Our distal 16p11.2 BP2-BP3 deletion subgroup showed a more severe obesity phenotype (73.7% of cases, earlier age of onset and higher average BMI SDS) than cases with typical 16p11.2 BP4-BP5 deletion (Table 3A, B). The gene discussed is IGFBP2; the disease is obesity due to melanocortin 4 receptor deficiency.