A series of biochemical reactions comprises the metabolic functions in biological entities. The micro- and micronutrition are processed in different pathways through anabolic or catabolic reactions. IEM refers to partial dysfunction of any enzyme involved in these biochemical pathways. The partial malfunction is caused genetically as a result of a mutation or alteration in nuclear or mitochondrial genes responsible for programming, controlling and executing the metabolic functions. The pattern of inheritance is variable, as well as the age of onset, the manifestation and the severity.

The defects have considerable adverse impact, usually with systemic manifestations. The outcome largely depends on the extent of the deactivation of the affected enzyme. The high percentage of defects leads to steady production of toxic intermediate metabolites. Depending on their affinities, these metabolites reside in different tissues or organs and accumulate over time. The accumulation rate correlates with the defect percentage and defines the progression course.