Microdeletions of the chromosomal region 22q11.2 are associated with defects in cardiac and craniofacial development that are referred to as the CATCH 22 phenotype and include DiGeorge syndrome, the velo-cardio-facial syndrome, and the Opitz GBBB syndrome. Deleted in CATCH 22 patients, UFD1L encodes the human homolog of the yeast ubiquitin fusion degradation 1 protein (UFD1p), an essential component of the ubiquitin-dependent proteolytic pathway. The murine homolog (Ufd1l) is expressed in the eyes and in the inner ear primordia during embryogenesis. In rat liver cytosol, Ufd1l binds to the nuclear transport protein Npl4 and this binary complex competes with p47 for binding to p97, which inhibits Golgi membrane fusion. The tertiary complex Ufd1l/Npl4/p97 may also be involved in mitotic ubiquitin-dependent processes. Both Ufd1l and Npl4 are found in the nucleus, while p97 is found in the cytoplasm and nucleus. In humans, Ufd1L is primarily expressed in adult heart, placenta, skeletal muscle, and pancreas, and fetal liver and kidney. Thus, Ufd1L is thought to be involved in cell functions that are critical for normal cell development in the cardiac and craniofacial regions.