With Regard to Treatment of Inborn Errors of Metabolism (IEM)

With regard to treatment of inborn errors of metabolism (IEM) , which of the following statements, if any, is false?

A) IEMs are all single gene disorders that have been studied for many decades, leading to the development of successful treatment in all cases.
B) IEMs can be treated by augmentation therapy, treatment to inhibit positively harmful effects, or by prevention therapy.
C) Treatment for some individual IEMs can involve both augmentation therapy plus treatment to inhibit positively harmful effects.
D) Treatment of some IEMs involves artificially forcing an increase in a minor metabolic pathway to counteract a build-up in a toxic metabolite produced by a metabolic block in a major metabolic pathway.