Background: There are few centres which specialise in the care of adults with inborn errors of metabolism (IEM). To anticipate facilities and staffing needed at these centres, it is of interest to know the distribution of the different disorders.

Methods: A survey was distributed through the list-serve of the SSIEM Adult Metabolic Physicians group asking clinicians for number of patients with confirmed diagnoses, types of diagnoses and age at diagnosis.

Results: Twenty-four adult centres responded to our survey with information on 6,692 patients. Of those 6,692 patients, 510 were excluded for diagnoses not within the IEM spectrum (e.g. bone dysplasias, hemochromatosis) or for age less than 16 years, leaving 6,182 patients for final analysis. The most common diseases followed by the adult centres were phenylketonuria (20.6%), mitochondrial disorders (14%) and lysosomal storage disorders (Fabry disease (8.8%), Gaucher disease (4.2%)). Amongst the disorders that can present with acute metabolic decompensation, the urea cycle disorders, specifically ornithine transcarbamylase deficiency, were most common (2.2%), followed by glycogen storage disease type I (1.5%) and maple syrup urine disease (1.1%). Patients were frequently diagnosed as adults, particularly those with mitochondrial disease and lysosomal storage disorders.

Conclusions: A wide spectrum of IEM are followed at adult centres. Specific knowledge of these disorders is needed to provide optimal care including up-to-date knowledge of treatments and ability to manage acute decompensation.