Thalassemia due to a mutation in the cleavage-polyadenylation signal of the human beta-globin gene

A beta-globin gene cloned from a person with beta-thalassemia contained a T----C substitution within the conserved sequence AATAAA that forms a portion of the recognition signal for endonucleolytic cleavage and polyadenylation of primary mRNA transcripts. By Northern blot analysis a novel beta-globin RNA species, 1500 nucleotides in length, was detected in erythroid RNA. Nuclease protection studies of erythroid RNA, as well as RNA generated upon transient expression of the cloned mutant gene in HeLa cells, located the 3' terminus of this novel, polyadenylated RNA 900 nucleotides downstream of the normal poly(A) addition site, within 15 nucleotides of the first AATAAA in the 3'-flanking region of the beta-globin gene. These findings define the in vivo terminus of an elongated RNA and establish that human beta-globin transcription may extend at least 900 nucleotides 3' of the normal polyadenylation site.

A lectin on the hemocyte membrane of the oyster (Crassostrea virginica)

Using antisera produced against a serum lectin we have shown by employing immunocytofluorescence that hemocytes from the oyster, Crassostrea virginica, possess a lectin which is situated on the external surface of the cell membrane. The antisera block the binding of hemocyte microsomes to protease-treated vertebrate erythrocytes, thus confirming that the hemocyte membrane lectin is serologically related to the serum lectin. The major serum lectin has an apparent mass of 34,000. Flow cytometry has revealed that the distribution of the surface lectin on hemocytes represents a heterogeneous expression on a population basis, but no discrete cell subpopulations can be identified.

Genetic selection for tolerance to niclosamide and copper in Biomphalara glabrata (Mollusca: Pulmonata)

Successive generations of the PR-79 and M-line laboratory stocks of Biomphalaria glabrata were exposed in the LC90 of niclosamide or copper sulfate. Survivors from each generation produced the succeeding generation by self fertilization. The PR-79 stock showed no evidence of tolerance to either molluscicide following five generations of selection. On the other hand, M-line F5 snails demonstrated approximately two-fold higher tolerance to both molluscicides than did non-selected M-line snails.

beta-Thalassemia in Chinese: use of in vivo RNA analysis and oligonucleotide hybridization in systematic characterization of molecular defects

To perform a systematic analysis of beta-thalassemia genes among Chinese, we have determined the DNA haplotype in the beta-globin gene region of 37 Chinese beta-thalassemia chromosomes. Only four haplotypes were found. Blot hybridization analysis of erythroid RNA from patients homozygous for haplotypes 1, 2, and 3 demonstrated different patterns, suggesting that a different mutation was associated with each haplotype. The mutation associated with haplotype 1 was a C----T substitution at IVS-2, position 654. This mutation produces a new donor splice site and leads to formation of a beta-globin RNA with an insertion of 73 nucleotides. The mutation associated with haplotype 2 was a nucleotide insertion of A between codons 71 and 72, which results in a frameshift and premature termination of beta-globin synthesis. Haplotype analysis suggests that these two mutations may account for up to 85% of beta-thalassemia genes in this ethnic group. The haplotype 3 gene contained a transcriptional "TATA" box mutation that has been previously reported. Oligonucleotide hybridization demonstrated that the mutation associated with haplotype 4 was the same IVS-1 position 5 substitution commonly observed among beta-thalassemia genes in Asian Indians. Since haplotype 4 of Chinese differs at polymorphic sites on either side of the IVS-1 position 5 mutation from the haplotype associated with this mutation in Indians, the mutation presumably arose independently in these two populations.

beta-Thalassemia in American Blacks: novel mutations in the "TATA" box and an acceptor splice site

beta-Thalassemia genes, although often mild in their effects, are common among American Blacks. We have begun a systematic molecular analysis of beta-thalassemia mutations in this group. DNA polymorphisms in the beta-globin gene cluster were examined among 22 beta-thalassemia chromosomes. Six different haplotypes were observed. beta-globin genes of two of these were cloned, and their phenotypes were examined both in heterologous cells upon transient expression and in vivo. The gene found in the most common haplotype (9 of 22 chromosomes) contained a single base substitution (A----G) at position -29 within the highly conserved proximal promoter element (the "TATA" box). This mutant gene directed beta-globin RNA at 25% of normal levels both in heterologous cells and in vivo. It was associated with a mild beta +-thalassemia phenotype. A different gene, isolated from an apparently rare haplotype (1 of 22 chromosomes), had a single base substitution (A----G) within the acceptor splice site of the second intervening sequence. This mutation abolished normal RNA splicing so that the only RNA made from the gene in vitro was an alternatively spliced RNA, which could not encode beta-globin. The mild deficit in beta-globin production attributable to the -29 A----G mutant allele most likely accounts for the frequently mild nature of beta-thalassemia among American Blacks.

Etiology of growth hormone deficiency in little, Ames, and Snell dwarf mice

There are three recessive genes (little, Snell, and Ames) which cause dwarfism and GH deficiency in mice. These genes are nonallelic, and in the case of little mice, GH deficiency is isolated, while Snell and Ames dwarfs have deficiencies of GH as well as other anterior pituitary hormones. Previous reports in which restriction endonuclease analyses were used suggested that the GH genes are grossly intact in each of these types of dwarfs. In this report, ultrastructural studies of the anterior pituitary glands of little mice showed a deficiency or absence of secretory granules within somatotropes, while Snell and Ames dwarf pituitaries lacked identifiable somatotropes. Furthermore, there were deficiencies of GH precursor RNA and mRNA in total RNA from little pituitaries, while GH transcripts appeared to be absent in total RNA from Snell or Ames dwarf pituitaries. Thus, the primary defect in little mice may be in the production of GH transcripts, while GH deficiency in Snell and Ames dwarfs is probably due to defects other than alterations of the GH genes.

ATA box transcription mutation in beta-thalassemia

DNA sequence analysis of a cloned beta-globin gene from a Chinese patient with beta-thalassemia revealed a single nucleotide substitution (A leads to G) within the ATA box homology and 28 base pairs upstream from the cap site. The patient was homozygous for this particular allele based on restriction mapping at nine different polymorphic sites in the beta-globin gene cluster. Upon transient expression in HeLa cells this gene directed the production of 3-5-fold less beta-globin mRNA than the normal beta-gene. In RNA isolated from the patient's erythroid cells beta-RNA was 10-fold less abundant relative to alpha-RNA than normal, indicating close approximation of the heterologous cell expression results and the in vivo state. These findings support the validity of such transient expression assays for analysis of phenotypes associated with naturally occurring mutant genes and establish the functional significance of nucleotide substitutions at position -28 for human beta-globin gene transcription.

Missed large left ventricular thrombus. Failure of two-dimensional echocardiography in one case

In the case reported, two-dimensional echocardiographic study of a man six weeks after he sustained an extensive transmural anterolateral infarct failed to show evidence of an intraventricular thrombus. Ten days later the patient suddenly died. Autopsy findings included a large fibrin clot, weighing 50 gm, in the left ventricle. Two-dimensional echocardiography is a very sensitive method of defining aneurysm in the apex of the heart and identifying and locating ventricular thrombi usually associated with aneurysm. I consider the false-negative finding in this case to be a rare exception.

Electrical alternans. An association with coronary artery spasm

A patient's condition was unique for having both QRS- and ST-segment alternans. The close association between ST-segment alternans and ischemic episodes is reproducible in an animal experimental study. Although such phenomena are usually associated with extensive myocardial disease, the postulated mechanism is far from perfected. It is more than likely that no single hypothesis will explain all types of phasic cardiac electrical phenomena.

Severe chest pain due to infectious mononucleosis

Infectious mononucleosis complicated by acute myopericarditis was finally diagnosed in a 17-year-old boy who presented with sore throat and severe left-sided chest pain. A mononucleosis spot test and heterophil agglutination test turned strongly positive only on the sixth hospital day. The natural course of infectious mononucleosis complicated by myopericarditis appears to be benign.

Refractory left ventricular failure: use of two-dimensional echocardiography in identification of thrombi

A 65-year-old woman was hospitalized several times after having an acute anteroseptal transmural infarction. Her course was complicated by recurrent ventricular tachycardia and severe left ventricular failure. Chest x-ray films showed pulmonary congestion and mild right pleural effusion. Two-dimensional echocardiography revealed a large left ventricular thrombus, which resolved after two months of treatment. The course of anticoagulation was later complicated by massive gastrointestinal hemorrhage. Finally, the patient died in her sleep, probably as a result of arrhythmia. An autopsy revealed extensive left ventricular mural thrombi. The early identification of left ventricular thrombus by two-dimensional echocardiography has lifesaving implications. It is possible that, with proper medical management, further formation of pulmonary emboli could be prevented.

Thrombocytopenia associated with minidose heparin therapy

Thrombocytopenia developed in an elderly woman who was being treated for an impacted fracture of the right femoral neck. The complication was attributed to heparin because the platelet count decreased each time the drug was administered, and when the drug was stopped, the count increased. By the time of death, the patient's platelet count had dropped to 30,000/cu mm. This case is presented to alert physicians to the possibility of thrombocytopenia with the prophylactic use of minidose heparin.