Atypical genetic variant exist for plasma cholinesterase but not for AChE, why?

Answer 1

It is difficult to assign specific etiologies to genetic variants, since they arise and occur rather randomly, as a result of chance mutation that can persist

Answer 2

there are two different enzymes: plasma cholinesterase and another enzyme called pseudocholinesterase. the pseudocholinesterase is the one responsible for metabolizing acetylcholine.

Answer 3

I imagine that AChE is so important and necessary that any mutation is considered undesirable and not compatible with life. Just a guess.