Background and objective: Non-islet-cell tumour hypoglycaemia (NICTH) is a rare disorder and has been explained by oversecretion of non mature IGF-II and dysregulation of the IGFs sytem. The mechanisms responsible for tumoural IGF-II overexpression in NICTH have been rarely studied. We report an extensive study of IGF-II and IGFBPs as well as chromosome 11p15 gene expression regulation in a case of a pleural fibrosarcoma in a 63-year-old patient presenting with NICTH.
Methods and results: Abnormal high molecular weight precusor forms of IGF-II were present in the patient's serum and were associated with dramatic alterations in the circulating levels of IGF-I, IGF-II and their binding proteins, as well as an inhibition of the somatotroph axis. These alterations returned to normal following complete surgical removal of the tumour. No structural change in chromosome 11p15 region was apparent in the tumour. However, dysregulation of this imprinted region was demonstrated, leading to the loss of imprinting of the IGF-II gene associated with high IGF-II expression, and by contrast decreased level of expression of H19 and p57KIP2 genes. Recurrence of the tumour four years latter was not associated with hypoglycaemia or changes in the levels of circulating IGFs or IGFBPs, despite IGF-II overexpression by the tumour. This suggests that a large tumour volume is required to reach high enough levels to cause changes in the levels of circulating IGFs and IGFBPs, and to cause hypoglycaemia.
Conclusion: These results suggest that a dysregulation of gene expression and imprinting of chromosome 11p15 region is associated with tumour growth and IGF-II overexpression in non-islet-cell tumour hypoglycaemia.