The molecular spectrum of beta-thalassemia and abnormal hemoglobins in the allochthonous and autochthonous dutch population

The prevalence at birth of hemoglobin defects in the autochthonous North-European population is low. However, the long immigration and colonial history of the Netherlands has resulted in a group of about 1-2 million 'autochthonous' inhabitants, with Asian, South-European or African ancestors, in whom a moderate birth prevalence of globin gene mutations can be expected. Furthermore, at least 10% of the Dutch population consists of recent immigrants from different countries with high birth prevalence of hemoglobinopathies. Because of the endogamous partner choice, which is prevalent in this population, the risk for homozygous progeny remains elevated. At least 100,000 carriers of hemoglobinopathies of recent allochthonous origin are present in the Netherlands, and the number of homozygous children is rising. Prevention by prenatal diagnosis requires a suitable protocol and knowledge about the molecular defects present in the country. Therefore we have analyzed a large number of patients and carriers, both at the hematological and at the DNA level. Our survey revealed 47 different beta-thalassemia determinants, characterized on 223 independent chromosomes from individuals of different ethnic origins. As expected, the most prevalent mutations were largely represented. The cd39 (C-->T) mutation was found in 70% of the immigrants from Morocco, Sardinia and other Central-West-Mediterranean regions while the IVS-I-110 (G-->A) was prevalent in the East-Mediterranean populations. The IVS-I-5 (G-->C) mutation was found in 45% of the patients of Indonesian origin. We also registered 308 independent chromosomes with common structural defects (HbS, HbC, HbE, Hb Lepore, Hb Constant Spring and HbD Punjab) and 33 chromosomes with 19 different, less frequent, rare or very rare mutants. Seven structural mutants were described for the first time and published separately. Furthermore, 139 independent chromosomes with deletional and nondeletional alpha-thalassemia defects were characterized.

Molecular spectrum of alpha-thalassemia in the Iranian population of Hormozgan: three novel point mutation defects

We describe the molecular spectrum of alpha-thalassemia mutations in a population sample of newborns in the South-Iranian province of Hormozgan. Out of 660 randomly collected blood samples 218 (33%) had visibly elevated Hb Bart's. DNA was extracted from 78 samples out of this selection (n=156), of which 114 alleles were found to carry an alpha-thalassemia defect. Besides the common -alpha3.7 (79.1%), -alpha4.2 (1.7%), and alpha-5nt alpha alleles (4.3%), three novel nondeletional alpha-thalassemia mutations were found; the alpha2 cd19 (-G) frameshift mutation (12.2%), the alpha1 IVS1-148(A-->G) (0.9%) affecting the splice acceptor site consensus sequence and the cd14 (TGG-->TAG) (0.9%), which creates a premature stop codon in the first exon of the alpha1-gene. A fourth mutation in the alpha1-gene, the IVS1-38 (C-->T) (0.9%) of undetermined effect, was found in an individual heterozygous for the alpha2 cd19(-G) mutation.

alpha-thalassaemia as a result of a novel splice donor site mutation of the alpha1-globin gene

We describe the characterization of an alpha+-thalassaemia determinant as a result of a transition of G-->A of the donor splice consensus site sequence of the first intron of the alpha1-globin gene (alpha1IVS I-1). The mutation was found in combination with the South-East Asian alpha0-thalassaemia deletion in an haemoglobin (Hb)H patient and her sister, both of Thai origin. Sequencing of the abnormally spliced mRNA product revealed the presence of a cryptic splice site in exon 1 of the alpha1-globin gene. No normally spliced alpha1mRNA was detected. The abnormally spliced mRNA product from the alpha1-gene carrying the mutation does not lead to functional protein and causes a mild HbH-disease phenotype when in combination with the deletion type alpha0-thalassaemia.

Hb Nijkerk: a new mutation at codons 138/139 of the beta-globin gene inducing severe hemolytic anemia in a Dutch girl

We describe a new structural mutant of the beta-globin chain in a 17-year-old Dutch Caucasian girl. The mutant is associated with a severe pathology as a consequence of hyper-instability of the hemoglobin tetramer. The proband, whose parents had no history of hemolysis, was admitted to the hospital at 5 months of age with hemolytic anemia and splenomegaly. No indications for autoimmune defects or enzymopathies were found. Repeated hemoglobin electrophoresis on cellulose acetate revealed no abnormalities. At the age of 17 years, a minor abnormal band of less than 1% was detected on starch gel electrophoresis, migrating slightly faster than Hb A2. Sequencing of the beta-globin gene revealed heterozygosity for a 4 bp deletion (GCTA) in combination with a 1 bp insertion (T) at codons 138/139. This event eliminates two amino acids (Ala-Asn) and introduces a new residue (Tyr). We discuss the hematological and the pathophysiological consequences of this mutant, which is fully expressed as a gene product, and apparently assembled into unstable tetramers that precipitate shortly after.

A complex haemoglobinopathy diagnosis in a family with both beta zero- and alpha (zero/+)-thalassaemia homozygosity

The occurrence of point mutation alpha-thalassaemia and of complex combinations of haemoglobin defects is underestimated. Haemoglobinopathies, the most frequent monogenic recessive autosomal disorder in man, occur predominantly in Mediterranean, African and Asiatic populations. However, countries of immigration with a low incidence in the indigenous population, are now confronted with a highly heterogeneous array of imported defects. Furthermore, the occurrence of severe phenotypes is bound to increase in the near future because of the endogamous growth of the ethnical minorities and the lack of prevention. We describe an Afghan family in which both partners of a consanguineous relationship are carriers of a beta- as well as an alpha-thalassaemia determinant. The combination of defects was revealed by the in vitro measurement of the beta/alpha biosynthetic ratio and was characterised at the DNA level. The molecular defects involved are the Cd5(-CT), a Mediterranean beta zero-thalassaemia mutation, and the alpha 2(zero/+)-thalassaemia AATA(-AA) polyadenylation defect. The alpha-thalassemia defect is a rare RNA-processing mutant described only twice before in heterozygous form in Asian-Indian patients. The mutation suppresses the expression of a alpha 2 gene and reduces the expression of the less efficient, 3' located alpha 1 gene as well, inducing a near alpha zero-thalassaemia phenotype. This defect is now described for the first time in the homozygous condition in one of the children who, in addition to being homozygous for the alpha-thalassaemia point mutation, is also a carrier of the beta zero-thalassaemia defect. A previously described homozygous case of the alpha (zero/+)-thalassaemia condition, caused by a similar polyadenylation defect, was characterised by a severe HbH disease. However, the patient described here present at 7 years of age with severe caries, like his beta-thalassaemia homozygous brother but without hepatosplenomegaly, haemolysis or severe anaemia. The haematological analysis revealed 9.5 g/dl Hb; 5.4 x 10(12)/I RBC; 0.33 I/I PCV; 61 fl MCV; 17.6 pg MCH and 6.2% of HbA2. The biosynthetic ratio beta:alpha was 1.6 and no HbH fraction was detectable either on electrophoresis or as inclusion bodies. The parents reported no complications during pregnancy, at birth, or in the neonatal period in rural Afghanistan. We presume therefore that the counterbalancing effect induced by the co-existing beta-thalassaemia defect could have modified a potentially severe perinatal HbH disease into a strongly hypochromic but well compensated 'alpha zero-like heterozygous' thalassaemia phenotype. The risk of a severe HbH disease, could have been easily missed in this family which was referred because of a child affected with beta-thalassaemia major.

Phenotype variability of the dominant beta-thalassemia induced in four Dutch families by the rare cd121 (G-->T) mutation

Eight patients who were carriers of beta-thalassemia induced by the cd121 (G-->T) mutation are described in four nonrelated Dutch families. This mutant, which is considered rare and inherited in a dominant manner, is expressed in a different way among each of the four families and even among carriers of the same family. The symptoms vary from an hemolytic anemia of intermediate gravity with hepatosplenomegaly, inclusion bodies and erythroblastosis, to a mild anemia with minor hematological abnormalities. We report the analytical procedures used for the detection of the mutant, the hematological and clinical data of the four families and discuss the variable physiopathology of this molecular defect. We also compare the variation in fetal hemoglobin expression in relation to the haplotypes of the beta-gene cluster and to the different hematological conditions. The presence of this rare mutant in four nonrelated Dutch families could derive from a single mutation or from multiple events. The existence of the four mutations in three different haplotypes suggests the occurrence of at least two independent events. The presence of five abnormal hemoglobins and the beta-thalassemia defect on different haplotypes at cd121 also suggests a relatively increased rate of mutations at this particular site.

A case of non-beta-globin gene linked beta thalassaemia in a Dutch family with two additional alpha-gene defects: the common -alpha3.7 deletion and the rare IVS1-116 (A-->G) acceptor splice site mutation

We describe a family with beta thalassaemia, apparently not linked to the beta-globin gene cluster, in combination with alpha thalassaemia. The propositus, an adult Dutch Caucasian male, and his son presented with microcytic hypochromic parameters. Their lysates displayed the normal adult pattern on electrophoresis. The HbA2 concentration, which is usually increased in beta thalassaemia, was normal. The in vitro biosynthetic rate of the globin chains was strongly unbalanced even in the presence of a coexisting alpha-thalassaemia defect. Routine analysis of the beta genes, including the promoter region, was performed repeatedly by polymerase chain reaction (PCR), denaturing gradient gel electrophoresis (DGCE) and direct sequencing. No molecular abnormalities were detected. Large beta deletions were excluded by haplotype determination, using seven polymorphic markers distributed over an area of 50 kb, from 1 kb 5' of the epsilon gene to 4 kb 3' of the beta gene. The haplotype analysis of the beta-gene cluster revealed that the unaffected daughter had received the same beta haplotype as her beta-thalassaemic brother from their beta-thalassaemic father. These data suggest that the beta-gene cluster shared by father and son was not directly associated with a reduced beta-globin chain expression. In order to exclude the remote possibility of a beta-locus-control region (LCR) rearrangement in the paternal haplotype of the daughter, the sequence of the HS2 element was examined in the nuclear family. We compared the haematological and clinical data of this family with the data reported in the limited number of similar cases. We discuss the possibility that the mutation of a trans-acting erythroid factor(s), not linked to the beta-genes cluster, may impair the beta-gene expression of both alleles.

Atypical HbH disease in a Surinamese patient resulting from a combination of the -SEA and -alpha 3.7 deletions with HbC heterozygosity

The first case of haemoglobin H (HbH) disease in combination with haemoglobin C (HbC) is reported in a man of Surinamese origin. Only haemoglobin A (HbA) and HbC were detected by electrophoresis. The amount of HbC was much less than expected in HbC heterozygotes. The synthesis ratio (beta A+ beta C/alpha) indicated an alpha-thalassaemia defect with two non-functional alpha genes, which did not correlate with the degree of haemolysis and anaemia displayed by the patient. The DNA analysis of the alpha-genes clusters revealed a defect combination -SEA/-alpha 3.7. The haematological data and the physiopathology of this atypical case are compared with the typical HbH disease found in a first cousin of the propositus. Data on the globin chains expression and on the formation of beta A and beta C homotetramers in HbH/HbC disease are presented.

Hb Utrecht [alpha 2 129(H12)Leu-->Pro], a new unstable alpha 2-chain variant associated with a mild alpha-thalassaemic phenotype

We describe a new alpha 2-globin gene point mutation found in six individuals of a three-generation Dutch family. The mutant, which is associated with a mild alpha-thalassaemic phenotype, is not detectable at the protein level. The alpha 2 cd129 (CTG-->CCG) transition was found by molecular analysis using denaturing gradient gel electrophoresis (DGGE) and single-strand conformation analysis (SSCA) followed by direct sequencing of the alpha 2-globin gene. Southern analysis revealed a triplication of the zeta-gene in cis with the mutant alpha-globin gene.