Analysis of the methylation status of the KCNQ1OT and H19 genes in leukocyte DNA for the diagnosis and prognosis of Beckwith-Wiedemann syndrome

Beckwith-Wiedemann syndrome (BWS) is an overgrowth disorder involving devel opmental abnormalities, tissue and organ hyperplasia and an increased risk of embryonal tumours (most commonly Wilms tumour). This multigenic disorder is caused by dysregulation of the expression of imprinted genes in the 11p 15 chromosomal region. Molecular diagnosis of BWS is currently difficult, m ostly due to the large spectrum of genetic and epigenetic abnormalities. Th e other difficulty in managing BWS is the identification of patients at ris k of tumour. An imprinted antisense transcript within KCNQ1, called KCNQ1OT (also known as LIT1), was recently shown to be normally expressed from the paternal allele. A loss of imprinting of the KCNQ1OT gene, associated with the loss of maternal allele-specific methylation of the differentially met hylated region KvDMR1 has been described in BWS patients. The principal aim of this study was to evaluate the usefulness of KvDMR1 methylation analysi s of leukocyte DNA for the diagnosis of BWS. The allelic status of the 11p1 5 region and the methylation status of the KCNQ1OT and H19 genes were inves tigated in leukocyte DNA from 97 patients referred for BWS and classified i nto two groups according to clinical data: complete BWS (CBWS) (n=61) and i ncomplete BWS (IBWS) (n=36). Fifty-eight (60%) patients (39/61 CBWS and 19/ 36 IBWS) displayed abnormal demethylation of KvDMR1. In 11 of the 56 inform ative cases, demethylation of KvDMR1 was related to 11p15 uniparental disom y (UPD) (nine CBWS and two IBWS). Thirteen of the 39 patients with normal m ethylation of KvDMR1 displayed hypermethylation of the H19 gene. These 13 p atients included two siblings with 11p15 trisomy. These results show that a nalysis of the methylation status of KvDMR1 and the H19 gene in leukocyte D NA is useful in the diagnosis of 11p15-related overgrowth syndromes, result ing in the diagnosis of BWS in more than 70% of investigated patients. We a lso evaluated clinical and molecular features as prognostic factors for tum our and showed that mosaicism for 11p15 UPD and hypermethylation of the H19 gene in blood cells were associated with an increased risk of tumour.