Metatropic dysplasia

Metatropic dysplasia refers to a rare subgroup of the skeletal dysplasias. It is part of the wider category of rhizomelic dwarfism. Disorders in this group include:

• fibrochondrogenesis
• lethal metatropic dysplasia (type 2) or hyperchondrogenesis
• lethal hyperplastic metatropic dysplasia (type 1)
• Schneckenbecken dysplasia

Clinical presentation

Post-natal clinical findings include a narrow chest and shortened extremities with a coccygeal tail seen in some cases. Joint contractures and kyphoscoliosis can manifest within the first year of life. As the kyphoscoliosis worsens with time, eventually patients can have a comparably short appearing torso when compared to the limbs, despite associated limb shortening.

Radiographic features

Characteristic radiological features include:

• short diaphyses with wide 'mushroom' shape metaphyses (dumbbell shape)
• distinctive pelvic morphology: halberd-shaped pelvis 
  • hypoplastic ilia with narrow sacrosciatic notches
  • horizontal acetabular roofs with small associated notches superior to their lateral borders
  • prominent flaring of crescentic iliac wings
• delayed ischiopubic mineralization
• kyphoscoliosis
• severe platyspondyly
• thin dense vertebral bodies

History and etymology

The term 'metatropic' originates from the Ancient Greek 'μετατροπος' (metatropos) which means 'changing patterns'. This name has been given in light of the fact that the skeletal phenotypes of this group of dysplasias change with time as patients age.