= autosomal recessive lethal chondrodystrophy characterized by extreme micromelia, short trunk, large cranium

Triad:

1. severe short-limb dwarfism
2. lack of vertebral calcification
3. large head with normal / decreased calvarial ossification

Birth prevalence: 2.3÷100,000

Path: disorganization of cartilage

1. TYPE I = Parenti-Fraccaro disease
   = defective enchondral + membranous ossification
   • complete lack of ossification of calvarium + spine + pelvis
   • absent sacrum + pubic bone
   • extremely short long bones without bowing: especially femur, radius, ulna
   • thin ribs with multiple fractures (frequent)
2. TYPE II = Langer-Saldino disease
   = defective enchondral ossification only
   • good ossification of skull vault
   • nonossification of lower lumbar vertebrae + sacrum
   • short + stubby horizontal ribs without fractures

• often subcutaneous edema

• irregular flared metaphyses: esp. humerus
• short trunk with narrow chest + protruding abdomen
• redundant soft tissues
• polyhydramnios (common)
• increase in HC÷AC ratio

Prognosis: lethal often in utero / within few hours or days after birth (← respiratory failure)

DDx: often confused with thanatophoric dwarfism