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Perspective interview - François Feillet

Perspective interview - François Feillet

Third Issue of the PKU Academy Newsletter PKU Perspectives an interview with Prof François Feillet

François Feillet shares his concerns about the need to understand the lifetime effect of a PKU diet.

Today’s PKU patients have a greater range of treatment options and a wider range of dietary supplements than ever before. This certainly has benefits for quality of life of patients but presents new challenges too. We spoke to Prof François Feillet1 about the issues raised by greater choice.

Prof Feillet gave the opening presentation session of the 2nd Dietitians’ Workshop in Rome (Italy) on March 22nd 2012. He reviewed the ongoing work to gain better understanding of the bioavailability of micronutrients supplied in supplements and the effect on the health of patients of an excess or deficiency of such vitamins and minerals. He is a member of the Serono Symposia International Foundation (SSIF) PKU Faculty.

Risks from PKU diet


Prof Feillet reminded us that the biggest risk a PKU patient faces day to day is still blood Phe levels that are higher than the recommended range due to a lack of compliance with diet. However, he pointed out that there are issues with the PKU diet over a lifetime that concern researchers. ‘The principle of dietary treatment for PKU has not changed significantly over the last 60 years, but how we do it has changed greatly. Where once patients had a choice of just a couple of low protein foods, today there are many more supplements available with different tastes, textures and compositions. Also, patients now have a number of ways to manage their blood Phe levels.’

As examples he cited:

  • patients without any diet or treatment, – or with diet only
  • patients with BH4 plus diet – or with BH4 only.


‘And these patients are all quite different’ he said. ‘Some patients have vitamin supplements while others do not. Some have meat in their diet and some have none. If you are taking a long-term meat-free diet, even if you have correct metabolic control you can be at risk of vitamin and mineral deficiencies, particularly vitamins like B12 and minerals like Selenium and Zinc.

‘We have to be careful because we don’t know what the effects of these deficiencies are over the patient’s lifetime. We need to follow up adult patients yearly and to adapt their diet or the vitamin supplements or anything they need, each time we have the results of this follow up.’

But the professor said that, at present, there is no consensus on the need to identify and correct nutritional imbalance in adults. ‘Few colleagues are adopting a policy of active nutritional intervention after the yearly follow up. I think this is because they are not yet convinced of the clinical relevance of the deficiencies.

‘This is a mistake,’ he warned ‘because we do not know the effects the deficiencies will have over 30 or so years when the patients age. I think we need to look at how specific products could be created to address these issues.’

Improving supplements


He acknowledged that creating suitable nutritional products is not easy. ‘Firstly, there is the question of the harmonisation of the product. A company that is creating a dietary supplement needs to sell its product all over the world, but the nutritional environment of all countries is quite different.

‘You are not eating the same natural proteins in France, in Japan, in the USA or in the UK, or wherever. We have different foods, we have different habits, we have different ways to eat and so on. However, to factor in these natural foods and habits, we would need to tailor the supplements for each country or sub-population. Of course, it isn’t realistic for substitutes to be adapted for each country and, even if you tried, you would need to have knowledge about the real vitamin and mineral content of the natural food and how the natural food interacts with the dietary product.

‘I think the companies are doing their best, but we hope that the problems we have detected through scientific research will be useful in the development of new products with improved composition. We particularly need to concentrate on the bioavailability of the vitamins and minerals contained in these products. Our research group is compiling a database of the nutritional status of our patients and we hope to gain a greater understanding of the balance between nutritional intake and nutritional status.’

Accepting variety


The best way to achieve dietary control may vary from country to country but why was there still no consensus on guidelines for PKU management, we asked. ‘The recommendations still vary greatly from country to country,’ agreed Prof Feillet ‘but this is because the preferred outcomes for patients also vary.

‘In France, for example, we are considered very relaxed because we accept blood Phe levels of 1,200 µmol/l in adulthood, while in some countries even 600 µmol/l is thought too high. Who is right? Obviously, we do not want to put our patients in danger by allowing poor metabolic control, but we need to consider the impact of a very strict diet for life on the quality of the patient’s life. Where is the benefit in putting an adult patient at 600 µmol/l compared with 1,200 µmol/l? In France, we feel that our adult patients are doing well; we are very happy with our patients. So, we think we are not losing anything and the patients are gaining psychological comfort, quality of life and the opportunity to eat a greater range of natural foods.’

Professor Feillet added ‘If evidence emerges that at these levels patients are suffering decreased executive functions and it is affecting their ability to have a job, enjoy a social life or is leading to problems in old age, then we will look again at our recommendations. For this reason I don’t think the world consensus is for tomorrow. But we do have to build more data on the outcomes for adult patients to find a good metabolic control range. In my research group, we have a neuropsychologist working on a new test for assessing the executive function in adulthood. I think it’s really important to assess the real capacity or the appearance of real disabilities.’

A battle won?

Battle won

With so much achieved to reduce the harmful effects of PKU and with new, better, treatments on the horizon, is the battle to provide patients with improved outcomes nearly over, we asked? ‘As a PKU specialist, my dream would be that more and more patients in the world can have access to diagnosis and efficient treatment. In many countries there is still no newborn screening, so it is impossible to detect the patient before they are sick. Then, once they have the handicap it is not that easy to treat.

‘But even if you make the diagnosis, the products are too expensive and access to treatment too difficult. If we could encourage these countries to build low-protein products we could begin to make a huge difference. Even if these products were less effective than the best currently available they could still make a huge difference. I think this should be done. I think it could be done.’

François Feillet

Centre de référence des maladies héréditaires du métabolisme
Vandoeuvre les Nancy, France