Non-deletion Type Research Articles

Alpha thalassaemia/mental retardation syndrome (non-deletional type): report of a family supporting X linked inheritance.

In 1990 the existence of an X linked form of the alpha thalassaemia/mental retardation syndrome was postulated after the description of six isolated cases who were all cytogenetically male. The segregation pattern in the family described here supports X linked inheritance. The clinical details of our two patients are remarkably similar to the previously delineated phenotype. In addition, renal anomalies were identified in one patient, but their significance will remain uncertain until further cases have been assessed. Affected subjects could be identified by the presence of Hb H inclusions, and were also noted to have abnormalities of several haematological indices. Examination of blood from obligatory carriers in this family suggests that Hb H inclusions are not an invariable finding and that haematological indices appear to be unaffected by the condition in female heterozygotes.

The non-deletion type of alpha thalassaemia/mental retardation: a recognisable dysmorphic syndrome with X linked inheritance.

The non-deletion type of alpha thalassaemia/mental retardation: a recognisable dysmorphic syndrome with X linked inheritance.

δβ Thalassemia and Hereditary Persistence of Fetal Hemoglobin

Delta beta Thalassemia and hereditary persistence of fetal hemoglobin (HPFH) constitute a heterogeneous group of disorders characterized by absent or reduced synthesis of adult hemoglobin (Hb A) and increased synthesis of fetal hemoglobin (Hb F). Coinheritance of these disorders with other beta chain hemoglobinopathies, such as beta thalassemia and the sickle cell (beta s) gene, can result in attenuation of the clinical severity of these hemoglobinopathies owing to the increased Hb F levels. The molecular basis of these disorders is quite heterogeneous and consists of both deletion and nondeletion types of mutations. The characterization of these molecular defects has provided new insights on the structure and function of important regulatory elements that are involved in the normal control of expression of the beta- and gamma-globin genes and in hemoglobin switching.

Detection of the common Hb F Sardinia [ Aγ(E19)Ile → Thr]variant by isoelectric focusing in normal newborns and in adults affected by elevated fetal hemoglobin syndromes

A simple and rapid conventional isoelectric focusing technique for the detection of the silent Hb F Sardinia variant, containing the mutated A γ T chain, is described. The method is based on thin-layer gels of shallow pH gradient (pH 6.7–7.7) and allows the direct detection of this rather common and widespread Hb variant at a screening level. 15–30 hemolysates from newborns and adults affected by elevated Hb F syndromes, both in the heterozygous and homozygous condition, could be examined simultaneously. The frequency of the A γ T gene in Sardinian newborn ( f = 0.175), in β o -thalassemia ( f = 0.722), in β +-thalassemia ( f = 0.346), and in the non-deletional type of Aγ-HPFH ( f = 0), as evaluated with this method, is in accordance with that previously reported by means of other methodologies.

The von Willebrand Factor Gene and Genetics of von Willebrand's Disease

The von Willebrand factor (vWF) gene spans 178 kilobases in the human genome, is interrupted by 51 introns, and has been localized to human chromosome 12p12----12pter. In addition, a pseudogene that duplicates the midportion of the vWF gene has been identified on chromosome 22. In several families, large vWF gene deletions have been identified as the basis for von Willebrand's disease (vWD). In most patients, however, the vWF gene is found to be grossly intact by Southern blot analysis, a result that implies a more subtle molecular defect. The advent of the polymerase chain reaction has allowed a more direct analysis in this group of patients. By this approach, missense mutations, all clustered within the same small region in the midportion of the vWF molecule, have been identified in several patients with type IIA vWD. Expression of mutant vWF by transfection into COS cells suggests that the characteristic loss of high-molecular-weight multimers seen in type IIA vWD may occur through at least two distinct mechanisms. In preliminary studies of nondeletional type III vWD, a family has been identified with decreased vWF as a result of failure of production of messenger RNA from the affected vWF allele. This disorder could be due to defects in vWF gene transcription, RNA processing, or stability. As additional defects are identified, the accurate diagnosis of vWD at the molecular level may eventually become possible.

Hemoglobinopathies Among the Gond Tribal Groups of Central India; Interaction of α- and β-Thalassemia with β Chain Variants

We have investigated the frequencies and types of alpha-thal, beta-thal, and Hb variants among nearly 200 inhabitants of villages in the Mandla and Jabalpur districts of Madhya Pradesh in Central India. Over 85% were tribals of the Gond group. alpha-Thal, as -alpha 3.7/and -alpha 4.2/, and the nondeletional Koya Dora mutation were present at the combined frequency of 0.54. There were indications for the presence of other nondeletional types of alpha-thal. alpha-Globin gene triplications were not observed. Four of the six beta-thal alleles observed were in the tribal groups; two (G----C at codon 30 and G----A at IVS-I-1) were found for the first time. The simultaneous presence of an alpha-thal (-alpha/alpha alpha or -alpha/-alpha) greatly improved the clinical and hematological condition of the patients with Hb S-beta(+)-thal (IVS-I-5; G----C). The lower frequency of alpha-thal among the beta-thal heterozygotes (f = 0.32) may indicate that some of the beta-thal alleles in the tribal populations originated from an outside source. Forty-one subjects had SS; all but one had beta S with haplotype #31, while one chromosome had haplotype #17. The presence of an alpha-thal-2 (f = 0.53) in the SS patients did not affect hematological data. The Hb F levels varied between 7.5% and 42.5% with high G gamma values. No difference in Hb F level between males and females was observed. Lower Hb F levels were present in 10 SS patients with an alpha-thal-2 homozygosity (average 16% versus 23.5% for eight SS patients with alpha alpha/alpha alpha) suggesting a decreased formation of alpha gamma dimers in severe alpha chain deficiency. Several younger SS patients (less than 10 years) also had high Hb F levels (32-42%). Variations in the sequence at -530 of the beta-globin gene; i.e. in the so-called silencer sequence, were present in all beta S chromosomes with haplotype #31, but were not considered important for understanding the variability in the Hb F level. gamma-Globin gene deletions (gamma-thal) and triplications were not observed.

Occurrence of the alpha thalassaemia-mental retardation syndrome (non-deletional type) in an Australian male.

The rare association of alpha thalassaemia and mental retardation has been described previously. Molecular studies of the alpha globin cluster in these cases have been heterogeneous, with some patients having large deletions while in others the alpha globin complex appears to be intact (non-deletional). The non-deletional cases form a distinct group whose features include severe mental retardation, haematological changes of haemoglobin H (Hb H) disease, developmental defects, and unusual patterns of inheritance. To date, five cases have been described with non-deletional alpha thalassaemia-mental retardation. We present here a further example of a young male of Northern European origin who appears to have the non-deletional form of the disease. Clinical features included severe mental retardation, Hb H disease, and developmental defects similar to those reported previously. DNA mapping, including pulsed field electrophoresis, showed no evidence of deletions within the alpha globin cluster. Karyotypic analysis indicated an increase in random breakage, which has been observed previously in one case of deletional alpha thalassaemia-mental retardation. Profuse Hb H bodies and Hb H on electrophoresis were consistent with Hb H disease. However, the latter was present at a relatively low level (1.6%) and, as well, the mean corpuscular volume (82.8 fl) and mean corpuscular haemoglobin (26.4 pg) were surprisingly high. Our findings are compared to other cases described with the non-deletional Hb H-mental retardation syndrome.

The levels of ?, ?, and ? chains in patients with Hb H disease

Details are given of a study of blood samples from 24 patients with Hb H disease from different Mediterranean countries and from the Far East. Four different types of alpha-thal-1 (--) were observed, namely -(alpha) (approximately 20.5-kb deletion); --MED-I (approximately 17.5-kb deletion); --MED-II (greater than 26.5-kb deletion); and --SEA (approximately 18-kb deletion, in Orientals only). The alpha-thal-2 was mainly of the deletion type (16 with the 3.7-kb deletion; 1 with the 4.2-kb deletion), while 4 of the 7 patients with a nondeletional type had the five-nucleotide deletion at the donor splice site of the first intron of the alpha 2 gene. All patients had a mild-to-moderate hemolytic anemia; no significant differences in hematology were observed between the groups. Hb A2 was decreased to about one-third of the normal level. The Hb H formation varied considerably and its quantitation was not always satisfactory. Patients with Hb H disease due to any alpha-thal-1 combined with a nondeletional alpha-thal-2 had the highest Hb H levels and a more marked anemia. The zeta chain production was small and absent in patients with the MED-II type of alpha-thal-1 because this deletion included the zeta and psi zeta genes. The highest zeta chain levels were present in the four patients with the SEA type of alpha-thal-1. The gamma chain production was increased, particularly in patients with a mutation of C----T at position -158 to the G gamma globin gene. This gamma chain was primarily present as Hb Bart's (or gamma 4) and only about 15% was recovered as Hb F or alpha 2 gamma 2. The evaluation of the rate of gamma chains produced in these patients was greatly facilitated by data from one patient who had Hb H disease and a heterozygosity for the A gamma-beta+-HPFH. The low levels of Hb A2 and of Hb F (relative to Hb Bart's) can be explained by a decreased affinity of alpha chains for delta and gamma chains as compared with beta chains in conditions of severe alpha chain deficiency.

Increased γ-globin expression in a nondeletion HPFH mediated by an erythroid-specif ic DNA-binding factor

In man, a shift from gamma- to beta-globin gene expression in erythroblasts underlies a switch from fetal to adult haemoglobin during development. In hereditary persistence of fetal haemoglobin (HPFH), inappropriately high gamma-globin expression in adult life is associated with deletions in the beta-globin cluster or with single-base changes upstream of the gamma-globin genes. To account for enhanced gamma-gene expression in HPFH of the non-deletion type, we tested the nuclear proteins of human erythroleukaemia cells that bind gamma-promoter sequences in vitro by correlating specific mutations in their binding sites with promoter activity. An erythroid-specific factor (GF-1) binds as a single molecule to the -195 to -170 region and contacts two TATCT(AGATA) motifs, but not the conserved octamer (ATGCAAAT) that separates them. We observe that a single change (at -175, T----C) found in HPFH leads to increased promoter activity only in erythroid cells. This effect is mediated by GF-1, the human counterpart of the chicken erythroid factor Eryf 1. The form of HPFH we studied here is an inherited disorder which can be ascribed to the action of a cell-specific DNA-binding factor on a mutant promoter.

An Aγ Type of Nondeletional Hereditary Persistence of Fetal Hemoglobin With a T→ C Mutation at Position -175 to the Cap Site of the Aγ Globin Gene

The nondeletional types of hereditary persistence of fetal hemoglobin (ndHPFH) concern the continued synthesis of hemoglobin (Hb) F with either G gamma or A gamma chains in amounts varying from 5% to 30%. Several mutations have been identified in either the A gamma or G gamma promoter which are considered causative to the continued production of one of the two gamma chains because the substitutions occur in sequence motifs essential for the expression characteristics of the gamma-globin gene in the 3' position. We report the discovery of a T----C mutation at position -175 in the A gamma promoter which was associated with a greatly increased level of Hb F (with mainly A gamma) and a decreased level of Hb A in the one (Black) heterozygote who had a beta c gene in trans. The same mutation has been observed in the G gamma promoter of a Black heterozygote who had high levels of Hb F with G gamma chains only. A detailed comparison between these two individuals indicated significant differences in the levels of Hb F and Hb A which may result from an additional mutation at position -158 in the G gamma promoter.

An A gamma type of nondeletional hereditary persistence of fetal hemoglobin with a T----C mutation at position -175 to the cap site of the A gamma globin gene

The nondeletional types of hereditary persistence of fetal hemoglobin (ndHPFH) concern the continued synthesis of hemoglobin (Hb) F with either G gamma or A gamma chains in amounts varying from 5% to 30%. Several mutations have been identified in either the A gamma or G gamma promoter which are considered causative to the continued production of one of the two gamma chains because the substitutions occur in sequence motifs essential for the expression characteristics of the gamma-globin gene in the 3′ position. We report the discovery of a T----C mutation at position -175 in the A gamma promoter which was associated with a greatly increased level of Hb F (with mainly A gamma) and a decreased level of Hb A in the one (Black) heterozygote who had a beta c gene in trans. The same mutation has been observed in the G gamma promoter of a Black heterozygote who had high levels of Hb F with G gamma chains only. A detailed comparison between these two individuals indicated significant differences in the levels of Hb F and Hb A which may result from an additional mutation at position -158 in the G gamma promoter.

The types and distribution of alpha-thalassemia-2 in China.

We studied 111 cases of Hb H disease from different families using Bam HI and Bgl II restriction enzymes. The results showed that 76 cases (68.5%) were of the deletion type, eight cases (7.2%) had Hb Constant Spring (Hb CS), and 27 cases (24.3%) were of the nondeletion and Hb CS types (alpha T). Distribution of the alpha-thalassemia-2 (alpha-thal-2) gene varies with the different regions in China. The rightward deletion (alpha -3.7) is found chiefly in Guangdong Province, the leftward deletion (alpha -4.2) mostly in Jiangxi Province, and the nondeletional type in Guangxi Province where the Han nationality is most prominent. We studied the nondeletional Hb H type by DNA gene mapping, digestion with Msp I, and hybridization with a 32P-alpha probe for the presence of the Hb Quong Sze [alpha 125(H8)Leu----Pro] mutation. It appears that none of these alpha-thal-2 genes contain the Hb Quong Sze mutation.

Different forms of Hb H disease in the Chinese.

A marked genetic and clinical variability of the Hb H syndrome occurs because of the molecular heterogeneity of alpha-thalassemia (thal). The hallmark is the presence of excess beta chains forming Hb H (beta tetramer). In the Chinese, classical Hb H disease presents as "alpha-thalassemia intermedia" and is due to a double heterozygosity for two deletional forms of alpha-thal, alpha-thal-1 and alpha-thal-2. The majority of cases with an alpha-thal-1 defect have a deletion of at least 18.1 kb starting 3' to the zeta 1 gene which includes the psi alpha and the two alpha genes; it is similar to that described in Thais. However, two families had a deletion of the entire zeta-alpha gene cluster, i.e. zeta-alpha-thal-1. Of 33 alpha-thal-2 defects studied, 26 were the rightward deletion (alpha -3.7 kb, all type I defects) and seven the leftward deletion (alpha -4.2 kb); one of the latter was associated with Hb Q. About 10% of the alpha-thal defects belong to the nondeletion type, the most common form being Hb Constant Spring (CS). This anomaly, when coinherited with alpha-thal-1, produces Hb H-CS disease which has a most marked anemia and splenomegaly due to the instability of the alpha-CS chain. Hb Quong Sze produces an alpha-thal-2 because of the unstable alpha-Quong Sze chain. One patient who inherited classical Hb H disease and Hb New York (NY) [alpha 113(G15)Val----Glu] had severe anemia, and required frequent blood transfusions due to the deleterious effect of an increased alpha-NY chain turnover.(ABSTRACT TRUNCATED AT 250 WORDS)

Overview of the β Thalassemias: Genetic and Clinical Aspects

There has been much progress in basic studies of the beta-thalassemia disorders in recent years, as well as in the practical aspects of prenatal diagnosis and clinical management. Alterations in a single or a few nucleotides account for most of the types of beta-thalassemia syndromes that have been characterized, and a variety of deletions have been found associated with beta O thalassemia, delta beta thalassemia, gamma delta beta thalassemia, and hereditary persistence of fetal hemoglobin (HPFH). Studies of nondeletional types of HPFH have revealed several single base changes 5' to the G gamma and A gamma genes, suggesting that these regions may be of major importance in the switchover from fetal to adult hemoglobin synthesis and in the relative production of the G gamma and A gamma globin chains during development. Evaluation of restriction enzyme polymorphisms and the assignment of haplotypes in the beta-like globin region of chromosome 11 have allowed delineation of the origin and distribution of thalassemia mutations, and have provided an important means for prenatal diagnosis. These studies have accumulated much new information about the function and expression of eukaryotic genes, and have served as a model for the investigation of human genetic disorders. The clinical management of patients with Cooley's anemia has benefited greatly from changes in transfusion practice, clear guidelines for splenectomy, and the availability of effective chelation therapy for iron overload. Current basic and clinical studies may lead to new approaches to management, treatment and eventual cures for this disease, including safe bone marrow transplantation, oral chelation treatment, and gene therapy.

Approach to the diagnosis of beta-thalassaemia by DNA analysis.

Over the last few years, the new techniques of DNA analysis have enabled efficient strategies for the detection and characterisation of the different mutations causing beta-thalassaemia of which a total of 41 have now been characterised. Since the majority of the beta-thalassaemia molecular defects are of the non-deletion type and not directly detectable by Southern blotting, a comprehensive approach to the identification of these mutations entails the use of several different techniques, including direct identification by restriction enzyme analysis and synthetic oligonucleotide probes, indirect identification by linkage analysis to restriction fragment length polymorphisms and globin chain synthesis analysis. As the majority of beta-thalassaemia in each population is accounted for by a few mutants, it should be possible to work out a combination of techniques to directly detect the majority of beta-thalassaemia in a defined population.

Alpha thalassaemia in an Italian population.

The incidence of alpha-thalassaemia in an Italian population has been determined by a survey of random cord bloods for the presence of Hb Bart's. 144 out of 4730 (3%) had detectable amounts of Hb Bart's. Furthermore, alpha-globin gene analysis of 100 random cord bloods showed that five out of 100 had the common type of alpha-thalassaemia caused by a single alpha-globin gene deletion (-alpha). The molecular basis of alpha-thalassaemia was also determined in a selected group of 34 newborns with detectable levels of Hb Bart's. 25 of these cases had the -alpha 3.7 deletion type of alpha-thalassaemia and nine had nondeletion types of alpha-thalassaemia in four of which the molecular defect was detectable directly by restriction enzyme analysis.

GγAγ(δβ)°‐thalassaemia and a new form of γ globin gene triplication identified in the Yugoslavian population

Among several hundred apparently healthy Yugoslavian adults with slightly elevated levels of fetal haemoglobin, we have identified two distinct abnormalities. (a) A G gamma A gamma(delta beta)0-thalassaemia heterozygosity with an approximately 15 kb deletion which involves part of the delta globin gene and the beta globin gene. This deletion is probably the same as that seen among Italians (Ottolenghi et al, 1982; Carè et al, 1984). (b) A nondeletion form of hereditary persistence of Hb F which is caused by a gamma globin gene triplication of the (+)G gamma.(+)G gamma.A gamma type. It is characterized by the presence of some 5% Hb F in the heterozygote containing nearly 100% G gamma chains. The C----T mutation at position--158 5' to the G gamma chain [(+)G gamma], identified through analyses of Xmn I digests, was present at both G gamma globin genes. This mutation is known to be associated with increased G gamma chain production (Gilman & Huisman, 1985), and thus is responsible for the increased G gamma chain production in these heterozygotes. The condition is different from the (+)G gamma.(+)G gamma nondeletion type of HPFH which has been observed in heterozygotes of two Black families, and is associated with the presence of 3-4% Hb F (with mainly G gamma chains) in heterozygotes.

Gene mapping of Malaysian alpha thalassemias with alpha and zeta globin gene probes.

Restriction enzyme analysis of the alpha and zeta globin genes was carried out in four cases of Hb Bart's hydrops fetalis, in three patients with Hb H disease without Hb CoSp, in three patients with Hb H disease with Hb CoSp, in 47 individuals with alpha thalassemia trait, and in 47 normal individuals. All four cases of Hb Bart's hydrops fetalis resulted from deletions of alpha 1 and alpha 2 globin genes which did not extend to the psi zeta 1 and zeta 2 globin genes. The same type of deletion was observed in alpha thal1 carriers, but two newborns (one Malay and one of Chinese extraction) had a nondeletion type of alpha thal1 which was confirmed by quantitative alpha globin gene analysis. In addition, two other newborns diagnosed as alpha thal1 trait carriers (one Malay, one Chinese) were shown to have a deletion of both alpha globin genes by quantitative alpha globin gene analysis, but further testing with zeta globin gene probe failed to reveal an abnormal fragment length characteristic of an alpha globin gene deletion. We believe that this last condition is due to a large deletion which includes all alpha globin genes and all zeta globin genes on the same chromosome. On another front, Bgl II restriction analysis of all four Hb Bart's hydrops fetalis cases and the alpha thal1 trait carriers showed a 10.5-kb Bgl II restriction fragment, in the hydrops fetalis as a single band, while in the carriers this 10.5-kb fragment was accompanied by the usual normal 12.5-kb and 11.3-kb fragments. We report that this 10.5-kb fragment, previously thought to be specific for the Southeast Asian alpha thal1 gene deletion, is also common in normal individuals. Nevertheless, digestion with other enzymes can clearly differentiate the alpha thal1 and normal genotypes. We distinguish the findings in the alpha thalassemias from the extensive DNA polymorphism in the region of the alpha and zeta globin genes.

Alpha thalassaemia in Sardinian newborns.

In this study we describe the correlation between the haematological parameters (red cell indices and Hb Bart's levels) and the alpha-globin genotype in Sardinian newborns. Increased Hb Bart's levels at birth always indicates alpha-thalassaemia, either of the deletion or non-deletion variety. Infants with two alpha-globin genes deleted (- alpha/- alpha and --/ alpha alpha genotypes) had microcytosis, low MCH and Hb Bart's in the 2.0-7.1% range. A minority (38.9%) of infants with the (- alpha/ alpha alpha) globin genotype had detectable Hb Bart's, in the 0.78-2.5% range, frequently associated with minimal microcytosis while the remainder (61.1%) were completely silent. Infants carriers of a non-deletion type of alpha-thalassaemia showed Hb Bart's levels within the range found in the (- alpha / alpha alpha) genotype. The association of heterozygous beta 0-thalassemia seems to have no effect on the expression of any of these alpha-thalassaemia lesions at birth.

Initiation codon mutation as a cause of alpha thalassemia.

Cloning and sequence analysis of the alpha-globin genes from a Sardinian patient with the nondeletion type of hemoglobin-H disease revealed a new type of thalassemia lesion. A mutation in the alpha 2-globin gene changes the initiation codon ATG to ACG and abolishes the function of this gene. Globin mRNA output from the affected alpha 2 locus is decreased relative to the alpha 1 locus. The mutation is detectable in genomic DNA by restriction analysis with the enzyme NcoI. Of the seven Sardinian patients with nondeletion alpha thalassemia screened with this enzyme, six had the initiation codon lesion.