LMAN1 is encoded by a gene of ∼29 kb located on chromosome 18q21 and containing 13 exons , while MCFD2 is encoded by a gene of ∼19 kb located on chromosome 2p21 and containing 4 exons . Mutations in MCFD2 and LMAN1 are associated with very similar phenotypes [8,18]. However, a selective delay in secretion of the proteins procathepsin C has been observed in HeLa cells overexpressing a dominant-negative form of LMAN1 . These results were confirmed by Nyfeler et al., showing that LMAN1 also interacts with the two lysosomal glycoproteins cathepsin Z and cathepsin C whereas MCFD2 is dispensable for the binding of them to LMAN1 .
To date, 47 mutations are described in LMAN1 (n = 32, 68%) and MCFD2 (n = 15, 32%) genes [http://www.med.unc.edu/isth/mutations-databases/FVandVIII_2006numbers.htm, 18,26,28,30] (Figs 1 and 2). A vast majority of these mutations (non-sense, frame shifts, splicing defects or missense mutations) predict null alleles and are predominantly identified in LMAN1 (95%, n = 38/40). Among them, also recurrent mutations in both the LMAN1 and MCFD2 genes are described. LMAN1 mutations, such as p.M1T, c.86_89insG, p.R202X, c.822G>A, p.K302X, c.1140 + 2T>C, have been observed in more than four patients [7,13,17–20,27]. Similarly, the c.149 + 5G>A and p.I136T mutations in MCFD2 have also been commonly reported [18,26,27]. The MCFD2 c.149 + 5G>A appears to be one of the most common mutation causing F5F8D and it has now been identified in at least 13 unrelated families from different geographic regions and particularly from India (n = 6) [25,26], followed by Italy (n = 4) [10,18], USA (n = 1) , Serbia (n = 1)  and Germany (n = 1) . In case of recurrent mutations in a particular geographic area, haplotype analysis has to be considered as a tool to evaluate whether or not a founder effect exists. The founder effect is, indeed, a potential diagnostic tool of genetic disease, particularly in countries with a high prevalence of the disease and low economic facilities. In the LMAN1 gene, for example, the nt89–90insG mutation leading to a premature stop at codon 102 was found to be particularly frequent in Iranians and Iraqi Jews, while the IVS9 + 2T>C mutation was frequent among Jews originating from the island of Djerba .
In vitro expression studies have proved to be an invaluable tool to understand the nature of the genetic defect and to unravel the underlying molecular mechanism of deficiencies. In vitro expression studies of mutations in LMAN1 and MCFD2 genes and characterization of the activity of the corresponding recombinant proteins in the secretion of coagulation FV and FVIII could thus significantly help to describe the mechanism of the deficiency. In the literature, all the five missense mutations identified in MCFD2 were expressed in COS-1 transfected cells [8,18]. All the other identified mutations were demonstrated to be associated with the deficiency through analysis performed on Epstein Barr Virus-transformed lymphoblasts of the patients that showed the presence/absence of the mutated protein [8,10,17].