Gene amplification in PNETs/medulloblastomas: mapping of a novel amplifiedgene within the MYCN amplicon

Objectives-The pathological entity of primitive neuroectodermal tumour/medu lloblastoma (PNET/MB) comprises a very heterogeneous group of neoplasms on a clinical as well as on a molecular level. We evaluated the importance of DNA amplification in medulloblastomas and other primitive neuroectodermal t umours (PNETs) of the CNS. Method-Restriction landmark genomic scanning (RLGS), a method that allows t he detection of low level amplification, was used. RLGS provides direct acc ess to DNA sequences circumventing positional cloning efforts. Furthermore, we analysed several samples by CGH. Design-Twenty primary medulloblastomas, five supratentorial PNETs, and five medulloblastoma cell lines were studied. Results-Although our analysis confirms that gene amplification is generally a rare event in childhood PNET/MB, we found a total of 17 DNA fragments th at were amplified in seven different tumours. Cloning and sequencing of sev eral of these fragments confirmed the previous finding of MYC amplification in the cell line D341 Med and identified novel DNA sequences amplified in PNET/MB. We describe for the first time amplification of the novel gene, NA G, in a subset of PNET/MB. Despite genomic amplification, NAG was not overe xpressed in the tumours studied. We have determined that NAG maps less than 50 kb 5' of DDX1 and approximately 400 kb telomeric of MYCN on chromosome 2p24. Conclusion-We found a similar but slightly higher frequency of amplificatio n than previously reported. We present several DNA fragments that may belon g to the CpG islands of novel genes amplified in a small subset of PNET/MB. As an example we describe for the first time the amplification of NAG in t he MYCN amplicon in PNET/MB.