Congenital Hyperinsulinism is the most common cause of low blood sugar (hypoglycemia) in infants and children.Infants who are born with this problem have low blood sugar, which can cause seizures or brain damage.

We are doing this study to see if the patterns of abnormalities in controlling insulin in children and adults with hyperinsulinism are related to any underlying genetic cause and to identify possible new genetic causes.This will be done by standard clinical tests of insulin control: a glucose tolerance test, a protein tolerance test, and a fasting test.

Our team is working on a study to better understand neurological problems, including seizures and developmental delays, that occur in children with hyperinsulinism, including HI/HA syndrome, and type 1 diabetes mellitus. The study involves a one-day visit to The Children's Hospital of Philadelphia and The University of Pennsylvania for a specialized magnetic resonance imaging scan (MRI) of the brain, an electroencephalogram (EEG), blood draw, and completion of questionnaires to evaluate development and behavior. The entire study visit is expected to take about five hours. If you are interested in learning more, please contact us at HIResearch@email.chop.edu.

Our team is working on a study to better understand neurological problems, including seizures and developmental delays, that occur in many individuals with HI/HA syndrome. The study involves a one day visit to The Children's Hospital of Philadelphia and The University of Pennsylvania for a specialized magnetic resonance imaging scan (MRI) of the brain, an electroencephalogram (EEG), blood draw, and completion of questionnaires to evaluate development and behavior. The entire study visit is expected to take about four hours. If you are interested in learning more, please contact us at HIResearch@email.chop.edu.

You or your child are being asked to take part in this research study because you have Glycogen Storage Disease Type III (GSD III). The purpose of this research study is to better understand blood sugar variability, muscle strength and function, and impact of Glycogen Storage Disease Type III (GSD III) on overall health. You will not receive any treatment for your GSD III as part of this study, but the information you provide 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 about 26 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 III as part of this study.

As a participant in the research you will:

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

The main risks of this study are from hypoglycemia related to your diagnosis of GSD III and a loss of confidentiality. There are no direct benefits to you for participating in this study but the information collected as part of this study will help researchers better understand GSD III.

We are currently enrolling adolescents ages 15-21 of South Asian ancestry, African American ancestry, and European American or "White" ancestry. This study is looking to better understand ancestry related differences in risks for developing cardiovascular disease and type 2 diabetes. The study involves 2 visits to the CHOP Main Hospital in Philadelphia, and participants will be compensated for their efforts.