Recently Brzezinski et al. reported three individuals with Beckwith–Wiedemann syndrome (BWS) due to a loss of methylation at imprinting center 2 (IC2 LOM), who had intra-abdominal masses, and advocated strict tumor surveillance for individuals with BWS and IC2 LOM [1]. BWS is a rare imprinting disorder, with an increased risk of embryonic tumor during early infancy. It is due to various (epi) genetic abnormalities within the 11p15 region, the most prevalent one being IC2 LOM identified in about 50% of BWS patients. For years, a strong correlation between tumor risk and BWS has been reported. Present day knowledge has been summarized by Maas and co-workers [2] who collected data on all known larger series of BWS patients, with additional data from their own center, and in total representing almost 2000 patients. Tumor risk was the highest for individuals with a gain of methylation (GOM) of IC1 (28%) and paternal uniparental disomy (pUPD) of 11p15 (16%), whereas patients with IC2 LOM presented with the lowest risk (2.6%). Furthermore, they subdivided chances depending on the nature of tumors and reported the prevalence of Wilms tumor (WT) to be high for patients with IC1 GOM and 11p15 pUPD (24% and 7.9%, respectively) and very low for IC2 LOM (0.2%) and CDKN1C mutations (0%). These data on the reliably diagnosed large series of BWS individuals have been taken into consideration by a group of 30 experts to establish international recommendations for tumor screening in BWS [3]. Considering the low rate of abdominal tumors in individuals with IC2 LOM, the experts recommended no abdominal screening for this subgroup of patients, but only for the three other subgroups.

Brzezinski et al. suggest in their paper that the risk of WT in patients with IC2 LOM might be underestimated, and therefore suggest that those patients should be screened for WT. However, in our opinion their data about an increased risk of WT do not allow to raise such conclusions. Indeed, patient 1 had a false initial molecular diagnosis (IC2 LOM with an IC1 “borderline” GOM, which led to a misdiagnosis of IC2 LOM). The correct molecular diagnosis was detected only after the detection of a WT in their