Two enzyme of keratan suphate metabolism can be deficient: either N-acetylgalactosamine-6 sulfatase or beta-galactosidase, also mutated in Galactomannan 1-gangliosidosis. Children with fructose 1, 6-bisphosphatase deficiency have a greater tolerance to fructose than those with hereditary fructose intolerance as they can metabolise fructose 1-P to lactate. Ammonia, the key diagnostic metabolite in the acute setting, is a respiratory stimulant and a respiratory alkalosis may be found early in the illness. Any new hyperammonaemic patient should be transferred to a metabolic centre. Ammonia is neurotoxic and lowering the plasma concentration immediately is essential. Once treated, children often have further episodes of metabolic decompensation, especially during periods of intercurrent illness. Ketone bodies acetoacetate and 3-hydroxybutyric acid are metabolites derived from fatty acids and ketogenic amino acids, such as leucine. Children with untreated phenylketonuria may have blond hair, blue eyes and fair skin due to metabolic defect restricting melanin production.