Adult patients with inherited metabolic disease tend to fall into one of two groups; 1) those who presented in childhood and have been successfully managed by paediatric services and then transferred to the adult clinic; and 2) those who present for the first time in adulthood.
As patients diagnosed in childhood grow older, the emphasis shifts from their growth and development to dealing with long-term complications and living with a chronic condition. For those patients who first present in adulthood, diagnosis may be delayed as awareness of metabolic disease is generally not as high among general adult physicians as among paediatricians. Management is focused on preventing progression of disease and/or acute metabolic decompensation, with an overall aim of helping an adult to achieve their potential, play a full role in society and raise a family of their own if they wish.
Transition of a young person from paediatric to adult services should begin early to prepare a teenager (and their family) for the move to adult services. Encouraging independence and self-confidence is important to allow young people to deal with potentially complex issues such as a modified diet, multiple medications, physical and/or learning disability, fertility and heredity issues. Specialist centres have a role in monitoring and managing the long-term complications specific to adult patients and supporting patients, parents and carers in accessing appropriate services as required (eg. community adult learning disability teams, patient support groups, advocacy services, respite care, adult educational services etc).
Patients surviving into adulthood may wish to have children of their own. Issues of fertility (eg. galactosemia), prenatal/preimplantation diagnosis, teratogenicity (eg. PKU), potential metabolic decompensation (eg. urea cycle defects) and energy requirements during labour and delivery thus need to be addressed.
Training of doctors/nurses/dietitians specialising in inherited metabolic disease in the adult patient is currently limited in many countries, and in many cases care continues to be provided well into adulthood by paediatricians. This is slowly beginning to change as a number of countries have introduced specific training programmes for the diagnosis and management of inherited metabolic disease in adults.
Long-term outcomes in treated patients with inherited metabolic disease remain uncertain. International patient registries and multi-centre case series will be important in determining outcome and response to more recent therapies (particularly high-cost medications), and hence providing the data on which the future allocation of resources and management guidelines may be based.