Achondrogenesis, type 1B is a severe autosomal recessive skeletal disorder, invariable fatal in the perinatal period. It is characterized by extremely short limbs, a narrow chest, and a prominent, rounded abdomen. The fingers and toes are short and the feet may be rotated inward. Affected infants frequently have a soft out-pouching around the belly-button (an umbilical hernia) or near the groin (an inguinal hernia).

Achondrogenesis, type 1B is a rare genetic disorder; its incidence is unknown. Achondrogenesis, type 1B is the most severe condition in a spectrum of skeletal disorders caused by mutations in the "SLC26A2" gene. This gene provides instructions for making a protein that is essential for the normal development of cartilage and for its conversion to bone. Mutations in the "SLC26A2" gene disrupt the structure of developing cartilage, preventing bones from forming properly and resulting in the skeletal problems characteristic of achondrogenesis, type 1B.

Achondrogenesis, type 1B is inherited in an autosomal recessive pattern, which means two copies of the gene in each cell are altered. Most often, the parents of an individual with an autosomal recessive disorder are carriers of one copy of the altered gene but do not show signs and symptoms of the disorder.

Achondrogenesis is a number of disorders that are the most severe form of congenital chondrodysplasia (malformation of bones and cartilage). These conditions are characterized by a small body, short limbs, and other skeletal abnormalities. As a result of their serious health problems, infants with achondrogenesis are usually born prematurely, are stillborn, or die shortly after birth from respiratory failure. Some infants, however, have lived for a while with intensive medical support.

Researchers have described at least three forms of achondrogenesis, designated as Achondrogenesis type 1A, achondrogenesis type 1B and achondrogenesis type 2. These types are distinguished by their signs and symptoms, inheritance pattern, and genetic cause. Other types of achondrogenesis may exist, but they have not been characterized or their cause is unknown.

Achondrogenesis type 1A is caused by a defect in the microtubules of the Golgi apparatus. In mice, a nonsense mutation in the thyroid hormone receptor interactor 11 gene (Trip11), which encodes the Golgi microtubule-associated protein 210 (GMAP-210), resulted in defects similar to the human disease. When their DNA was sequenced, human patients with achondrogenesis type 1A also had loss-of-function mutations in GMAP-210. GMAP-210 moves proteins from the endoplasmic reticulum to the Golgi apparatus. Because of the defect, GMAP-210 is not able to move the proteins, and they remain in the endoplasmic reticulum, which swells up. The loss of Golgi apparatus function affects some cells, such as those responsible for forming bone and cartilage, more than others.

Achondrogenesis type 1B is caused by a similar mutation in SLC26A2, which encodes a sulfate transporter.

Platyspondylic lethal skeletal dysplasia, Torrance type is a severe disorder of bone growth. People with this condition have very short arms and legs, a small chest with short ribs, underdeveloped pelvic bones, and unusually short fingers and toes (brachydactyly). This disorder is also characterized by flattened spinal bones (platyspondyly) and abnormal curvature of the spine (lordosis).

As a result of these serious skeletal problems, many infants with platyspondylic lethal skeletal dysplasia, Torrance type are born prematurely, are stillborn, or die shortly after birth from respiratory failure. A few affected people with milder signs and symptoms have lived into adulthood, however.

This condition is one of a spectrum of skeletal 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 cartilage and in the clear gel that fills the eyeball (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, resulting in a reduced amount of this type of collagen in the body. Instead of forming collagen molecules, the abnormal "COL2A1" protein builds up in cartilage cells (chondrocytes). These changes disrupt the normal development of bones and other connective tissues, leading to the skeletal abnormalities characteristic of platyspondylic lethal skeletal dysplasia, Torrance type.

This condition is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. In some cases, an affected person inherits the mutation from one affected parent. Other cases may result from new mutations in the gene. These cases occur in people with no history of the disorder in their family.

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).

As a result of these serious health problems, infants are usually premature and stillborn or die shortly after birth from respiratory failure. Some infants have lived for a time, however, with intensive medical support. Babies who live past the newborn period are usually reclassified as having spondyloepiphyseal dysplasia congenita, a related disorder on the spectrum of abnormal bone growth.

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 collagenopathy, types II and XI, and is similar to another skeletal disorder, achondrogenesis type 2, although the spinal changes seen in hypochondrogenesis tend to be somewhat milder.

Spondyloepiphyseal dysplasia congenita is one of a spectrum of skeletal disorders caused by mutations in the "COL2A1" gene. The protein made by this gene forms type II collagen, a molecule found mostly in cartilage and in the clear gel that fills the eyeball (the vitreous). Type II collagen is essential for the normal development of bones and other connective tissues. Mutations in the "COL2A1" gene interfere with the assembly of type II collagen molecules, which prevents bones from developing properly and causes the signs and symptoms of this condition.

Spondyloepiphyseal dysplasia congenita is inherited in an autosomal dominant pattern, which means one copy of the altered gene is sufficient to cause the disorder.

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.

Infants with achondrogenesis, type 2 have short arms and legs, a small chest with short ribs, and underdeveloped lungs. 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 bones may be soft, but they often appear normal on X-ray images. In contrast, bones in the spine (vertebrae) and pelvis do not harden.

Achondrogenesis, type 2 and hypochondrogenesis (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" 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 (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 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.

More than 1 in 2 people with OI also have dentinogenesis imperfecta (DI) - a congenital disorder of formation of dentine. Dental treatment may pose as a challenge as a result of the various deformities, skeletal and dental, due to OI. Children with OI should go for a dental check-up as soon as their teeth erupt, this may minimize tooth structure loss as a result of abnormal dentine, and they should be monitored regularly to preserve their teeth and oral health.

Achondroplasia is caused by a mutation in fibroblast growth factor receptor 3 (FGFR3). In normal development FGFR3 has a negative regulatory effect on bone growth. In achondroplasia, the mutated form of the receptor is constitutively active and this leads to severely shortened bones. The effect is genetically dominant, with one mutant copy of the FGFR3 gene being sufficient to cause achondroplasia, while two copies of the mutant gene are invariably fatal (recessive lethal) before or shortly after birth (known as a lethal allele). A person with achondroplasia thus has a 50% chance of passing dwarfism to each of their offspring. People with achondroplasia can be born to parents that do not have the condition due to spontaneous mutation.

Studies have demonstrated that new gene mutations for achondroplasia are exclusively inherited from the father and occur during spermatogenesis; it is theorized that oogenesis has some regulatory mechanism that prevents the mutation from being passed on in females.

There are two other syndromes with a genetic basis similar to achondroplasia: hypochondroplasia and thanatophoric dysplasia.

Gene based therapy is being studied. In June 2015, BioMarin announced positive results of their Phase 2 study, stating that 10 children experienced a mean increase of 50% in their annualized growth velocity.

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.

Autosomal dominant porencephaly type I is rare and its prevalence and incidence are unknown. It affects males and females equally.

The type II and XI collagenopathies are a group of disorders that affect connective tissue, the tissue that supports the body's joints and organs. These disorders are caused by defects in type II or type XI collagen. Collagens are complex molecules that provide structure, strength, and elasticity to connective tissue. Type II and type XI collagen disorders are grouped together because both types of collagen are components of the cartilage found in joints and the spinal column, the inner ear, and the jelly-like substance that fills the eyeball (the vitreous). The type II and XI collagenopathies result in similar clinical features.

OI caused by mutation in the gene "LEPRE1" is classified as type VIII.

Acrocephalosyndactylia (or acrocephalosyndactyly) is the common presentation of craniosynostosis and syndactyly.

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.

Genetic changes are related to the following types of collagenopathy, types II and XI.

The system for classifying collagenopathies is changing as researchers learn more about the genetic causes of these disorders.The clinical features of the type II and XI collagenopathies vary among the disorders, but there is considerable overlap. Common signs and symptoms include problems with bone development that can result in short stature, enlarged joints, spinal curvature, and arthritis at a young age. For some people, bone changes can be seen only on X-ray images. Problems with vision and hearing, as well as a cleft palate with a small lower jaw, are common. Some individuals with these disorders have distinctive facial features such as protruding eyes and a flat nasal bridge.

It has several different types:

- type 1 - Apert syndrome

- type 2 - Crouzon syndrome

- type 3 - Saethre-Chotzen syndrome

- type 5 - Pfeiffer syndrome

A related term, "acrocephalopolysyndactyly" (ACPS), refers to the inclusion of polydactyly to the presentation. It also has multiple types:

- type 1 - Noack syndrome; now classified with Pfeiffer syndrome

- type 2 - Carpenter syndrome

- type 3 - Sakati-Nyhan-Tisdale syndrome

- type 4 - Goodman syndrome; now classified with Carpenter syndrome

- type 5 - Pfeiffer syndrome

It has been suggested that the distinction between "acrocephalosyndactyly" versus "acrocephalopolysyndactyly" should be abandoned.

Short rib – polydactyly syndrome is a family of four closely related dysplasias:

- I - "Saldino-Noonan type"

- II - "Majewski type"

- III - "Verma-Naumoff type" (associated with DYNC2H1)

- IV - "Beemer-Langer type"

Treatment for autosomal dominant porencephaly type I is based on the symptoms that an individual is experiencing - for example, treatment of seizures with anticonvulsants. It is particularly important for individuals with this disorder and hypertension to control their blood pressure, as they are at higher risk of stroke. Other stroke prevention treatments include avoiding anticoagulants, smoking, and situations that may lead to head trauma.

Griscelli syndrome type 2 (also known as "partial albinism with immunodeficiency") is a rare autosomal recessive syndrome characterized by variable pigmentary dilution, hair with silvery metallic sheen, frequent pyogenic infections, neutropenia, and thrombocytopenia.

Dentinogenesis imperfecta (DI) is a genetic disorder of tooth development. This condition is a type of dentin dysplasia that causes teeth to be discolored (most often a blue-gray or yellow-brown color) and translucent giving teeth an opalescent sheen. Although genetic factors are the main contributor for the disease, any environmental or systemic upset that impedes calcification or metabolisation of calcium can also result in anomalous dentine.

Consequently, teeth are also weaker than normal, making them prone to rapid wear, breakage, and loss. These problems can affect both primary (deciduous) teeth and permanent teeth. This condition is inherited in an autosomal dominant pattern, as a result of mutations on chromosome 4q21, in the dentine sialophosphoprotein gene (DSPP). It is one of the most frequently occurring autosomal dominant feature in humans. Dentinogenesis imperfecta affects an estimated 1 in 6,000 to 8,000 people.

Glutaric acidemia type 2 often appears in infancy as a sudden metabolic crisis, in which acidosis and low blood sugar (hypoglycemia) cause weakness, behavior changes, and vomiting. There may also be enlargement of the liver, heart failure, and a characteristic odor resembling that of sweaty feet. Some infants with glutaric acidemia type 2 have birth defects, including multiple fluid-filled growths in the kidneys (polycystic kidneys). Glutaric acidemia type 2 is a very rare disorder. Its precise incidence is unknown. It has been reported in several different ethnic groups.

Glutaric acidemia type 2 is an autosomal recessive metabolic disorder that is characterised by defects in the ability of the body to use proteins and fats for energy. Incompletely processed proteins and fats can build up, leading to a dangerous chemical imbalance called acidosis.