MSX1 and cleft lip: However, families in which some individuals present with cleft lip and others with cleft palate only have been noted with shared mutations in a handful of genes, such as interferon regulatory factor 6 (IRF6) [3], tumor protein p63 (TP63) [4,5], fibroblast growth factor receptor 1 (FGFR1) [6], and msh homeobox 1 (MSX1) [7].