Update: April 2009
Thanks to the financial support of the Rotary Club of Pennant Hills, the Rotary Club of Liverpool-Greenway and Australian Rotary Health, we have been able to initiate research into PKU at the Children's Hospital at Westmead. Our research currently has two main directions.
Genetic and Functional Studies of the Phenylalanine Hydroxylase (PAH) Gene: As we all know, individuals with PKU are unable to clear excessive amounts of phenylalanine from the blood because the liver enzyme phenylalanine hydroxylase (PAH) does not work properly. This in turn is a result of mistakes (mutations) in the gene that encodes PAH. To date well over 500 different mutations have been identified in the PAH gene.
There is value in knowing which PAH mutations have caused PKU in individuals for several reasons. Firstly, knowing the mutations may give us some idea as to the level of phenylalanine tolerance in that individual. Secondly, we now know that for perhaps up to a third of people with PKU, treatment with the cofactor tetrahydrobiopterin (BH4), which comes in tablet form, may lead to an improvement in phenylalanine tolerance, ie these people would be able to have a higher protein intake and yet keep their blood phenylalanine levels in the satisfactory range. We can predict with some confidence whether someone is likely to respond to BH4 treatment if we know what their PAH mutations are.
Gladys Ho, who started her PhD studies into PKU in mid 2008, has established an efficient process for screening the PAH gene for mutations. The aim is to provide us with information that will allow us to predict whether someone with PKU is likely to have more severe or milder PKU, and whether they are likely to be responsive to BH4. She has already screened DNA from over 80 individuals with PKU, and has indeed found that a significant number are likely to be responsive to BH4. This will be very important information when BH4 eventually becomes available in Australia (hopefully in the next 12 months). A form of BH4 called Kuvan, has already been approved for use in PKU patients in the US and Europe.
Gladys has also discovered a number of mutations which have not been previously reported. She hopes to be able to study the effect of these mutations on PAH function using a range of test tube studies.
If you have not yet had mutation testing done and would like to, please discuss this with the doctor who you see for your PKU management. Your doctor could then contact us to arrange for testing. There are no charges for this for patients residing in NSW.
Development of Genetically Modified Probiotics for the Treatment of PKU: Whilst there have been pleasing developments in the range of more palatable low-phenylalanine products available for patients with PKU, it would be fair to say that there have been no major advances in the dietary treatment of PKU in the last two decades. Dietary treatment of PKU becomes more onerous for everyone concerned as children mature into adolescence and adulthood. The development of new treatments that might overcome the need for diet would be a great advance in the treatment of PKU. Once such approach, gene therapy, where a correctly functioning copy of the PAH gene is delivered to the liver, where it needs to be active, would be one such approach. However, gene therapy is has a number of potential problems associated with it, and for now at least does not appear to be an option in the immediately foreseeable future.
We have decided to take a different approach, and see if it is possible to overcome the dysfunctional PAH enzyme with an alternative enzyme that might do the job of clearing phenylalanine. One such enzyme is phenylalanine-ammonia lyase (PAL). PAL is not normally found in humans (it is in yeast and plants). Research performed in Canada a number of years ago showed that if purified PAL was injected into PKU mice (yes, there is a mouse with PKU!), the blood phenylalanine levels could be reduced by up to 50%. However, purification of PAL is a time-consuming and very expensive process, and so does not seem a practical option. We have taken a different approach, that being to see if we can genetically modify probiotic organisms (eg Lactobacillus and Lactococcus, which are harmless bacteria that have been found to have many health benefits when regularly consumed), so that they can make PAL. The idea is that the genetically modified PAL-producing probiotics could taken be taken on a regular basis, and break down dietary phenylalanine in the gut before it is absorbed into the bloodstream. If this approach worked then it should be possible for the diet to be relaxed, allowing a higher natural protein intake.
It has proven quite tricky working with the probiotic bugs because they are finicky little critters! However, XingZhang Tong, a postdoctoral research scientist in our laboratory, has been working hard at this, and we now believe he has been able to trick a Lactococcus bug to make PAL. There is much work to be done to make this process as efficient as possible, but we hope to be able to commence studies to assess the safety and effectiveness of our GM Lactococcus in one of the PKU mouse models in the next 12-18 months. If these studies are promising, then we would hope to move into human trials after that.
There is still much work to be done, but we are excited about our results so far. We hope that with ongoing support we will be able to progress these two research themes to the benefit of everyone touched by PKU.