Endocrine Abstracts

Background: Monogenic obesity is generally considered to only be responsible for a small proportion of genetic obesity with the vast majority attributable to polygenic obesity. Previous studies estimate that monogenic obesity accounts for less than 5% of obesity in Caucasian populations.

Aims and method: To identify prevalence and clinical characteristics of monogenic obesity, we reviewed clinical notes of 219 patients currently, or recently (within 24 months), under the care of a tier 3 childhood obesity service. In those with positive genetic results, testing was mostly performed using targeted obesity gene panels or by CGH array in a minority of patients for another clinical reason. Genetic testing for monogenic causes was particularly considered in patients with early-onset obesity before 5 years of age or defining clinical features. Prader-Willi and Beckwith-Wiedemann syndrome were excluded from the analysis.

Results: In a cohort of 219 patients, we identified 26 with mutations in single genes and 2 with specific chromosomal deletions implicated in early onset obesity. Overall, the prevalence of monogenic obesity in our cohort was 12.7%. MC4R mutations were the most frequent monogenic cause. Of these 28 patients, mean parentally-reported age of onset of obesity was 19.3 months (range 6-48 months) and mean age of referral to our service was 7.1 years (range 1-15 years). Mean BMI-SDS in these patients was +3.45 (range 1.90-5.45). 19/28 (67.8%) patients had hyperphagia, 14/28 (52%) behavioural difficulties and 3/28 (11%) a diagnosis of autism. 17/28 (60.7%) patients had a family history of obesity.

Discussion: Diagnosis of genetic obesity is important as some forms have personalised treatment (e.g. Setmelanotide for LEPR, PCSK1, POMC) and may help reduce stigma. Monogenic obesity is probably not as rare as previously described, increasingly being detected by targeted gene panels. Onset under two years of age, hyperphagia, behavioural problems and family history of obesity should raise suspicion of monogenic obesity.