Autosomal dominant

Hereditary characteristic that has a 50 % chance of being passed on. A dominant gene on an autosome – exerts genetic dominance. Every cell contains two copies of each gene. One gene might be mutant and the other “normal”. If the mutant gene is expressed in the cells (resulting in a particular characteristic or a disorder), the mutant gene is said to be dominant over the other “normal” copy of the gene. A disorder or characteristic caused by a dominant gene mutation only requires one of the genes to be mutated.

Autosomal recessive

A recessive gene on an autosome, usually producing little or no physical effect. Every cell contains two copies of each gene. One gene might be mutant and the other “normal”. If a mutant gene is not expressed in the cells, the mutant gene is said to be recessive to the other “normal” copy of the gene. An individual with this genetic constitution is said to be a “carrier” of a recessive gene mutation. For a recessive gene mutation to result in a particular characteristic or a disorder both copies of the genes must be mutated.

Autosome

Chromosomes which code for the stature of a person and which are not responsible for the sex .

Basilar impression (BI)

Also called basilar invagination. Upward protrusion of the top of the spine into the base of the skull. Occurs in some people with type III or IV OI. Usually devellops early in childhood.
Symptoms can be:

  • a flattening of the back of the skull
  • headaches
  • double vision
  • nystagmus (wiggly eyes)
  • facial neuralgia
  • inbalance and incoordination
  • arm or eye weakness or spasticity
  • increased intracranial pressure

BI is not neccesarily threatening but needs to be observed by a neurologist. In severe cases neurosurgical intervention may be necessary. There are a few specialized centers in the world.

Bailey nails (Bailey-Dubow nails)

Extendable metal support rods (telescopic nails) that can be inserted into the long bones (arms and legs) during surgery.

Bisphosphonates

The bisphosphonates are synthetic analogs of pyrophosphate, a natural inhibitor of osteoclastic bone resorption. Some of these compounds are used to treat osteoporosis and other bone diseases. At the moment several of these are also used for treating OI. There are bisphosphonates which can be taken oral and there are some which have to be administered as intravenous infusion.

Callus

New bone formed in the healing process following a fracture.

Cochlea

Coiled part of the inner ear concerned with the perception of sound, containing the auditory nerve endings.

Congenital

Similar to hereditary: present at birth.

Connective tissue

All those tissues in the human body that connect or support the structure. This comprises bone, skin, and various membranes in the eye and the ears, but also teeth, ligaments, tendons, heart-valves, and the inner lining of blood vessels.

Chromosome

Complex strains of a type of protein (DNA) that are contained in every human cell. Each chain has a specific sequence of only 4 basic building blocks, coded with the 4 letters A, C, G and T. Humans have 46 different chromosomes. They come in pairs, so 23 of your chromosomes are from your father and 23 from your mother. The reproductive cells (egg, sperm) contain only one copy of each chromosome.

Collagen

Collagens are a family of proteins mainly secreted by connective tissue cells, their function is to provide strength and flexibility to the connective tissues. Collagen type I which accounts for 90% of our total body collagen is the most important one. It is made up of three alpha chains of procollagen. Two Chains of procollagen a1(I) and one chain of a2(I). After the three alpha chains have folded up in a triple helix the end parts are split of and the collagen type I molecule is ready. Many of these molecules can align, forming collagen fibrils, and these fibrils can form collagen fibers. In most cases of OI collagen type I is either defective in structure (quality) or in amount (quantity).

Cortex

Compact bone at the outer surface of bones.

Dentinogenesis imperfecta

Dental problems experienced by people with OI. A disorder of tooth development, autosomal dominantly inherited, and characterized by relatively soft enamel. It occurs in primary and permanent teeth and makes the teeth abnormally vulnerable to fracture, abrasion and wear.

Dominant inheritance

See autosomnal dominant

DEXA

Dual Energy X-ray Absorptiometry. In a DEXA Scan the bone density is measured, using low dose X-ray radiation

DNA

Deoxiribonucleic acid. A compound consisting of 4 different subunits, the exact order of which spells out the genetic code.

Epiphyses

The ends of the long bones which, during growth, are attached to the main bone by cartilage. They eventually fuse with the principal bone.

Femur

The thighbone.

Fibula

The splint-bone, the smaller of the two bones of the lower.

Gene(s)

Specific part of a chromosome that codes for some property, like e.g. hair color. A gene occupies a specific site on a chromosome known as a locus.

Genome

A complete set of chromosomes founds in each cell of the human body.

Greenstick fracture

An incomplete fracture of a long bone. The bone does not break all the way through (seen mainly in children).

Haematoma

Blood which was shifted into the tissue (e.g. after a fracture), causing a swelling and discoloration and is resorbed slowly.

Humerus

The upper arm bone.

Hypertrophic callus

Also called hyperplastic callus. Increased amount of callus after fracture or minor trauma. Mostly seen in patients with OI type V. Sometimes mimicking bone cancer.

Interosseous

Between bones. Membrana interosseum between the two bones of the forearm.

Kyphosis

A bending/deformation of the spinal column in the forward direction. Caused by a weakness of the vertebrae or the disks. Exaggerated forward curvature of the spine, usually in the thoracic region. c.c. Scoliosis

Kyphoscoliosis

Sideways (lateral) curvature of the spine with vertebral rotation, associated with a forwards to backwards (anteroposterior) hump in the spinal column.

Lordosis

Inward curvature of the spine. c.c. Scoliosis.

Matrix

The bone matrix is the intercellular structure of connective tissue to which the mineral matters attaches, giving the tissue its strengths.

Medullary canal

Internal cavity of a bone.

Mutation

Change in the DNA, often leading to a change in the message it encodes. For instance giving rise to a shortened or a faulty protein or to a gene which is non-functional. A permanent change in a gene (either a physical change in chromosome relations or a biochemical change in the codons that make up genes) which is then able to be inherited. Mutations can occur naturally and spontaneously or they might be due to exposure to mutagens. Mutations are sporadic, unpredictable events which change the DNA informational content.

Neridronate

A bisphosphonate, prescribed under the commercial name Nerixia which is administered intravenously.

Nosology

Classification or list of diseases.

Osteoblasts

Cells which produce bonematrix.

Osteoclasts

Cells which remove and remodel bone.

Osteoporosis

Weakening and loss of the normal density of bone. Osteoporosis leads to unusually porous bone that is more compressible like a sponge than dense like a brick. This disorder of the skeleton weakens the bone leading to an increased risk of fractures. It is a disease that is quite common in elderly people (particularly women) and is characterized by porous bone, low bone mass and structural deterioration of bone tissue. OI people are prone to developing this condition.

Osteotomy

Procedure of cutting the bone during surgery to correct deformities.

Pamidronate

A bisphosphonate, prescribed under the commercial name Aredia which is administered intravenously.

Phenotype

Physical findings caused by a mutation.

Procollagen

The product of the collagen genes, three procollagen chains join together in a triple helix to form a collagen molecule.

Protein

Substances which are major components of the body structure, essential to body function. They are made up of smaller units called amino acids.

PQCT

Peripheral Quantitative Computertomography. Method to analyse bone density and muscle mass at the forearm and the lower leg.

Radius

The shorter of the two bones of the forearm, ending on the side of the thumb.

Sclerae

The sclera, also known as the white of the eye, is the opaque, usually white, fibrous, protective, outer layer of the eye containing collagen and elastic fiber. The sclera forms the posterior five sixths of the connective tissue coat of the globe. In children, it is thinner and shows some of the underlying pigment, appearing slightly blue. In the elderly, however, fatty deposits on the sclera can make it appear slightly yellow.
In OI (specially type I) this white is sometimes colored blueish instead of white. In some patients the color fades over time to a pale blue or white.

Scoliosis

A bending/deformation of the spinal column. Lateral (sideways) curvature of the spine caused by a weakness of the vertebrae or the disks. Exaggerated sidewise curvature of the spine, usually in the thoracic region. c.c. Kyphosis.

Spica

A plaster cast that extends from toes to hips. It immobilizes not only the leg but in fact the whole person. This cast prevents the patient from sitting therefore bone loss (osteoporosis) affects the spine.

Stapes

Innermost of the small bones in the ear.

Stapedectomy

Surgical intervention on the stapes.

Telescopic rods

Rods inserted in the bone during surgery to correct deformities, which will extend during the physiological growth of a child.

Tibia

The shinbone, the larger of the two bones of the lower leg.

T-score

A statistical number to compare an individual’s bone mineral density to the so called “young normal” standard peak density of a healthy 30 year old adult. Ask your doctor for an interpretation of your T-score. A low T-score can be associated with an increased risk for fractures.

Ulna

The longer of the two bones of the forearm.

Wormian bones

Small bones in the skull.

Zolendronate

A bisphosphonate, prescribed under the commercial name Zometa and which is administered intravenously.

Z-score

A statistical number to compare an individual’s bone mineral density to the so called “age matched” standard. This takes into account one’s age and body size. Ask your doctor for an interpretation of your Z-score. Low z-scores can be associated with an increased risk for fractures.