Alagille syndrome inherited from a phenotypically normal mother with a mosaic 20p microdeletion.

We report an 18-month-old girl with Alagille syndrome, caused by a submicroscopic deletion of chromosome 20p, including the Jagged1 (JAG1) gene. FISH using a BAC probe containing JAG1 identified the deletion. Chromosomes were normal at the 550 band level.