Loss-of-function mutations in the EGF-CFC gene CFC1 are associated with human left-right laterality defects

Ail vertebrates display a characteristic asymmetry of internal organs with the cardiac apex, stomach and spleen towards the left, and the liver and ga ll bladder on the right(1-3). Left-right (L-R) axis abnormalities or latera lity defects are common in humans (1 in 8,500 live births). Several genes ( such as Nodal, Ebaf and Pitx2) have been implicated in L-R organ positionin g in model organisms(2-4), In humans, relatively few genes have been associ ated with a small percentage of human situs defects. These include ZIC3 (re f. 5), LEFTB (formerly LEFTY2; ref. 6) and ACVR2B (encoding activin recepto r IIB; ref, 7). The EGF-CFC genes(8), mouse Cfc1 (encoding the Cryptic prot ein; ref. 9) and zebrafish one-eyed pinhead (oep; refs 10,11) are essential for the establishment of the L-R axis(12,13). EGF-CFC proteins act as co-f actors for Nodal-related signals(11), which have also been implicated in L- R axis development(4). Here we identify loss-of-function mutations in human CFC1 (encoding the CRYPTIC protein) in patients with heterotaxic phenotype s (randomized organ positioning). The mutant proteins have aberrant cellula r localization in transfected cells and are functionally defective in a zeb rafish oepmutant rescue assay. Our findings indicate that the essential rol e of EGF-CFC genes and Nodal signalling in left-right axis formation is con served from fish to humans. Moreover, our results support a role for enviro nmental and/or genetic modifiers in determining the ultimate phenotype in h umans.