Defining the Etiology of Childhood Obesity Through DNA Exploration; a Study Investigating Clinical Application of Genetic Testing in Childhood Obesity

Childhood obesity is a major and growing health concern in the UK. Around 1 in 7 children aged 2-15 are living with obesity, which can lead to serious health problems and early death later in life. Some children develop obesity very early, before the age of 5. We now know that genes (our biological instructions) can play an important role alongside lifestyle and environment. Certain rare single-gene conditions ("monogenic obesity") can strongly influence a child's weight.

The NHS already offers genetic testing for children with severe early-onset obesity, but we do not yet know how useful these tests are in everyday clinical practice. This study will help answer that question.

The DECODE study will look back at information already collected from children aged 2-18 who attended specialist Complications of Excess Weight (CEW) clinics in England between 2021 and 2025. These clinics support children with severe obesity and related health problems. The study will include children whose obesity started before age 5 and who have already had one or both NHS genetic tests: the R149 obesity gene panel or a comparative genomic hybridisation (CGH) array (a test that looks for missing or extra pieces of DNA).

We aim to find out how often these tests detect a genetic cause of obesity ("diagnostic yield") and whether certain clinical features-such as developmental delay, neurodivergence, short stature or different eating behaviours -help predict a positive result.

No new tests or visits are required for this study. Only anonymised information from medical records will be used. Around 500-800 children from up to ten hospitals are expected to be included.

The findings will help the NHS understand who benefits most from genetic testing and how results can guide treatment, support families, and shape future services.