The OPD spectrum encompasses five X-linked disorders, in order of severity: OPD1, OPD2, frontometaphyseal dysplasia (FMD), Melnick-Needles syndrome (MNS), and terminal osseous dysplasia with/without pigmentary defects (TOD(PD)). This evidence concerns the gene FLNA and Terminal osseous dysplasia - pigmentary defects.