FN1 codes for two types of fibronectin-1 protein: a soluble plasma protein, mainly produced by the liver and involved in blood clotting and wound healing; and an insoluble protein released to the extracellular space, helping with formation of fibrils and the extracellular matrix (Frantz et al., 2010; Pankov and Yamada, 2002; Rebhan et al., 1997). Both types of proteins are involved in cell adhesion, spreading, migration, and differentiation (Frantz et al., 2010; Pankov and Yamada, 2002). It is therefore possible that this gene will be similarly involved in neurite outgrowth or a similar process during brain development. Indeed, homozygous knockout mice display neural tube defects and shortened anterior-posterior axes (George et al., 1993). Variants in FN1 also appear to be involved in glomerulopathy with fibronectin deposits (Castelletti et al., 2008). Unlike the probands with NIPBL variants, affected individuals do not appear to have overlapping phenotypic characteristics, although this disorder has a late onset (Castelletti et al., 2008).
