Hereditary urea cycle diseases in Finland

Aim: To estimate the incidence of urea cycle diseases (UCDs) in Finland and determine the course of the various disorders as well as the outcome. Methods: The original data were collected in the years 1998-2001. The diagnoses made after 2001, as well as the current status of the patients, were updated by surveys in the spring of 2007. Results: We found a total of 55 cases of UCDs in Finland by 2007: 30 cases of ornithine transcarbamylase (OTC) deficiency, 20 of argininosuccinate lyase (ASL) deficiency, 3 of carbamyl phosphate synthetase (CPS-I) deficiency, 1 of type 1 citrullinaemia and 1 of argininaemia. The estimated total incidence of UCDs was 1:39 000. The incidences of individual disorders were: OTC deficiency 1:62 000, ASL deficiency 1:144 000, CPS deficiency 1:539 000 and citrullinaemia 1:1 616 000. Eighteen (33%) of the patients with a diagnosis of UCD have died, most during their first hyperammonaemic crisis. One patient with OTC deficiency has had a liver transplant. Neurological symptoms of varying severity are common among these patients, particularly those with ASL deficiency. Conclusion: The first survey on the incidence of UCDs in Finland shows some differences in the occurrence rates compared to other countries. Hyperammonaemia, and the neurological symptoms caused by it, can be avoided in most patients with late-onset UCDs with a standard treatment. However, in patients with ASL deficiency, the development of neurological symptoms seems to be inevitable in spite of careful treatment and avoidance of hyperammonaemia.