This study will follow Mucopolysaccharidosis Type II (MPS II) patients after enrolling and receiving study drug RGX 121 in the parent study RGX 121-101. The purpose of this study is to determine drug safety and efficacy of RGX 121. No study drug is being given in this study.

If you agree to take part, your participation will last for up to 3 years after having completed participation in the parent studies. It will include up to 7 visits: up to 4 on-site study visits and 3 check-ins (e.g., over the phone or by internet). The impact of RGX-121 on biomarkers in patients' cerebrospinal fluid (CSF), blood plasma, and urine will also be evaluated in the long-term.

This research study is called the Lysosomal Storage Disease Registries. A registry is a database that gathers information about people and their medical treatment. This observational registry is supported by Genzyme Corporation. The goal is to collect information on people with Gaucher, Fabry, MPS I, or Pompe disease. The information might be used for many different research studies about Lysosomal Storage Diseases. It is hoped that healthcare professionals can use this information to better understand these diseases. We expect these registries will continue for a number of years.

This is an observational registry study intended to document the course of Lysosomal Acid Lipase Deficiency (LALD), in order to further understand the disease, its progression, which treatments are effective, and any related complications. As an observational study, no additional study visits - outside of subjects usual Metabolism clinic visit - are required. Eligible patients will be asked to sign an informed consent form prior to enrollment and will periodically have the option of completing questionnaires about their quality of life.