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.

This is a clinical and genomic study designed to investigate monogenic causes of severe early childhood obesity.

Participants with severe early onset obesity will be identified by screening of the clinical database or referred for the study. These subjects will be invited to participate in the study. After obtaining informed consent, the investigators will obtain history on the proband and the family, and perform a brief examination in addition to collecting genetic material.

Targeted sequencing of genes associated with monogenic and syndromic forms of obesity will be performed using next-generation sequencing. In selected individuals with favorable family history, exome or whole genome sequencing will be performed. Functional analysis of newly identified variants will be performed where possible.

Inclusion Criteria:

- BMI > 99th percentile documented at age < 6 years of age

Exclusion Criteria:

• Known genetic causes of obesity
• Known Endocrine causes of obesity.
• Neurologic tumor, trauma or surgery
• Prior malignancy or transplant
• Known autoimmune diseases
• Edema of a known or unknown cause
• Prolonged steroid use.

This study will enroll children with BMI > 99th percentile for age noted prior to 6 years of age. Current age of the child can vary from 0-21 years.

Deidentified data will be deposited in public databases at the end of the study