We confirm a marked increase in the risk of severe childhood obesity in carriers of the 220 kb deletion, which accounts for a total of 0.5% of the combined cases from our study and the original report. The impact on obesity status in adult carriers appears less pronounced, but there is nevertheless an appreciable increase in BMI (corresponding to 15–19 kg in weight for subjects 160–180 cm in height). There are several possible reasons for the apparent difference between children and adults: it may reflect population differences (the child carriers of the GSV were from France and the UK, the adults primarily from Nordic countries); it may reflect cohort ascertainment, for instance that the child cohorts did not include overweight or mildly obese subjects – it is notable, however, that the deletion was not reported at a comparable frequency in cohorts of children with common obesity [16]; it may reflect a genuine attenuation of the effect of the deletion in adults, so that impact of the GSV on obesity becomes less pronounced with increasing age; or the severe obesity observed
