I’ve been meaning to write about this for some time; however, life kept getting in the way. I thought it would be important to write down our experience of trialing Sapropterin.

At first, I was very suspicious of Sapropterin. I understand that for those children on very low exchanges, this would potentially be a life-changing treatment. Just a small increase in protein could make a big difference in their quality of life. Since Keir was already on 10 exchanges a day, we felt that this was quite a large number of exchanges, and we were concerned about potential side effects and nervous about the changes that we would need to make to Keir’s diet.

Shortly after Sapropterin became available in the UK on the NHS, Keir and I attended the clinic together at GOSH (Great Ormond Street Hospital). We met with the Dietitian and the Pediatrician, and discussed Sapropterin. It was pointed out that a blood test would need to be carried out to determine if Keir was a likely responder, followed by a trial. I asked questions about the benefits and potential consequences in terms of the trial not being successful, as well as potential side effects. After being reassured, both Mum and I decided that it should be up to Keir to decide. He was very keen to go ahead and see if he could have more exchanges.

The first step was a blood test to check his mutation type to give an indication of whether he is likely to be a responder. Keir and I traveled to GOSH in November 2021. Keir was extremely brave, and I almost cried for him as this was not pleasant. Keir is used to the Guthrie tests; however, the nurse at the clinic wanted to take a lot of blood, and her preferred method was to take it from the back of his hand. He had some gel applied to the back of his hand to help numb it, and then, after a short wait, a cannula was inserted. Keir had tears in his eyes, and he did say it really hurt. He looked quite shocked from the whole experience but told the nurse she could go ahead. I was extremely proud of how brave he was.

We then had to wait for the results. This took an extremely long time to get – about a year and a half. When we received them, it was a bit of a surprise. As you likely already know, Keir inherited two PKU genes, one from Mum and one from Dad. It turned out that only one child in the world has a match with one of the genes, and the other had no other match. We understood from GOSH that this was unusual, and typically there would have expected about 500 or more other children with matching genes. Keir was extremely proud to be so unique. We concerned that the gene that matched with another child was labeled as not responsive to Sapropterin. So we had no idea whether Keir was going to be a responder.

After discussions with the dietitian, it was agreed that Keir could start the trial. In part because we did not know if the gene that Keir shared with the other child was dominant or recessive, the statistics were low, and Keir had a relatively high exchange number, which could indicate he would likely respond.

It was October 2022 when we started the trial. We had to push Keir’s exchanges to the limit of what he could take before taking Sapropterin. This made me nervous. We had always taken a fairly conservative approach to exchanges, trying to keep his test results below 250. We also had a hiccup as Keir had a fever once we started increasing his exchanges, but luckily, he soon got over this. We pushed his exchanges to 15, where he averaged approximately 370, and then started taking Sapropterin. I thought the Sapropterin would come in the post, but it turned out not to – I had to drive to GOSH to get the medicine on a Friday. I was very thankful to the pharmacist who agreed over the phone to stay late for me, and very glad that subsequent prescriptions would be delivered by post.

The next step was to take the Sapropterin. Keir was keen to take this in apple juice with a syringe, just like a friend he had seen take it at the NSPKU conference. His blood test results quickly came back with his levels dropping to between 100 and 150. We were so relieved and happy for Keir. The next step in the test was to increase his exchanges. This felt a little daunting as we understood his target was 30 exchanges.

We did this and nervously and very gradually increased his exchanges to 30! He has been on 30 exchanges now for a couple of months, and we understand that the next step of the trial is to reduce the number of Sapropterin tablets he takes – he is taking 5 of these every morning. We’ll let you know how this stage goes. However, while it has been a long journey, we are so pleased for Keir. It has made such a difference to his diet – increased portions of natural protein, and he has been able to try foods he thought he would never have, such as eggs, regular pasta, and bagels (he has been enjoying them very much).

We kept reservations about introducing new foods into Keir’s diet in case he didn’t pass the trial and had to give up his extra exchanges. We thought it would be awful and hard to ask him to give them up.

New foods that we have introduced: Regular Pasta, Fresh Eggs from our own hens, Regular Bread, Regular Bagels.

He is also enjoying having bigger portions of his favorite foods like breakfast cereals, ice cream cones (no ice cream), and chips. His favorite chips are homemade chips with low-calorie spray (a Slimming World Recipe).

Here is the official website for information about sapropterin: https://www.sapropterin.teva/

If you have any questions about the trial, please feel free to drop us a message in the comments box or privately if you prefer, and we will get back to you as soon as we can.

Erik (Keir’s Dad)