Final answer:
A genome-wide association study (GWAS) is commonly used for rare diseases. It involves comparing the genetic makeup of individuals with the disease to those without the disease, in order to identify potential genetic risk factors and therapeutic targets.
Step-by-step explanation:
A study design commonly used for rare diseases is a genome-wide association study (GWAS). In a GWAS, two groups of individuals are chosen: one group has the disease and the other group does not. The genetic makeup of these individuals is analyzed to identify differences, specifically in single nucleotide polymorphisms (SNPs), that may be involved in causing the disease. This information can be used to identify genetic risk factors and potential therapeutic targets.