Phenylketonuria (PKU) is treated by a life long reduced phenylalanine (phe) diet started as soon as possible after diagnosis. A normal diet contains more phe than can be tolerated by the child with PKU. The aim of treatment is to stabilise whole blood phe within safe limits, usually 120-350 ยต mol/L.
While the outlook for PKU is one of normal growth and development with good metabolic control, adherence to the diet and treatment plan is commonly the cause of significant stress for children and parents. Parents play a pivotal role in facilitating the child's treatment and adjustment to the condition. Parent coping requires a process of emotional adjustment, learning a complex set of new skills and long term adaptation of the family.
Apart from a diet and regular blood tests, children with PKU should be treated exactly as other children. They are no more or less likely to develop coughs, colds or other illnesses. Routine immunisations should be given at the usual times. Most medications are suitable but those containing additives 950, 951, 961 and 962 (also called Nutrasweet, Equal, Canderal, Neotame or aspartame-acesulphame), which all contain aspartame (a commonly used artificial sweetener) should be avoided if possible.
The aim of the diet is to control phe intake and provide enough phe, other amino acids, energy and micronutrients for normal growth and development. Tolerance of phe intake will vary from child to child and with age, so regular monitoring is needed.
Phe is found in all types of foods containing protein. Foods which are high in protein such as meat, chicken, fish, eggs, dairy foods, legumes and nuts are omitted from the PKU diet. Therefore a special protein supplement which provides amino acids (other than phe), vitamins and minerals is essential.
Phe is essential for growth and therefore cannot be totally eliminated from the diet. Phe tolerance is assessed biochemically and an allowance is prescribed as grams of natural protein. In infants the phe is provided as either human milk or infant formula. In children and adults measured amounts of fruits, vegetables and cereals provide the phe units.
Specially developed low protein products (bread, biscuits, pasta, rice, cheese, chocolate) are important in the PKU diet to provide energy and variety. Other foods devoid of phe are encouraged to provide energy, variety and palatability e.g margarines, oils and sugar containing foods (eg ice blocks, soft drinks).
Aspartame is a phe containing artificial sweetener used commonly in diet drinks, chewing gums and some other foods, and should be avoided in PKU. Most food labelling will list if additives 950, 951, 961 and 962 (also called Nutrasweet, Equal, Canderal, Neotame or aspartame-acesulphame) are contained in the product, and all should be avoided.
There are nutritional and immunological advantages of human milk over infant formulas. Partial breastfeeding can be combined with a low phenylalanine formula to successfully maintain blood phe levels within the safe range. This also provides the opportunity for the maternal-infant bond to be strengthened.
The initial challenge for parents is to learn how to manage the diet within the normal developmental changes of infancy e.g. starting solid foods, self feeding. For the older child a new style of eating and cooking is often necessary as making an interesting diet consisting entirely of fruit, vegetables and cereals challenges families that are used to basing meals around meat. Outings can rarely be spontaneous as suitable food must be provided.
Food refusal and fussiness is common in toddlers and in those with PKU, can impact on metabolic control. All caregivers must be familiar with the necessity of the diet and food allowed eg child care centre. School age children must cope with peer pressure to conform, and accept that the food they eat is different. Teaching children about the diet is encouraged from a young age, with the aim of self-management and acceptance of responsibility around adolescence.