Absence of FAN1 and FA cellular phenotype in MD patients. (A) Fragments amplified by PCR corresponding to exons 1 and 15 of the FAN1 gene were observed using DNA templates from a healthy person (WT) and a FANCA-deficient FA patient included as controls, whereas they were absent when templates from microdeletion patients (MD1 to MD4) were used, confirming the biallelic deletion of FAN1 in the MD patients (top panel). Immunoblotting against FAN1 protein revealed a FAN1-specific band in WT and FA (FA1 and FA2) LCL that failed to be detected in MD1 and MD2. (bottom panel). (B) Dot plot of CFI showing individual values and average (solid line) of DEB-induced chromosome breakage from non-FA (n = 56), FA (n = 90, excluding mosaics) and MD (n = 4) persons. The CFI values of all MD patients ranged within the non-FA population. (C) Mild sensitivity of MD LCL to MMC on survival assay. The graph shows intermediate sensitivity to MMC of MD1 and MD2 compared with the highly sensitive FA (FANCA) cell line. (D) Near-normal sensitivity of MD LCL to MMC on cell cycle analysis. The graph plots the percentage of cells in G2/M phase after exposure to increasing concentrations of MMC for 72h. A WT and an FANCA cell lines were included as controls.