This clinical trial is focused on studying a rare genetic disorder called Mucopolysaccharidosis Type II, also known as Hunter Syndrome. This condition affects the body’s ability to break down certain complex sugars, leading to various health issues. The study involves a treatment called JR-141, which is a medication in the form of a lyophilized powder that is prepared for injection. The active substance in JR-141 is pabinafusp alfa, a type of protein. The medication is administered through an intravenous injection, which means it is given directly into a vein.

The purpose of this study is to evaluate the long-term effects of JR-141 on symptoms affecting the central nervous system in individuals with Hunter Syndrome. Participants in this study will have previously completed a related study and will continue to receive JR-141 to assess its safety and effectiveness over an extended period. The study will monitor various health aspects, including liver and spleen size, shoulder movement, and walking ability, as well as other health indicators like heart and lung function.

Throughout the study, participants will undergo regular assessments to track their quality of life, sleep patterns, and overall health. These assessments will help researchers understand how JR-141 impacts the symptoms of Hunter Syndrome over time. The study aims to provide valuable insights into the long-term benefits and safety of JR-141 for individuals living with this condition.