Being -MAO-A means that the enzyme acts faster than for +MAO-A.
Please note this promoter polymorphism does NOT correlate with rs6323 (MAOA R297R) as is often erroneously claimed, nor does this SNP result in a slower or faster enzyme. Actually the SNP does nothing - the product of the variant gene is identical to that produced by the wild-type gene.
In the very rare Brunner syndrome a truncated form of the enzyme was produced which did have reduced activity - but this condition is extremely rare.
These are the only significant MAOA polymorphisms that I am aware of.