[Identification of the breakpoint-flanking markers on chromosomes 1 and 17 of a constitutional translocation T(1;17)(P36;Q12-21) in a patient with neuroblastoma].

Neuroblastoma is a childhood cancer which originates in the embryonic tissue of the developing sympathetic neural crest. In 1972, Dr. A. Knudson hypothesised a similar 'two-hit mutation' model for the origin of neuroblastoma as for retinoblastoma and Wilms tumor. In this model, malignant cell growth is caused by mutations of both alleles of a tumor suppressor gene. In hereditary tumors, a germinal mutation is present in all cells of the individual, a mutation of the remaining allele by a somatic hit causes loss of gene function. Sporadic tumors result from two somatic mutations of a tumor suppressor gene involving both alleles within the same cell. The occurrence of patients with a constitutional chromosomal deletion syndrome in association with tumor facilitated the cloning of a retinoblastoma gene and of a Wilms tumor suppressor gene. In neuroblastoma, cytogenetic and molecular studies suggest the existence of a neuroblastoma (suppressor) gene at chromosome 1, at subband 1p36. A constitutional chromosomal deletion syndrome was not known for neuroblastoma. We described a constitutional chromosome translocation t(1;17)(p36.31-21; q11.2-12) in a patient with neuroblastoma. We hypothesised that this translocation, involving the chromosomal band 1p36, predisposed the patient to neuroblastoma development by disturbance of a gene located at the translocation breakpoint. Consequently, identification of the breakpoint flanking markers can be an important step towards the identification and cloning of a neuroblastoma suppressor gene. Radioactive in situ hybridization methods were first applied on the patient's fibroblasts. Soon it became evident that cells with better growth characteristics were needed and that the availability of sufficient patient material was essential. Therefore a somatic cell fusion experiment was performed between the patient's fibroblasts and a thymidine kinase-deficient Chinese hamster cell line. Somatic cell hybrid clones were selected on the presence of the derivative human chromosomes 1 and 17, and of the normal homologues. With the use of fluorescence in situ hybridisation (FISH), the position of chromosome 1 and chromosome 17 markers respective to the breakpoints was determined on chromosome metaphases of the hybrid cell lines containing the human derivative chromosomes. The pronatriodilatine (PND) and the adenovirus 12 modification site (A12M2) were identified as distal and proximal 'single copy' flanking markers of the chromosome 1 breakpoint, respectively. The chromosomal break occurred in a highly repetitive region containing an adenovirus modification site and genes encoding transfer RNA and small U1-RNA genes. The breakpoint on chromosome 17 is located in a region with as proximal boundary the distal part of the neurofibromatosis 1 (NF1) gene locus and as distal flanking marker the SCYA7 locus, encoding the monocyte chemotactic protein-3. Southern blot analysis showed no rearrangements of hybrid DNA using single copy probes for the four flanking markers. Identification of the four breakpoint flanking markers on chromosomes 1 and 17 constitutes a pivotal step for the cloning of the translocation breakpoints and for the identification of a presumed neuroblastoma suppressor gene.