Disease mapping using association

Allele D is found more frequently among cases than controls.

We can say that a marker allele is associated with a disease if the allele is found more frequently among cases than in the background population, or in a group of unaffected controls.

Causes of association

• Direct effect of polymorphism on risk
• Linkage disequilibrium
• Population stratifications

Tests for association

• Case-control studies
• Transmission-disequilibrium test
• Using siblings to provide control alleles