Inborn errors of metabolism form a large class of genetic diseases involving congenital disorders of enzyme activities. The majority are due to defects of single genes that code for enzymes that facilitate conversion of various substances (substrates) into others (products). In most of the disorders, problems arise due to accumulation of substances which are toxic or interfere with normal function, or due to the effects of reduced ability to synthesize essential compounds. Inborn errors of metabolism are now often referred to as congenital metabolic diseases or inherited metabolic disorders. To this concept it's possible to include the new term of Enzymopathy. This term was created following the study of Biodynamic Enzymology, a science based on the study of the enzymes and their derivated products. Finally, inborn errors of metabolism were studied for the first time by British physician Archibald Garrod (1857–1936), in 1908. He is known for work that prefigured the "one gene-one enzyme" hypothesis, based on his studies on the nature and inheritance of alkaptonuria. His seminal text, Inborn Errors of Metabolism, was published in 1923. Classification and symptoms of metabolic diseases Traditionally the inherited metabolic diseases were classified as disorders of carbohydrate metabolism, amino acid metabolism, organic acid metabolism, or lysosomal storage diseases. In recent decades, hundreds of new inherited disorders of metabolism have been discovered and the categories have proliferated. Following are some of the major classes of congenital metabolic diseases, with prominent examples of each class. Because of the enormous number of these diseases the wide range of systems affected badly, nearly every "presenting complaint" to a healthcare provider may have a congenital metabolic disease as a possible cause, especially in childhood and adolescence. The following are examples of potential manifestations affecting each of the major organ systems. Diagnostic Dozens of congenital metabolic diseases are now detectable by newborn screening tests, especially expanded testing using mass spectrometry. gas chromatography–mass spectrometry-based technology with an integrated analytics system, which has now made it possible to test a newborn for over 100 mm genetic metabolic disorders. Because of the multiplicity of conditions, many different diagnostic tests are used for screening. An abnormal result is often followed by a subsequent "definitive test" to confirm the suspected diagnosis. Common screening tests used in the last sixty years: Ferric chloride test (detects abnormal metabolites in urine) Ninhydrin paper chromatography (detects abnormal amino acid patterns) Guthrie test (detects excessive amounts of specific amino