Kevin J. Trainor

Mutation frequency in human lymphocytes increases with age.

Several theories of ageing predict that somatic mutations should increase with age. This prediction was tested for human lymphocytes using a recently developed clonal technique for enumeration of mutations, and an increase of 1.6% per year in mutations with age was detected.

Lack of an effect of vitamin E on lifespan of mice

It has been speculated that ageing results from accumulation ofdamage to macromolecules, particularly DNA, owing to the actionof oxidising free radicals. This possibility would predict thatadministration of anti-oxidants might prolong lifespan, butprevious data on this prediction are conflicting. Three groups ofmice were exposed throughout life, from the time of conceptionuntil death, to 20, 40 and 400 mg/Kg of vitamin E in the diet. Noeffect on lifespan was observed and the median lifespans in thethree groups were 804, 830 and 801 days, respectively. The designof the study also enabled an effect of parental age on lifespanof female progeny to be sought, but no effect was detected.

Residual marrow injury following cytotoxic drugs

Abstract A number of cytotoxic drugs were tested in mice for their ability to produce residual damage to the bone marrow. This was assessed by the ability of the drug to produce depletion of pluripotential stem cells and granulocytic progenitor cells persisting for at least two months after cessation of the drug. Evidence of residual damage was found after administration of mitomycin, chlorambucil and melphalan but not after nitrogen mustard, dimethyl-triazeno-imidazole-carboxamide or adriamycin. Residual damage has previously been found following busulphan and bischloro-nitrosurea and the features in common of the drugs causing residual damage suggest that the effect may require the ability to alkylate pluripotential stem cells. These experimental findings may explain a number of clinical observations in man.

IS APLASTIC ANÆMIA DUE TO ABNORMALITY OF D.N.A.

Lymphocytes from eleven patients with aplastic anaemia were cultured with various agents which interact with D.N.A., and the proliferative responses to phytohaemagglutinin were measured. Lymphocytes from seven of the eleven patients were unduly sensitive to bleomycin, an agent causing strand breaks in D.N.A. The findings suggest that D.N.A. in these seven patients was abnormal, possibly as a result of an abnormality of D.N.A. repair. It is suggested that in aplastic anaemia D.N.A. damage in stem cells may lead to a failure of proliferation.

Sensitivity of human lymphocytes to bleomycin increases with age

The sensitivity of human peripheral blood lymphocytes to bleomycin and mitomycin-C was assessed by measuring the inhibition of phytohemagglutinin stimulated proliferation. The sensitivity to bleomycin, and not to mitomycin-C, increased with the age.

Frequency of the ATM IVS10-6T→G variant in Australian multiple-case breast cancer families

BackgroundGermline mutations in the genes BRCA1 and BRCA2 account for only a proportion of hereditary breast cancer, suggesting that additional genes contribute to hereditary breast cancer. Recently a heterozygous variant in the ataxia–telangiectasia mutated (ATM) gene, IVS10-6T→G, was reported by an Australian multiple-case breast cancer family cohort study (the Kathleen Cuningham Foundation Consortium for Research into Familial Breast Cancer) to confer a substantial breast cancer risk. Although this variant can result in a truncated ATM product, its clinical significance as a high-penetrance breast cancer allele or its role as a low-penetrance risk-modifier is controversial.MethodsWe determined the frequency of ATM IVS10-6T→G variants in a cohort of individuals affected by breast and/or ovarian cancer who underwent BRCA1 and BRCA2 genetic testing at four major Australian familial cancer clinics.ResultsSeven of 495 patients (1.4%) were heterozygous for the IVS10-6T→G variant; the carrier rate in unselected Australian women with no family history of breast cancer is reported to be 6 of 725 (0.83%) (P = 0.4). Two of the seven probands also harboured a pathogenic BRCA1 mutation and one patient had a BRCA1 unclassified variant of uncertain significance.ConclusionThese findings indicate that the ATM IVS10-6T→G variant does not seem to occur at a significantly higher frequency in affected individuals from high-risk families than in the general population. A role for this variant as a low-penetrance allele or as a modifying gene in association with other genes (such as BRCA1) remains possible. Routine testing for ATM IVS10-6T→G is not warranted in mutation screening of affected individuals from high-risk families.

Cloning of lymphocytes from whole blood by limiting dilution

A simple whole blood limiting dilution technique was developed to clone human lymphocytes non-specifically. The geometric mean frequency of clone forming cells in 13 normal individuals was found to be 31.1%. Compared with measurement of proliferation in mass suspension culture, cloning provides a quantitative and easily interpretable endpoint for a variety of lymphocyte studies and its use in measurement of radiation sensitivity is presented as an example.