Bloom's syndrome

D1Z2 is a highly polymorphic DNA locus composed of a tandem of repetitive units. Its molecular constitution has been examined in 61 clonal cell lines selected at random from two lymphoblastoid cell lines (LCLs), each of which had been proliferating in vitro for several hundred days. Thirty-three of the cells were selected from an LCL derived from the blood of a person with Bloom's syndrome (BS), and the others from a normal person. A total of 20 distinctive band alterations in D1Z2 were observed, all in BS cells: appearance of a novel band(s); disappearance of a band(s), or alterations in the intensity of a band(s). Unequal sister-chromatid exchange giving rise to intra-locus mutation is considered the most plausible explanation for the accumulation of the changes detected.This paper is dedicated to Ulrich Wolf on his 60th birthday and acknowledges his important contributions to human biology     

Bloom's syndrome

Summary The biochemical defect in Bloom's syndrome (BS) remains unknown, but two characteristic features of BS cells point to a disturbance of DNA replication, namely, an excessive number of sister-chromatid exchanges (SCEs) in bromodeoxyuridine (BrdU)-substibuted cells and an abnormally slow rate of replicon elongation. The hypothesis of an abnormal DNA polymerase as the explanation for these observations was tested using an in situ assay system for DNA polymerase activity and to estimate molecular weights in cellular extracts of cultured BS cells. DNA polymerase subunits in cellular extracts from the BS cells when separated electrophoretically on polyacrylamide gels showed the same mobilities (i.e., molecular weights) as the controls and were equally effective at promoting the incorporation of isotopically labeled nucleosides. It is concluded that the genetic defect in BS has no direct effect on either DNA-polymerase activity or the amounts and molecular weights of the different forms of the enzyme.     

Effects of X-irradiation in G1 and G2 on Bloom's syndrome and normal chromosomes

Summary The X-ray sensitivity of chromosomes from a Bloom's syndrome patient and a normal control was compared in G₁ and G₂. There was no significant difference in the number of aberrations induced by irradiation in G₁. An increased sensitivity of the BS chromosomes was found in G₂. The frequency of mitotic chiasmata in the BS cells was not increased by the G₂-irradiation, even though the frequency of chromatid translocations was much increased. This provides further evidence for the fundamental difference of these two phenomena. Evidence from the types of aberrations induced suggests that there is no appreciably increased frequency of pairing of homologous chromosomes in the BS cells over that in normal cells.     

Cancer predisposition in Bloom's syndrome.

This article focuses upon defining those factors which may contribute to the pathogenesis of cancer. The molecular basis of tumour etiology is discussed with reference to cancer predisposing syndromes, and in particular to the human inherited disease, Bloom's syndrome. In Bloom's syndrome, patients are predisposed to a wide variety of malignant disease. We propose a model in which overexpression of the ubiquitous c-myc proto-oncogene contributes to this process.     

DNA synthesis in Bloom's syndrome fibroblasts

The relationship between relative rates of DNA synthesis and DNA content in Bloom's syndrome fibroblasts (BS cells) was investigated by flow cytometry. The cells were pulse labelled with 5-bromo-2'-deoxyuridine (BrdU). The BrdU content and cellular DNA content of individual BS cells were simultaneously measured by flow cytometry in which the cells were double-stained by a FITC-conjugated anti BrdU monoclonal antibody (mAb) for the BrdU content (green) and by PI (propidium iodide) (red) for total DNA content. Their red fluorescence histograms were analysed by a microcomputer to evaluate the cell fractions of each S compartment. The BrdU uptake in the early S phase of BS cells was lower than that of normal cells (fibroblasts from skin of a normal human), whereas the uptake in the middle and late S phase was essentially the same as that of normal cells. The early S phase in BS cells accounted for over 50% of the S phase cells. These findings suggest that, in comparison with normal cells, the rate of DNA synthesis in the early S phase of BS cells is lower, but is identical to controls in the middle and late S phases.     

DNA synthesis in Bloom's syndrome fibroblasts

Abstract. The relationship between relative rates of DNA synthesis and DNA content in Bloom's syndrome fibroblasts (BS cells) was investigated by flow cytometry. The cells were pulse labelled with 5-bromo-2'-deoxyuridine (BrdU). The BrdU content and cellular DNA content of individual BS cells were simultaneously measured by flow cytometry in which the cells were double-stained by a FITC-conjugated anti BrdU monoclonal antibody (mAb) for the BrdU content (green) and by PI (propidium iodide) (red) for total DNA content. Their red fluorescence histograms were analysed by a microcomputer to evaluate the cell fractions of each S compartment. The BrdU uptake in the early S phase of BS cells was lower than that of normal cells (fibroblasts from skin of a normal human), whereas the uptake in the middle and late S phase was essentially the same as that of normal cells. The early S phase in BS cells accounted for over 50% of the S phase cells. These findings suggest that, in comparison with normal cells, the rate of DNA synthesis in the early S phase of BS cells is lower, but is identical to controls in the middle and late S phases.     

The Bloom's syndrome helicase: keeping cancer at bay

Bloom's syndrome, a very rare inherited disorder, predisposes its sufferers to the full range of cancers that afflict humanity. This predisposition is rooted in just one defective gene on chromosome 15. It encodes the BLM helicase - an enzyme that ordinarily protects against DNA damage arising during replication.     

The Bloom's syndrome gene product interacts with topoisomerase III

Bloom's syndrome is a rare genetic disorder associated with loss of genomic integrity and a large increase in the incidence of many types of cancer at an early age. The Bloom's syndrome gene product, BLM, belongs to the RecQ family of DNA helicases, which also includes the human Werner's and Rothmund-Thomson syndrome gene products and the Sgs1 protein of Saccharomyces cerevisiae. This family shows strong evolutionary conservation of protein structure and function. Previous studies have shown that Sgs1p interacts both physically and genetically with topoisomerase III. Here, we have investigated whether this interaction has been conserved in human cells. We show that BLM and hTOPO IIIalpha, one of two human topoisomerase III homologues, co-localize in the nucleus of human cells and can be co-immunoprecipitated from human cell extracts. Moreover, the purified BLM and hTOPO IIIalpha proteins are able to bind specifically to each other in vitro, indicating that the interaction is direct. We have mapped two independent domains on BLM that are important for mediating the interaction with hTOPO IIIalpha. Furthermore, through characterizing a genetic interaction between BLM and TOP3 in S. cerevisiae, we have identified a functional role for the hTOPO IIIalpha interaction domains in BLM.     

Hypersensitivity of Bloom's syndrome fibroblasts to N-ethyl-N-nitrosourea

Fibroblast cells from two Japanese patients with Bloom's syndrome (BS) and normal donors were studied for the inactivation of colony-forming ability and the induction of sister-chromatid exchanges (SCEs) after N-ethyl-N-nitrosourea (ENU) treatment. The reduction of ENU-induced SCEs as a function of post-treatment incubation time was also compared between BS and normal fibroblasts. BS cells were approximately 4 times more sensitive than normal cells to the lethal effect of ENU and remarkably hypersensitive to the SCE induction by ENU. The post-treatment incubation of ENU-treated normal cells in the fresh medium resulted in a time-dependent decrease of the SCE level until 6 h after which time the SCE level remained the plateau of about 50% of the initial level. In contrast, the ENU-induced SCEs in BS cells decreased much more slowly with post-treatment incubation time and its half life was 24 h. These results collectively support the view that BS cells may be defective in the rapid repair of certain type(s) of DNA damages induced by ENU.     

Bloom's syndrome in an Iranian Jewish male.

Bloom's syndrome is described in an Iranian Jewish male who subsequently developed myocardial disease. This may represent the first definitely non Ashkenazi Jewish patient in the literature and the only one to develop this complication.     

Normal uracil-DNA glycosylase activity in Bloom's syndrome cells

Cells from patients with Bloom's syndrome, a rare human disease with autosomal recessive mode of inheritance, exhibit cytological abnormalities involving DNA metabolism. Bloom's syndrome is characterized by a greatly increased cancer frequency which may reflect a specific defect in DNA repair and replication. Evidence has recently been presented of the existence in Bloom's syndrome of an abnormality of the DNA ligase involved in semiconservative DNA replication. Another abnormality, in the excision-repair pathway of Bloom's syndrome cells, is reportedly due to an aberrant immunological reactivity of the DNA-repair enzyme uracil-DNA glycosylase. In this investigation we show, however, that the catalytic activity of uracil-DNA glycosylase appears to be normal in Bloom's syndrome lymphoblastoid cells.     

Bloom's syndrome in a 12-year-old Iranian girl

BACKGROUND:

Bloom''s syndrome, an autosomal recessive inherited disorder, belongs to the group of chromosomal breakage syndromes. The clinical diagnosis of BS is confirmed cytogenetically. Its frequency in the general population is unknown but it is common in eastern European Ashkenazi Jews.

CASE REPORT:

A 12-year-old girl was referred to us because of short stature. She was the second child of the first cousin marriage. She had a slender body frame, short stature, and microcephaly. Her face was long and narrow with prominent nose, and malar and mandibular hypoplasia. The spots of hyper and hypo pigmentation were observed in the trunk and limbs. Telangectasia spots were observed in some areas of the trunk. Additionally, generalized hirsutism was present in the whole body. Cytogenetic findings revealed an abnormality in the structural chromosome.

CONCLUSION:

This is the first BS case that has been reported in Iranian female population.     

Cytogenetic investigations in a new case of Bloom's syndrome

Summary Cytogenetic studies of an 8-year-old caucasian girl with typical but mild manifestation of Bloom's syndrome showed a characteristic increase of homologous chromatid translocations and prematurely condensed chromosomes. The average frequency of sister chromatid exchanges (SCE) in lymphocytes with 133 was much higher than in skin fibroblasts with 49. The inter- and intrachromosomal distributions of SCE in lymphocytes were analyzed.Prof. Dr. H.-R. Wiedemann to his 60th birthday.     

The Bloom's syndrome helicase stimulates the activity of human topoisomerase IIIalpha

Bloom’s syndrome (BS) is a disorder associated with chromosomal instability and a predisposition to the development of cancer. The BS gene product, BLM, is a DNA helicase of the RecQ family that forms a complex in vitro and in vivo with topoisomerase IIIα. Here, we show that BLM stimulates the ability of topoisomerase IIIα to relax negatively supercoiled DNA. Moreover, DNA binding analyses indicate that BLM recruits topoisomerase IIIα to its DNA substrate. Consistent with this, a mutant form of BLM that retains helicase activity, but is unable to bind topoisomerase IIIα, fails to stimulate topoisomerase activity. These results indicate that a physical association between BLM and topoisomerase IIIα is a prerequisite for their functional biochemical interaction.     

The Bloom's syndrome helicase promotes the annealing of complementary single-stranded DNA

The product of the gene mutated in Bloom's syndrome, BLM, is a 3′–5′ DNA helicase belonging to the highly conserved RecQ family. In addition to a conventional DNA strand separation activity, BLM catalyzes both the disruption of non-B-form DNA, such as G-quadruplexes, and the branch migration of Holliday junctions. Here, we have characterized a new activity for BLM: the promotion of single-stranded DNA (ssDNA) annealing. This activity does not require Mg²⁺, is inhibited by ssDNA binding proteins and ATP, and is dependent on DNA length. Through analysis of various truncation mutants of BLM, we show that the C-terminal domain is essential for strand annealing and identify a 60 amino acid stretch of this domain as being important for both ssDNA binding and strand annealing. We present a model in which the ssDNA annealing activity of BLM facilitates its role in the processing of DNA intermediates that arise during repair of damaged replication forks.     

Mitotic recombination and segregation of satellites in Bloom's syndrome

Mitotic recombination in satellite stalks — a phenomenon often difficult to distinguish from satellite association — was studied in a sister and a brother with Bloom's syndrome. Segregation after recombination was analyzed in the lymphocytes of the sister who had Q-bright satellites. Her cells varied greatly both in regard to the acrocentrics which displayed Q-bright satellites and the number of such satellites per cell. In 58 cells a total of 31 different patterns were seen. In 83 cells of 6 controls who also had Q-bright satellites on at least one acrocentric chromosome, not one cell was found in which the pattern differed from that characteristic of the person. Obviously exchanges between satellite stalks in patients with Bloom's syndrome are fairly frequent (estimated lower limit 6/1000) and very rare in persons who do not have this syndrome (estimated 0.1/1000).     

Bloom's syndrome: the German experience.

Ten patients with Bloom's syndrome observed in Germany during the last 20 years are described. They were born between 1964 and 1986. Seven are alive at the age of 8 to 27 years. Three have died at the age of 5 years (acute leukemia), 18 years (pulmonary fibrosis and bronchiectasis), and 21 years (Hodgkin lymphoma and subsequently leukemia). All show the characteristic clinical and cellular phenotype. In addition to the known early occurrence of malignancies, certain behavioral patterns, the occurrence of hyper- and hypopigmented areas in the skin, pulmonary manifestations, and exquisite sensitivity to chemotherapy and probably also to radiotherapy are emphasized. The potential usefulness of bone marrow preservation for later use in autologous transplantation has not yet been determined. Several features of Bloom's syndrome can be understood on the basis of a genetically determined high rate of somatic recombination.     

Sensitivity of Bloom's syndrome lymphocytes to ethyl methanesulfonate

Summary Ethyl methanesulfonate induced several times as many sister chromatid exchanges (SCEs) in lymphocytes from individuals affected with Bloom's syndrome as in lymphocytes from controls or heterozygotes. In cultures of cells from an individual with Bloom's syndrome who had two populations of lymphocytes circulating in his blood—low cells having normal spontaneous frequencies of SCEs and high cells having elevated frequencies—only the high cells showed the increased sensitivity to ethyl methanesulfonate.To whom offprint requests should be sent