Forkhead bo, Xenopus/Amphibian, protein P1 (Fo, Xenopus/Amphibian,P1) is a transcriptional repressor. Fo, Xenopus/Amphibian,P1 plays an important role in the specification and differentiation of lung epithelium. Fo, Xenopus/Amphibian,P1 is an essential transcriptional regulator of B cell development. Defects in Fo, Xenopus/Amphibian,P1 are the cause of mental retardation with language impairment and autistic features (MRLIAF). MRLIAF is a developmental disorder characterized by mild to moderate mental retardation, language impairment, and autistic features.