In a study of inheritance of the cystic fibrosis gene (CFTR), the genetic mutations in carriers and affected individuals are documented. Based on these findings, investigators determine that there is no simple screening test to detect all carriers of mutations of the CFTR gene. Which of the following is most likely to be the greatest limitation to development of a screening test for CFTR mutations?

When a genetic disease (e.g., cystic fibrosis) is caused by many different mutations, with different frequencies among populations, there is no simple screening test that can detect all the mutations. Although 70% of patients with cystic fibrosis have a 3-base pair deletion that can be readily detected by PCR (the AF508 mutation), the remaining 30% have disease caused by several hundred allelic forms of CFTR. To detect all would require sequencing of the CFTR genes. This prohibits mass screening. The other listed options do not apply.