ABSTRACT
An error may occur in any metabolic pathway due to a genetically inherited enzyme defect. A characteristic phenotype results and many of the defects can now be identified by enzyme assays or by DNA technology. Most are recessively inherited and the majority are uncommon, but they may cause severe neurological impairment and are often fatal. An enzyme deficiency results in organ damage by:
• accumulation of the enzyme substrate, e.g. hyperphenylalaninaemia in phenylketonuria (PKU), glycogen due to defects of the glycogen degradation pathway.
