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Bloom's syndrome (BS) and EM9 cells both display elevated frequencies of sister chromatid exchange (SCE) following growth for two rounds of DNA replication in bromodeoxyuridine (BrdU)-containing medium. To learn whether hyperresponsiveness to BrdU itself might play a role in causing the SCE elevation, the effects of BrdU on two other parameters, cellular proliferation and chromosome disruption, were examined, comparing the responses of BS and normal lymphoblastoid cells and of EM9 and CHO cells. BS and normal cells responded similarly with respect to growth for 4 days in BrdU-containing medium (0, 1, 3, and 5 micrograms/ml). Chromosome aberrations were increased only slightly in the BS and normal cells after 2 days in BrdU. CHO cells responded to growth in BrdU-containing medium like BS and normal cells; however, little growth of EM9 was detected at any of the BrdU concentrations employed. CHO and EM9 cells also exhibited strikingly different amounts of chromosome damage following growth in BrdU. After 2 days in 1, 3, and 5 micrograms/ml BrdU 21%, 46%, and 50%, respectively, of the CHO cells had chromosome aberrations in contrast to 92%, 96%, and 98% of the EM9 cells. Most of the aberrations in the BrdU-treated CHO cells consisted of what appeared to be polycentric and ring chromosomes or chromosomes exhibiting telemere association. Acentric fragments were absent from most cells with polycentric and ring chromosomes, indicating either that the abnormal chromosomes were formed during an earlier cell cycle or that the abnormal chromosomes represent a form of association in which the telomeres are apposed so tightly that the juncture between chromosomes cannot be identified microscopically.(ABSTRACT TRUNCATED AT 250 WORDS)

Bloom's syndrome (BS) is a rare autosomal recessive hereditary disorder associated with pre- and postnatal growth deficiency, a characteristic facial configuration, an increased risk of chromosome instability, and an increased risk of neoplasia. BS is often lumped together with Fanconi's anaemia, ataxia telangiectasia and xeroderma pigmentosum, known as "chromosome instability syndromes". Since 1954, when Bloom's syndrome was defined, more then 100 cases have been diagnosed. The "Bloom's Syndrome International Registry" does not include any case detected in Argentina. Here, we report the cytogenetic study of a family affected by BS. Two siblings were studied. A 10-year-old boy named DaYu and a 17-year-old sister named CeYu. Both showed growth retardation from one month of age onwards, facial configuration characteristic, erythematous and sun-sensitive lesions of the skin of the face. To confirm the BS diagnosis of both, obtained from their clinical aspects, they were referred to our cytogenetic laboratory. Standard cultures of peripheral blood from DaYu and CeYu (homozygotes bl/bl) and their parents (heterozygotes bl/+) were performed for sister chromatid exchange (SCE) study. A group of 3 healthy donors (homozygotes +/+) was added for spontaneous and induced chromosomal aberration (CA) analysis. For the SCE study, bromodeoxyuridine was present in the cultures and slides were stained using the fluorescence plus Giemsa technique. For the analysis of induced CA, diepoxybutane (DEB) 0.1 microgram/mL was added 48 hours before harvesting. Both patients had a spontaneously increased rate of sister-chromatid exchanges (71.3 +/- 28.2 for DaYu and 76.9 +/- 37.9 for CeYu) similar to that found in Bloom's syndrome homozygotes.(ABSTRACT TRUNCATED AT 250 WORDS)

Three types of Bloom syndrome B-lymphoblastoid cell lines, as well as one derived from a normal person, treated with 4-nitroquinoline-N-oxide and N-methyl-N'-nitro-N-nitrosoguanidine (0.3 micrograms/ml for 24 hr), were studied for tumorigenicity in nude mice, colony formation in soft agar, cytogenetic changes, and immunoglobulin markers. When normal and Bloom syndrome cells with normal sister chromatid exchange (SCE) levels and karyotypes (type I) were treated with carcinogens, no significant changes occurred in the immunoglobulin profile and karyotype, only rare colony formation was seen, and no tumors were produced. In contrast, when Bloom syndrome cells with high SCE levels (type II with normal karyotype and type III with an abnormal karyotype) were treated with carcinogens, tumors were produced in 22 of 53 nude mice injected; a high rate of colony formation in soft agar was seen; the cells exhibited virtual loss of immunoglobulin markers; and structural changes in chromosomes 1, 2, 3, 4, 5, 7, 11, 14, and 15 were found in the tumors in addition to the original chromosome abnormalities present in the injected cells. It appears that Bloom syndrome B-lymphoblastoid cell lines with high levels of SCE are highly susceptible to the action of carcinogens, as evidenced by tumor formation in nude mice and colony formation in agar. Apparently, the carcinogens were capable of transforming only those cells that had a critical level of SCE (approximately 140 per cell) and not those with only mildly increased levels (approximately 13 per cell).

Experimental hybridization of cultured cells was employed to determine whether the strikingly elevated rates of sister-chromatid exchange (SCE) exhibited by Bloom's syndrome (BS) and hamster cell line EM9 have the same or different bases. Seventeen cell lines were developed from polyethylene glycol-treated mixtures of BS and EM9 cells. Cytogenetic analysis proved the hybrid nature of 12 of the lines; 9 of those 12 exhibited low (normal) numbers of SCEs, signifying complementation. The parental BS and EM9 cells, although resembling each other in exhibiting very high SCE frequencies in BrdUrd-containing medium, differ from one another with respect to their proliferative abilities in such medium, the EM9 cells but not the BS cells being exquisitely hypersensitive to BrdUrd. In the low-SCE hybrid lines, hypersensitivity to growth in BrdUrd-containing medium was restored to normal whereas the hypersensitivity was retained by the high-SCE hybrids. It is concluded, first, that the mutations in BS and EM9 cells are different and, second, that both the elevated SCE frequency and the excessive BrdUrd hypersensitivity of EM9 cells are due to the same mutation.

The effects of the carcinogens (4NQO, 4-nitroquinoline-N-oxide; MNNG, N-methyl-N'-nitro-N-nitrosoguanidine; AFLG1, aflatoxin G1; AFLB1, aflatoxin B1; BNU, butylnitrosourea; MNU, methylnitrosourea) and the tumor promoter (TPA, 12-O-tetradecanoylphorbol-13-acetate) on sister chromatid exchanges (SCE), chromosome aberrations and colony formation (CF) were examined in three types of Bloom syndrome (BS) B-lymphoblastoid cell lines (B-LCLs); type I with normal SCE and normal karyotype; type II with high SCE and normal karyotypes; type III with high SCE and abnormal karyotypes. BS type I cells had the same SCE and CF response as normal cells to these carcinogens and TPA. In BS type II and III cells treated with carcinogens the SCE frequency increased to 140/cell from a baseline of 70/cell versus an increase of only 10/cell in normal cells. Colony formation occurred at the concentrations that caused the highest SCE. TPA caused a significant SCE increase and highly enhanced CF with dose dependency only in type III cells, suggesting that type III cells may be already in a pre-malignant state; type II cells appear to be one step behind those of type III in the process of becoming malignant. BS type II and III cells may be usable to establish a sensitive system to detect SCE-inducing agents.