Quantitative RT-PCR studies with BOEC-derived mRNA. Using the SNP c.2365G/A (rs1063856) to differentiate the 2 VWF transcripts, the index case who is heterozygous G/A for this SNP (n = 3 experiments) was studied and compared with 6 healthy control individuals: 2 A/A subjects (lane 1, n = 6 experiments), 1 G/G subject (lane 2, n = 3 experiments), and 3 G/A heterozygotes (lane 3, n = 9 experiments). The graph shows the average A:G transcript ratio (± SEM). In lane 1, The A:G ratio in the A/A homozygotes is not infinite because there is some variable “background” binding of the G probe to the A transcripts. In lane 2, the A:G ratio was always “0,” because there were never any A transcripts detected in the G/G homozygote. In the index case (lane 4, n = 3 experiments), the A:G ratio is 4.6-fold lower that the mean A:G ratio in the 3 normal G/A heterozygous subjects (P = .007). The VWF mutation is in cis with the c.2365A/G (rs1063856) SNP “A” allele, and thus, the promoter deletion is associated with reduced VWF transcript production.