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The Bristol GDNF clinical trial


Glial-cell line Derived Neurotrophic Factor (GDNF) has shown promise as a potential disease-modifying treatment for Parkinson's, and research into its use has been actively supported by Parkinson's UK and the Cure Parkinson's Trust. Results published in 2016 were inconclusive on the treatment's efficacy, but it appeared to be safe so the trial continued. The full trial reported on 27th February 2019 and the results have been eagerly awaited, with much hype in social media and elsewhere.

The research reports and commentary

To save you some searching, we've gathered links here to the research reports and other announcements.

Original papers in academic journals

The results, from Alan Whone and his research group in Bristol, were published on 27th February 2019 in two respected academic journals, Brain and Journal of Parkinson's Disease. Both papers are Open Access, so anyone is able to read and download them. Here are direct links to the papers:

Summaries of the results

Academic papers are inevitably rather technical, so it can also be helpful to read summaries from reliable authors. Here are some that we trust. We will continue to add to this list as new publications become available.

Our meeting with one of the trial participants

Several members of the trial are understandably frustrated at the inconclusive results and are campaigning to fund further work. Shortly after the results were published, we met with Dr Simon Stott of Cure Parkinson's Trust and Lesley Gosden, one of the trial participants who is trying to raise funds to continue the work. Lesley is convinced that outcome measures used in the trial were flawed and did not correctly reflect the improvements experienced by participants.

Notes of our meeting

Notes on a meeting with Lesley Gosden, one of the 42 volunteers who underwent brain surgery in order to participate in the GDNF drug trial in Bristol, about which the BBC2 screened the programme The Parkinson's Drug Trial: A Miracle Cure? on Thursday 27 February, and Thursday 7 March 2019

Date and place of meeting: 5.00pm Wednesday 6 March 2019 at The Fishes Restaurant, Oxford, in between the screening of the two BBC documentaries.

Present: Lesley Gosden and husband Colin; Sally Bromley, Jonathan Bromley, Paul Mayhew-Archer (Chair), Julie Mayhew-Archer, Ian Sargent, Kevin McFarthing, Dr Simon Stott (Deputy Director of the Cure Parkinson's Trust), Xanthia Woltjer (student), Pen Keyte

We had all seen the content of the first BBC programme, but had not yet seen the second programme. Since the programmes could not be screened before the publication of papers about the research, however, some of the group had read the research findings and were aware that the outcomes of the trial were regarded as mixed. Lesley had chosen not to be filmed for the second programme, though she continued to participate in the trial. She told us her story:

Lesley's story

At first she was in the placebo group, for a total of 9 infusions. Although treatment with placebo is seen in some cases to have a beneficial effect, this is attributable to the higher level of care and support that patients received on the trial, resulting in improved psychological states and diminished stress. Lesley reported that she herself felt little or no benefit from the placebo stage. She was then infused with GDNF for the remainder of the trial (? 11 or 12 cycles)

Did the trial fail?

Lesley expressed the view that the trial cannot be said to have failed, because it had not been adequately assessed, monitored and evaluated. For example:

  • The trial used UPDRS which assesses for symptoms which some patients may not have. Lesley did not have a tremor at the start of the trial, therefore could not be said to have improved in this area. An improvement of 20% was required to report the drug as a success.
  • She felt it would have been more accurate to assess the symptoms which affect the quality of life and Activities of Daily Living (ADL).
  • Patients had to stay off meds for 24 hours before testing and arrived in differing states of disability. Tests over such extremes of disability could not be compared.
  • Tests did not accurately reflect patients' ability to cope with ADL; e.g. one patient could perform pill-rolling actions but not take the top off her pill bottle.
  • No qualitative assessments were undertaken.
  • When Lesley had cramping in her foot, filming was stopped, her foot was massaged until she could walk again; diazepam was offered to a patient to relax them.
  • She kept a diary, but it was not looked at.
  • Friends and family were not asked for their views on whether she was benefiting from the drug.
  • The same quantity of drug was administered to each patient regardless of their size.

BUT in her own experience:

  • Her condition has improved in some areas by 70%, such that she feels she has recovered to where she was five years ago; able to run upstairs, drive for long stretches, can walk further, experiences a marked reduction in foot cramps, and is generally feeling more alive and less lethargic than when she was first diagnosed 15 years ago.
  • Lesley has maintained improvement; she is still on a lower drug dose, and has experienced no degeneration.
  • While on the placebo, no brain development was detected in the PET scan, whereas brains cells had 'sprouted' while on GDNF.


Lesley feels that further trials should be made with GDNF, using different assessment and evaluating tools. £5 million is needed for Steven Gill to set up a new trial, and she has set up a fundraising page.

Understanding the facts

Research into potential Parkinson's treatments is challenging and complicated. However, reliable websites such as The Science of Parkinson's and the Parkinson's UK research pages provide valuable explanations for non-specialists. Here at Oxford Branch we will be observing this closely, and we will add more information and explanation to this page as soon as we have it.

Updates and corrections

If you find any errors or omissions on this page, please let us know by email to

History of updates

27th Feb 2019, 14:25 Text added to acknowledge the lead role of Parkinson's UK in funding the Bristol work
1st Mar 2019, 08:50 Added links to SoPD article and BBC support page
13th May 2019, 19:30 Removed some obsolete information, noted that the documentary is no longer available. Added notes on our meeting with Simon Stott and Lesley Gosden.