Inborn errors of metabolism are a large class of genetic diseases involving disorders of metabolism.
The majority are due to defects of single genes that code for enzymes. These enzymes facilitate conversion of various substances (substrates) into other products. In most of the disorders, problems arise due to accumulation of substances which are toxic or interfere with normal function. It could also be due to the effects of reduced ability to synthesize essential compounds. Inborn errors of metabolism are individually rare but many disorders are now recognized and a significant proportion of these present during the neonatal period. Even though inborn errors of metabolism can lead to permanent damage if left untreated, many patients can now be treated successfully, especially if diagnosed at an early stage.