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Asher RC, Jakstas T, Lavelle F, Wolfson JA, Rose A, Bucher T, Dean M, Duncanson K, van der Horst K, Schonberg S, Slater J, Compton L, Giglia R, Fordyce-Voorham S, Collins CE, Shrewsbury VA. Development of the Cook-EdTM Matrix to Guide Food and Cooking Skill Selection in Culinary Education Programs That Target Diet Quality and Health. Nutrients 2022; 14:nu14091778. [PMID: 35565746 PMCID: PMC9103694 DOI: 10.3390/nu14091778] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2022] [Revised: 04/08/2022] [Accepted: 04/18/2022] [Indexed: 12/04/2022] Open
Abstract
Culinary education programs are generally designed to improve participants’ food and cooking skills, with or without consideration to influencing diet quality or health. No published methods exist to guide food and cooking skills’ content priorities within culinary education programs that target improved diet quality and health. To address this gap, an international team of cooking and nutrition education experts developed the Cooking Education (Cook-EdTM) matrix. International food-based dietary guidelines were reviewed to determine common food groups. A six-section matrix was drafted including skill focus points for: (1) Kitchen safety, (2) Food safety, (3) General food skills, (4) Food group specific food skills, (5) General cooking skills, (6) Food group specific cooking skills. A modified e-Delphi method with three consultation rounds was used to reach consensus on the Cook-EdTM matrix structure, skill focus points included, and their order. The final Cook-EdTM matrix includes 117 skill focus points. The matrix guides program providers in selecting the most suitable skills to consider for their programs to improve dietary and health outcomes, while considering available resources, participant needs, and sustainable nutrition principles. Users can adapt the Cook-EdTM matrix to regional food-based dietary guidelines and food cultures.
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Affiliation(s)
- Roberta C. Asher
- School of Health Sciences, College of Health, Medicine and Wellbeing, The University of Newcastle, Callaghan, NSW 2308, Australia; (R.C.A.); (T.J.); (A.R.); (C.E.C.)
- Hunter Medical Research Institute, New Lambton Heights, NSW 2305, Australia; (T.B.); (K.D.)
| | - Tammie Jakstas
- School of Health Sciences, College of Health, Medicine and Wellbeing, The University of Newcastle, Callaghan, NSW 2308, Australia; (R.C.A.); (T.J.); (A.R.); (C.E.C.)
- Hunter Medical Research Institute, New Lambton Heights, NSW 2305, Australia; (T.B.); (K.D.)
| | - Fiona Lavelle
- School of Biological Sciences, Institute for Global Food Security, Queen’s University Belfast, Belfast BT9 5DL, UK; (F.L.); (M.D.)
| | - Julia A. Wolfson
- Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205, USA;
- Department of Health Policy and Management, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205, USA
- Department of Health Management and Policy, School of Public Health, University of Michigan, Ann Arbor, MI 48109, USA
| | - Anna Rose
- School of Health Sciences, College of Health, Medicine and Wellbeing, The University of Newcastle, Callaghan, NSW 2308, Australia; (R.C.A.); (T.J.); (A.R.); (C.E.C.)
- Hunter Medical Research Institute, New Lambton Heights, NSW 2305, Australia; (T.B.); (K.D.)
| | - Tamara Bucher
- Hunter Medical Research Institute, New Lambton Heights, NSW 2305, Australia; (T.B.); (K.D.)
- School of Environmental and Life Sciences, College of Engineering, Science and Environment, The University of Newcastle, Callaghan, NSW 2308, Australia
| | - Moira Dean
- School of Biological Sciences, Institute for Global Food Security, Queen’s University Belfast, Belfast BT9 5DL, UK; (F.L.); (M.D.)
| | - Kerith Duncanson
- Hunter Medical Research Institute, New Lambton Heights, NSW 2305, Australia; (T.B.); (K.D.)
- School of Medicine and Public Health, College of Health Medicine and Wellbeing, The University of Newcastle, Callaghan, NSW 2308, Australia
| | - Klazine van der Horst
- School of Health Professions, Bern University of Applied Sciences, 3012 Bern, Switzerland; (K.v.d.H.); (S.S.)
| | - Sonja Schonberg
- School of Health Professions, Bern University of Applied Sciences, 3012 Bern, Switzerland; (K.v.d.H.); (S.S.)
| | - Joyce Slater
- Department of Food and Human Sciences, Faculty of Agricultural and Food Sciences, University of Manitoba, Winnipeg, MB R3T 2N2, Canada;
| | - Leanne Compton
- Victorian Curriculum and Assessment Authority, Melbourne, VIC 3000, Australia;
| | - Roslyn Giglia
- Foodbank Western Australia, Perth, WA 6105, Australia;
| | | | - Clare E. Collins
- School of Health Sciences, College of Health, Medicine and Wellbeing, The University of Newcastle, Callaghan, NSW 2308, Australia; (R.C.A.); (T.J.); (A.R.); (C.E.C.)
- Hunter Medical Research Institute, New Lambton Heights, NSW 2305, Australia; (T.B.); (K.D.)
| | - Vanessa A. Shrewsbury
- School of Health Sciences, College of Health, Medicine and Wellbeing, The University of Newcastle, Callaghan, NSW 2308, Australia; (R.C.A.); (T.J.); (A.R.); (C.E.C.)
- Hunter Medical Research Institute, New Lambton Heights, NSW 2305, Australia; (T.B.); (K.D.)
- Correspondence: ; Tel.: +61-4921-7860
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Jenkins EC, Brown WT, Schonberg S, Krawczun MS, Goldberg J, Golbus MS. Prenatal detection of fra(X)(q27.3) in female identical twins: reliability of low level cytogenetic prenatal expression in females. Am J Med Genet 1992; 43:128-35. [PMID: 1605181 DOI: 10.1002/ajmg.1320430120] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
UNLABELLED Recently, we detected fra(X)(q27.3) in amniocyte cultures from female identical twins. The pregnant woman did not exhibit fra(X)(q27.3) in whole blood cultures but was the sister of 2 affected brothers. DNA marker analyses showed that she was a carrier of FRAXA. Amniotic fluid cultures (AFCs) from twins A and B exhibited the fragile X [fra(X)] chromosome, but the level of cytogenetic expression was very low in twin A's AFCs. DNA marker studies indicated both twins were carriers of FRAXA. Peripheral umbilical blood sample (PUBS) cultures exhibited fra(X)(q27.3) at a frequency of about 10% for both twins. DNA fingerprinting indicated that the twins were identical, confirming the clinical impression, with a very thin separating amniotic membrane. To our knowledge, this is the only report of prenatal fra(X)(q27.3) detection in female identical twins, and the second report of identical twin detection [Rocchi et al., 1985]. We have diagnosed prenatally fra(X)(q27.3) in 5 female fetuses using AFCs. The average fra(X) frequency was 4% for these positive female fetuses with a range of 0.5% to 8.5%. Follow-up whole blood studies confirmed our original results at an average fra(X) frequency of 25%. IN CONCLUSION 1. Low frequencies, perhaps 1 or 2%, or a few positive cells in AFCs, are likely to increase in magnitude when confirmed in whole blood cultures either pre- or postnatally. 2. It appears likely that the risk is low for false positive results in AFCs when low frequencies of fra(X)(q27.3) are encountered.
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Affiliation(s)
- E C Jenkins
- Department of Genetics, New York State Institute for Basic Research in Developmental Disabilities Staten Island 10314
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Jenkins EC, Brown WT, Krawczun MS, Duncan CJ, Lele KP, Cantu ES, Schonberg S, Golbus MS, Sekhon GS, Stark S, Kunaporn S, Silverman WP. Recent experience in prenatal fra(X) detection. Am J Med Genet 1988; 30:329-36. [PMID: 2972205 DOI: 10.1002/ajmg.1320300133] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
At least 35 cases of prenatal fra(X) diagnosis have been confirmed and reported. Amniotic fluid, fetal blood and chorion -ic villus samples have exhibited fra(X) (q27.3) in cultures from 26 males and 9 females. Here we have detected fra(X) in female and male amniotic fluid specimens, AF1/fra(X),X and AF2/fra(X),Y, respectively, and a male CVS/fra(X),Y using both FUdR and excess thymidine (THY) to demonstrate the marker chromosome. Both FUdR and THY detected fra(X) and usually FUdR was superior to THY with the exception of placental cultures. It was important to examine more than one culture per protocol since no fra(X) was observed in one AF2 FUdR culture while another exhibited 19.2% expression. Similarly, confirmation studies in lung fibroblast cultures for AF2 exhibited 4.3% fra(X) in one lab while another found negative results. A similar observation in whole blood cultures was also made recently by us. In addition, we have recently experienced our first false negative fra(X),X prenatal diagnosis. We have observed another case where only one cell in 300 exhibited fra(X) where the male fetus was 50% at-risk and was referred to us after the 20th week of gestation by sonography. On the basis of our experience we recommend the following: 1) the excess THY fra(X) induction system is effective but not superior to FUdR; 2) at least two duplicate cultures per induction system should be analyzed for the marker chromosome to avoid the possibility of false-negative diagnosis; 3) where fra(X) is not demonstrated or is present in very low frequencies in CVS and/or amniotic fluid cultures, complementary DNA marker studies and/or fetal blood cultures must be made available; 4) gestational age dating by ultrasonography is recommended as early as possible.
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Affiliation(s)
- E C Jenkins
- Institute for Basic Research, New York State Office of Mental Retardation and Developmental Disabilities, Staten Island 10314
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Gray JW, Trask B, van den Engh G, Silva A, Lozes C, Grell S, Schonberg S, Yu LC, Golbus MS. Application of flow karyotyping in prenatal detection of chromosome aberrations. Am J Hum Genet 1988; 42:49-59. [PMID: 3337112 PMCID: PMC1715321] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
This paper describes the application of bivariate flow karyotyping to (1) classification of chromosomes isolated from cultures of cells taken by amniocentesis and (2) detection of numerical and structural aberrations. Chromosomes were isolated from primary cultures 2-5 wk after amniocentesis, stained with Hoechst 33258 and chromomycin A3, and analyzed using dual beam flow cytometry. Information about chromosome DNA content and DNA base composition was derived from the locations of the peaks in the flow karyotypes, each peak being produced by one or more chromosome types with similar DNA content and DNA base composition. Information about the relative frequency of each chromosome type was determined on the basis of the relative volume of the peak for that chromosome type. Cytogenetic information determined on the basis of flow karyotypes was compared with that obtained by visual analysis following G-banding. Variability among the peak means and volumes in flow karyotypes was determined from analyses of 50 normal amniocyte cultures. Numerical aberrations involving chromosomes 21, 18, and Y were detected correctly in all of 28 analyses, including eight in a blind study. Structural aberrations involving chromosomes 1, 2, 3, 6, 9-12, 13, 14, 15, 21, and 22 were detected in all of seven cultures in a blind study. Flow karyotypes proved to be insensitive to small, normally occurring chromosome polymorphisms detected by banding analysis. In addition, a few samples were erroneously scored as having numerical aberrations.
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Affiliation(s)
- J W Gray
- Lawrence Livermore National Laboratory, Biomedical Sciences Division, Livermore, CA 94550
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Johnston K, Schonberg S, Littman V, Gregory T, Gelbart S, O'Donnell J, Cox DR. De novo X;Y translocation associated with imperforate anus and retinal pigmentary abnormalities. Am J Med Genet 1987; 27:603-11. [PMID: 3631132 DOI: 10.1002/ajmg.1320270313] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Cytogenetically detectable translocations of Y chromosome material onto the distal short arm of an X chromosome are rare and result in a variable and poorly defined phenotype of short stature and short limbs occasionally associated with mental retardation. We report on a patient with a de novo 46,X,t(X;Y)(p22;q11) chromosome constitution who has additional features not previously described with this chromosome abnormality, including abnormal retinal pigmentation, imperforate anus, and hydronephrosis. Our patient extends the phenotype associated with X;Y translocations, raising new considerations for the clinical management and genetic counseling of such patients and their families.
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German J, Schonberg S, Caskie S, Warburton D, Falk C, Ray JH. A test for Fanconi's anemia. Blood 1987; 69:1637-41. [PMID: 3107630] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
A simple and reliable cytogenetic test for Fanconi's anemia (FA) that is based on the hypersensitivity of FA cells to mitomycin C (MC) is described. Equal volumes of whole blood from a patient in whom the diagnosis of FA is suspected and from a normal person of the opposite sex are co-cultured in phytohemagglutinin-containing medium in the presence and absence of MC. After five days' co-cultivation, 100 quinacrine-stained metaphases from both the MC-containing and the MC-free cultures are examined for the presence of a Y chromosome using fluorescence microscopy. In all bona fide FA patients in whom testing was successful, hypersensitivity to MC was readily demonstrated by the striking deficiency of FA metaphases (0.9% to 14.9%) in the MC-containing co-cultures. In contrast, none of the three patients with Diamond-Blackfan anemia and none of the five with undiagnosed conditions reminiscent of FA exhibited hypersensitivity to MC; cells from them, from parents of FA patients, and from several normal laboratory personnel constituted approximately half of the metaphases (40.4% to 71.2%) of MC-containing co-cultures, as would be expected in the absence of hypersensitivity to MC.
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Hogge DE, Shannon KM, Kalousek DK, Schonberg S, Schaffner V, Zoger S, Eaves CJ, Eaves AC. Juvenile monosomy 7 syndrome: evidence that the disease originates in a pluripotent hemopoietic stem cell. Leuk Res 1987; 11:705-9. [PMID: 3626612 DOI: 10.1016/0145-2126(87)90006-3] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The present study was undertaken to investigate the hemopoietic cell from which malignant change evolves in juvenile dyshemopoiesis with monosomy 7. Two male patients, aged 18 and 5 months, were studied using progenitor assays combined with cytogenetics. Both had hepatosplenomegaly, cytopenias and a cellular marrow. The karyotype in direct marrow was 45,XY-7/47,XY,+8/46,XY in patient 1 and 45,XY,-7/46,XY in patient 2. Patient 1 received chemotherapy but developed acute nonlymphocytic leukemia after 17 months and died 20 months after diagnosis. During this time marrow metaphases with 45,XY,-7 increased to 100% (25/25). Patient 2 received an allogeneic marrow transplant 4 months after diagnosis which did not engraft. In both patients progenitors of both small (CFU-E) and large (BFU-E) erythroid colonies were present at normal frequencies. However, the colonies produced were small and poorly hemoglobinized with some erythropoietin-independent maturation. Progenitors of large granulocyte/macrophage colonies (CFU-GM) were present at an elevated frequency in the marrow of patient 1 and in the blood all progenitor classes were markedly increased. Cytogenetic analysis of colonies from this patient showed BFU-E to be 45,XY,-7 or 47,XY,+8 and CFU-GM to be 45,XY,-7 or 47,XY,+8 or 46,XY. In patient 2, most BFU-E were 45,XY,-7, although a few were 46,XY. These data indicate that malignant change in this disease involves hemopoietic stem cells capable of erythroid and in at least some cases, myeloid differentiation.
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Abstract
We previously reported the cloning and detailed analysis of the integrated hepatitis B virus sequences in a human hepatoma cell line. We report here the integration of at least one of hepatitis B virus at human satellite DNA sequences. The majority of the cellular sequences identified by this satellite DNA were organized as a multimeric composition of a 0.6-kilobase EcoRI fragment. This clone hybridized in situ almost exclusively to the centromeric heterochromatin of chromosomes 1 and 16 and to a lower extent to chromosome 2 and to the heterochromatic region of the Y chromosome. The immediate flanking host sequence appeared as a hierarchy of repeating units which were almost identical to a previously reported human satellite III DNA sequence.
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MESH Headings
- Carcinoma, Hepatocellular/genetics
- Carcinoma, Hepatocellular/microbiology
- Cell Line
- Chromosomes, Human
- Chromosomes, Human, 1-3
- Chromosomes, Human, 16-18
- DNA, Satellite/genetics
- DNA, Viral/genetics
- Hepatitis B virus/genetics
- Humans
- Liver Neoplasms/genetics
- Liver Neoplasms/microbiology
- Nucleic Acid Hybridization
- Recombination, Genetic
- Repetitive Sequences, Nucleic Acid
- Y Chromosome
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Lau YF, Schonberg S. A male-specific DNA probe detects heterochromatin sequences in a familial Yq- chromosome. Am J Hum Genet 1984; 36:1394-6. [PMID: 6517059 PMCID: PMC1684645] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Using a recombinant DNA probe, we have demonstrated the presence of residual 3.4-kilobase (kb) repeat sequences in a family with a Yq- chromosome. The heterochromatin of this Y variant was not readily detectable with conventional chromosome-banding techniques. These data suggest that the breakpoint of the deletion occurs at the heterochromatin region proximal to the euchromatin/heterochromatin junction.
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Schonberg S, Niermeijer MF, Bootsma D, Henderson E, German J. Werner's syndrome: proliferation in vitro of clones of cells bearing chromosome translocations. Am J Hum Genet 1984; 36:387-97. [PMID: 6324581 PMCID: PMC1684414] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Each of several cultures of Werner's syndrome (WS) fibroblasts and lymphoblasts examined was found to be composed of one or several clones of cells with mutated chromosome complements. Two "sister" fibroblasts cell lines (FCLs) that were derived from a mixture of explants cut from the same WS skin biopsy were found to have completely different rearranged chromosome complements. Daily observation of the skin explants from which these two sister FCLs were derived revealed not only that no more than a few fibroblasts ever migrated from a given explant but also that fibroblasts migrated from only a few of the explants. Two of three lymphoblastoid cell lines (LCLs), each probably developed as an independent clone from a different cell from the same WS blood sample, were mosaic, comprised of cells having both normal and rearranged chromosome complements. The third LCL studied, although nonmosaic, had a rearranged chromosome complement, but one that was completely different from those in the other two lines. Based on the observations described, hypotheses have been formulated to explain both the preponderance in long-term WS cultures of clones with mutated chromosome complements and the abbreviated lifespan characteristic of WS fibroblast cultures.
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Abstract
A portion of the DNA within intact nuclei of a spontaneously transformed Chinese hamster ovary cell line (CHO-Kl) is relatively resistant to digestion by pancreatic deoxyribonuclease, as compared to nuclei from primary cultures of Chinese hamster ovary fibroblasts. Treatment of CHO-Kl cells with derivatives of 3',5' cyclic AMP (cAMP) under conditions which effect the reverse transformation (RT) of these cells, results in restoration of the increased sensitivity of their DNA to hydrolysis by pancreatic deoxyribonuclease, to the level characteristic of an untransformed, morphologically normal Chinese hamster fibroblast cell line. Dibutyryl (db-)cAMP and 8-bromo-cAMP (Br-cAMP) yielded similar results. The cAMP derivatives employed had no effect on the normal fibroblasts.
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Schonberg S. LACK OF SPONTANEOUS SISTER CHROMATID EXCHANGES IN SOMATIC CELLS OF DROSOPHILA MELANOGASTER. Genetics 1980; 94:518-9. [PMID: 17249008 PMCID: PMC1214155 DOI: 10.1093/genetics/94.2.518] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Affiliation(s)
- S Schonberg
- Laboratory of Human Genetics The New York Blood Center 310 East 67th Street New York, New York 10021
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German J, Schonberg S, Louie E, Chaganti RS. Bloom's syndrome. IV. Sister-chromatid exchanges in lymphocytes. Am J Hum Genet 1977; 29:248-55. [PMID: 868871 PMCID: PMC1685310] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
An abnormally great amount of exhange between both sister and nonsister-but-homologous chromatids is a highly characteristic feature of cultured blood lymphocytes from individuals with Bloom's syndrome. However, a population of lymphocytes which exhibit a normal amount of exchange can be detected in the blood of some individuals with this syndrome. This coexistence of cells with a greatly increased number of sister-chromatid exchanges and others with a normal number results in a phenotypic dimorphism, in apparent contradiction to the autosomal recessive mode of inheritance of the syndrome.
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Abstract
Dividing cells from persons with Bloom's syndrome, an autosomal recessive disorder of growth, exhibit increased numbers of chromatid breaks and rearrangements. A highly characteristic feature of the chromosome instability in this syndrome is the tendency for exchanges to occur between chromatids of homologous chromosomes at homologous sites. In the present experiments, a cytogenetic technique by which the sister chromatids of a metaphase chromosome are stained differentially has been used to demonstrate a striking and possibly specific, but hitherto unrecognized, increase in the frequency with which sister chromatids also exchange segments. The cells were grown in bromodeoxyuridine and stained with 33258 Hoechst and Giemsa. Whereas phytohemagglutinin-stimulated lymphocytes from normal controls had a mean of 6.9 sister chromatid exchanges per metaphase (range 1-14), those from persons with Bloom's syndrome had a mean of 89.0 (range 45-162). Normal frequencies of sister chromatid exchanges were found in cells heterozygous for the Bloom's syndrome gene, and also in cells either homozygous or heterozygous for the genes of the Louis-Bar (ataxia telangiectasia) syndrome and Fanconi's anemia, two other rare disorders characterized by chromosome instability. In a differentially stained chromatid interchange configuration discovered during the study, it was possible to determine the new distribution of both sister and non-sister-but-homologous chromatids that had resulted from numerous exchanges. By following shifts in the pattern of staining from chromatid to chromatid, visual evidence was obtained that the quadriradial configurations long recognized as characteristic of Bloom's syndrome represent exchanges between homologous chromosomes, apparently at homologous points. We postulate that the increase in the frequency of exchanges between nonsister-but-homologous chromatids and those between sister chromatids in Bloom's syndrome represents aspects of one and the same disturbance. A study of this phenomenon in relation to the clinical features of Bloom's syndrome may be helpful eventually in understanding the biological significance of chromatid exchange in somatic cells.
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