A girl with learning and behavioral problems was identified with an (X;14)(q28;q11) translocation in which the normal X chromosome was inactivated. A cosmid has been isolated that is covering the breakpoint on the X chromosome and two cDNA are hybridizing with this cosmid. The purpose of this project is to isolate the gene that is interrupted by the translocation and to determine the complete sequence of this gene. Subsequently I will characterize in more detail this gene by studying the protein and the expression pattern of the protein in different tissues, in particularly in the brain. Antibodies will be raised against the protein and protein expression will be studied in adult tissues as well as during embryonal development. Furthermore, I will study whether this gene is involved in the mental retardation that is found in a number of families in which the gene defect has been localized in Xq28.