Mutation in an intervening sequence splice junction in man

The Spectrum of α-Thalassemia Mutations in Syrian Patients

α-Thalassemia (α-thal) is a globally prevalent genetic disorder of hemoglobin (Hb) structure where the rate of α-globin chain synthesis is reduced or absent due to the presence of α-globin mutation(s). The aim of this study is to define the spectrum of α-globin gene mutations and evaluate their allele frequency in a group of α-thal carriers. A total of 55 individuals with possible α-thal patients were referred from the thalassemia centers in Syria. They have unexplained hypochromia and microcytosis. All patients were genetically tested for 21 common α-globin gene mutations using reverse hybridization kit. Seven different α-globin gene mutations and 13 different genotypes were detected in 55 patients. The two most frequently encountered mutations were -α3.7 deletion (47.1%) and --MED mutation (21.4%). The most commonly observed genotype was -α3.7/αα (40%), followed by --MED/αα genotype (21.8%). We determined the most common α thalassemia mutations in the Syrian patients. α-Thalassemia mutations with deletions were mostly observed in our study.

Splicing mutations in inherited retinal diseases

Mutations which induce aberrant transcript splicing represent a distinct class of disease-causing genetic variants in retinal disease genes. Such mutations may either weaken or erase regular splice sites or create novel splice sites which alter exon recognition. While mutations affecting the canonical GU-AG dinucleotides at the splice donor and splice acceptor site are highly predictive to cause a splicing defect, other variants in the vicinity of the canonical splice sites or those affecting additional cis-acting regulatory sequences within exons or introns are much more difficult to assess or even to recognize and require additional experimental validation. Splicing mutations are unique in that the actual outcome for the transcript (e.g. exon skipping, pseudoexon inclusion, intron retention) and the encoded protein can be quite different depending on the individual mutation. In this article, we present an overview on the current knowledge about and impact of splicing mutations in inherited retinal diseases. We introduce the most common sub-classes of splicing mutations including examples from our own work and others and discuss current strategies for the identification and validation of splicing mutations, as well as therapeutic approaches, open questions, and future perspectives in this field of research.

α-Thalassemia Mutations in Ilam Province, West Iran

Despite several studies performed in different provinces of Iran to identify the spectrum of α-globin gene mutations, no such study has so far been carried out in Ilam Province. A total of 274 individuals, including 201 α-thalassemia (α-thal) carriers and 73 normal subjects, originating from the northern counties of Ilam Province, participated in this study. Analysis of α-globin defects was performed using multiplex gap-polymerase chain reaction (gap-PCR), amplification refractory mutation system (ARMS)-PCR and direct sequencing, which revealed a total of 11 different mutations and 22 different genotypes. The -α^3.7 (rightward) (NG_000006.1: g.34164_37967del3804), α^-5 ntα (HBA2: c.95 + 2_95 + 6delTGAGG), and -α^4.2 (leftward) deletions were the most prevalent mutations identified in our study, with frequencies of 66.23, 10.09 and 8.33%, respectively. In conclusion, the present study showed that the α-thal mutation spectrum in Ilam Province, at least in the northern part of the province, is different from that in other geographical regions of Iran. These results increase our knowledge about the spectrum and distribution of α-globin gene mutations in Iran.

Estimating the burden of α-thalassaemia in Thailand using a comprehensive prevalence database for Southeast Asia

Severe forms of α-thalassaemia, haemoglobin H disease and haemoglobin Bart’s hydrops fetalis, are an important public health concern in Southeast Asia. Yet information on the prevalence, genetic diversity and health burden of α-thalassaemia in the region remains limited. We compiled a geodatabase of α-thalassaemia prevalence and genetic diversity surveys and, using geostatistical modelling methods, generated the first continuous maps of α-thalassaemia mutations in Thailand and sub-national estimates of the number of newborns with severe forms in 2020. We also summarised the current evidence-base for α-thalassaemia prevalence and diversity for the region. We estimate that 3595 (95% credible interval 1,717–6,199) newborns will be born with severe α-thalassaemia in Thailand in 2020, which is considerably higher than previous estimates. Accurate, fine-scale epidemiological data are necessary to guide sustainable national and regional health policies for α-thalassaemia management. Our maps and newborn estimates are an important first step towards this aim.

Editorial note: This article has been through an editorial process in which the authors decide how to respond to the issues raised during peer review. The Reviewing Editor's assessment is that all the issues have been addressed (see decision letter).

A cytosine-rich splice regulatory determinant enforces functional processing of the human α-globin gene transcript

The establishment of efficient and stable splicing patterns in terminally differentiated cells is critical to maintenance of specific functions throughout the lifespan of an organism. The human α-globin (hα-globin) gene contains 3 exons separated by 2 short introns. Naturally occurring α-thalassemia mutations that trigger aberrant splicing have revealed the presence of cryptic splice sites within the hα-globin gene transcript. How cognate (functional) splice sites are selectively used in lieu of these cryptic sites has remained unexplored. Here we demonstrate that the preferential selection of a cognate splice donor essential to functional splicing of the hα-globin transcript is dependent on the actions of an intronic cytosine (C)-rich splice regulatory determinant and its interacting polyC-binding proteins. Inactivation of this determinant by mutation of the C-rich element or by depletion of polyC-binding proteins triggers a dramatic shift in splice donor activity to an upstream, out-of-frame, cryptic donor. The essential role of the C-rich element in hα-globin gene expression is supported by its coevolution with the cryptic donor site in primate species. These data lead us to conclude that an intronic C-rich determinant enforces functional splicing of the hα-globin transcript, thus acting as an obligate determinant of hα-globin gene expression.

A Unique Interaction of IVS-I-1 (G>A) (HBA2: c.95+1G>A) with Hb Adana (HBA2: c.179G>A) Presenting as Transfusion-Dependent α-Thalassemia

Nondeletional α-globin mutations are known to cause more serious clinical effects than deletional ones. A rare IVS-I-1 (G>A) (HBA2: c.95+1G>A) donor splice site mutation interferes with normal splicing of pre mRNA and results in activation of a cryptic splice site as well as a frameshift mutation. Hb Adana [HBA2: c.179G>A (or HBA1)] is a highly unstable variant hemoglobin (Hb) resulting from a mutation at codon 59 on the HBA2 or HBA1 gene, recognized to cause severe α-thalassemia (α-thal) syndromes. We report a unique case of compound heterozygosity for these two mutations in a 9-year-old boy who presented with a Hb level of 5.3 g/dL and hepatomegaly at the age of 15 months. He required regular blood transfusions in view of a Hb level of <7.0 g/dL and failure to thrive. He had thalassemic red cell indices and peripheral blood film. The Hb electrophoresis only showed a raised Hb F level (3.3%) and a pre run peak but the Hb H inclusion test was negative. His father had thalassemic red cell indices but a normal Hb level. His mother had almost normal Hb levels and red cell indices. Hb Adana involving the HBA2 gene was detected by mutiplex amplification refractory mutation system-polymerase chain reaction (ARMS-PCR) in the proband and his father. DNA sequencing of the HBA2 gene confirmed the IVS-I-1 mutation in the proband and his mother. This case highlighted the unique interaction of the IVS-I-1 mutation with Hb Adana in a young Malay boy presenting with transfusion-dependent α-thal.

Impact of annotation error in α-globin genes on molecular diagnosis

Background

Recent studies on the variants in duplicated human alpha globin genes (HBA2 and HBA1) actively target the α-globin gene as molecular modulators for the treatment of β-thalassemia major. Identification of the exact position of variant in HBA1, HBA2 or its patchworks is mandatory to support the therapeutic aims in β-thalassemia major, by identifying specific modulators for the reactivation of fetal hemoglobin production. Hence, accurate identification of the variants in α-globin genes is crucial for the proper diagnosis, treatment and genetic counseling.

Method

The objective was to reveal the annotation errors produced in α-globin gene sequence analysis while using different analytic tools. An HBA2 gene sequence with the HBA2:c.95+2_95+6delTGAGG variant and a recently reported HBA12 gene convert have been taken as examples to prove annotation error in α-globin gene from different analytic tools.

Results and discussion

Although various bioinformatics tools used to predict variants are usually of high reliability, the current study using the an alpha globin 2 sequence with the HBA2:c.95+2_95+6delTGAGG variant and a recently reported HBA12 gene convert, has showcased ambiguous outputs among the three bioinformatics tools used and against the manual analytical method adopted.

Conclusions

This report emphasizes the necessity for caution in the usage of DNA sequence analysis tools during molecular diagnosis and the importance of the selection of more appropriate tools for analysis. Furthermore, ethnic specific sequences should be considered as reference sequence for the analysis to bypass sequence dissimilarities among diverse populations.

RNA splicing in human disease and in the clinic

Defects at the level of the pre-mRNA splicing process represent a major cause of human disease. Approximately 15-50% of all human disease mutations have been shown to alter functioning of basic and auxiliary splicing elements. These elements are required to ensure proper processing of pre-mRNA splicing molecules, with their disruption leading to misprocessing of the pre-mRNA molecule and disease. The splicing process is a complex process, with much still to be uncovered before we are able to accurately predict whether a reported genomic sequence variant (GV) represents a splicing-associated disease mutation or a harmless polymorphism. Furthermore, even when a mutation is correctly identified as affecting the splicing process, there still remains the difficulty of providing an exact evaluation of the potential impact on disease onset, severity and duration. In this review, we provide a brief overview of splicing diagnostic methodologies, from in silico bioinformatics approaches to wet lab in vitro and in vivo systems to evaluate splicing efficiencies. In particular, we provide an overview of how the latest developments in high-throughput sequencing can be applied to the clinic, and are already changing clinical approaches.

A Case of Iron Deficiency Anemia with Co-existing Hb Fontainebleau

Hb Fontainebleau is a rare alpha chain variant in the Indian population which generates an unknown peak on hemoglobin HPLC study and does cause diagnostic difficulty to those who are not acquainted with this entity. We present a case of Hb Fontainebleau, an eighteen year old patient who presented with symptoms related to anemia to our department and unknown peak observed in HPLC plots lead us to family study and molecular characterization for this case.

Molecular and cellular analysis of a novel HBA2 mutation (HBA2: c.94A > G) shows activation of a cryptic splice site and generation of a premature termination codon

In this study, we describe the clinical features and provide experimental analyses of a novel point mutation affecting the penultimate nucleotide of the first exon of the HBA2 (HBA2: c.94A > G) gene identified in a 26-year-old female who also carries a heterozygous Hb E (HBB: c.79G > A) variant. The aim of the study was to investigate the impact of this point mutation on the transcriptional activity of the HBA2 gene using a combination of an initial in silico prediction followed by in vitro mutagenesis and transcriptional activity assessment. The analyses revealed that the HBA2: c.94A > G point mutation causes the activation of a cryptic splice site located 49 bp upstream of the exon1-intron1 boundary in both HBA2 long and short isoforms, thus generating a frameshift and a premature termination codon between codons 48 and 49 in the second exon. A rapid degradation of the aberrantly spliced transcripts by the nonsense mediated decay (NMD) surveillance system is highly indicative of an α-thalassemia (α-thal) phenotype. However, the abnormal mRNA may not be entirely degraded since the proband presents a slight splenomegaly that could be the sign of extra vascular hemolysis.

Epidemiological profile of common haemoglobinopathies in Arab countries

Haemoglobinopathies including the thalassemias and sickle cell disease are known to be prevalent inherited disorders in most Arab countries with varying prevalence rates and molecular characterisation. β-thalassemia is encountered in polymorphic frequencies in almost all Arab countries with carrier rates of 1-11 % and a varying number of mutations. The most widespread mutation in Lebanon, Egypt, Syria, Jordan, Tunisia and Algeria is the IVS-I-110 (G>A). In the Eastern Arabian Peninsula, the Asian Indian mutations (IVS-I-5 (G>C), codons 8/9 (+G) and IVS-I (-25 bp del)) are more common. The α-thalassemias are encountered in the majority of Arab countries in frequencies ranging from 1 to 58 % with the highest frequencies reported from Gulf countries. The (-α(3.7)) mutation is the most frequent followed by the non-deletional α2 polyadenylation signal mutation (AATAAA>AATAAG) and the α2 IVS1 5-bp deletion. The rates of sickle cell trait in Arab countries range from 0.3 to 30 %, with the Benin, the Arab-Indian and the Bantu haplotypes constituting the bulk of the haplotypes, leading to two major phenotypes; a mild one associated with the Arab-Indian and a severe one with the Benin and Bantu haplotypes. Public health approaches targeting prevention of haemoglobinopathies in Arab countries include newborn screening for sickle cell disease, and premarital screening for carriers of β-thalassemia and sickle cell disease. These services are still patchy and inadequate in many Arab countries recommending the upgrade of these services with strengthening of the education and training of health care providers and raising public awareness on the feasibility of prevention and care for haemoglobinopathies.

The spectrum of α-thalassemia mutations in the Kurdish population of Northeastern Iraq

In an attempt to determine the spectrum of α-thalassemia (α-thal) mutations in the Kurdish population of Northeastern (NE) Iraq, a total of 101 unrelated adults with unexplained hypochromia and/or microcytosis were enrolled. α-Thalasssemia mutations were characterized by gap polymerase chain reaction (gap-PCR), multiplex PCR (m-PCR) and reverse hybridization and sequencing for both α genes. A total of nine α-thal mutations were characterized including four deletional ones: -α(3.7) (rightward), - -(MED-I), -(α)(20.5), -α(4.2) (leftward) and five nondeletional ones: α(polyA1)α, αα(Adana), α(-5 nt)α, α(CS)α and α(polyA2)α. These determinants were arranged in 12 different genotypes, the most frequent of which were: -α(3.7)/αα, - -(MED-I)/αα, -α(3.7)/-α(3.7), α(polyA1)α/αα, αα(Adana)/αα and -(α)(20.5)/αα. This pattern is similar to that reported in Turkey, western (W) Iran, Cyprus and Greece, and to some extent, different from the pattern observed in the Arabian Peninsula.

An α‐Thalassemia Phenotype in a Dutch Hindustani, Caused by a New Point Mutation that Creates an Alternative Splice Donor Site in the First Exon of the α2‐Globin Gene

The proband is an elderly woman (79 years of age) of Surinamese-Hindustani origin, suspected of being a carrier of a nondeletional alpha-thalassemia (thal) because of a moderate microcytic hypochromic anemia at normal ferritin levels and in the absence of any other alpha-thal deletions. Sequence analysis revealed a silent mutation (GGC-->GGT) at codon 22 of the alpha2-globin gene. This mutation generates a splice donor site consensus sequence (GGTGAG) between codons 22 and 23. The abnormally spliced mRNA leads to a premature termination between codons 48 and 49. The presence of a downstream intron may induce the intracellular degradation of the affected mRNA, a pathway known as nonsense mediated decay (NMD), and this explains the alpha(+)-thal phenotype observed in the patient. The codon 22 (GGC-->GGT) transition described in this report is the first mutation creating a splice donor site in one of the alpha-globin genes.

Clinical and molecular analysis of haemoglobin H disease in Sardinia: haematological, obstetric and cardiac aspects in patients with different genotypes

In this study, 251 Sardinian patients (187 adults and 64 children) with haemoglobin (Hb) H disease were evaluated. Two-hundred and sixteen patients (86%) had the deletional type (- -/-alpha) and 36 (14%) patients had the non-deletional type (- -/alpha(ND)alpha). A clear genotype-phenotype correlation was found, with the non-deletional type more severe than the deletional type. Diagnosis of Hb H disease was incidental in about 60% of cases. Aplastic crises due to B19 parvovirus infection were found in five patients (2.1%), while 23 patients (9.6%) experienced one or more haemolytic crises. Nineteen patients with Hb H received sporadic red blood cell transfusions and three patients were repeatedly transfused. Forty-seven of 61 married women (77%) had 82 pregnancies. In children, mean serum ferritin was 87 +/-92 mug/l and in adults, was 192 +/- 180 mug/l in females and 363 +/- 303 mug/l in males. For the 98 male patients, a significant correlation was found between ferritin values and age (r2 = 0.33, P < 0.0001). In the Sardinian population, Hb H disease needs regular monitoring for early detection and treatment of possible complications, such as worsening of anaemia that may require red cell transfusion, cholelithiasis and iron overload.

Hemoglobinopathies mimicking Hb S/beta-thalassemia: Hb S/S with alpha-thalassemia and Hb S/Volga

There are approximately 1200 known natural mutations of the human globin genes. In most clinical laboratories, the diagnosis of hemoglobin disorders is based on blood counts, hemoglobin electrophoresis, or column chromatography, which can identify common variant hemoglobins such as Hb S, C, and E, but are unable to definitively diagnose most other hemoglobin variants and thalassemia mutations. We report two unrelated cases, both thought initially to have Hb S/beta-thalassemia. Subsequent mutational analyses revealed that one is Hb S/S with compound heterozygosity for nondeletional alpha-thalassemia mutations. The other is the first reported case of compound heterozygosity for Hb S and an unstable hemoglobin, Hb Volga. Correct diagnoses of these hereditary disorders are needed for prognosis and proper management and also for genetic counseling. These studies underscore the importance to correlate clinical course with laboratory diagnosis and to make DNA-based diagnostics more widely available for patients with unusual or complicated hemoglobin disorders.

Alpha-2-globin gene polyadenylation (AATAAA-->AATAAG) mutation in hemoglobin H disease among Kuwaitis

OBJECTIVES

In the Arabian Gulf region, hemoglobin (Hb) H disease usually results from homozygosity or compound heterozygosity involving the alpha2-globin gene polyadenylation (poly A) signal (AATAAA-->AATAAG) mutation (alpha(T)alpha). Here we document the clinical and hemato logical characteristics of children with Hb H disease being followed in Kuwait.

SUBJECTS AND METHODS

Twenty-four patients (0.5-12 years old, mean 4.7 +/- 3.5 years) with persistent microcytic, hypochromic anemia (and normal iron status as well as normal Hb A2 levels) were referred to the pediatric hematology clinic for further investigations. They were all screened for the alpha+-thalassemia (alpha+-thal; -3.7 kb) deletion using a standard PCR method. They were also screened for the alpha2-globin gene alpha(T)alpha allele and the 5nt deletion (-alpha5nt) in the first intervening sequence, which are common alpha-thal alleles in this population. They were followed up for periods ranging from 2 to 8 years.

RESULTS

Of the 24 patients, 4 (16.7%) also had sickle cell trait (Hb-AS), while 7 (29.2%) were glucose-6-phosphate dehydrogenase deficient. Only 1 patient had significant hepatosplenomegaly and 1 developed gallstones. While none was on chronic transfusion therapy, 8 (33.3%) had been transfused at least once and, in 3 instances, this was secondary to parvovirus B19 +ve aplastic crisis. The alpha-globin genotype was successfully determined in almost all patients. The results showed that 17 (70.8%) patients were homozygous for the poly A mutation (alpha(T)alpha/alpha(T)alpha), 6 (25.0%) were compound heterozygotes for this and the alpha+-thal (-3.7 kb) deletion (-alpha/alpha(T)alpha) and 1 (4.2%) was undetermined. There were no significant differences in the phenotypes of the 2 genotypes and their hematological features were identical.

CONCLUSIONS

Hb H disease involving the poly A mutation is a mild thal intermedia phenotype among Kuwaitis. There are no serious complications and there is no need for regular blood transfusion.

Sequence variations of the ?-globin genes: Scanning of high CG content genes with DHPLC and DG-DGGE

The alpha-globin chains are encoded by two duplicated genes (HBA2 and HBA1, 5'-3') showing overall sequence homology >96% and average CG content >60%. alpha-Thalassemia, the most prevalent worldwide autosomal recessive disorder, is a hereditary anemia caused by sequence variations of these genes in about 25% of carriers. We evaluated the overall sensitivity and suitability of DHPLC and DG-DGGE in scanning both the alpha-globin genes by carrying out a retrospective analysis of 19 variant alleles in 29 genotypes. The HBA2 alleles c.1A>G, c.79G>A, and c.281T>G, and the HBA1 allele c.475C>A were new. Three pathogenic sequence variations were associated in cis with nonpathogenic variations in all families studied; they were the HBA2 variation c.2T>C associated with c.-24C>G, and the HBA2 variations c.391G>C and c.427T>C, both associated with c.565G>A. We set up original experimental conditions for DHPLC and DG-DGGE and analyzed 10 normal subjects, 46 heterozygotes, seven homozygotes, seven compound heterozygotes, and six compound heterozygotes for a hybrid gene. Both the methodologies gave reproducible results and no false-positive was detected. DHPLC showed 100% sensitivity and DG-DGGE nearly 90%. About 100% of the sequence from the cap site to the polyA addition site could be scanned by DHPLC, about 87% by DG-DGGE. It is noteworthy that the three most common pathogenic sequence variations (HBA2 alleles c.2T>C, c.95+2_95+6del, and c.523A>G) were unambiguously detected by both the methodologies. Genotype diagnosis must be confirmed with PCR sequencing of single amplicons or with an allele-specific method. This study can be helpful for scanning genes with high CG content and offers a model suitable for duplicated genes with high homology.

Molecular spectrum of alpha-thalassemia in Tunisia: epidemiology and detection at birth

We present the characterization of the molecular spectrum and frequency data of alpha-thal (thal) defects in Tunisia, and an evaluation of the efficacy and limitations of Hb Bart's (gamma4) measurement for the screening of alpha-thal at birth. Cord blood samples were collected from two different areas: the northeast of the country, an area where Hb H (beta4) disease frequently occurs, and Tunis, the capital city, representative of the average Tunisian population. From the first group, 110 samples with Hb Bart's and/or microcytosis at birth were selected from 1270 randomly collected samples. Two additional population samples, one from the same northeastern region (n = 90), the other from Tunis (n = 104) were collected randomly. Nine common deletional alpha-thal defects and nondeletional mutations were screened. In the northeastern samples, selected for the presence of Hb Bart's and microcytosis, the -alpha3.7 deletion was the most common defect (4.5% allele frequency) followed by a polyadenylation (poly A) signal mutation (1.8%), the five nucleotide (nt) deletion and the -alpha4.2 deletion (both 0.9%). The African polymorphism (G-->TCGGCCC at position 7238 and T-->G at 7174) was found with an allele frequency of 11% in the selected northeastern samples. In the random population samples, the overall alpha-thal allele frequency was 4% in the northeast region, against 2% in the average Tunisian population. The +14 (G-->C) polymorphism in the 5'UTR (untranslated region) of the alpha2 gene and the African polymorphism in the second intron of the same gene, were found in 3.5% of the alleles. No alpha0-thal alleles were found among the 304 blood samples studied at the DNA level during this survey.

Hb G-San Josè variant levels correlate with alpha-thalassemia genotypes

Hb G-San Josè or beta7(A4)Glu-->Gly has been reported in Southern Italian or Mexican families. We have studied four families from Sicily and Campania, Southern Italy. In six carriers, the hemoglobin variant level ranged from 32 to 38%. In four double heterozygotes for Hb G-San Josè and alpha-thalassemia the variant level showed a strong correlation with the alpha-thalassemia genotype. In fact, the variant level was 15% when interacting with the - (alpha)20.5/alphaalpha, 19.6% with the alphaalpha/alphaPoly Aalpha, and 24.8% with alphaalpha/alpha(-5) ntalpha genotypes. In two double heterozygotes for Hb G-San Josè and beta+ -IVS-I-6 (T-->C) the hemoglobin variant level was 67%. These data show that the reduced synthesis of alpha chains causes drastic reduction of probability to form Hb G-San Josè in favor of the formation of Hb A. Moreover, this reduction, (i) correlates with the type of alpha-thalassemia genotype and with the degree of the alpha chain deficiency, and (ii) is, most probably, more marked than the degree of alpha chain reduction. The minor affinity of the beta chain variant for the alpha chains associated with the reduced synthesis of the alpha chains is probably the principal cause of the variant hemoglobin reduction. Moreover, the rapid removal of the abnormal chains by proteolytic enzymes must have an essential role in order to reduce the chain variant pool. These conclusions are in agreement with the results obtained in reticulocyte and in vitro recombination experiments.

Alpha-thalassaemia prenatal diagnosis by two PCR-based methods

In Cyprus all couples carrying alpha0-thalassaemia mutations are detected in the course of the thalassaemia carrier screening program and prenatal diagnosis is offered to all of them. Prenatal diagnosis for alpha-thalassaemia is routinely done by two independent molecular methods. With the first method, the mutations of the parents are directly determined by gap-PCR and then the chorionic villus sample (CVS) is examined for the presence of these mutations. With the other method, a (CA)n repeat polymorphic site located between the psialpha1- and alpha2-globin genes is used for determining the presence or absence of the normal and mutant alleles. In the period from 1995 to 1999, molecular analysis of 46 couples in which haematological data were consistent with deletion of two alpha-globin genes in both partners indicated that only 13 of them were actually at risk for haemoglobin (Hb) Bart's hydrops fetalis and prenatal diagnosis was provided in 16 pregnancies. The molecular diagnosis was possible in all cases with the use of both gap-PCR and (CA)n repeat polymorphisms analysis. No misdiagnosed cases for alpha-thalassaemia have been reported to date.

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 Bart's levels in cord blood and alpha-thalassemia mutations in Cyprus

The purpose of this study was to examine the frequency of alpha-thalassemia in the population of Cyprus using cord blood samples. The levels of Hb Bart's were compared with the hematological indices and the results correlated with the presence of alpha-thalassemia mutations. The protocols for the polymerase chain reaction detection of the six most common alpha-globin mutations encountered in Cyprus were optimized, and the frequency of each mutation was determined through the screening of 495 random cord blood samples. The total allele frequency for the mutations examined was 10.6%, of which 1% is due to the triplication of the alpha-globin genes. The -alpha(3.7 kb) deletion accounts for 72.8% of all detectable mutations, while the--MED-I and -(alpha)-20.5 kb mutations account for 7.8%. The level of Hb Bart's and the MCV and MCH values in cord blood samples were found to correlate closely with the severity of alpha-thalassemia, although the -alpha(3.7 kb) deletion and perhaps other mild alpha-thalassemia mutations may not give detectable Hb Bart's levels. A reasonably accurate estimate of the alpha-thalassemia carrier frequency may be obtained from cord blood studies if Hb Bart's estimates are combined with hematological indices. When molecular methods are added, these give the best way to use cord bloods to survey populations for alpha-thalassemia.

Hb Sallanches [alpha104(G11)Cys-->Tyr]: a rare alpha2-globin chain variant found in the homozygous state in three members of a Pakistani family

We have identified a rare alpha2-globin chain variant, Hb Sallanches [alpha104(G11) Cys-->Tyr], in a Pakistani family having three homozygous patients with transfusion-dependent Hb H disease. This variant, previously reported in a French patient and a West Indian homozygous patient with Hb H disease, is due to a mutation at codon 104 (TGC-->TAC). This is the third case of Hb Sallanches and the first case with three homozygous patients reported in Pakistan. Due to the different ethnic origins of the patients, it is very likely an independent mutation.

Alpha-thalassemia carrier identification by DNA analysis in the screening for thalassemia

Differentiation between heterozygous alpha-thalassemia and several phenotypically resembling alleles at the beta-globin gene cluster such as coinherited delta- and beta-thalassemia or gammadelta beta-thalassemia is a critical step in genetic counseling. In this paper we report our experience in the identification of the alpha-thalassemia carrier state using polymerase chain reaction (PCR)-based methods, and the feasibility and simplification of screening for thalassemia using this approach. Alpha-globin genotype was determined by PCR-based method in 526 adult subjects with reduced mean corpuscular volume (MCV) and mean corpuscular hemoglobin (MCH), normal hemoglobin A2 and F, and normal serum iron. To verify the reliability of the protocol used, in 68 of these subjects we performed globin chain synthesis analysis and in 101 we determined alpha-globin genotype by Southern blot analysis. Five hundred twenty-one (99%) of 526 subjects examined were identified as carriers of one or two alpha-thalassemia alleles. The identification of the alpha-thalassemia carrier state may be fast and accurate by PCR-based method, avoiding other cumbersome and expensive methods such as globin chain synthesis and Southern blot analysis.

Different hematological phenotypes caused by the interaction of triplicated alpha-globin genes and heterozygous beta-thalassemia

The pathophysiology and clinical severity of beta-thalassemia are related to the degree of alpha/non-alpha-chain imbalance. A triplicated alpha-globin gene locus can exacerbate effects of excess alpha-chains caused by a defective beta-globin gene, although this is not observed in all cases. Extensive studies on this condition are lacking. We report a group of 17 patients who are heterozygous for both the alpha alpha alpha(anti-3.7) allele and a mutation in the beta-globin gene cluster. Their clinical phenotypes varied: six had mild anemia with microcytosis and hypochromia, while 11 had more severe anemia with splenomegaly requiring splenectomy (three cases) and blood transfusions (four cases). Different phenotypes were also evident in the presence of the same beta-thalassemia mutation: in one family, two individuals had the same alpha- and beta-globin genotypes but presented with different hematologic phenotypes. In addition, the complex interaction involving a triplicated alpha-globin gene, beta39- and delta+27-thalassemia mutations is studied in a family with two siblings presenting with hemolytic anemia, normal Hb A2 and increased Hb F. Analysis of this series of patients suggests that additional genetic determinants play a role in modulating phenotypic expression in individuals with identical alpha- and beta-globin genotypes. Interaction with a triplicated alpha-gene can play a role in the clinical presentation of patients with defective beta-globin gene expression and should be considered in the diagnosis of atypical cases.

Nondeletional alpha-thalassemia: first description of alpha Hph alpha and alpha Nco alpha mutations in a Spanish population

Several different deletions underlie the molecular basis of alpha-thalassemia. The most common alpha-thalassemia determinant in Spain is the rightward deletion (-alpha 3.7). To our knowledge, however, no cases of alpha-thalassemia due to nondeletional mutations have so far been described in this particular Mediterranean area. Here, we report the existence of nondeletional forms of alpha-thalassemia in ten Spanish families. The alpha 2-globin gene was characterized in ten unrelated patients and their relatives only when the presence of deletional alpha-thalassemia was ruled out. The alpha 2-globin gene analysis was performed using the polymerase chain reaction (PCR) followed by restriction enzyme analysis or by allelespecific priming. This allowed the identification of a 5-base pair (bp) deletion at the donor site of IVS I (alpha Hph alpha) in 9 cases and the alpha 2 initiation codon mutation (alpha Nco alpha) in one case. Although these alpha 2-globin gene mutations are found in other mediterranean areas, our results demonstrate their presence in the Spanish population and suggest that the alpha Hph alpha/alpha alpha genotype is probably the most common nondeletional form of alpha-thalassemia in Spain.

Rapid detection of point mutations and polymorphisms of the alpha-globin genes by DGGE and SSCA

We report the application of DGGE and SSCA for the identification of point mutations causing alpha-thalassemia. The alpha-globin genes were amplified in three overlapping fragments of 250 bp (I), 540 bp (II), and 600 bp (III), respectively. Fragments II and III were analysed by DGGE, while fragments I and II were analysed by SSCA. A panel of seven previously identified mutations was employed to test the combined DGGE/SSCA strategy: 5/5 and 6/7 mutations were detected by SSCA and DGGE, respectively. The same approach has also led to the identification of eight disease-causing mutations in a sample of 18 presumed non-deletional alpha-thalassemia carriers. During this pilot study, two novel mutations as well as three new polymorphisms were found. The combined application of SSCA and DGGE allows the rapid identification of mutations responsible for alpha-thalassemia and abnormal globin chain variants. Moreover, it will prove extremely useful for pre- and postnatal diagnosis and in screening programs for non-deletional alpha-thalassemias.

alpha-Thalassaemia in the population of Cyprus

We have determined the alpha-thalassaemia (alpha-thal) determinants in 78 patients with Hb H disease from Cyprus; 25 were Turkish Cypriots and 53 were Greek Cypriots. Four deletional and three non-deletional alpha-thal alleles were present; the -alpha(3.7 kb) alpha-thal-2 and the --MED-I alpha-thal-1 were most frequently seen; --MED-II and -(alpha)20.5 deletions occurred at considerably lower frequencies. About 15% of all chromosomes carried a non-deletional alpha-thal-2 allele; of these the 5 nucleotide (nt) deletion at the first intervening sequence (IVS-I) donor splice site was present in approximately 8% of all chromosomes. Two types of polyadenylation signal (poly A) mutations were observed. No striking frequency differences were seen between Greek and Turkish Cypriot patients. Combinations of the various types of alpha-thal resulted in eight different forms of Hb H disease. The phenotypes were comparable except for great variations in the level of Hb H which was highest (average approximately 22%) in the 12 patients with the alpha 5nt alpha/--MED-I combination. One patient with the same form of Hb H disease but with an additional beta-thal (IVS-I-110,G-->A) heterozygosity had a most severe microcytosis and hypochromia with < 1% Hb H. Variations in the level of Hb H might correlate with the severity of the disease, although this was not evident from the haematological data.

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.

Osteogenesis imperfecta type I: molecular heterogeneity for COL1A1 null alleles of type I collagen

Osteogenesis imperfecta (OI) type I is the mildest form of inherited brittle-bone disease. Dermal fibroblasts from most affected individuals produce about half the usual amount of type I procollagen, as a result of a COL1A1 "null" allele. Using PCR amplification of genomic DNA from affected individuals, followed by denaturing gradient gel electrophoresis (DGGE) and SSCP, we identified seven different COL1A1 gene mutations in eight unrelated families with OI type I. Three families have single nucleotide substitutions that alter 5' donor splice sites; two of these unrelated families have the same mutation. One family has a point mutation, in an exon, that creates a premature termination codon, and four have small deletions or insertions, within exons, that create translational frameshifts and new termination codons downstream of the mutation sites. Each mutation leads to both marked reduction in steady-state levels of mRNA from the mutant allele and a quantitative decrease in type I procollagen production. Our data demonstrate that different molecular mechanisms that have the same effect on type I collagen production result in the same clinical phenotype.

A novel polyadenylation signal mutation in the alpha 2-globin gene causing alpha thalassaemia

In a family of Indian origin we have identified a deletion of two bases at the polyadenylation signal sequence of the alpha 2-globin gene (AATAAA-->AATA). Three individuals heterozygous for this mutation display an alpha o-thalassaemia-like phenotype. Single-stranded conformation analysis and automatic sequencing showed no additional mutations in either alpha 1- or alpha 2-globin genes. A previously described polyadenylation sequence mutation (AATAAA-->AATAAG), alpha TSaudi alpha, causes HbH disease in homozygotes. In this study the patients heterozygous for the AATA(-AA) mutation show a similar phenotype observed in the alpha TSaudi alpha heterozygotes. This confirms the observation that the inefficient transcriptional termination due to mutations of the polyadenylation sequence of the alpha 2-gene might interfere with the alpha 1-gene expression.