An important caveat for all genotyping tests is that the decision to assign an allele a "wild- type" status is based upon a genotyping test that interrogates only the most common and already-proven sites of functional variation. In human DNA, it is always possible that a new, previously undiscovered (and therefore un-interrogated) site of variation may confer loss-of- function in an individual, and thus lead to the rare possibility of a non-functional allele being erroneously called as "wild-type"