Abstract
In the recently developed International Classification of Inherited Metabolic Disorders (ICIMD), more than one third of the 1450 listed conditions involve gene products required for intermediary metabolism. 225 of these diseases represent deficiencies of enzymes or transport proteins in the breakdown of nutrients, many of which cause acute "metabolic" presentations with typical biochemical features that are amenable to specific treatments. A group-based approach to these conditions not only assists in understanding and remembering them but facilitates the best choice of diagnostic tests and acute treatment. This review describes the basic characteristics of the 25 disease groups in the four categories of nutrient breakdown in intermediary metabolism, outlines the often relatively straight-forward diagnostic approach, and summarizes important therapeutic principles. It should also assist in the retrospective identification of likely metabolic disorders in the family history for genetic counselling.