Opitz G/BBB syndrome (OS) is a genetically heterogeneous disorder with an 
X-linked locus and an autosomal locus linked to 22q11.2. OS affects multiple 
organ systems with often variable severity even between siblings. The clinical 
features, which include hypertelorism, cleft lip and palate, defects of cardiac 
septation, hypospadias, and anorectal anomalies, indicate an underlying 
disturbance of the developing ventral midline of the embryo. The gene 
responsible for X-linked OS, FXY/MID1, is located on the short arm of the human 
X chromosome within Xp22.3 and encodes a protein with both an RBCC (RING finger, 
B-box, coiled coil) and a B30.2 domain. The Fxy gene in mice is also located on 
the X chromosome but spans the pseudoautosomal boundary in this species. Here we 
describe a gene closely related to FXY/MID1, called FXY2, which also maps to the 
X chromosome within Xq22. The mouse Fxy2 gene is located on the distal part of 
the mouse X chromosome within a region syntenic to Xq22. Analysis of genes 
flanking both FXY/MID1 and FXY2 (as well as their counterparts in mouse) 
suggests that these regions may have arisen as a result of an intrachromosomal 
duplication on an ancestral X chromosome. We have also identified in both FXY2 
and FXY/MID1 proteins a conserved fibronectin type III domain located between 
the RBCC and B30.2 domains that has implications for understanding protein 
function. The FXY/MID1 protein has previously been shown to colocalize with 
microtubules, and here we show that the FXY2 protein similarly associates with 
microtubules in a manner that is dependent on the carboxy-terminal B30.2 domain.