Rare genetic tweaks may not be behind common diseases

Variants thought to be behind inherited conditions prove difficult to pin down

SAN FRANCISCO — Rare tweaks in single letters of DNA are not as powerful a force in health and in common diseases as scientists hoped, new work suggests.

Common genetic variants contribute only a tiny bit to a person’s risk of developing particular diseases, so researchers have turned to rare variants as a possible explanation for why some people inherit a propensity for heart disease, diabetes or other common ailments.