Proportion of phenotype in populatuion

I am dealing with the following problem and would like to ask for your opinion and help.
I am looking at a population where large portion of the population have a certain genotype G. Some of the carriers present a certain medical condition M, which is suspected to be a phenotype (it is possible that other factors are involved). The initial goal is to determine if the proportion of M in the population of G carriers is (in some sense) “large”.

Also, note that testing for G is not routine, and the test result can be of course positive or negative (we can assume 100% accuracy/precision etc.). The reasons for reffering a patient to test for G are more or less the same for both positives and negatives, and therefore we can assume that the populations fo positives and negatives are similar.

We consider the following aproaches:

  1. Match the carriers to a cohort from the general population (and then should we include the G-negarive in the general population?
  2. Compare the G-positives to the G-negative.
  3. We know the real proportion of M in the general population (we have the full data), and therefore we can consider the proportion of M as a constant and proceed accordingly.

Thank you for your help!