Term Glossary
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Abnormal — Differing from normal.

Analysis — Examination to discover characteristics or meanings.

Allele — One of the two copies of each gene containing specific inheritable characteristics.

Ambulation (Ambulatory) — Walking or being able to walk.

Autosomal — The gene for the disorder is not on a sex chromosone (X or Y), indicating that the abnormal gene can affect males or females equally.

Autosomal Dominant — Describes a genetic disorder such as OI that is caused by a gene that is not linked to a sex chromosome and that is cause by a single abnormal gene.

Autosomal recessive — Autosomal recessive is one of several ways that a trait, disorder, or disease can be passed down through families. An autosomal recessive disorder means two copies of an abnormal gene must be present in order for the disease or trait to develop.

Bisphosphonates — A group of drugs that were originally developed to treat conditions such as Paget's Disease of Bone and osteoporosis. The different compounds each have slightly different characteristics and potency. These drugs are being investigated as treatments for OI. They include, pamidronate, alendronate, and zoledronate.

BMD(Bone Mineral Density) — The amount of bone per unit of skeletal area. Tests for BMD are used to evaluate bone health and fracture risk.

Bone Density Test — Bone density tests, also called bone mineral density (BMD) tests, measure bone density in various sites of the body. It is most important to measure bone mass in the spine, hips, and arms because these areas are likely to fracture when bone mass is low. These tests are useful for people with OI as a method for estimating fracture risk and to assess the result of treatments.

Bone Mass — The weight of the skeleton, overall or in specific regions such as the spine or hip.

Bowing — A curve in a normally straight long bone. This can be the result of angulation from healed fractures or gradual deformation of the bone over time as a response to the forces upon it.

Brittle Teeth (Dentigenesis Imperfecta) — Hereditary condition characterized by translucent gray to yellow-brown teeth involving both dedicuous (baby) and permanent teeth. The enamel fractures easily. Dentigenesis Imperfecta can be seen in people with osteogenesis imperfecta or it can be caused by a separate inherited autosomal dominant trait.

Cell — The basic structural unit of all living organisms. It is surrounded by a membrane and contains a nucleus which carries genetic material.

Chromosome — A microscopic rod-shaped structure present in the nucleus of all body cells except red blood cells. Chromosomes store genetic information (genes). Normally, humans have 23 pairs for a total of 46 chromosomes. In each pair, one chromosome is inherited from the mother and one from the father.

Collagen — The major structural protein in the human body. Collagen forms the long fibers that are the underlying structure in connective tissue, such as cartilage, skin and bone. There are many types of collagen in the human body. Defects of type 1 collagen are known to cause OI.

DNA (Deoxyribonucleic Acid) — Deoxyribonucleic acid is the 'building block' for all genetic material.

Deletion Mutation — Occurs when part of a gene is missing. In cases of osteogenesis imperfecta, part of one of the genes for type 1 collagen has been deleted; it is missing. The resulting gene is shorter than it should be and this contributes to the genetic causes for OI.

Dentinogenesis Imperfecta (Brittle Teeth) — Hereditary condition characterized by translucent gray to yellow-brown teeth involving both dedicuous (baby) and permanent teeth. The enamel fractures easily. Dentinogenesis Imperfecta can be seen in people with osteogenesis imperfecta or it can be caused by mutations in dentin sialophosphoprotein (DSPP).

Dominant — Term used to describe a genetic disorder such as OI that is caused by a single abnormal gene. This gene can be inherited from the mother or the father or be the result of a spontaneous mutation.

Dual Energy X-Ray Absorptiometry (DEXA Scan) — A common method for measuring bone mass. The results of this test are usually reported as BMD or bone mineral density.


Genetics — The branch of science concerned with heredity.

Genome — A complete set of chromosomes found in each cell of the human body. Chromosomes are microscopic structures composed of DNA.

Histology — The science concerned with the minute structure of cells, tissues, and organs. The study of tissue.

Histomorphometry — The form and structure of an organism or any of its parts as seen through a microscope.

Imperfecta — The Greek word for "imperfect." The words "osteogenesis imperfecta" mean bone that is imperfectly made from the beginning of life.

In vitro — Describes a process that occurs in an artificial environment such as a test tube.

In vivo — Describes a process that occurs in the living body.


Kyphoscoliosis (Kyphosis) — Curving forward or a hunched deformity of the spine, combined with scoliosis, a side-to-side curve of the spine.

Kyphosis (Kyphoscoliosis) — Curving forward or a hunched deformity of the spine, combined with scoliosis, a side-to-side curve of the spine.


Metabolism — Chemical changes that occur in tissues.

Novel — An unusual or non-standard form. OI Type V and Type VI are referred to as "novel forms of OI," because they have a significant characteristic that is different from the four generally recognized types. No defect in the genes that control the body's production of Type 1 collagen has been found in people who have been diagnosed with these types of OI. The other types of OI all are associated with defects in Type 1 collagen.

Orthopedic Surgery — Surgery that involves the musculoskeletal system. The most common orthopedic surgery for people with OI is rodding surgery.

Ossification — Changing other tissues, including cartilage, into bone. It is the process of normal bone formation performed by the osteoblast, a cell in the body that specifically performs this function.

Osteogenesis — The development or formation of bone.

Osteogenesis imperfecta — A genetic disorder of connective tissue characterized by bones that break easily, often from little or no apparent trauma. osteogenesis imperfecta (OI) is a highly variable disorder with signs and symptoms ranging from mild to severe. Most people with OI have a faulty gene that instructs their bodies to make either too little type 1 collagen or poor quality type 1 collagen. Type 1 collagen is the protein "scaffolding" of bone and other connective tissues. In addition to fractures, people with OI sometimes have muscle weakness or joint laxity, easy bruising, abnormal teeth and skeletal deformities. People with OI may experience respiratory difficulties and hearing loss. Those with the more severe forms are short in stature, while those with the milder forms will be shorter than average compared to others in their family. There are four generally recognized types of OI. OI is reported to occur with equal frequency in males and females and among all ethnic and racial groups. Two additional forms of OI have recently been identified that do not appear to have a type 1 collagen defect.

Osteopenia — Too little bone formation as measured by a Dexa Scan or radiographs Bone mass is below normal but not low enough to be called osteoporosis. The bones may be described as "thin". This term is applied to conditions such as OI, osteoporosis and osteomalcia.

Osteoporosis — A condition in which the bones become weakened either due to decreased quality or quantity of bone, and more likely to fracture. This disease is characterized by porous bone, low bone mass and structural deterioration of bone tissue, leading to bone fragility.

Prevalence — A term used by epidemiologists (scientists who study diseases in populations) to describe how often a disorder occurs in a population. For genetic disorders such as OI, prevalence refers to the number of cases in a specified population at a designated time. The question, "How many people in the United States today have OI?" is asking about the prevalence of OI.


Rodding — Internal support for the long bones by surgical insertion of a metal rod. This procedure is recommended to control repeated fractures, and to improve bone deformities that interfere with function. Different types of rods are used for different circumstances.

Rodding Surgery — Rodding surgery involves internal "splinting" of the long bones by means of the insertion of a metal rod. (See Rodding.)

Sclera — The part of the eye around the colored pupil commonly referred to as "the whites of the eyes." Some, not all, people with OI appear to have a blue, purple or gray tint to their sclera. The color may range from barely noticeable to very dark and may change with age.

Spontaneous Mutation — This is a change in a gene that occurs without an obvious cause, in a family where there is no history of the particular gene mutation. OI is inherited as an autosomal dominant trait. Approximately 35% of cases have no family history and are called "sporadic" cases. In sporadic cases, OI is believed to result from a spontaneous new mutation.

T-Score — One method of reporting the results of a bone density test. BMD is compared to two norms, "young normal" and "age-matched." Young normal, known as your T-score, compares BMD to optimal or peak density of a 30-year old healthy adult. Fracture risk increases as BMD falls below young-normal levels. Age-matched, known as your Z-score, compares the individual's BMD to what is expected in adults of the same age and body size.

Transcription Factor — A protein that activates gene expression.

Type 1 Collagen — The major structural protein which functions as a significant part of the underlying structure of bone, ligaments, skin and other connective tissue.

Type I OI (OI Type I) — The most common and the mildest form of osteogenesis imperfecta (OI).

Type II OI (OI Type II) — The most severe form of osteogenesis imperfecta. Infants are usually born with multiple fractures, an unusually soft skull, an unstable neck and are quite small. Almost all infants with Type II OI die at or shortly after birth, often due to respiratory problems. In the newborn period, it can be difficult to distinguish between Type II and severe type III OI. Very rare exceptions of true Type II infants with longer survival have been reported.

Type III OI (OI Type III) — A severe form of osteogenesis imperfecta that is sometimes referred to a "Progressive Deforming OI." Common signs include short stature, fractures present at birth, progressive long bone deformities, spinal curvature and barrel-shaped rib cage.

Type IV OI (OI Type IV) — Sometimes referred to as the "moderate" form of osteogenesis imperfecta. It is in between Type I and Type III in severity.

Type V OI (OI Type V) — A recently identified form of osteogenesis imperfecta. It does not appear to have a collagen defect and is characterized by a dense band adjacent to the growth plate of the long bones, development of unusually large calluses at the sites of fractures or surgical procedures and calcification of the membrane between the bones of the forearm.