Crime scene causation

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Could a new DNA technique, which claims to prove the cause of an illness, end the 'trench warfare' that so often the characterises occupational disease claims? Mark Treacher assesses its implications

Proving the cause of an occupational disease can be difficult where exposure information is lacking. The problems are often compounded when many years have elapsed since this exposure, or where another lifestyle factor is present that may have also been capable of causing the illness.

Where it is impossible to produce evidence as to the cause - or where it is not entirely understood - claimants and insurers are forced to rely upon the opinions of experts or statistics from epidemiological studies.

But a US-based research group has now announced a new technique, which it claims can produce scientific evidence determining whether injury was caused by exposure to a particular agent or not.

To claim damages, sufferers of 'long tail' type occupational diseases have to satisfy the ordinary test of causation and show that, on the balance of probabilities, their particular condition was caused by exposure to a known agent.

Even where it is known that an individual's work involved exposure to a certain agent, medical science at best relies on experience and epidemiology to show that this caused the disease.

From a logical perspectives, however, this method of proving causation can always be criticised. Invariably, there will be individuals whose illness was not caused by such exposure or, worse still, some who have genuine claims but who cannot prove the connection. There are further margins for error due to the passage of time; mis-equating one type of exposure for another; poor information about dosages; and varying information about relative toxicities. So using epidemiological evidence in all cases of occupational disease becomes less attractive to achieve evidential certainty.

Court adaptation

The last 50 years have demonstrated that the law on causation is adaptable. Where proof of causation is a scientific impossibility, or where there is an alternative cause, the courts have been prepared to accept 'material contribution' or 'materially increasing a risk of injury' as satisfying the test of causation. From the point of view of achieving a fair outcome in difficult cases, some might argue that any concerns are misplaced and that the current law achieves fairness - albeit through imaginative reasoning.

However, the tone of the House of Lords' decision in the mesothelioma case of Barker v Corus seems to underpin the importance of proof of causation. The comments of Lady Hale suggest the landscape is changing and it is becoming more difficult for claims to succeed in cases where attaining such proof is difficult or impossible.

Many practitioners would rather avoid the tough legal arguments presented by causation problems if their clients could take a simple test to see whether or not the case should proceed. And it is no surprise such problems have focused scientific efforts on discovering how human DNA can be affected by exposure to certain chemicals.

MSDS1 - the technique devised by Dr Bruce Gillis, toxicologist and chief executive of the Cytokines Institute in Los Angeles - claims to bring an end to this uncertainty. Dr Gillis purports to be able to determine whether a person has had an injurious exposure to virtually any chemical or toxin by analysing how certain chemicals affect 36,000 known parameters of their DNA. He also claims it can be determined whether pain has been experienced.

Specifically, it measures the release of small proteins called cytokines, which can uniquely be identified to mark exposure to known agents. Peer-reviewed papers claim it is able to identify human cell responses to hexavalent chromium, a known carcinogen, as well as benzene and benzene metabolites.

Dr Steven Roche, managing director of the Cytokine Institute, says the tests are reliable, repeatable, subject to peer review and widely accepted in the scientific community. It is claimed that the research is also applicable to other chemicals and toxins where the suspect chemical or metabolite is known.

The technique does appear to have the potential to eliminate claims where the disease is not related to exposure and has already been used to provide authoritative evidence in US cases. However, some UK insurers remain sceptical as to its use in court; while other medical experts and epidemiologists believe the claims are 'too good to be true'. Meanwhile, lawyers take issue over privacy if the test was used to determine predisposition to illness or employee or policyholder screening.

Nevertheless, it has already been used in evidence in around 15 to 20 litigated cases in the US - and with some success. Colour-coded charts, easily understood by juries, have been shown in court to illustrate whether a person's DNA is a match for the DNA signature expected from a particular chemical.

The US Supreme Court has historically set a high hurdle for admission of scientific testimony, requiring that evidence is both subject to peer review and has widespread acceptance in the relevant community. It has previously dismissed scientific opinion where it depended upon unreliable methodologies or privately gathered data.

There are no reported US cases examining MSDS1 and it is not known to what extent the evidence has yet been challenged at trial. Certainly, the technique appears to be established in relation to benzene exposure but it is not known how this will translate into other potential exposures, or whether equivalent peer-reviewed research is available outside that area - for example, in cases of asbestos exposure or smoking-related cancer.

Possible limitations

Those dealing with claims relating to asbestos exposure might consider the technique is of limited use in these cases; where disease is known only to follow exposure and such exposure can be proven.

But a potential Pandora's box of problems could follow if the technique can isolate specific types of fibre as causative and dismiss others as irrelevant. Equally, mesothelioma claimants in multi-defendant claims could put aside concerns about what portion of blame each defendant must take, and actually directly pursue the correct defendants whose fibres had caused the condition.

Relying upon this technique in the UK can be foreseen, and disputes will centre on the validity of its conclusions against medical or epidemiological evidence. Both claimants and insurers are understandably conservative in how they currently choose scientific experts, and it will be a bold step to engage this technique with a view to providing a definite answer - particularly where both sides disagree as to its value.

In cases where the test results are disputed, there is little doubt we would see a return to trench warfare by expert evidence, which has so characterised this type of litigation in the past.

Many will argue that the current approach has served us well and provides litigants with compensation even if the method is not perfect. But if this new technique is shown to be accurate, it is hard to argue the issue of causation should be left to the judge, the stars or chance when certainty is within grasp. Litigants are advised to watch the US with interest to see how MSDS1 develops.

- Mark Treacher is a partner in the occupational health team at law firm DWF.

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