Hyperleptinaemia in young adults following cranial irradiation in childhood: growth hormone deficiency or leptin insensitivity?

Abstract

OBJECTIVE: In order to explore the mechanism of obesity in long-term survivors of childhood leukaemia, fat mass, lean body mass and serum leptin were assessed in a cohort of 32 (17 males) adults who had received cranial irradiation (XRT) in childhood as part of their treatment for acute lymphobiastic leukaemia (ALL), and compared with 35 age and body mass index (BMI) matched young adults (18 male). DESIGN: Thirty-one patients and 18 controls had fat mass and lean body mass assessed by dual x-ray absorptiometry (DEXA), using a lunar DPX-L scanner. Serum leptin concentrations were also measured in 27 patients and all controls. Growth hormone status had previously been determined using an insulin tolerance test and arginine stimulation test. Nine patients were classified as severe growth hormone (GH) deficient (group 1), 12 patients as GH insufficient (group 2) and 11 patients as normal (group 3). RESULTS: BMI and absolute fat mass were not significantly different between the patients and controls regardless of their gender (P = 0.1 and P = 0.14 respectively). In contrast, absolute lean mass was significantly reduced (P < 0.01) and leptin concentrations were significantly increased (P < 0.001) in patients compared with controls. BMI, fat mass and leptin concentrations but not lean mass were significantly different between the three GH status groups (P < 0.01, P < 0.01, P = 0.004, and P = 0.67 respectively). When leptin concentrations were expressed per unit of fat mass, they were increased in the patients compared with the controls (P = 0.03) with significant differences between the GH status groups (P = 0.004), being significantly higher in the severe GH deficient group. CONCLUSIONS: Young adults who receive cranial irradiation in childhood are prone to GH deficiency and hyperleptinaemia. The pathophysiological significance of the hyperleptinaemia remains to be established but it has occurred either as a consequence of radiation induced hypothalamic damage or GH deficiency.