Achondrogenesis, type 2 results in short arms and legs, a small chest with short ribs, and underdeveloped lungs at birth.
Achondrogenesis, type 2 is a subtype of
collagenopathy, types II and XI. This condition is also associated with a lack of bone formation (ossification) in the spine and pelvis. Typical facial features include a prominent forehead, a small chin, and, in some cases, an opening in the roof of the mouth (a cleft palate). The abdomen is enlarged, and affected infants often have a condition called hydrops fetalis in which excess fluid builds up in the body before birth. The
skull
The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, t ...
bones may be soft, but they often appear normal on
X-ray
X-rays (or rarely, ''X-radiation'') are a form of high-energy electromagnetic radiation. In many languages, it is referred to as Röntgen radiation, after the German scientist Wilhelm Conrad Röntgen, who discovered it in 1895 and named it ' ...
images. In contrast, bones in the spine (
vertebrae
The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristi ...
) and pelvis do not harden.
Achondrogenesis, type 2 and
hypochondrogenesis
Hypochondrogenesis is a severe genetic disorder causing malformations of bone growth. The condition is characterized by a short body and limbs and abnormal bone formation in the spine and pelvis.
Hypochondrogenesis is a subtype of collagenopat ...
(a similar skeletal disorder) together affect 1 in 40,000 to 60,000 births. Achondrogenesis, type 2 is one of several skeletal disorders caused by mutations in the ''
COL2A1
Collagen, type II, alpha 1 (primary osteoarthritis, spondyloepiphyseal dysplasia, congenital), also known as COL2A1, is a human gene that provides instructions for the production of the pro-alpha1(II) chain of type II collagen.
Function
This g ...
'' gene. This gene provides instructions for making a protein that forms type II
collagen. This type of collagen is found mostly in cartilage and in the clear gel that fills the
eyeball
Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and conv ...
(the vitreous). It is essential for the normal development of bones and other tissues that form the body's supportive framework (connective tissues). Mutations in the ''COL2A1'' gene interfere with the assembly of type II collagen molecules, which prevents bones and other connective tissues from developing properly.
Achondrogenesis, type 2 is considered an
autosomal dominant
In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant and ...
disorder because one copy of the altered gene in each cell is sufficient to cause the condition. The disorder is not passed on to the next generation, however, because affected individuals hardly survive past puberty.
References
''This article incorporates public domain text fro
The U.S. National Library of Medicine'
External links
{{Scleroprotein disease
Congenital disorders
Collagen disease
Rare syndromes