Biomedical subjects
Publications and source records attributed to D G Harnden.
The author describes his introduction to the field of cytogenetics, with his first viewing of himself, cytogenetically, down the microscope, and the progression of human cytogenetics as an area of study up to its modern integration with molecular genetics and computer technology.
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Toxic effects of ionizing radiation and elevated O2 levels (hyperoxia) are both thought to be mediated by oxidizing free radicals. In view of the reported hypersensitivity of ataxia telangiectasia (A-T) cells to the clastogenic effect of ionizing radiation, the chromosomal sensitivity of A-T cells to hyperoxic culture conditions was investigated in unirradiated and G0-irradiated A-T lymphocyte cultures. Unlike Fanconi's anaemia lymphocytes, which tend to respond to oxygen, especially after treatment with mitomycin C, both non-irradiated and G0-irradiated A-T lymphocytes failed to show an effect. We conclude that the excessive spontaneous and radiation-induced chromosomal breakage in A-T does not result from a deficiency in the cellular defences against the clastogenic effect of hyperoxia.
At the beginning of this century Theodor Boveri predicted that specific chromosome changes would be found to have a causal role in neoplasia. We are now beginning to acquire the evidence to substantiate this hypothesis. The evidence comes from two particular sources, (i) genetic environmental interactions and (ii) specific constitutional chromosome aberrations. Cancer incidence varies throughout the world. This is often due to the interaction of an environmental agent with a genetically varied population. Using UV and ionising radiation as examples it is argued that some individuals are more susceptible to genetic damage by these agents. Moreover, the genetic lesions which are caused by these agents are now being shown to be relevant to cancer. In the radiosensitive syndrome ataxia-telangiectasia for example, specific chromosome rearrangements have been defined which seem likely to be directly involved in the development of leukaemia in these patients. The second line of evidence comes from the study of patients who have constitutional chromosome abnormalities associated with susceptibility to specific cancers. It has now been shown that these chromosome changes mark the location of genes which are involved in the development of cancer and that these same loci are also important in the non-familial forms of these diseases. Thus we are beginning to understand for the first time the mechanistic pathway that leads from environmental agents, through chromosome damage, to the alteration of specific genes which control the neoplastic process.
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No difference in survival was observed between cultured cells from basal cell naevus syndrome (BCNS) patients and normal controls following exposure of fibroblasts to ionizing radiation. Potential lethal damage repair in BCNS cells, measured by holding experiments, was also no different from normal. G0-irradiated lymphocytes from BCNS patients were found to have a significantly higher level of X-ray-induced chromosome aberrations compared with normals. This increase is, however, small, and, taken together with the survival data, suggests that increased cell killing as a measure of the unusual clinical radiosensitivity is not the major effect of the BCNS gene.
A survey carried out to detect children with aniridia/Wilms's tumour syndrome identified 8 living and 3 dead children. The incidence of aniridia was found to be 1 in 43 among Wilms's tumour patients in the UK. The clinical features included complete bilaterial aniridia, cataracts, glaucoma, mental retardation, hyperkinesis, hypospadias, and undescended testes. A high incidence of bilateral tumours (36%), male sex, presentation at a young age, and advanced maternal age appeared to be associated with the syndrome. The 8 living children each had a deletion on the short arm of chromosome 11. In contrast, although 2 patients with sporadic aniridia without Wilms's tumour had other malformations, neither had genitourinary anomalies, and the only additional problems in patients with familial aniridia were cataracts. Among 49 children with Wilms's tumour without aniridia ony one had bilateral tumours. No chromosome abnormalities were detected in patients with familial aniridia, nor were they detected in patients with Wilms's tumour without aniridia or in those with sporadic aniridia without Wilms's tumour. While many infants with the Wilms's tumour/aniridia syndrome are clinically diagnosable at birth, chromosome analysis using the elongated chromosome method is especially valuable to confirm the diagnosis in girls with sporadic aniridia and in boys who lack the genitourinary malformations. The presence of an 11p13 deletion confirms the diagnosis of the Wilms's tumour/aniridia syndrome and indicates a very high risk for the development of Wilms's tumour.
The segregation of chromosomes 13 distinguishable by Q band fluorescent polymorphisms has been studied in three families with retinoblastoma. The recombination fraction for two of these families and four families previously reported did not differ significantly from 50%. Since a high recombination fraction has been predicted from chiasma frequency between the centromere of chromosome 13 and 13q14 these results neither confirm nor refute the location of the autosomal dominant gene predisposing to retinoblastoma in 13q14. The use of fluorescent markers is not suitable for early recognition of gene carriers in families with retinoblastoma.
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The amount of chromosome damage in peripheral blood lymphocytes following 400 rads G0 X-irradiation in 10 of 11 hereditary retinoblastoma patients was shown to be intermediate between that in normals and damage in trisomy 21 patients. The difference between normals and hereditary retinoblastoma patients was small, it varied between hereditary retinoblastoma patients, and no difference was detected following 200 rads G0 X-irradiation. No difference was found in levels of spontaneous chromosome damage in hereditary retinoblastoma patients, trisomy 21 patients, and normals. These results suggest that, although sensitivity to ionizing radiation may be associated with hereditary retinoblastoma, the observed difference is so small that it is probably not the major effect of the gene predisposing to retinoblastoma.
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