The von Recklinghausen neurofibromatosis (NF1) gene has been localized to the 
pericentromeric region of chromosome 17. We have screened six multigenerational 
families with multiple, tightly linked markers to aid in mapping this region of 
the chromosome. More than 150 members in six families were typed with probes 
including HHH202, D17Z1, EW203, EW206, EW207, EW301, pA10-41, D17S37, and 
D17S36. Two-point lod scores for NF1 versus all markers were calculated. HHH202 
demonstrated the tightest linkage to NF1 with theta = .0, z = 3.86 (95% 
confidence limits [CL] of theta = .0-.13), suggesting that HHH202 be considered 
as a potential candidate marker for use in carrier detection and prenatal 
diagnosis. Pairwise marker-to-marker lod scores were used in examining the most 
likely order of subsets of the markers. Of those tested, the most likely order 
was (pter)-pA10-41-EW301-D17Z1-HHH202-NF1-E W206-EW207-EW203-(qter). In 
addition, we have ascertained an NF1 x NF1 half-cousin mating in which there are 
four affected family members who are potentially homozygous for the disease 
gene. Two of these four individuals have been sampled and typed for marker loci. 
When their D17Z1 genotypes are considered, the probability that both these 
individuals are heterozygous is 85%.