RecruitingStudy to Investigate Genetic Causes of Severe Early Childhood Onset Obesity.This study aims to investigate genetic causes of early childhood obesity. The investigators will enroll children and adults with severe early onset obesity (BMI \> 99th percentile) diagnosed prior to 6 years of age. The investigators will ask questions about the health and eating behavior of the participants, and perform a brief physical examination. The investigators will collect saliva or blood to perform genetic testing from the participants and invite family members to enroll in the study.