Characterization of Two Deep Intronic Variants on the ß-Globin Gene with Inconsistent Interpretations of Clinical Significance.

Sequence variants located in the introns of the ß-globin gene may affect the mRNA processing and cause ß-thalassemia (ß-thal). Sequence variants that change one of the invariant dinucleotides at the exon-intron boundaries may have fatal consequences for normal mRNA splicing. Intronic variants located far from obvious regulatory sequences can be more difficult to evaluate. There is a potential for misinterpretation of such sequence variants. Hence, thorough evaluation of patient data together with critical use of databases and in silico prediction tools are important. Here, we describe two rare sequence variants in the second intron of the ß-globin gene, HBB: c.316-70C>G and HBB: c.316-125A>G (NM_000518.4), both previously reported as variants causing ß-thal, and later as benign sequence variants. Due to the limited number of published cases and inconsistent interpretations, the significance of these sequence variants has been unclear. We have identified these two sequence variants in multiple individuals, alone and in a variety of combinations with other δ- and ß-globin defects, and we find no influence of the sequence variants on the phenotype.

Towards a prevention program for ß-thalassemia. The molecular spectrum in East Java, Indonesia.

Defining the spectrum of specific thalassemia mutations is an important issue when planning prevention programs in large multi ethnic countries as is Indonesia. In a first attempt to define the prevalence of the common mutations in East Java we selected a cohort of 17 transfusion-dependent patients attending the Dr. Soetomo Hospital, Surabaya, Indonesia. After basic diagnostics we performed direct DNA sequencing for all ß-globin genes. The results obtained on 34 independent chromosomes revealed the following prevalence rates: c.79 G>A p. Glu27Lys (Hb E) 47.0%; c.92+5G>C (IVS-I-5 G>C) 20.6%; c.109_110 delC p.Pro37Leu fs X7 [codon 35 (-C)] 17.6%; c.46del T p.Trp16Gly fsX4 [codon 15 (-T)] 5.9%; c.126_129delCTTT p. Phe42Leu fs X19 (codons 41/42) 2.9%; c.316-197 C>T [IVS-II-654 (C>T)] 2.9%; c*112 A>G (PolyA) 2.9%. Our preliminary results show that the distribution of the prevalent mutations in our cohort is quite homogeneous but with different forms than previously reported. This indicates that more studies on a larger scale and in different geographical areas are needed to refine our provisional results and to characterize the molecular background of the disease in the whole country.

The hemoglobinopathies, molecular disease mechanisms and diagnostics.

Hemoglobinopathies are the most common monogenic disorders in the world with an ever increasing global disease burden each year. As most hemoglobinopathies show recessive inheritance carriers are usually clinically silent. Programmes for preconception and antenatal carrier screening, with the option of prenatal diagnosis are considered beneficial in many endemic countries. With the development of genetic tools such as Array analysis and Next Generation Sequencing in addition to state of the art screening at the hematologic, biochemic and genetic level, have contributed to the discovery of an increasing number of rare rearrangements and novel factors influencing the disease severity over the recent years. This review summarizes the basic requirements for adequate carrier screening analysis, the importance of genotype-phenotype correlation and how this may lead to the unrevealing exceptional interactions causing a clinically more severe phenotype in otherwise asymptomatic carriers. A special group of patients are ß-thalassemia carriers presenting with features of ß-thalassemia intermedia of various clinical severity. The disease mechanisms may involve duplicated α-globin genes, mosaic partial Uniparental Isodisomy of chromosome 11p15.4 where the HBB gene is located or haplo-insufficiency of a non-linked gene SUPT5H on chromosome 19q, first described in two Dutch families with ß-thalassemia trait without variants in the HBB gene.

Hb Boskoop [HBA2c.112C>T p.Pro38Ser]: a new α2 chain variant observed in a Morrocan family.

We describe a new nondeletional α-thalassemia (α-thal) determinant found in a Moroccan infant and in two members of his family. The new mutation generates an abnormal hemoglobin (Hb) as a consequence of a Pro→Ser amino acid substitution at codon 37 (old nomenclature) of the α2 gene. The new Hb variant is barely separable on high performance liquid chromatography (HPLC) but the expression of the α chain mutant measured on reversed phase chromatography is one-third of that expected from a stable α2 variant, which explains the mild α-thal phenotype observed in the carriers. As shown for other mutations described in our laboratory (i.e., Hb Gouda), this variant could also be common in the North African population, overlooked because of the mild phenotype and silent behavior on HPLC. Nevertheless, these silent variants could generate intermediate Hb H diseases in association with Mediterranean α(0)-thal deletion defect.

A new alpha(0)-thalassemia deletion found in a Dutch family (--(AW)).

Alpha-thalassemia is an inherited hemoglobin disorder characterized by a microcytic hypochromic anemia caused by a quantitative reduction of the alpha-globin chain. The majority of the alpha-thalassemias is caused by deletions in the alpha-globin gene cluster. A deletion in the alpha-globin gene cluster, which was found in a Dutch family, was characterized by MLPA, long-range PCR and direct sequencing. We describe the molecular characterization of a novel 8.2kb deletion (--(AW)), involving both alpha-globin genes in cis. The deletion is caused by a non-homologous recombination event between an Alu and an L1-repeat sequence. This deletion is the third example of a non-homologous recombination event involving an Alu and an L1 repeat, and the first described in the human alpha-globin gene cluster. Because of a 25% risk of Hb Bart's with hydrops foetalis in the offspring when in combination with another alpha(0)-thalassemia allele, it is important to diagnose this deletion.

alpha-thalassaemia masked by beta gene defects and a new polyadenylation site mutation on the alpha2-globin gene.

We report three examples of chronic anaemia involving complex combinations of alpha- and beta-globin gene defects. The first case had a potential Hb H disease caused by the classic SEA/RW deletions masked by Hb E [beta26(B8)Glu-->Lys] in the homozygous state. The second had an unusual Hb H disease caused by compound heterozygosity for two different alpha2 polyadenylation site mutations masked by a beta-thalassaemia heterozygosity. The third had an intermediate alpha-thalassaemia with considerable anaemia caused by an as yet unknown polyadenylation site (AATAAA>AATAAC) mutation in combination with a common RW deletion masked by a common Hb C [beta6(A3)Glu-->Lys] heterozygosity. Diagnostic methods, genotype/phenotype correlations and the chance of overlooking these combinations during risk assessment in a multiethnic society are discussed.

Two new alpha1-globin gene point mutations: Hb Nedlands (HBA1:c.86C>T) [alpha28(B9)Ala-->Val] and Hb Queens Park (HBA1:c.98T>A) [alpha32(B13)Met-->Lys].

We report two new point mutations of the alpha1-globin gene found in a Greek and a Burmese patient, both living in Western Australia. The patients were initially selected for their microcytic hypochromic parameters as belonging to a group suspected for uncommon (deletion) defects. Gap-polymerase chain reaction (gap-PCR) and multiplex ligation-dependent probe amplification (MLPA) technologies were applied, and in those cases not showing deletions, direct sequencing was performed. We have found 1) HBA1:c.86C>T, Hb Nedlands [alpha28(B9)Ala-->Val] which, based on the red cell indices and phenotype prediction scores, is presumed to be clinically silent, and 2) HBA1:c.98T>A, Hb Queens Park [alpha32(B13)Met-->Lys] which seems to be associated with a mild alpha-thalassemia (alpha-thal) phenotype. The phenotype/genotype correlation is briefly described.

Hb St. Truiden [α68(E17)Asn→His] and Hb Westeinde [α125(H8)Leu→Gln]: two new abnormalities of the α2-globin gene.

We report two new abnormal hemoglobins (Hbs) caused by mutations on the α2 gene. One resulted into an Asn→His substitution at position 68, the other in a Leu→Gln substitution at position 125. The first mutation was observed in a 61-year-old North European Belgian male during Hb A(1c) analysis and subsequently in other members of his family. The variant was expressed at a normal level and caused no hematological abnormalities in the carriers. The second was found in a 27-year-old Turkish male living in The Hague, The Netherlands, who presented with microcytic hypochromic parameters without iron deficiency and was also carrier of the common α2 IVS-I (-5 nt) deletion.

New and known ß-thalassemia determinants masked by known and new δ gene defects [Hb A(2)-Ramallah or δ6(A3)Glu→Gln, GAG>>CAG].

We report a novel thalassemia determinant found in a Nigerian woman living in the Netherlands, resulting from a 2 bp insertion at codons 9/10 of the ß-globin gene (HBBc.28_29insTA p.Ser10LeufsX11). The novel defect causes a frameshift with a consequent premature TGA stop codon, located at 11 positions downstream from the mutated codon. The phenotype was typical of a ß-thalassemia (ß-thal), trait with high RBC counts and compensated mild microcytic anemia. However, the Hb A(2) level was reported to be normal due to the presence of the common Hb A(2)' or Hb B2 [δ16(A13)Gly→Arg, GGC>CGC] variant that was not taken into account. We also present the opposite but comparable situation found in an a Palestinian man living in the USA. He was a carrier of a common ß-globin gene defect [codon 6 (-A), HBB:c.20delA] in combination with a novel δ-globin gene defect at codon 6 [HBD. c.19G>C, Glu6Gln] that we have named Hb A(2)-Ramallah. In both cases, the provisional diagnosis could have been compromised when based on the measurement of the normal Hb A(2) fraction only.

Hb Den Haag [beta45(CD4)Phe-->Tyr]. A new hemoglobin variant observed during early pregnancy diagnostics.

During a second pilot study, intended to explore the possibility of a country wide implementation of carrier diagnostics for hemoglobinopathies in The Netherlands, we observed a new abnormal hemoglobin (Hb) variant in three members of a family of Scandinavian origin living in the Dutch city of The Hague (Den Haag). The proband, a 34-year-old female presented with low Hb, packed cell volume (PCV) and red blood cell (RBC) values but was normocytic and normochromic. High performance liquid chromatography (HPLC) analysis revealed a partially separated fraction following Hb A. Molecular diagnostics disclosed a TTT>TAT transversion at HBB:c.137 causing a Phe-->Tyr single amino acid substitution at position 45 of the beta-globin gene. Previously described heterozygous mutations at the same position [Hb Cheverly (Phe-->Ser) and Hb Arta (Phe-->Cys)] were reported to be associated with mild chronic hemolysis similar to this case. We describe the hematological features of the six family members, the biochemical and molecular data and we discuss the possible consequences in combination with the common beta-thalassemia (beta-thal) trait.

Codon 24 (TAT>TAG) and codon 32 (ATG>AGG) (Hb Rotterdam): two novel alpha2 gene mutations associated with mild alpha-thalassemia found in the same family after newborn screening.

We report two novel alpha2-globin gene mutations found in the same Surinamese family. The proband, a newborn presenting during neonatal screening with 21.3% Hb Bart's (gamma4), proved to be a carrier of the common -alpha(3.7) deletion and a novel codon 32 (ATG>AGG) transversion that we named Hb Rotterdam. The father carried the same point mutation with borderline hemoglobin (Hb), MCV and low MCH values. The mother presented with a significant microcytic hypochromic anemia and also carried the -alpha(3.7) deletion and a second novel TAT>TAG transversion generating a stop codon at position 24. Shortly thereafter, Hb Rotterdam was again found in two unrelated adult females and in a Canadian newborn, all of African origin, suggesting that Hb Rotterdam could be a frequently occurring alpha(T) determinant in the Black population. Screening and characterization of the mutations, phenotype/genotype correlation and the issue of reporting newborn carriers of alpha-thalassemia (alpha-thal) are discussed.

Hb Lepore-Leiden: a new delta/beta rearrangement associated with a beta-thalassemia minor phenotype.

The Lepore hemoglobins (Hbs) are a group of structural defects resulting from different recombination events between the delta- and beta-globin genes. They may come with different beta-thalassemia (beta-thal) minor-like phenotypes in the carrier and with variably severe phenotypes in the rare homozygote, and in the common compound heterozygote with beta-thal. The most seriously affected patients are those of Yugoslavian origin presenting with severe transfusion-dependent hemolytic anemia, dyserythropoiesis, hepatosplenomegaly and skeletal malformations. Because of genetic risk, couples where both partners are carriers of these combinations may require prognosis and prenatal diagnosis. In these cases, recognition of the defect must be done with particular care. We report a case of Hb Lepore induced by a yet unknown crossover event found in a 24-year-old Turkish male and compare the novel mutation with those previously reported.

A brief review on newborn screening methods for hemoglobinopathies and preliminary results selecting beta thalassemia carriers at birth by quantitative estimation of the HbA fraction.

OBJECTIVES: We present in a brief summary the basic aspects of the most rational technologies used for new born screening (NBS) of the hemoglobinopathies and we report the preliminary results for the identification of beta-thalassemia carriers at birth by measuring the expression of the HbA fraction. DESIGN AND METHODS: Separation and measurement of the Hb fractions in 1.500 cord blood samples collected among the multi-ethnic Dutch population using different methods. RESULTS: By using a cut of <15% HbA we have found 4 carriers of point mutations defects 3 of which among a group of 34 newborns of ethnic origin and one among 120 north Europeans. DISCUSSION: All methods for NBS summarized in this paper provide identification at practically 100% sensitivity and high specificity. However, all methods should be followed by routine parent's analysis to confirm the provisional results. Taking into consideration the gestation age and the HbA expression, we believe that carriers of beta-thalassemia can be preselected at birth with a reasonable degree of sensitivity and be confirmed by parent analysis.

The first case of Hb Groene Hart [alpha119(H2)Pro-->Ser, CCT-->TCT (alpha1)] homozygosity confirms that a thalassemia phenotype is associated with this abnormal hemoglobin variant.

Hb Groene Hart [alpha119(H2)Pro-->Ser, CCT-->TCT (alpha1)] has been reported in heterozygotes of Moroccan origin and also in association with the common -alpha(3.7) deletion. In all cases, the mutated protein was not detectable but was apparently associated with a mild alpha-thalassemia (thal) phenotype, presumably due to a modification of the alpha-globin chain domain that is recognized by the a hemoglobin stabilizing protein (AHSP). The present case of Hb Groene Hart homozygosity, confirms that the alpha-thal phenotype is associated with this alpha-globin chain. Hb Groene Hart must be quite frequent not only in Morocco but probably also among the northern African coastal population.

Hb Geldrop St. Anna [beta94(FG1)Asp --> Tyr]: a new hemoglobin variant observed in a diabetic patient.

An abnormal hemoglobin (Hb) fraction was observed during a high performance liquid chromatographic (HPLC) Hb A1c control for diabetes mellitus in a 56-year-old north European woman. Family analyses revealed the abnormal fraction in three of her five siblings and in her son. Elevated Hb and packed cell volume (PCV) values and red blood cell (RBC) counts were present in all carriers. No histories of anemia, hemolytic or circulatory episodes were reported. The abnormal Hb fraction estimated at 40%, migrated just below Hb F on alkaline electrophoresis and overlapped the Hb A2 peak on cation exchange HPLC. Direct sequencing of the beta-globin genes revealed a new GAC --> TAC transversion in heterozygous form at codon 94 of the beta-globin gene. Based on the hematological/biochemical data and the decreased P50 value, we conclude that the new variant is a stable Hb associated with a slightly elevated oxygen affinity.

Hb zoeterwoude [beta23(B5)Val-->Ala)]: a new beta-globin variant found in association with erythrocytosis.

We describe the characterization of a new hemoglobin (Hb) variant found in a 77-year-old Dutch woman, suspected of hypoxia-mediated erythrocytosis. The typical blood parameters (Hb 17.3 g/dL; PCV 0.525 L/L; RBC 5.82 x 10(12)/L) could not be explained by any of the pathological or physiological conditions causing erythrocytosis. The patient was preventively phlebotomized because of intermittent claudication and erythrocytosis. At the hematological and biochemical levels, no anemia or hemolysis were present and no abnormal Hb fractions were detectable on alkaline electrophoresis or high performance liquid chromatography (HPLC). Molecular analysis revealed intact alpha-globin genes and a heterozygosity for a GTT-->GCT transition at codon 23 of the beta-globin gene, causing a Val-->Ala amino acid substitution. The P50 measured in full blood indicated that this mutant has an elevated oxygen affinity. This is the fourth single nucleotide substitution at codon 23 of the beta gene and the second associated with erythrocytosis. Because the family was not available for investigation no information was obtained as to whether the mutation represents a de novo event or was inherited, and might be a more common cause of erythrocytosis in Dutch patients. Considering the relatively high frequency of beta-thalassemia (thal) in the large allochthonous population in The Netherlands, combinations of Hb Zoeterwoude and beta-thal traits may lead to hemizygosity, with severe hypoxia and erythrocytosis from a few months after birth.

Hb Buffalo [alpha89(FG1)His-->Gln (alpha1)], observed solely and in the presence of an Hb S [beta6(A3)Glu-->Val] heterozygosity.

The hemoglobin (Hb) pattern of a 32-year-old Somali male living in The Netherlands, during routine diabetes mellitus monitoring, showed two more peaks in addition to the characteristic heterozygous Hb A/S pattern. A major peak of 15% faster than Hb A, and a minor one of 10.8%, overlapping Hb A2 and the glycated Hb S1c fraction were present. The patient was not anemic or microcytic but had a low haptoglobin level, possibly indicating a slightly elevated red blood cell (RBC) turnover. Hb S was confirmed by a sickle test and at the DNA level. The DNA sequence of the alpha1 gene revealed a C-->G transversion at position 89, changing the local positively charged histidine to a neutral glutamine. This mutant has been previously described in a Yemenite woman and two apparently unrelated Somali males. Our case is the first showing Hb Buffalo in combination with Hb S and a G6PD deficiency, and is again observed in a Somali. No functional abnormalities associated with mutations at this amino acid residue are reported in the literature. Also, in this case no sign of any hematological abnormalities that could not be explained by the Hb S heterozygosity G6PD deficiency was found. The abnormal alpha chain is expressed at the expected rate and without thalassemic effect or instability. The mutated alpha chain seems to associate with a slight preference to the beta(A) (15%) rather than with the beta(S) counterpart. The sum of both Hb A(Buffalo) and Hb S(Buffalo) results in about 19-20% of total Hb. This figure is in agreement with a stable mutant of the alpha1 gene.