CTNNA1 Familial Expansion Study

This study (the CTNNA1 Familial Expansion Study) is collecting clinical data and biological samples from people who carry a loss-of-function variant in the CTNNA1 gene, or who are a close relative of someone who does. CTNNA1 mutations are linked to a hereditary form of diffuse gastric cancer. The goal is to better understand how this genetic variant is associated with cancer risk and other health outcomes over time. **You may be eligible if...** - You are 18 or older - You carry a CTNNA1 loss-of-function variant (a genetic change that disrupts the gene's function), OR you are a first-degree relative (parent, sibling, or child) of someone who does - You can read and understand English and provide informed consent **You may NOT be eligible if...** - You are under 18 - You do not carry the variant and are not a direct family member of a carrier - You cannot speak or read English - You have major psychiatric illness or cognitive impairment that would prevent you from participating Talk to your doctor to see if this trial is right for you.