group II) mutations and 32% had homozygosity or double heterozygosity for severe mutations (group III). Seventy-six percent of patients with thalassemia major were classified in group III and 24% in group II. Deletion type-alpha3.7 thalassemia, assessed in a part of the cases, was found in 5% of thalassemia major and 19.5% of intermedia patients in groups II and III. Structural analysis of gamma promoters and beta-LCR HS2 and HS4 regions, carried out in order to look for alterations associated with Hb F increase, did not reveal new mutations. Only rare polymorphic changes were observed at the HS2 and HS4 level. The -158G gamma C T change was found with an increased incidence in intermedia patients in groups II and III. A subset of 10 beta-thalassemia heterozygotes with mild intermedia phenotype resulted from coinheritance of a triplicated alpha-locus. We have been unable to find a molecular basis for the benign clinical course in approximately 20% of patients with thalassemia intermedia. Other genetic or acquired factors must be hypothesized which ameliorate the clinical condition.

Molecular characterization of homozygous (high HbA2) beta-thalassemia intermedia in Greece

Homozygous beta-thalassemia is usually characterized by severe anemia requiring regular blood transfusion for survival. For homozygous patients with milder clinical manifestations and no dependence on transfusion therapy, the term thalassemia intermedia is usually applied. Genetic mechanisms that may ameliorate the clinical expression of homozygous beta-thalassemia include coinheritance of alpha-thalassemia, inheritance of mild beta-globin gene mutations, and increased gamma-globin chain production, which may partially compensate for the lack of beta-globin chain synthesis. To identify which of these factors may contribute to the modification of childhood homozygous, high-hemoglobin A2 (HbA2) beta-thalassemia in Greece, the interaction of alpha-thalassemia, types of beta-thalassemia mutations, and the presence of a polymorphic site 5' to the G gamma-globin gene, which has been described as associated with increased gamma-globin chain production in some cases, was assessed. The results were analyzed in light of similar studies in 150 randomly selected, homozygous, high-HbA2 beta-thalassemia patients with the aim of assessing whether thalassemia genotypes can provide information useful for prognosis and/or more appropriate management of homozygous beta-thalassemia patients. The results indicate that, in general, the major factor modifying the clinical expression of homozygous, high-HbA2 beta-thalassemia in Greece is the inheritance of mild beta-thalassemia mutations. Although there is not always a complete correlation of genotype with clinical phenotype, the inheritance of two mild beta-thalassemia alleles results in almost all cases (11 of 12 cases in this study) in thalassemia intermedia phenotype.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular basis of alpha-thalassemia in Portugal

We have estimated the incidence and molecular basis of alpha-thalassemia in a Portuguese population, mostly from the Greater Lisbon area. In a group of 100 consecutive cord blood samples, the gene frequency of the rightward deletion (-alpha 3.7) was 0.035, and the leftward deletion (-alpha 4.2) was 0.015. In this group, we have also found four heterozygotes for the triple alpha-globin gene rearrangement (alpha alpha alpha anti 3.7. gene frequency 0.020). We have characterized the subtypes of -alpha 3.7 and alpha alpha alpha anti 3.7 rearrangements. On the whole, these results give an incidence of 10% for deletional alpha-thalassemia carriers in the studied Portuguese population. In a group of 342 subjects presenting beta-thalassemia, or Hb S trait, beta-thalassemia major sickle cell disease or low red blood cell indices, the -alpha 3.7, -alpha 4.2, -SEA, -MED, (alpha alpha)MM, and alpha alpha alpha anti 3.7 haplotypes were found in different combinations. Only one nondeletional alpha-thalassemia determinant (a 5 nucleotide deletion in the alpha 2-globin gene in the second intervening sequence donor site) was detected, which might suggest a low incidence of these defects in the Portuguese population.

Cystic fibrosis mutation analysis: report from 22 U.K. regional genetics laboratories

We have collated the results of cystic fibrosis (CF) mutation analysis conducted in 22 laboratories in the United Kingdom. A total of 9,807 CF chromosomes have been analysed, demonstrating 56 different mutations so far observed and accounting for 86% of CF genes in the native Caucasian population of the United Kingdom. delta F508 is the most common at 75.3% of CF mutations (range 56.5-83.7%), followed by G551D (3.08%; range 0.71-7.60%), G542X (1.68%; range 0.85-3.66%), 621 + 1 (G > T) (0.93%; range 0.41-3.16%), 1717-1(G > A) (0.57%; range 0.17-1.14%), 1898 + 1)(G > A) (0.46%), R117H (0.46%), N1303K (0.46%), and R553X (0.46%). The data show a clear geographical variation in the distribution of some of the mutations, most notably a marked regional variation in the distribution of 621 + 1 (G > T) and 1989 + 1(G > A), which are both apparently more frequent in Wales. R560T and R117H appear to be more frequent in Ireland and Scotland, and G551D more frequent in Scotland. In summary, these data illustrate that the mutations present within a particular population need to be defined in order to provide meaningful carrier screening and testing for rare mutations in affected individuals. Furthermore, it is apparent that the ethnic origin of a patient, even within a small country such as the United Kingdom, should be taken into account.

The frequency of 14 beta-thalassemia mutations in the Arab populations

The beta-thalassemias are a heterogeneous group with respect to molecular pathogenesis, and different populations and ethnic groups differ with respect to the predominating mutations. This variable spectrum of beta-thalassemia mutations has resulted in extensive studies in each population and ethnic group to identify the major mutations. In this study we investigated the prevalence of 14 mutations in 253 beta-thalassemia patients drawn from eight Arab countries (i.e. Jordan, Egypt, Syria, Lebanon, Yemen, and Saudi Arabia), living in Saudi Arabia and attending Ministry of Health hospitals. The mutations investigated included IVS-I-110 (G-->A), IVS-II-1 (G-->A), IVS-I-5 (G-->C), codon 39 (C-->T), IVS-I-1 (G-->A), frameshift at codons 8/9 (+G), frameshift at codons 41/42 (-TTCT), codon 15 (TGG-->TAG), IVS-I-6 (T-->C), frameshift at codon 16 (-C), IVS-II-745 (C-->G), codon 6(-A), IVS-I, 3' end (-25 bp), and Cap +1 (A-->C). The most frequently encountered mutations were IVS-I-110 and IVS-II-1 which were identified in the population of each Arab country. The IVS-I-1 and IVS-II-745 mutations were encountered in Jordanians, Egyptians, and Syrians. The IVS-I-5, codon 39, codon 6, IVS-I, 3' end (-25 bp), and Cap +1 mutations were encountered only in Saudis and not in other Arabs, except codon 39 which was present in the Syrians and Lebanese. Other mutations were generally rare and not specific to any Arab ethnic group. This paper presents preliminary data on the prevalence of 14 mutations in the Arab populations and shows wide variation in the molecular basis of beta-thalassemia in different Arab ethnic groups. Further detailed studies to identify the entire spectrum of beta-thalassemia mutations are stressed.

The amplification refractory mutation system (ARMS): a rapid and direct prenatal diagnostic technique for beta-thalassaemia in Singapore

beta-Thalassaemia major patients have chronic anaemia and since 3-4 per cent of Singaporeans carry the beta-gene, prenatal diagnosis is essential. We evaluated the amplification refractory mutation system (ARMS) technique as a routine test for prenatal diagnosis of beta-major. Six mutations along the beta-gene were studied--41-42 (-TCTT), IVSII #654 (C-T), 17 beta (A-T), -28 TATA (A-G), IVSI #5 (G-C), and IVSI #1 (G-T). Our results indicate that prenatal diagnosis using these mutations can be offered to 90 per cent (35/39) of our Chinese couples and 54.6 per cent (12/22) of our Malay couples at risk. Confirmation of ARMS results was carried out using allele-specific oligonucleotide hybridization. Prenatal diagnosis using ARMS was successfully carried out in nine cases which included a set of triplets and twins. The triplets were diagnosed with the beta-trait carrying the 41-42 mutation. The couple with twins possessed the #654 mutation and one twin was diagnosed with the beta-trait and the other with #654 homozygosity. Genomic sequencing of the undefined mutations in the Chinese couples revealed rarer mutations at -29 and an ATG-AGG base substitution at the initiation codon for translation. In the Malay couples, genomic sequencing detected mutations at codon 15 (TGG-TAG) and codon 26 (GAG-AAG). We conclude that ARMS with its direct detection of amplified products by gel electrophoresis provides an accurate, rapid, and simpler method for our beta-thalassaemia prenatal diagnosis programme in Singapore.

Association of a novel high oxygen affinity haemoglobin variant with delta beta thalassaemia

We report an uncommon association of delta beta thalassaemia and a haemoglobin (Hb) variant with high oxygen affinity in an Asian Indian family. Minimal polycythaemia was seen in a heterozygote for this novel Hb variant, Hb Headington (beta 72 (E16) Ser-->Arg), while compound heterozygosity for Hb Headington and the Indian G gamma (A gamma delta beta)(0) thalassaemia produces a marked increase in erythrocytosis with a concomitant increase in the level of the variant Hb. The HbF in such compound heterozygotes remains at a level consistent with that usually observed in individuals heterozygous for the G gamma (A gamma delta beta)(0) thalassaemia alone. The purified Hb variant showed an increased oxygen affinity, moderately decreased co-operativity and a normal Bohr effect. Results of functional studies suggest that the high oxygen affinity of Hb Headington is due to the Ser-->Arg substitution which disrupts the normal and tight interaction between A, B and E helices leading to a destabilization of the T deoxy-structure of the abnormal haemoglobin.