Somatic deletion of the NF1 gene in a neurofibromatosis type 1-associated malignant melanoma demonstrated by digital PCR

Background: Neurofibromatosis type 1 (NF1) is the most common hereditary neurocutaneous
disorder and it is associated with an elevated risk for malignant tumors of tissues derived from
neural crest cells. The NF1 gene is considered a tumor suppressor gene and inactivation of both
copies can be found in NF1-associated benign and malignant tumors. Melanocytes also derive from
neural crest cells but melanoma incidence is not markedly elevated in NF1. In this study we could
analyze a typical superficial spreading melanoma of a 15-year-old boy with NF1 for loss of
heterozygosity (LOH) within the NF1 gene. Neurofibromatosis in this patient was transmitted by
the boy's farther who carried the mutation NF1 c. 5546 G/A.
Results: Melanoma cells were isolated from formalin-fixed tissue by liquid coverslip laser
microdissection. In order to obtain statistically significant LOH data, digital PCR was performed at
the intragenic microsatellite IVS27AC28 with DNA of approx. 3500 melanoma cells. Digital PCR
detected 23 paternal alleles and one maternal allele. Statistical analysis by SPRT confirmed
significance of the maternal allele loss.
Conclusion: To our knowledge, this is the first molecular evidence of inactivation of both copies
of the NF1 gene in a typical superficial spreading melanoma of a patient with NF1. The classical
double-hit inactivation of the NF1 gene suggests that the NF1 genetic background promoted
melanoma genesis in this patient.