Type of Pathogenic Variants according to Gene. Gray: null genotype; white: hypomorphic genotype. Horizontal axis: gene, number of patients; vertical axis: percent of cases within each gene. *p<0.05. The type of variant could be determined in 380 out of 561 cases (68%) based on available information; 62% of patients had null variants. The frequency of null and hypomorphic variants varied among the genes. FANCB, G, J, and N were more frequently associated with null variants (p≤0.03); FANCC with hypomorphic variants (p=0.004); and, null and hypomorphic variants were equally distributed in the rest of the genes.