| Achondroplasia (commonest non‑lethal skeletal dysplasia) | FGFR3, AD (80% new mutations) | rhizomelic shortening; narrowing interpedicular distance caudally in the lumbar spine; posterior vertebral scalloping, short pedicles (canal stenosis); bullet‑shaped vertebrae (infants); champagne‑glass pelvic inlet, tombstone (squared) iliac wings, flat acetabular roofs, small sacrosciatic notches; trident hand; large skull, small foramen magnum (cervicomedullary compression); chevron (V‑shaped) physes |
| Thanatophoric dysplasia | FGFR3 | lethal; telephone‑receiver femurs, cloverleaf skull, severe platyspondyly |
| Osteogenesis imperfecta | type I collagen (COL1A1/A2); Sillence types I–IV (+ more) | osteopenia, multiple fractures (antenatal in type II), bowing, Wormian bones, platyspondyly, kyphoscoliosis, blue sclera (types I, II; type IV typically normal sclera), dentinogenesis imperfecta, otosclerosis; shepherd's crook; differentiate from NAI |
| Osteopetrosis (Albers–Schönberg) | osteoclast failure | diffuse sclerosis, bone‑within‑bone, sandwich vertebrae, Erlenmeyer flask, brittle bones (transverse fractures), marrow failure, cranial nerve compression |
| Cleidocranial dysplasia | RUNX2, AD | absent/hypoplastic clavicles (lateral third), wide sutures and fontanelles, Wormian bones, persistent metopic suture, delayed dentition with supernumerary teeth, wide symphysis pubis; "hot cross bun" skull (frontal + parietal bossing) |
| Mucopolysaccharidoses | lysosomal | dysostosis multiplex: J‑shaped sella, oar/paddle‑shaped ribs, proximally pointed metacarpals, bullet phalanges, inferior beaking (Hurler, MPS I) vs central beaking (Morquio, MPS IV), odontoid hypoplasia (Morquio), wide flared iliac wings |
| Melorheostosis (Léri) | MAP2K1 (somatic) | flowing cortical hyperostosis "dripping candle wax" along one side of a bone, sclerotomal |
| Osteopoikilosis / osteopathia striata | — | multiple bone islands / linear striations; benign |
| Pyknodysostosis | cathepsin K | sclerosis + acro‑osteolysis, obtuse mandibular angle, wide sutures (Toulouse‑Lautrec) |
| Diaphyseal dysplasia (Camurati–Engelmann) | TGFB1 | symmetric diaphyseal cortical thickening |