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.

Spondyloepiphyseal dysplasia congenita (abbreviated to SED more often than SDC) is a rare disorder of bone growth that results in dwarfism, characteristic skeletal abnormalities, and occasionally problems with vision and hearing. The name of the condition indicates that it affects the bones of the spine (spondylo-) and the ends of bones (epiphyses), and that it is present from birth (congenital). The signs and symptoms of spondyloepiphyseal dysplasia congenita are similar to, but milder than, the related skeletal disorders achondrogenesis type 2 and hypochondrogenesis. Spondyloepiphyseal dysplasia congenita is a subtype of collagenopathy, types II and XI.

People with spondyloepiphyseal dysplasia are short-statured from birth, with a very short trunk and neck and shortened limbs. Their hands and feet, however, are usually average-sized. This type of dwarfism is characterized by a normal spinal column length relative to the femur bone. Adult height ranges from 0.9 meters (35 inches) to just over 1.4 meters (55 inches). Curvature of the spine (kyphoscoliosis and lordosis) progresses during childhood and can cause problems with breathing. Changes in the spinal bones (vertebrae) in the neck may also increase the risk of spinal cord damage. Other skeletal signs include flattened vertebrae (platyspondyly), a hip joint deformity in which the upper leg bones turn inward (coxa vara), and an inward- and downward-turning foot (called clubfoot). Decreased joint mobility and arthritis often develop early in life. Medical texts often state a mild and variable change to facial features, including cheekbones close to the nose appearing flattened, although this appears to be unfounded. Some infants are born with an opening in the roof of the mouth, which is called a cleft palate. Severe nearsightedness (high myopia) is sometimes present, as are other eye problems that can affect vision such as detached retinas. About one-quarter of people with this condition have mild to moderate hearing loss.

This gene encodes the alpha-1 chain of type II collagen, a fibrillar collagen found in cartilage and the vitreous humor of the eye. Mutations in this gene are associated with achondrogenesis, chondrodysplasia, early onset familial osteoarthritis, SED congenita, Langer-Saldino achondrogenesis, Kniest dysplasia, Stickler syndrome type I, and spondyloepimetaphyseal dysplasia Strudwick type. In addition, defects in processing chondrocalcin, a calcium binding protein that is the C-propeptide of this collagen molecule, are also associated with chondrodysplasia. There are two transcripts identified for this gene.

Type II collagen, which adds structure and strength to connective tissues, is found primarily in cartilage, the jelly-like substance that fills the eyeball (the vitreous), the inner ear, and the center portion of the discs between the vertebrae in the spine (nucleus pulposus). Three pro-alpha1(II) chains twist together to form a triple-stranded, ropelike procollagen molecule. These procollagen molecules must be processed by enzymes in the cell. Once these molecules are processed, they leave the cell and arrange themselves into long, thin fibrils that cross-link to one another in the spaces around cells. The cross-linkages result in the formation of very strong mature type II collagen fibers.

The COL2A1 gene is located on the long (q) arm of chromosome 12 between positions 13.11 and 13.2, from base pair 46,653,017 to base pair 46,684,527.

Children can benefit from a four stage in-home treatment program based on the principles of systematic desensitization. The four stages of the treatment are record, reward, relax and review.

- In the record stage, children are encouraged to keep a log of their typical eating behaviors without attempting to change their habits as well as their cognitive feelings.

- The reward stage involves systematic desensitization. Children create a list of foods that they might like to try eating some day. These foods may not be drastically different from their normal diet, but perhaps a familiar food prepared in a different way. Because the goal is for the children to try new foods, children are rewarded when they sample new foods.

- The relaxation stage is most important for those children that suffer severe anxiety when presented with unfavorable foods. Children learn to relax to reduce the anxiety that they feel. Children work through a list of anxiety-producing stimuli and can create a story line with relaxing imagery and scenarios. Often these stories can also include the introduction of new foods with the help of a real person or fantasy person. Children then listen to this story before eating new foods as a way to imagine themselves participating in an expanded variety of foods while relaxed.

- The final stage, review, is important to keep track of the child's progress. It is important to include both one-on-one sessions with the child, as well as with the parent in order to get a clear picture of how the child is progressing and if the relaxation techniques are working.

With time the symptoms of ARFID can lessen and can eventually disappear without treatment. However, in some cases treatment will be needed as the symptoms persist into adulthood. The most common type of treatment for ARFID is some form of cognitive-behavioral therapy. Working with a clinician can help to change behaviors more quickly than symptoms may typically disappear without treatment. Also hypnotherapy may be used. In that it lessens the anxiety associated with food.

There are support groups for adults with ARFID.