Incidence is the frequency of new cases. It is equal to the number of cases (genetically affected individuals) appeared during the period considered (eg, one year) in relation to the population at risk (here, the number of births) regardless of the frequency of the disease at the time of the study.
The prevalence relates the number of affected individuals, in a given time, with the average rate of population in the same time.
Affects both male and female.
As it is said before everything depends on the disease.