Research Study for Patients with GSD III

You or your child are being asked to take part in thisresearch study because you have Glycogen Storage Disesase Type III (GSD III).The purpose of this research study is to better understand blood sugarvariability, muscle strength and function, and impact of Glycogen StorageDisease Type III (GSD III) on overall health. You will not receive anytreatment for your GSD III as part of this study, but the information youprovide will be helpful for the study sponsor, Ultragenyx Pharmaceutical Inc.,to develop a new therapy for GSD III.

If you agree to take part, your participation will last for about26 weeks and will involve up to 2 study visits to the hospital along with up to 26 phone calls. There will be no changes to your treatment regimen for GSD IIIas part of this study.

As a participant in the research you will:

• come to the hospital for 1-2 in person visits tocomplete interviews and questionnaires,
• wear a blinded continuous glucose monitor (CGM) 3months and an unblinded CGM for 3 months,
• complete fingerstick blood sugar checks, maintain a nutrition diary for 3 or more weeksthroughout the study,
• maintain a hypoglycemia symptom diary, and
• upload CGM and HHG device data to astudy-provided laptop weekly.

The main risks of this study are from hypoglycemia related toyour diagnosis of GSD III and a loss of confidentiality. There are no directbenefit to you for participating in this study but the information collected aspart of this study will help researchers better understand GSDIII.