Hypochondrogenesis is a rare form of skeletal dysplasia (or dwarfing syndrome) caused by mutations in the COL2A1 gene. The COL2A1 gene provides the instruction for the formation of collagen II, which is a major building block of cartilage, a major component of bone. Because of these mutations, infants with hypochondrogenesis have defects in their bone formation that cause them to have severely shortened limbs (arms and legs) and a small chest with short ribs.


shortened limbs (arms and legs) and a small chest with short ribs. As infants with hypochondrogenesis have small chests and abnormal ribs, their lungs are underdeveloped, which leads to respiratory (breathing) difficulties at birth.


Hypochondrogenesis is one of the most severe conditions in a spectrum of disorders caused by mutations in the COL2A1 gene. This gene provides instructions for making a protein that forms type II collagen. This type of collagen is found mostly in the clear gel that fills the eyeball (the vitreous) and in cartilage. Cartilage is a tough, flexible tissue that makes up much of the skeleton during early development. Most cartilage is later converted to bone, except for the cartilage that continues to cover and protect the ends of bones and is present in the nose and external ears.


Affected infants have short arms and legs, a small chest with short ribs, and underdeveloped lungs. The spinal bones (vertebrae) in the neck and part of the pelvis (the sacrum) do not harden, or ossify, properly. The face appears flat and oval-shaped, with widely spaced eyes, a small chin, and, in some cases, an opening in the roof of the mouth called a cleft palate. The abdomen is enlarged, and excess fluid may build up in the body before birth (a condition called hydrops fetalis).


There is no cure or treatment for hypochondrogenesis. If the diagnosis is made prior to birth, the parents may wish to meet with a neonatalogist to discuss management of the birth. If hypochondrogenesis is detected during a pregnancy, patients have the option to terminate the pregnancy based upon the lethality of this condition. This is a very personal decision and should be made following serious counseling about the nature and outcome of this diagnosis.