Abstract
The N-myc amplification unit was investigated using two restriction fragment length polymorphisms for SphI and PvuII which we previously found to occur in the 2nd intron and in the 3' region of the human N-myc oncogene, respectively. All the three haplotypes which are dominant in the Japanese population were observed in the amplified DNA after analyses of a total of 22 DNA samples of fresh neuroblastomas with N-myc amplification. We conclude that only one of the alleles was amplified and that either allele could be amplified with respect to both the SphI and PvuII polymorphisms.