THE INVESTIGATION OF INBORN-ERRORS IN-VIVO USING STABLE ISOTOPES

By labelling compounds with stable isotopes metabolic events can be st udied in vivo. Pathways can be investigated and both enzyme and substr ate kinetics measured. The concept of labelling substrates to investig ate metabolic events in vivo is straightforward but there are potentia l sources of error that must be recognised. Patients with a wide range of inborn errors have now been studied. In some there is negligible r esidual enzyme activity but in others, even those with no activity in vitro, residual enzyme activity is apparently present in vivo, probabl y as a result of metabolic activity of alternative pathways. These stu dies have demonstrated the importance of such pathways and have provid ed insight into the biochemical adaptations that occur in patients wit h inherited metabolic disorders.