Meeting of the Parliament 13 January 2026
I thank Fulton MacGregor for bringing this very important topic to the chamber. I feel privileged to have the opportunity to speak about phenylketonuria, known as PKU, which is a rare inherited metabolic condition, and the serious issues that face people in Scotland who are living with it.
PKU affects how the body breaks down phenylalanine, which is a natural part of protein. When levels build up in the blood, they cause damage to the brain; that damage is permanent and cannot be reversed. In Scotland, babies are diagnosed early through newborn screening, and that early diagnosis is vital. However, diagnosis is only the beginning—living with PKU is lifelong and demanding.
For decades, the main treatment has been a highly restrictive, low-protein diet. As we heard, protein intake must be tightly controlled every day, for life. Even when that diet is followed extremely well, there is evidence of on-going effects on brain health. We must consider the impact on those who struggle to maintain such a strict regime over many years. The reality is that that dietary treatment places a huge burden on individuals and families.
On hearing that I would be speaking in the debate, my friend and former colleague Alison Harris got in touch with me, as her family has experienced PKU at first hand. Her cousin John and his late wife AnneMarie had three children, all living with PKU. Throughout their entire lives, they have had to be extremely careful, and AnneMarie and John have worked tirelessly to ensure that they are on the correct diet.
That experience reflects what many families across Scotland face—quietly, every day. It affects education, employment, mental wellbeing and social life and it requires constant planning and monitoring, with very little flexibility.
That is why the medicine sapropterin, also known as BH4, which was approved for NHS use in Scotland in 2022, is so important. For some people with PKU, BH4 can significantly reduce phenylalanine levels and allow for a less restrictive diet. It does not remove all dietary requirements and limits, but it can reduce daily pressure and improve quality of life. For those who can access it, it is genuinely life changing.
However, despite the treatment being approved and available, many adults in Scotland are unable to access it—not because it would not work for them, but because the pathway that is required to start it, including response testing, is not consistently available. That raises a fundamental issue: a medicine that exists but cannot be accessed is not delivering any benefit. Availability on paper is not the same as access in practice.
I ask the Scottish Government for a clear commitment. Will it commit to identifying and removing the barriers that are preventing people with PKU from accessing BH4 in Scotland? Will it commit to supporting those individuals now, rather than leaving them reliant on diet alone, despite clear evidence that diet is not always enough?
Looking ahead, Scotland must also be ready to evaluate and adopt future treatments, such as sepiapterin, without unnecessary delay, so that people living with PKU are not once again left waiting for years to get access. That is not about convenience—it is about protecting brain health, reducing lifelong harm and recognising the limits of dietary treatment.
PKU may be rare, but its impact is lifelong. Families are doing everything that is asked of them, and it is time for the system to meet them with the same level of commitment. Scotland can do better for people who are living with PKU, and we must.
17:25