Genetic Characterization Of Williams Beuren Syndrome Associated With Non-Hodgkin Lymphoma

Constitutional chromosomal abnormalities are known to play a role in oncogenesis as shown by the increased incidence of leukemias in children with Down syndrome. Williams Beuren syndrome (WBS, OMIM#194050) is a rare multisystem disorder associating cardiovascular malformations, psychomotor and behavioral abnormalities, a characteristic facial dysmorphism and endocrine defects. WBS is caused by a hemizygous microdeletion on chromosome 7q11.23 spanning 1.5 Mb and encompassing 28 genes and 2 miRNAs. The incidence of typical forms is 1/20, 000 births. Malignancies are not included in the phenotype of this syndrome. However, a thorough review of the literature shows that 12 cases of cancer have been reported in these patients and strikingly 6 of them were Non Hodgkin Lymphoma (NHL). We studied 3 novel cases of cancer including 2 NHL and one esophageal adenocarcinoma (EAC) occurring in WBS patients, in order to characterize genetic abnormalities explaining the susceptibility to cancer in this genetic disease.

We characterized the microdeletion size and other chromosomal aberrations in the 3 WBS patients using Comparative Genomic Hybridization array. Next Generation Sequencing of the 28 genes and the 2 miRNA loci was performed. The mRNA and miRNA relative expression of tumor tissue and healthy material was investigated by quantitative real time PCR. Finally, DNA repair deficiency was also assessed by microsatellite instability analysis and UV-induced gammaH2AX production in EBV-transformed lymphocytes derived from PBMCs of 2 WBS patients.

The CGH-array analysis did not identify a recurrent chromosomal rearrangement and there was no evidence of recurrent mutation or biallelic deletion in the WBS genes or miRNA coding sequences. The WBS deletion had a typical 1.5 Mb length for the 2 patients diagnosed with NHL but the patient who presented an EAC had a larger deletion (15 Mb). Lymphoma cells of the first WBS patient showed a common biallelic deletion ofCDKN2A and the second WBS patient showed an atypical deletion of IKZF2. As far as we know, this deletion had never been described in NHL. The esophageal adenocarcinoma cells of the third WBS patient presented 2 amplifications flanking the WBS deletion and involving EGFR and CDK6. These amplifications had the same intensity and we may suggest that they resulted from a double minute formation. The microsatellites were found to be stable and gammaH2AX formation was quite similar in B-EBV transformed lymphocytes derived from WBS patients and healthy controls. As expected, mRNA expression of most of the WBS genes was diminished by approximately a half in normal tissues.Interestingly the expression of WSTF, GTF2IRD2, CLIP2 and STX1Aand the expression of hsa-mir-590 were found to be moreprofoundlydecreased in the tumor cells of the 3 WBS patients.

A number of genes deleted in WBS (PMS2L, WSTF, RFC2 and TFII-I family genes) are implicated in DNA repair pathways and may represent tumor suppressor genes. Furthermore, the atypical distribution of cancers in WBS is suggestive of a genomic instability associated cancer syndrome. Savina et al (Mutation research, 2011) confirmed experimentally the relationship between an abnormal DNA-damage response and the 7q11.23 hemizygous microdeletion when comparing the comet assay data in FISH-positive and FISH-negative lymphocytes from WBS-suspected patients. However, in our study, no genomic instability was found. Predisposition to NHL is rare and most often associated with inherited immunodeficiency and bone marrow failure syndrome (e.g. Wiskott-Aldrich syndrome, Bloom syndrome, Nijmegen Breakage syndrome). In the present study we focused on a possible link between WBS and NHL. The risk of cancer in this population needs to be accurately evaluated by an international epidemiological study, but the high proportion of NHL is of considerable interest given the scarcity of NHL in young children and the lack of current knowledge on NHL predisposing genes in children without immunodeficiency. NHL was associated with significant underexpression of WSTF, GTF2IRD2, CLIP2, STX1A and has-mir-590. Further investigations are needed to elucidate the molecular pathways involved in NHL initiation in this population. In addition, we propose the constitution of a clinical and biological database of WBS associated cancer cases.

No relevant conflicts of interest to declare.