Analysis of CDKN1C in Beckwith Wiedemann syndrome

In this study we have examined 32 patients with Beckwith Wiedemann Syndrome (BWS) for mutations affecting the CDKN1C gene, including seven cases of familial BWS. Mutations were not detected in the coding region of the CDKN1C gene in any individual with BWS. However in two patients, two G/A base substitutions at adjacent positions in the 5'UTR were detected. These substitutions were also found in normal controls. Expression of CDKN1C in somatic tissues was examined in 18 of the 32 cases using semi-quantitative RT-PCR. CDKN1C expression was significantly reduced in the peripheral blood of three cases compared with controls. These results suggest that, although coding region mutations in the CDKN1C gene are rare in BWS, mutations disrupting CDKN1C expression may be found. Three of five informative patients exhibited biallelic CDKN1C expression in lymphocytes, cord blood, and kidney tissue, respectively. Biallelic expression was not associated with overall CDKN1C levels significantly different to those in controls. Patients who expressed CDKN1C biallelically, or who were low CDKN1C expressors, maintained monoallelic methylation in the Differentially Methylated Region 2 (DMR2) of the IGF2 locus. One patient expressing CDKN1C biallelically, maintained imprinted gene expression at the IGF2 locus. These results suggest that biallelic CDKN1C expression does not significantly perturb the overall levels of CDKN1C expression in somatic tissue. They also confirm other studies showing that the mechanisms associated with regulating CDKN1C expression and imprinting are separate from those regulating IGF2 imprinting.