Further investigations into the validity of minisatellites as a new tool to monitor low-dose radiation exposure?

Hypermutable minisatellites have recently been put forward as potential markers for studying double-strand breaks in humans, regardless of whether they occur naturally or are due to external causes. Following the 1986 Chernobyl accident, studies investigating the effect of low-dose chronic exposure to ionising radiation in humans were performed and the results obtained suggest a twofold increase in the minisatellite germ line mutation rate. However, the validity of the Chernobyl study published is significantly weakened by the lack of an appropriate control population. In the present study, 163 Ukrainian families with children born before the accident (43) or after the April 1986 accident in unpolluted areas (South Ukraine; 120 children) were genotyped at 7 hypermutable minisatellite loci. The data was compared to the UK control group. The natural germinal mutation rate of the hypermutable minisatellites is identical in both control populations. This excludes the possibility of variation of average mutation rate with ethnic origin and lifestyle and therefore strengthens the initial conclusions. To further investigate the effect of radiation at minisatellite loci in the germline, families in which the father has been working on the Chernobyl site were collected (clean-up workers, referred to as "liquidators"). The measurement of minisatellite mutation ratios gives the same result (0.94) for control and liquidators group. Eighty eight children were conceived while their father was working on the Chernobyl site, whereas 95 were conceived more than 2 months after their fathers had stopped working on the site. The liquidator's children were selected on a questionnaire. The study shows that the frequency of mutant alleles is 1.5 times higher in the group of children conceived during the period of exposure (difference not statistically significant). If confirmed, this data could explain the negative results obtained in comparable studies involving the survivors of the Hiroshima-Nagasaki blast. The mutagenic effect of radiation monitored by minisatellites at the meiotic stage of germ line maturation would be transient in human, as it is in mice.