Phenylketonuria (PKU) : Introduction to PKU for Primary Care Clinicians

Phenylketonuria (PKU) is a rare autosomal recessive inborn error of metabolism caused by deficiency of the enzyme phenylalanine hydroxylase, which normally converts phenylalanine to tyrosine. In its absence, phenylalanine accumulates to toxic levels, leading to progressive brain damage and intellectual disability if untreated.

In the UK, PKU is detected through newborn blood spot screening on day 5, enabling early diagnosis and dietary intervention. While patients under specialist metabolic care are usually well managed, primary care clinicians play an important role in:

• Ensuring newborn screening is completed and results acted upon promptly.

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• Recognising potential signs in undiagnosed or poorly controlled children (e.g. developmental delay, fair complexion, musty odour).

• Supporting families with dietary management, especially during intercurrent illness, adolescence, and pregnancy.

• Being aware of contraindications (notably aspartame-containing products) and the need for close coordination with metabolic teams.