All humans share the burden of genetic disease, but the spectrum of disease is not necessarily the same in all populations. The study of forces that mold the frequency of genetic disease in different populations is the subject of population genetics.
Some genes are subject to a relatively high rate of new mutation.
For example, the prevalence of neurofibromatosis type 1 is about one per 3,500 population, and 50 percent of cases result from new mutation. Disorders that arise from new mutation are widely distributed around the world, without racial or ethnic predilection. If the mutation rate is low, a genetic disorder is likely to be rare, but the forces of selection or the founder effect can lead to aberrantly high frequencies in particular populations. This is best demonstrated by the globin mutations responsible for sickle cell anemia or thalassemia. Heterozygosity for globin variants tends to confer a relative resistance to malaria.