The tumorigenesis of sporadic endocrine tumors is still not fully understood. It 
is well known that patients with von Recklinghausen syndrome (NF-1) (OMIM 
162200) carrying NF1 germline mutations are predisposed to endocrine tumors 
including pheochromocytomas and duodenal somatostatinomas. It is unclear, 
however, whether the rarely reported occurrence of pancreatic insulinomas in 
NF-1 patients represents a coincidental finding or whether insulinomas are a 
rare manifestation of the NF-1 syndrome. To determine the potential association 
between the NF-1 syndrome and pancreatic endocrine tumors, we analyzed a NF-1 
patient with a well-differentiated pancreatic endocrine carcinoma for NF1 
mutation, allelic loss of the NF1 gene and its expression in peripheral blood 
and tumor cells. The germline mutation c. 499 del TGTT known in the family was 
confirmed by polymerase chain reaction (PCR) and direct sequencing of exon 4 in 
DNA extracted from peripheral blood. Loss of heterozygosity (LOH) analysis of 
the NF1 gene was carried out using 3 intragenic microsatellite markers on 
17q11.2. RNA expression was examined by reverse transcription and a consecutive 
PCR spanning intron 3 of the NF1 gene including the mutated site in exon 4. 
Immunohistochemistry was used to analyze NF-1 protein expression. Mutation 
analysis of peripheral blood leukocytes confirmed the 4 base pair deletion in 
exon 4 starting at codon 167 (499 del TGTT). LOH analysis of tumor tissue 
revealed retention of both NF1 alleles. While reverse transcriptase-PCR of 
peripheral blood showed bi-allelic expression of both the wild-type NF1 and the 
mutated form, reverse transcriptase-PCR of tumor extracts demonstrated 
expression of the mutated but not the wild-type NF1 allele. Additionally, 
neurofibromin, the NF1 gene product, was absent in the tumor tissue of the NF-1 
patient. These results show that the wild-type NF1 transcrips and protein are 
reduced, in the reported insulinoma, supposedly by epigenetic mechanisms. This 
provides strong evidence that there is a relationship between von Recklinghausen 
disease and the patient's insulinoma. In this line, insulinomas may be viewed as 
a rare manifestation of the NF-1 syndrome. Furthermore, the NF1 gene must be 
considered as a candidate tumor suppressor gene for sporadic insulinomas and 
probably other pancreatic endocrine tumors.