Basic molecular defect in ADA-SCID.
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Biomedical subjects
Publications and source records attributed to E Herbschleb-Voogt.
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A specific competitive radioimmunoassay (RIA) was employed to quantify human adenosine deaminase molecules produced in human-Chinese hamster somatic cell hybrids. Studies on a set of hybrids in which the normal and aberrant expressions of adenosine deaminase (assigned earlier to human chromosome 20) were segregating, have demonstrated that in the patient with ADA-SCID disease reported by Herbschleb-Voogt et al. (1981 a), the deficiency of ADA activity was associated with a comparable deficiency of adenosine deaminase specific immuno-crossreacting material (ADA-CRM).
The nature of the defect of a female baby who died of severe combined immunodeficiency (SCID) disease associated with adenosine deaminase deficiency (ADA-) was investigated. Since tissue or tissue culture material was not available for subsequent studies, the expression of ADA in her cells was investigated in the somatic cell hybrid clones derived from a fusion between the lymphocytes from one of her two obligate heterozygote parents and thymidine kinase deficient Chinese hamster (a3) fibroblasts. The results of analyses of the human chromosomes and biochemical markers in 12 independent clones and 27 subclones indicated that the ADA deficiency in the patient is determined probably by a mutation in the structural gene for ADA in chromosome 20 leading either to the production of catalytically defective molecules or to the cessation of the production of ADA. Incidentally, the involvement of chromosome 2, which carries a gene for adenosine deaminase complexing protein (ADCP), in the causation of ADA deficiency was excluded. The in vitro approach through the cells from an obligate heterozygote described in this paper may have a general application in pursuing studies on other cases of inborn errors of metabolism whenever the material from the affected individuals (i.e., the homozygotes) is not available or not suitable for direct investigations.
Six (four Hindus, one Sikh, and one Muslim) outr of 213 individuals originating from different parts of the Indian subcontinent (namely, Andhra Pradesh, Maharashtra, Uttar Pradesh, East Punjab, and West Punjab) were found to be Calcutta-1 (CAL1) variants of lactate dehydrogenase (LDH). The CAL1 variant was originally described (and thus, generally believed at present) as an allelic variant at the LDHA locus in chromosome 11. By using an improved Cellogel electrophoretic procedure the isozyme patterns observed in the erythrocytes and leukocytes of the variant have indicated that the CAL1 is not variant of LDHA but that of LDHB, a chromosome 12 marker. The suggestion was supported by the isozyme patterns of LDH in a set of segregating clones of man-mouse somatic cell hybrids with the variant as human partner. Moreover, the variant cosegregated consistently with the human chromosome 12 and with the markers firmly assigned to the latter but not with human chromosome 11 or its markers in these hybrids. These results confirmed that the CAL1 is an LDHB variant.
The experiments reported in this paper indicate that the expression of human adenosine deaminase complexing protein (ADCP) in the human-rodent somatic cell hybrids is influenced by the state of confluency of the cells and the background rodent genome. Thus, the complement of the L-cell derived A9 or B82 mouse parent apparently prevents the expression of human ADCP in the interspecific somatic cell hybrids. In the a3, E36, or RAG hybrids the human ADCP expression was not prevented by the rodent genome and was found to be proportional to the degree of confluency of the cell in the culture as in the case of primary human fibroblasts. An analysis of human chromosomes, chromosome specific enzyme markers, and ADCP in a panel of rodent-human somatic cell hybrids optimally maintained and harvested at full confluency has shown that the expression of human ADCP in the mouse (RAG)-human as well as in the hamster (E36 or a3)-human hybrids is determined by a gene(s) in human chromosome 2 and that neither chromosome 6 nor any other of the chromosomes of man carry any gene(s) involved in the formation of human ADCP at least in the Chinese hamster-human hybrids. A series of rodent-human hybrid clones exhibiting a mitotic separation of IDH1 and MDH1 indicated that ADCP is most probably situated between corresponding loci in human chromosome 2.
A pregnancy at risk for adenosine deaminase deficiency and severe combined immunodeficiency disease has been investigated by assay of adenosine deaminase activity in cultured amniotic fluid cells using a microradioassay. A low-normal level of activity consistent with heterozygote status in the foetus was found and confirmed after birth by assay of red cell and fibroblast adenosine deaminase activities. It is suggested that the radioassay method offers significant advantages in sensitivity and specificity over the standard spectrophotometric procedure.
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Several observations by independent investigators in the past have indicated that adenosine deaminase complexing protein (ADCP), present in considerable quantities in certain human tissues, was absent or decreased in the cancers originated from them. During the present study, electrophoretic analysis of adenosine deaminase (ADA) isozymes and radioimmunoassay for ADCP in the primary fibroblasts and the transformed as well as certain tumor derived cell lines have demonstrated that ADCP present in large quantities in the primary cells was absent or nearly absent in the transformed or tumor-derived cell lines. Though the mechanisms involved are not yet clear, the above observations indicate that ADCP has the potentials of a useful marker in the studies on transformed cells and cancer tissues.