LAUSR

We thank Brioude et al. for their interest in our report on children with Beckwith-Wiedemann Syndrome (BWS) who presented with Wilms tumors (WT) or preneoplastic lesions and an initial molecular diagnosis of loss of methylation at imprinting center 2 (IC2 LOM) [1]. We agree that IC2 LOM confers a lower risk for WT when compared with other BWS-associated molecular etiologies. However, defining which children with BWS should undergo tumor surveillance is a complex problem that, in our opinion, requires further investigation and discussion. We arrived at this position for a number of reasons including: (1) the challenges of molecular classification of BWS that impact accurate estimation of WT risk for each BWS subgroup; (2) the increasing number of WT in individuals with BWS and IC2 LOM that have come to our attention; (3) the relevance of hypertrophic nephrogenic rests to the development of WT; (4) the increased liability of individuals with BWS and IC2 LOM to develop end stage renal disease emphasizing the need for early detection of WT in this population. The challenge of accurately determining the molecular diagnosis in BWS is especially relevant in considering revisions of tumor surveillance guidelines. Brioude et al. underscore the need for testing to be undertaken in an experienced laboratory. In fact, the cases in our report were assessed by a highly experienced clinical laboratory that functions as a national/international reference center with decades of experience in diagnostics of imprinting disorders. Moreover, the clinical testing employed was the most robust available at that point in time. For case 1, this included MS-MLPA and STR analysis which highlighted the fact that somatic mosaicism for paternal uniparental disomy (pUPD11p15.5) may lead to a situation where gain of methylation at the H19 DMR may not be detectable in accessible tissues such as blood. Consideration of evolving testing approaches raises an important consideration in the estimation of tumor frequencies stratified by (epi)genotype. As noted by Brioude and others, SNP arrays can increase the accuracy of identifying the correct molecular etiology. Indeed, SNP array was undertaken as part of the extensive investigation after the development of WT in our case 1, supporting a diagnosis of UPD. However, this test modality was not available at the time of initial assessment. Therefore given the exigencies of BWS molecular testing, it should be expected that some children with low-level mosaicism for pUPD11p15.5will be misclassified as IC2 LOM. For the molecular analyses and meta-analysis of the participants in the Maas publication, this means that some patients used to inform the risk calculation may have been misclassified. Such misclassification would lead to an inflation of the number of patients diagnosed with IC2 LOM with a concomitant deflation in the number of patients with pUPD11p15.5. Since the majority of such misclassified cases would not present with WT, this would inflate the number of IC2 LOM cases without WT and lead to an inappropriate reduction in the risk estimate for WT in the LOM IC2 group. Similarly the WT risk for pUPD11p15.5 would be inflated. Accurate estimates of WT risk by BWS molecular subgroup therefore must await implementation of optimized molecular testing using multiple platforms that interrogate both SNPs and DNA methylation, and potentially include multiple tissues, as standard of care for all children with BWS. The implementation of such molecular testing should occur in the context of a broad prospective ascertainment of large numbers of children with BWS. Since the Brzezinski publication, we have been informed of two additional cases of WT associated with LOM IC2 not as yet reported. Therefore, at least five children in addition to the five previously reported by Maas et al. [2], Ibrahim et al. [3], and Niemitz et al. [4] would not have been screened using the guidelines proposed by Maas and * Rosanna Weksberg [email protected]