Mutation analysis of the DICER1 gene in Pleuropulmonary Blastoma ; Mutationsanalyse des DICER1 Gens beim Pleuropulmonalen Blastom

The pleuropulmonary blastoma is a very rare malignancy of childhood, but is still the most common pediatric lung tumor. It is an aggressive neoplasm and part of the newly discovered DICER1-Syndrome. This syndrome is characterized by mutations in the DICER1 gene and a wide variety of clinical phenotypes. In this thesis, molecular genetic examinations of the so far largest German patient collective were performed. The methods used, included PCR, Sanger sequencing, multiplex ligation-dependent probe amplification and OncoScan® (the latter not part of this thesis). In six patients, a total number of nine mutations and a large deletion spanning the entire DICER1 gene locus were detected. Of the nine mutations, four had not been described in the literature. It was determined, that splice site mutation c.1510-1G>A of patient 18 and the large DICER1 gene deletion of patient 12 were de novo germline mutations, predisposing these individuals to the DICER1-Syndrome. The deletion was detected by MLPA and could be specified to a size of 582kb by OncoScan®. Such a deletion has only been published once in a patient with PPB before. Five mutations were located on the RNase IIIb domain of DICER1. This domain contains hotspot regions for DICER1-Syndrome mutations. The distribution of the nine mutations, is in line with the so-called modified two-hit-hypothesis. Here, usually a germline DICER1 mutation predisposes to a greater risk of disease, which is later induced by somatic mutations. There is a retained function of DICER1, when there are hotspot DICER1 mutations in PPB. The mutations affect the processing of miRNA strands by DICER1 and are part of RNA interference (RNAi). A new equilibrium of the miRNA strands is thought to be a cancerogenous trigger of PPB. The exact mechanisms are not understood so far. Upon diagnosis of PPB, subsequent PCR and Sanger studies should be performed to look for DICER1 mutations. In germline negative cases, a screening for mosaicism and biallelic somatic mutations should follow. Analysis for ...