M-FISH evaluation of chromosome aberrations to examine for historical exposure to ionising radiation due to participation at British nuclear test sites
Reference: Lawrence, K. J., Scholze, M., Seixo, J., Daley, F., Al-Haddad, E., Craenen, K., Gillham, C., Rake, C., Peto, J and Rhona Anderson, R.M (l2024). M-FISH evaluation of chromosome aberrations to examine for historical exposure to ionising radiation due to participation at British nuclear test sites. Journal of Radiological Protection, volume 44 (1), 01150.
Background to research
Veterans of the British nuclear testing programme represent a population of ex-military personnel who had the potential to be exposed to ionising radiation through their participation at nuclear testing sites in the 1950s and 1960s. Questions as to whether veterans could have received sufficient radiation exposure to cause harm and, worry about potential (inherited) legacy in descendants of any historical radiation exposure, remain.
External radiation dose estimates recorded at the time of the tests suggest that any exposure would have been limited for the majority of those present. Of the ~20% of test veterans who were monitored, ~8% (1804 participants) were recorded as having a ‘non-zero dose’ of radiation. The UK Ministry of Defence also identified groups of veterans as potentially receiving higher doses than that recorded, principally due to the roles they performed. These ‘special groups’, included veterans who were involved in tasks such as air plume sampling and cleaning of ‘sampling’ aircraft. The majority of personnel present at test sites were involved in support roles, such as construction or transport, however additionally, were involved with the actual tests, including by working in contaminated areas following each test. Such roles may not have been accounted for by the formal categorization into a special group.
Fallout from atmospheric tests (e.g. GRAPPLE series in the South Pacific) and, from radioactivity which was dispersed into the environment during the Maralinga experimental programme in South Australia includes long-lived radionuclides such as Caesium-137, Strontium-90, Uranium-235/238, Plutonium-239, which if inhaled, ingested or otherwise internalized within the body would contribute to chronic radiation exposure. There is no public record of any historical internal dose measurements.
Ionising radiation exposure is effective in causing damage to DNA which can result in the formation of chromosome aberrations. Fluorescence in situ hybridisation (FISH) based techniques such as M-FISH, which ‘paints’ individual chromosomes, enables the detection of structural chromosome rearrangements, such as reciprocal translocations, for use in the assessment of radiation exposures. Damage to DNA (chromosomes) occurs throughout life from a range of normal cellular, lifestyle, medical and occupational sources, meaning the occurrence of reciprocal translocations will accumulate with age. Thus, detection of reciprocal translocations in individuals will reflect a lifetime of ‘all’ their exposures. Complex chromosome aberrations are another type of chromosome rearrangement which involve more breaks in multiple chromosomes. These aberrations are generally thought to arise rarely in general populations but are characteristically seen after exposure to low doses of high-linear energy transfer (LET) radiation such as α-particles.
What was the aim of the research?
The Genetic and Cytogenetic Family trio (GCFT) study is the first study to obtain blood samples from a group of British nuclear test veterans and their families for the purposes of identifying genetic alterations in offspring which may have arisen as a consequence of historical exposure of the veteran father to ionising radiation (for details see Rake et al, 2022).
The aim of this part of the GCFT study was to analyse veterans blood samples for chromosome aberrations using the technique of M-FISH. The amount (frequency) and type of chromosome aberration detected in a cohort of test veterans was compared to that seen in control veterans who were not present at nuclear test sites.
Specifically, we report the M-FISH findings to ask:
- is there any chromosomal evidence of historical radiation exposure in the nuclear test veterans?
- is there any relationship between the occurrence of chromosome aberrations in veteran fathers and the previously reported germline mutations detected in their adult child (Moorhouse et al., 2022)?
What did the research involve?
We examined for chromosomal evidence of historical radiation exposure in 48 nuclear test veterans using M-FISH and compared this with a matched group of 38 control veterans who were not present at nuclear test sites.
This involved identifying chromosomal aberrations, if present, in each veteran sample and classifying these according to the type of aberration. This resulted in the amount (or frequency) and type of chromosome aberration to be determined for each veteran.
All analysis was performed blind to nuclear test/control veteran status. After completion of analysis, the samples were decoded to allow for a comparison between test veteran and control veteran cohorts. Comparisons were also made for veterans allocated into previously defined (Rake et al., 2022) ‘exposure rank’ groups as a proxy for radiation dose and, according to the geographical location of tests attended (Christmas Island, Maralinga, on-board ship).
The M-FISH data was linked, where possible, with the whole genome sequence (WGS) data previously published in Moorhouse et al., 2022 to examine for any relationship between the occurrence of chromosome aberrations in the veteran father and the newly arising germline mutations detected in their adult child.
What did we find?
In total, 9379 and 7698 metaphase cells were analysed using M-FISH from 48 nuclear test and 38 control veteran samples, representing veteran servicemen from the Army, RAF and Royal Navy.
We found chromosome aberrations, including reciprocal translocations and complex-type aberrations, in both nuclear test and control veterans’ samples. Overall, we found no statistical difference in amount of any chromosome aberration type between the nuclear test and control veteran cohorts.
We found the frequency of reciprocal translocations to be consistent with what might be expected based upon veterans age.
We did find a higher average occurrence of complex chromosome aberrations in a very small subset of nuclear test veterans who had previously been identified as having a higher likelihood for radiation exposure (present at Maralinga and/or present on HMS Diana). This was associated with an increase in the proportion of unstable (through repeated cell division) aberrations suggesting their formation to be relatively recent.
We also observed a higher than expected occurrence of complex aberrations in a number of control veterans.
The M-FISH data was integrated with the de novo germline mutation data previously reported (Moorhouse et al., 2022) for all families where both M-FISH and WGS data was available (28 control and 30 nuclear test families). We found no relationship between the overall burden (or amount) of chromosome aberrations in the veteran father and the germline mutation frequency in their child.
A weak relationship was observed in a small number of families, representing both control and nuclear test veteran, between the veteran father’s occurrence of complex chromosome aberrations and the germline mutation sub-type, SBS16, previously reported in Moorhouse et al., 2022.
Self-reported information on clinical conditions of veterans’ children or grandchildren was also considered. However, no relationship between chromosome aberration burden in the veteran father, germline mutation frequency and self-reported occurrences of adverse health in descendants was seen.
What does this mean?
We find no chromosomal evidence of historical radiation exposure in the cohort of British nuclear test veterans sampled here. This is different to the findings and interpretation of the Rowland study of New Zealand test veterans.
Our findings should offer reassurance to veterans that attendance at nuclear tests sites per se was not associated with detectable levels of exposure to radiation.
The higher average occurrence of complex chromosome aberrations which was seen in a very small subset of nuclear test veterans may reflect chronic exposure to internalised long-lived radionuclides from radiation fallout. A contribution from medical sources e.g. diagnostic examinations cannot be ruled out for both control and nuclear test individual veterans.
SBS signatures are detectable ‘patterns’ of mutation which remain in the DNA sequence after DNA damage and repair processing. Different SBS signatures are therefore thought to reflect the different types of exposure the cell may have experienced. The higher representation of signature SBS16 in a small number of families reported by Moorhouse (2022) may have been observed by statistical chance or, it may reflect an exposure in the veteran father.
The observation here of a weak relationship between complex chromosome aberrations in (both control and nuclear test) veterans and SBS16, may represent a mutational pattern consistent with radiation exposure which is detectable in the germline. This remains to be established.
A small number of families with higher SBS16, representing both control and nuclear test, self-reported adverse health in one of their descendants. Overall, though we saw no relationship between veteran’s chromosome aberration burden and germline mutation frequency in families who reported a descendant health concern, suggesting the reported health issues in these families are unlikely to be associated with historical radiation exposure.
What is next?
Work on the GCFT study continues. We are finalising a chromosomal examination of adult children of veterans and undertaking a pilot analysis for the detection of long-lived radionuclides in the urine of veterans.
Who did this research?
The work presented here was carried out by researchers at Brunel University London and London School of Hygiene and Tropical Medicine. Previously published work utilised in the analysis also involved researchers at the University of Leicester.
This work was, in part, supported by the Nuclear Community Charity Fund (NCCF) through funds received by The Armed Forces Covenant Fund Trust under the Aged Veterans Fund Grant AVF16 and Brunel University London.
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M-FISH chromosomal analysis of 48 nuclear test veterans compared to 38 control veterans
Structural chromosome aberrations of varying complexity were measured
No difference in the amount or type of chromosome aberrations found between test and control veteran cohorts
Elevated average frequency of complex chromosome aberrations seen in small subset of veterans with higher potential for radiation exposure
The previously reported over-representation of mutation signature SBS16 in a small subset of nuclear test offspring was weakly associated with the occurrence of complex chromosome aberrations in veteran father
No relationship between veteran’s chromosome aberration burden and germline mutation frequency seen in those families who report a descendant health concern
Links to the research paper
This is a peer-reviewed study meaning that other scientists have reviewed this work before the authors published it in Official Journal of the Society for Radiological Protection in 2024.