IMD WATCH
THE COSTS OF A SPECIAL DIET In a health service concerned with limited resources, cost effectiveness is a consideration, as well as clinical effectiveness. This article will consider ‘the critical requirements’ for a very low-protein diet in inherited metabolic disease (IMD), specifically highlighting the diet in PKU. This includes outlining why this investment is needed and why an understanding of the cost is required. There are a few inborn errors of metabolism for which treatment is a very low-protein diet supplemented with a protein substitute or replacement. PKU is one of these conditions. Patients are required to consume specialist prescription-only protein substitutes and low phenylalanine (Phe) foods. Treatment is lifelong.1,2 Women with PKU who are pregnant, or who are planning a pregnancy, need to take particular care to manage their condition, as high Phe levels can damage their unborn child. There are other IMDs for which a low-protein diet is indicated, such as homocystinuria (HCU), tyrosinemia and maple syrup urine disease (MSUD). Patients with IMDs on ultra-lowprotein diets are supervised and monitored by Specialist Centres across the UK, commissioned centrally.3 The specialist dietary products are prescription only, are not available commercially and are approved by the Advisory Committee on Borderline Substances (ACBS). Patients require a regular and consistent supply of a large number of prescribed products as part of the synthetic diet, otherwise metabolic control is compromised. There are an estimated 10,000 patients attending metabolic clinics. We do not know how many patients are on a very low-protein diet requiring prescribable products, but it is estimated that, in the UK, 2500 patients with PKU are on a diet and a further 60 to 70 new diagnoses of PKU occur every year.
The rationale of PKU treatment is to achieve strict blood control to prevent any brain damage or impairment in children4-7 and avoid the reduced life chances via reductions in IQ. When treatment is compromised, it is clear that children with PKU have lower IQs than their non-PKU siblings.8,9 Historically, the diet was thought necessary only for children, since the evidence base on PKU in adulthood was ‘work in progress’. The accumulated evidence is now clear that adults with uncontrolled blood Phe levels are compromised in their executive function, their mental health and their psychosocial outcomes.10-14 There is international agreement and recommendation that lifelong treatment is essential.1,2 PRESCRIPTIONS PART 1 - PROTEIN SUBSTITUTE USE IN PKU
Protein substitutes are the lynchpin of a very low Phe diet, as the patients’ protein/nitrogen and micronutrient requirements must be met.15,16 The products should be taken at least three times daily, every day of a patient’s life following diagnosis and, thus, a range of palatable products are essential.17,18 A reminder: the nutrients being substituted are macro as well as micronutrients, thus, daily doses of substitutes are high, eg, 80 tablets per day for a 55kg woman. There have been considerable efforts in the last 30 years to develop these products to aid optimum safety,
Suzanne Ford, Dietary Advisor to NSPKU Suzanne Ford is a Metabolic Dietitian working with Adults at North Bristol NHS Trust and also for the National Society of Phenylketonuria (NSPKU).
Professor Anita MacDonald, OBE Consultant Dietitian in IMD, Birmingham Children's Hospital One of the UK’s top paediatric dietitians, Anita’s specialism lies with inherited metabolic disorders.
REFERENCES Please visit the Subscriber zone at NHDmag.com
www.NHDmag.com February 2019 - Issue 141
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