Thanatophoric dysplasia

Thanatophoric dysplasia (TD) is a lethal skeletal dysplasia. It is the most common lethal skeletal dysplasia followed by osteogenesis imperfecta type II. 

The estimated incidence is around 1:25,000-50,000 3.

Genetics

It results from a mutation coding for the fibroblast growth receptor 3 (FGFR3) located on chromosome 4p16.3. The type of receptor mutation is different from the FGFR mutation in achondroplasia. Inheritance is thought to be sporadic.

Subtypes

There are two recognised subtypes:

  • type I: marked underdevelopment of skeleton, telephone handle femurs more pronounced
  • type II
    • the presence of a cloverleaf skull may be a distinctive feature
    • limb shortening milder and bowing is not a feature 3
Associations
Antenatal ultrasound

It may be difficult to accurately diagnose before the 3rd trimester (≈22 weeks) 4. Before that time it can be in included in the differential if there is a short femur length measurement.  

Sonographically detectable features may include:

  • relatively narrow thoracic cavity 4
  • short, thick, bowed tubular bones, especially lower extremity 4
  • thickened soft tissues of extremities 4
  • comparatively large head with frontal bossing 
  • a cloverleaf skull appearance may also be seen: type II (see case 3)
Plain radiograph 

Plain films are usually done post-mortem if done at all. Features include:

Limbs
Iliac bones
Chest
  • narrow chest
  • short horizontal ribs
  • small scapulae
Skull and face
Spine
  • platyspondyly: flattening of vertebral bodies
  • normal trunk length

The condition is uniformly fatal within a few hours of birth either from respiratory failure or from brainstem compression from a narrow foramen magnum.

History and etymology

The term thanatophoric derives from the Greek words "thanatos" (θάνατος) meaning "death" 2 and "foros" meaning "bearing/carrying/bringing". 

See also

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Article Information

rID: 7325
Synonyms or Alternate Spellings:
  • Thanatophoric dwarfism
  • Thanatophoric dysplasia (TD)

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