This study is for patients with **Autosomal Dominant Polycystic Kidney Disease (ADPKD)**, a genetic condition that causes cysts in the kidneys. The study tests a drug called **RGLS8429** to see if it's safe and how it affects the disease. It's a **Phase 1b** trial, meaning it's in early stages to check safety and dosage. The study has two parts. In **Part A**, different doses of RGLS8429 or a placebo (a substance with no active drug) are given through a shot under the skin. In **Part B**, a fixed dose is given, also by injection. The study looks at how the drug affects kidney size, function, and its journey through the body (pharmacokinetics). Participants must be 18-70 years old, have specific kidney measurements, and agree to the study rules. You can't join if you've had certain drugs recently or have other medical issues.

• **Length**: Study has two parts with multiple injections.
• **Visits**: Regular visits for injections and monitoring required.
• **Risks**: Possible side effects from the drug or placebo.