Biomedical subjects
Publications and source records attributed to J German.
Evidence is presented for the existence of a gene, probably on the X chromosome, which prevents testis differentiation when present in 46,XY human embryos. Affected 46,XY women are not completely normal because of premature ovarian involution, as a result of which they have "streak gonads" similiar to those of 45,X women.
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The antenatal sonographic appearance of gastroschisis is described. The findings consist of numerous extra-abdominal "cystic masses" respresenting loops of fluid-filled bowel eviscerated through the abdominal defect. This patient also had associated polyhydramnios, possibly on the basis of a functional bowel abnormality.
Two families in which aberrations involving chromosome no. 2 had been previously used for linkage studies have been re-examined using banding techniques to identify the breakage sites. In one family a (2; 10)(q21;q24) translocation was identified in individuals previously thought to have a pericentric inversion of chromosome no. 2. In the other, a fragile secondary constriction site was localized to 2q13, and it was shown by bromodeoxy uridine incorporation that the origin of the triradial chromosome no. 2 was by isochromatid breakage and non-disjunction rather than by selective endoreduplication. The three marker sites, 2q13, 2q21 and 10q24, have been analysed for their linkage relationships with 15 informative marker loci which have not yet been assigned to chromosomes other than no. 2 or no. 10. No significant evidence for linkage with any of the loci tested was found.
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Analysis of DNA fiber autoradiograms from Bloom's syndrome skin fibroblasts and blood lymphocytes shows a retarded rate of replication fork movement compared to normal adult controls. Other measurements from the autoradiograms--replication unit length, incidence of bidirectional replication, and degree of initiation synchrony--are normal in Bloom's syndrome cells. These results suggest that a slow rate of fork movement is a specific manifestation of defective DNA synthesis in all Bloom's syndrome cells.
The Bloom's Syndrome Registry comprises the 71 individuals in whom this rare genetic disorder has been recognized between the time it was described in 1954 and the end of 1976. The major objective of the Registry is surveillance for cancer in both affected homozygotes and heterozygotes. Of the 61 homozygotes known to have had Bloom's syndrome before cancer was diagnosed and for whom follow-up has been possible, one in nine has developed cancer. Thirteen cancers have been diagnosed, in 12 individuals. The mean age in 1976 of the living individuals with the syndrome was 16.4 years. The mean age at the time cancer was diagnosed was 20 years. Cancers have been of multiple types and have affected various sites.
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.
An effort was made to identify all individuals with Bloom's syndrome living in Israel between September 1971 and September 1972. Each of the eight individuals located were Jewish and could readily be classified Ashkenazic. The frequency of the Bloom's syndrome gene in Ashkenazim was estimated to be .0042 (minimum), implying a heterozygote frequency greater than 1 in 120. A striking distortion of the sex ratio (M/F = 7.0) may have been due to underascertainment of affected females. One of the affected individuals ascertained during the survey subsequently has died from cancer, which is in keeping with the recognized cancer proneness of this condition. Four of the affected have married, but no conception is known to have occurred, which suggests that sub- or infertility is a feature of the syndrome.
Cytogenetic studies were done on 18 patients with myelofibrosis or the closely related syndrome, undifferentiated myeloproliferative disorder (MPD). Clones of cells with chromosome abnormalities were demonstrated in the blood of eight individuals, including two with a history of radiation therapy and two with "acute myelofibrosis". Trisomy 8 was present in the latter two patients, but otherwise, there was no consistent cytogenetic pattern or correlation with specific hematologic findings. Sixteen of these patients have been followed for more than 1 year or until death; none has progressed to leukemia. The results indicate that chromosome abnormalities are relatively common in this disorder, but as with polycythemia vera, and unlike some other "preleukemic" states, the aberrant clones in myelofibrosis do not appear to indicate that clinical leukemia is imminent.
A family is described in which a reciprocal translocation involving 5p and 21q appeared de novo in the chromosome complement of a woman who then transmitted it in both balanced and unbalanced form to her progeny. The proposita, a child with the cri du chat syndrome, had a deficiency for most of 5p, all of 21p, 21 centromere, and a small proximal segment of 21q. The reported cases of the cri du chat syndrome associated with translocations are reviewed and discussed in relation to this family.
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The cytogenetic observation that homologous chromatid interchange occurs in Bloom's syndrome more often than normal prompted an investigation of DNA replication in that rare genetic disorder. Using DNA fiber autoradiography, an estimation was made of the rate of one component of ongoing DNA replication, DNA chain growth. The rate in Bloom's syndrome dermal fibroblasts in tissue culture was found to be significantly slower than that in normal control cells. (The rate was found to be normal in Fanconi's anemia cells.) The explanation for the retarded chain growth may be either that an enzyme concerned directly with semiconservative DNA replication is defective or that a defective enzyme not itself concerned directly with replication results in disturbed cellular metabolism which in turn affects replication.
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Bloom's syndrome is a rare autosmal recessive disorder, first characterized by growth retardation and asum-sensitive facial telangiectasia and more recently demonstarted to have increased chromosome instability, a predisposition to malignancy, and increased susecptibitily to infection. The present report ocncern the immune function of Bloom's syndrom lymphoctes in vitro. Four affected homozgotes and five heterozygotes were studied. An abnormal serum concentartion of at least one class of immunoglobin was present in three out of four homozgotes. Affected homozgotes were shown capable of both a humoral and cellular response after antigenic challenge, the responses in general being weak but detectable. Blood lymphocytes from Bloom's syndrome individuals were cultured in impaired proliferavite response and synthesized less immunoglobulin at the end of 5 days than did normal controls. In contrast, they had a normal proliferative response to phytohemagglutinin except at highest concentrations of the mitogen. In the mixed lymphocte culture, Bloom's syndrome lymphocytes proved to be poor responder cells but normal stimulator cells. Lmyphoctes from the heterozgotes produced normal responses in these three systems. Distrubed immunity appears to be on of several major consequences of homozygosity for the Bloom's syndrome gene. Although the explanation for this pleiotropism is at present obscure, the idea was advanced that the aberrant immune function is, along with the major clincial feature-small body size, amanifestation of defect in cellular proliferation.
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