Hyperammonemia:

Why do organisms required to detoxify ammonia in the first place? The answer to this question is obvious when one considers what happens if there is a block in

Figure:  The urea cycle and the citric acid cycle are linked by fumarate and the transamination of oxaloacetate to aspartate.

the urea  cycle  due  to  a  defective  enzyme.  The block in any of the urea cycle enzymes leads to an increase in the amount of ammonia in the blood, so-called hyperammonemia. The most general cause of such a block is a genetic defect which becomes   apparent   soon after birth, when the af?icted   baby becomes vomits and lethargic periodically.  If left untreated, irreversible brain damage and coma will follow.  The  motivation  for  this  are  not  entirely  clear  but  should  be because the excess ammonia  leads to the increased  formation  of glutamine and glutamate.  These  reactions  result  through  depletion  of the citric  acid  cycle  intermediate   α-ketoglutarate  that  may  then  compromise energy  production and  especially  in the  brain.  It also leads to an increase in the acidic amino acids glutamate and glutamine that should straightly cause damage to the brain.