Incidence of inborn errors of metabolism in British Columbia, 1969-1996

Objective. To determine how many children with specific types of inborn err ors of metabolism are born each year in British Columbia, Canada. This popu lation provides a relatively unique setting for collection of accurate and uniform incidence data because the diagnoses are all made through one labor atory in a population with universal access to government-funded medical ca re. Methodology. We used the records of the Biochemical Diseases Laboratory, Ch ildren's Hospital, Vancouver (the central referral point for all metabolic diagnoses in British Columbia) to identify all patients diagnosed with the metabolic diseases defined below. We obtained incidence figures by includin g only the children diagnosed with the diseases covered in this article who were confirmed as having been born within the province for the years 1969 to 1996. The diseases covered were diseases of amino acids, organic acids, the urea cycle, galactosemia, primary lactic acidoses, glycogen storage dis eases, lysosomal storage diseases, and diseases involving specifically pero xisomal and mitochondrial respiratory chain dysfunction. Because the techno logy needed for diagnosis of specific disease groups was in place at differ ent times our data for the different disease groups correspond to different time frames. We have also adjusted the time frames used to allow for the l ikelihood that some diseases may not come to medical attention for some tim e after birth. For instance the incidence of amino acid diseases was assess ed throughout the whole of this time frame but the incidence of peroxisomal diseases was restricted to 1984 to 1996 because this was the time frame du ring which the technology needed for diagnosis was in place and reliable. M ost disease group statistics included at least 400 000 births. Results. The overall minimum incidence of the metabolic diseases surveyed i n children born in British Columbia is similar to 40 cases per 100 000 live births. This includes phenylketonuria (PKU) and galactosemia which are det ected by a newborn screening program. Metabolic diseases, which were not sc reened for at birth, ie, those with PKU and galactosemia subtracted from th e total, have a minimal incidence of similar to 30 cases per 100 000 live b irths. This diagnostic dilemma group would present to pediatricians for dia gnosis. Not all metabolic diseases have been surveyed and our data are rest ricted to the following metabolic disease groups. Approximately 24 children per 100 000 births (similar to 60% of the total disease groups surveyed) h ave a disease involving amino acids (including PKU), organic acids, primary lactic acidosis, galactosemia, or a urea cycle disease. These children all have metabolic diseases involving small molecules. Approximately 2.3 child ren per 100 000 births (similar to 5%) have some form of glycogen storage d isease. Approximately 8 per 100 000 births (20%) have a lysosomal storage d isease; similar to 3 per 100 000 births (7%-8%) have a respiratory chain-ba sed, mitochondrial disease and similar to 3 to 4 per 100 000 (7%-8%) of bir ths have a peroxisomal disease. The diseases involving subcellular organell es represent approximately half of the diagnostic dilemma group. The incide nce of each of the specific diseases diagnosed, including apparently rare d iseases such as nonketotic hyperglycinemia, is to be found in the text. The metabolic diseases reported in this survey represent over 10% of the total number of single gene disorders in our population. Conclusions. Our data provide a good estimate of metabolic disease incidenc e, for the disease groups surveyed, in a predominantly Caucasian population . Incidence data for metabolic diseases are hard to collect because in very few centers are diagnoses centralized for a population with uniform access to modern health care and this has been the case for our population during the course of the study. We foresee a need for accurate information on the incidence of metabolic diseases as a guide to how to provide diagnostic an d therapeutic services for metabolic diseases and the figures should help i n assessing such needs in similar populations.