Overview of Achondrogenesis Type 2: A Skeletal Disease
Achondrogenesis type 2 is a severe skeletal disease that affects the normal development of cartilage and bone. This skeletal disease causes infant death before birth,or children die soon after birth due to respiratory failure. However, some infants have lived for a while under an intensive care regime.
Characteristics of infants with achondrogenesis type 2 include underdeveloped lungs, a narrow chest with short ribs, and short arms and legs. Important bones of their bodies such as the skull, pelvis, and the vertebrae do not ossify which makes them soft and easily broken. They also have prominent foreheads, flat and oval-shaped face, small chins, widely spaced eyes, and cleft palates. They can also have an enlarged abdomen because of the condition called hydrops fetalis wherein excess fluid builds up in the infant's body before birth.
Achondrogenesis type 2 is caused by the absence of type 2 collagen produced by chondrocytes. Type 2 collagen is an important protein for cartilage and bone development. The absence of this protein is the result of COL2A1 gene mutation. Mutated COL2A1 gene produces a protein (procollagen) with an altered amino acid sequence: the amino acid glycine is replaced by another amino acid.
Procollagen is the precursor protein for the alpha 1 (II) chain of type 2 collagen. This is a long polypeptide and part of the triple helix structure of type 2 collagen. If the polypeptide is altered, the assembly of type 2 collagen into its triple helix structure will not happen and no functional type 2 collagen will be produced.
Chondrocytes replace type 2 collagen with either type 1 or type 3 collagen but these types of collagen are unable to promote the normal development of cartilage, bones and other connective tissues of the skeletal system.