Hunter Syndrome (MPS II) Enzyme Replacement Therapy (ERT) Extension Study

Mucopolysaccharidosis II (MPS II) or Hunter syndrome, is a rare genetic disorder caused by the decreased levels of a specific enzyme, iduoronate-2-sulfatase. Lack of this enzyme causes buildup of large sugar molecules called glycosaminoglycans (GAGs). The build up of GAGs causes significant damage to the body and brain. This study will evaluate the long-term use of DNL310, an enzyme replacement therapy, to provide the missing enzyme to the body and to break down the stored GAGs. DNL310 uses specific technology to cross the blood brain barrier so that the enzyme can get into the brain. DNL310 is expected to help both the cognitive (brain) and body effects of MPS II. This is an extension study to two current DNL310 clinical trials; only participants currently enrolled in these trials will have the opportunity to participate in this long-term study.