Collagen improperly formed, enough collagen is made but it is defective.

- Bones fracture easily, sometimes even before birth

- Bone deformity, often severe

- Respiratory problems possible

- Short stature, spinal curvature and sometimes barrel-shaped rib cage

- Triangular face

- Loose joints (double-jointed)

- Poor muscle tone in arms and legs

- Discolouration of the sclera (the 'whites' of the eyes are blue)

- Early loss of hearing possible

Type III is distinguished among the other classifications as being the "progressive deforming" type, wherein a neonate presents with mild symptoms at birth and develops the aforementioned symptoms throughout life. Lifespans may be normal, albeit with severe physical handicapping.

Collagen is not of a sufficient quality or quantity.

- Most cases die within the first year of life due to respiratory failure or intracerebral hemorrhage

- Severe respiratory problems due to underdeveloped lungs

- Severe bone deformity and small stature

Type II can be further subclassified into groups A, B, and C, which are distinguished by radiographic evaluation of the long bones and ribs. Type IIA demonstrates broad and short long bones with broad and beaded ribs. Type IIB demonstrates broad and short long bones with thin ribs that have little or no beading. Type IIC demonstrates thin and longer long bones with thin and beaded ribs.

Despite this excess bone formation, people with osteopetrosis tend to have bones that are more brittle than normal. Mild osteopetrosis may cause no symptoms, and present no problems.

However, serious forms can result in...

- Stunted growth, deformity, and increased likelihood of fractures

- Patients suffer anemia, recurrent infections, and hepatosplenomegaly due to bone expansion leading to bone marrow narrowing and extramedullary hematopoiesis

- It can also result in blindness, facial paralysis, and deafness, due to the increased pressure put on the nerves by the extra bone

- Abnormal cortical bone morphology

- Abnormal form of the vertebral bodies

- Abnormality of temperature regulation

- Abnormality of the ribs

- Abnormality of vertebral epiphysis morphology

- Bone pain

- Cranial nerve paralysis

- Craniosynostosis

- Hearing impairment

- Hypocalcemia

Pycnodysostosis causes the bones to be abnormally dense (osteopetrosis); the last bones of the fingers (the distal phalanges) to be unusually short; and delays the normal closure of the connections (sutures) of the skull bones in infancy, so that the "soft spot" (fontanelle) on top of the head remains widely open.

Those with the syndrome have brittle bones which easily break, especially in the legs and feet. The jaw and collar bone (clavicle) are also particularly prone to fractures.

Other abnormalities involve the head and face, teeth, collar bones, skin, and nails. The front and back of the head are prominent. Within the open sutures of the skull, there may be many small bones (called wormian bones). The midface is less full than usual. The nose is prominent. The jaw can be small. The palate is narrow and grooved. The baby teeth are late coming in and may be lost much later than usual. The permanent teeth can also be slow to appear. The permanent teeth are commonly irregular and teeth may be missing (hypodontia). The collar bones are often underdeveloped and malformed. The skin over the back of the fingers is very wrinkled. The nails are flat and grooved.

Pycnodysostosis also causes problems that may become evident with time. Aside from the broken bones, the distal phalanges and the collar bone can undergo slow progressive deterioration. Vertebral defects may permit the spine to curve laterally resulting in scoliosis. The dental problems often require orthodontic care and cavities are common.

Autosomal Dominant Osteopetrosis(ADO), also known as Albers-Schonberg disease. Most do not know they have this disorder because most individuals do not show any symptoms. However, the ones that do show symptoms, they will typically have a curvature of the spin(scoliosis), and multiple bone fractures. There are two types of adult osteopetrosis based on the basis of radiographic, biochemical, and clinical features.

Many patients will have bone pains. The defects are very common and include neuropathies due to the cranial nerve entrapment, osteoarthritis, carpal tunnel syndrome. About 40% of patients will experience recurrent fractures of their bones. 10% of patients will have osteomyelitis of the mandible.

Pycnodysostosis (from Greek: πυκνός (puknos) meaning "dense", "dys" ("defective"), and "ostosis" ("condition of the bone")), is a lysosomal storage disease of the bone caused by a mutation in the gene that codes the enzyme cathepsin K.

Fibrous dysplasia is a mosaic disease that can involve any part or combination of the craniofacial, axillary, and/or appendicular skeleton. The type and severity of the complications therefore depend on the location and extent of the affected skeleton. The clinical spectrum is very broad, ranging from an isolated, asymptomatic monostotic lesion discovered incidentally, to severe disabling disease involving practically the entire skeleton and leading to loss of vision, hearing, and/or mobility.

Individual bone lesions typically manifest during the first few years of life and expand during childhood. The vast majority of clinically significant bone lesions are detectable by age 10 years, with few new and almost no clinically significant bone lesions appearing after age 15 years. Total body scintigraphy is useful to identify and determine the extent of bone lesions, and should be performed in all patients with suspected fibrous dysplasia.

Children with fibrous dysplasia in the appendicular skeleton typically present with limp, pain, and/or pathologic fractures. Frequent fractures and progressive deformity may lead to difficulties with ambulation and impaired mobility. In the craniofacial skeleton, fibrous dysplasia may present as a painless “lump” or facial asymmetry. Expansion of craniofacial lesions may lead to progressive facial deformity. In rare cases patients may develop vision and/or hearing loss due to compromise of the optic nerves and/or auditory canals, which is more common in patients with McCune-Albright syndrome associated growth hormone excess. Fibrous dysplasia commonly involves the spine, and may lead to scoliosis, which in rare instances may be severe. Untreated, progressive scoliosis is one of the few features of fibrous dysplasia that can lead to early fatality.

Bone pain is a common complication of fibrous dysplasia. It may present at any age, but most commonly develops during adolescence and progresses into adulthood.

Bone marrow stromal cells in fibrous dysplasia produce excess amounts of the phosphate-regulating hormone fibroblast growth factor-23 (FGF23), leading to loss of phosphate in the urine. Patients with hypophosphatemia may develop rickets/osteomalacia, increased fractures, and bone pain.

Fibrous dysplasia is a disorder where normal bone and marrow is replaced with fibrous tissue, resulting in formation of bone that is weak and prone to expansion. As a result, most complications result from fracture, deformity, functional impairment, and pain. Disease occurs along a broad clinical spectrum ranging from asymptomatic, incidental lesions to severe disabling disease. Disease can affect one bone (monostotic) or multiple (polyostotic), and may occur in isolation or in combination with cafe-au-lait skin macules and hyperfunctioning endocrinopathies, termed McCune-Albright syndrome. More rarely, fibrous dysplasia may be associated with intramuscular myxomas, termed Mazabraud's syndrome. Fibrous dysplasia is very rare, and there is no known cure. Fibrous dysplasia is not a form of cancer.

Mild or early cases of Pagets are asymptomatic, and so most people are diagnosed with Paget's disease incidentally during medical evaluation for another problem. Approximately 35% of patients with Paget's have symptoms related to the disease when they are first diagnosed. Overall, the most common symptom is bone pain. When symptoms do occur, they may be confused with those of arthritis or other disorders, and so diagnosis may be delayed.

Paget's may first be noticed as an increasing deformity of a person's bones.

Paget's disease affecting the skull may lead to loss of hearing in one or both ears due to compression of the nerves in the inner ear. Rarely, skull involvement may lead to compression of the nerves that supply the eye, leading to vision loss.

The symptoms of Gorham's disease vary depending on the bones involved. It may affect any part of the skeleton, but the most common sites of disease are the shoulder, skull, pelvic girdle, jaw, ribs, and spine.

In some cases there are no symptoms until a fracture occurs either spontaneously or following minor trauma, such as a fall. There may be an acute onset of localized pain and swelling. More commonly there is pain of no apparent cause that increases in frequency and intensity over time and may eventually be accompanied by weakness and noticeable deformity of the area. The rate of progression is unpredictable and the prognosis can be difficult. The disease may stabilize after a number of years, go into spontaneous remission, or, in cases involving the chest and upper spine, prove fatal. Recurrence of the disease following remission can also occur. Involvement of the spine and skull base may cause a poor outcome from neurological complications. In many cases, the end result of Gorham's disease is severe deformity and functional disability.

Symptoms such as difficulty breathing and chest pain may be present if the disease is present in the ribs, scapula, or thoracic vertebrae. These may indicate that the disease has spread from the bone into the chest cavity. The breathing problems may be misdiagnosed as asthma, because the damage done to the lungs can cause the same types of changes to lung function testing that are seen in asthma. Extension of the lesions into the chest may lead to the development of chylous pleural and pericardial effusions. Chyle is rich in protein and white blood cells that are important in fighting infection. The loss of chyle into the chest can have serious consequences, including infection, malnutrition, and respiratory distress and failure. These complications or their symptoms, such as difficulty breathing, chest pain, poor growth or weight loss, and infection have sometimes been the first indications of the condition.

Gorham's disease (pronounced GOR-amz), also known as Gorham vanishing bone disease and phantom bone disease, is a very rare skeletal condition of unknown cause, characterized by the uncontrolled proliferation of distended, thin-walled vascular or lymphatic channels within bone, which leads to resorption and replacement of bone with angiomas and/or fibrosis. Current treatments are experimental only.

Paget's disease is a frequent component of multisystem proteinopathy.

Advanced Paget's disease may lead to other medical conditions, including:

- Osteoarthritis may result from changes in bone shape that alter normal skeletal mechanics. For example, bowing of a femur affected by Paget's may distort overall leg alignment, subjecting the knee to abnormal mechanical forces and accelerating degenerative wear.

- Heart failure is a rare, reported consequence of severe Paget's disease (i.e. more than 40% skeletal involvement). The abnormal bone formation is associated with recruitment of abnormal blood vessels, forcing the cardiovascular system to work harder (pump more blood) to ensure adequate circulation.

- Kidney stones are somewhat more common in patients with Paget's disease.

- Nervous system problems may occur in Paget's disease, resulting from increased pressure on the brain, spinal cord, or nerves, and reduced blood flow to the brain and spinal cord.

- When Paget's disease affects the facial bones, the teeth may become loose. Disturbance in chewing may occur. Chronic dental problems may lead to infection of the jaw bone.

- Angioid streaks may develop, possibly as a result of calcification of collagen or other pathological deposition.

Paget's disease is "not" associated with osteoporosis. Although Paget's disease and osteoporosis can occur in the same patient, they are different disorders. Despite their marked differences, several treatments for Paget's disease are also used to treat osteoporosis.

Hair abnormalities are very prominent in majority of the cases of TDO. Kinky/curly hair that is unusually dry and easily sheds is present at birth. In 80% of cases, the hair has a more relaxed appearance by adolescence. The presence of this hair texture type is a defining characteristic between a diagnosis of TDO verses amelogenesis imperfecta with hypomaturation. Additionally, in TDO the nails are usually abnormally thin, brittle, and split frequently. Cranial deficiencies are marked by the presence of having a long skull relative to its width, or protrusive foreheads due to increased thickness of the cranial bones and premature closing of the associated sutures in the skull. The long bones in the body (arms, legs) are also abnormally long and tend to fracture very easily. Osteosclerosis, commonly seen in TDO cases is characterized by an increase in bone density, affecting the skull and the mastoid process located behind the jawbone on the skull, as well as a shortened ramus seen in people with TDO. There are no known pathological problems associated with hair and bone changes in people with this disease. Changes in the long bones tend to appear later in development, but changes in the teeth appear once the teeth being to form, called primary dentition. The hair and bone abnormalities are evaluated radiographically during initial diagnosis, and visually during the course of the disease. Radiographic exams may be repeated if there is suspect of fracture.

Signs and symptoms of rickets can include bone tenderness, and a susceptibility for bone fractures particularly greenstick fractures. Early skeletal deformities can arise in infants such as soft, thinned skull bones – a condition known as craniotabes which is the first sign of rickets; skull bossing may be present and a delayed closure of the fontanelles.

Young children may have bowed legs and thickened ankles and wrists; older children may have knock knees. Spinal curvatures of kyphoscoliosis or lumbar lordosis may be present. The pelvic bones may be deformed. A condition known as rachitic rosary can result as the thickening caused by nodules forming on the costochondral joints. This appears as a visible bump in the middle of each rib in a line on each side of the body. This somewhat resembles a rosary, giving rise to its name. The deformity of a pigeon chest may result in the presence of Harrison's groove.

Hypocalcemia, a low level of calcium in the blood can result in tetany – uncontrolled muscle spasms. Dental problems can also arise.

An X-ray or radiograph of an advanced sufferer from rickets tends to present in a classic way: the bowed legs (outward curve of long bone of the legs) and a deformed chest. Changes in the skull also occur causing a distinctive "square headed" appearance known as "caput quadratum". These deformities persist into adult life if not treated. Long-term consequences include permanent curvatures or disfiguration of the long bones, and a curved back.

The following are symptoms characteristic with individuals having the disorder. Individuals may display some, most, or all of these symptoms throughout the course of their life, though symptoms may vary with each patient.

- Abnormal hair (coarse, thick, brittle)

- Calvarial hypomineralization (soft skull)

- Y-shaped cataracts by 1–2 years of age

- Skeletal defects

- Hypertelorism (wide-set eyes)

- Facial dysmorphisms

- Late-closing fontanels

- Abnormal accumulation of proteins in the endoplasmic reticulum

- Scoliosis

- Broad forehead, nose

- Missing, small teeth or abnormal teeth positioning

- Poor skull calcification

- Flat foot

- Motor delay

- Abnormal vertebrae

- Prominent forehead and brow

- High nose bridge

- Capillary hemangioma

- Delayed tooth eruption

- Long upper lip groove

- Large mouth

- High arched palate

- Narrow hips and rib cage

- Thin lips

- Narrow and sloping shoulders

- Hyperpigmentation

- Hyperextensible joints

Onset of the disease is in neonatal development and infancy, and symptoms tend to become evident soon after birth.

In many cases there is pain and discomfort in a joint which increases over time. While it can affect any bone, about half of cases show multiple sites of damage. Avascular necrosis primarily affects the joints at the shoulder, knee, and hip. The classical sites are: head of femur, neck of talus and waist of the scaphoid.

Avascular necrosis most commonly affects the ends of long bones such as the femur (the bone extending from the knee joint to the hip joint). Other common sites include the humerus (the bone of the upper arm), knees, shoulders, ankles and the jaw.

Tricho-dento-osseous syndrome (TDO) is a rare, systemic, autosomal dominant genetic disorder that causes defects in hair, teeth, and bones respectively. This disease is present at birth. TDO has been shown to occur in areas of close geographic proximity and within families; most recent documented cases are in Virginia, Tennessee, and North Carolina. The cause of this disease is a mutation in the DLX3 (distal-less 3) gene, which controls hair follicle differentiation and induction of bone formation. One-hundred percent of patients with TDO suffer from two co-existing conditions called enamel hypoplasia and taurodontism in which the abnormal growth patterns of the teeth result in severe external and internal defects. The hair defects are characterized as being rough, course, with profuse shedding. Hair is curly and kinky at infancy but later straightens. Dental defects are characterized by dark-yellow/brownish colored teeth, thin and/or possibly pitted enamel, that is malformed. The teeth can also look normal in color, but also have a physical impression of extreme fragility and thinness in appearance. Additionally, severe underbites where the top and bottom teeth fail to correctly align may be present; it is common for the affected individual to have a larger, more pronounced lower jaw and longer bones. The physical deformities that TDO causes become more noticeable with age, and emotional support for the family as well as the affected individual is frequently recommended. Adequate treatment for TDO is a team based approach, mostly involving physical therapists, dentists, and oromaxillofacial surgeons. Genetic counseling is also recommended.

Skeletal fluorosis is a bone disease caused by excessive accumulation of fluoride in the bones. In advanced cases, skeletal fluorosis causes painful damage to bones and joints.

Pediatric fractures can be classified as complete and incomplete:

- Incomplete: there are three basic forms of incomplete fractures:

- The first is the greenstick fracture, a transverse fracture of the cortex which extends into the midportion of the bone and becomes oriented along the longitudinal axis of the bone without disrupting the opposite cortex.

- The second form is a torus or buckling fracture, caused by impaction. They are usually the result of a force acting on the longitudinal axis of the bone: they are typically a consequence of a fall on an outstretched arm, so they mainly involve the distal radial metaphysis. The word torus is derived from the Latin word 'torus,' meaning swelling or protuberance.

- The third is a bow fracture in which the bone becomes curved along its longitudinal axis.

- Complete fractures

There are also physeal fractures (fractures involving the physis, the growth plate, which is not present in adults). The Salter-Harris classification is the most used to describe these fractures.

Avascular necrosis (AVN), also called osteonecrosis or bone infarction, is death of bone tissue due to interruption of the blood supply. Early on there may be no symptoms. Gradually joint pain may develop which may limit the ability to move. Complication may include collapse of the bone or nearby joint surface.

Risk factors include bone fractures, joint dislocations, alcoholism, and the use of high dose steroids. The condition may also occur without any clear reason. The most commonly affected bone is the femur. Other relatively common sites include the upper arm bone, knee, shoulder, and ankle. Diagnosis is typically by medical imaging such as X-ray, CT scan, or MRI. Rarely biopsy may be used.

Treatments may include medication, not walking on the affected leg, stretching, and surgery. Most of the time surgery is eventually required and may include core decompression, osteotomy, bone grafts, or joint replacement. About 15,000 cases occur per year in the United States. People 30 to 50 years old are most commonly affected. Males are more commonly affected than females.

A greenstick fracture is a fracture in a young, soft bone in which the bone bends and breaks. Greenstick fractures usually occur most often during infancy and childhood when bones are soft. The name is by analogy with green (i.e., fresh) wood which similarly breaks on the outside when bent. It was discovered by British-American orthopedist, John Insall, and Polish-American orthopedist, Michael Slupecki.

In orthopedic medicine, fractures are classified in various ways. Historically they are named after the physician who first described the fracture conditions, however, there are more systematic classifications in place currently.

Symptoms are mainly promoted in the bone structure. Due to a high fluorine concentration in the body, the bone is hardened and thus less elastic, resulting in an increased frequency of fractures. Other symptoms include thickening of the bone structure and accumulation of bone tissue, which both contribute to impaired joint mobility. Ligaments and cartilage can become ossified. Most patients suffering from skeletal fluorosis show side effects from the high fluorine dose such as ruptures of the stomach lining and nausea.

Fluorine can also damage the parathyroid glands, leading to hyperparathyroidism, the uncontrolled secretion of parathyroid hormones. These hormones regulate calcium concentration in the body. An elevated parathyroid hormone concentration results in a depletion of calcium in bone structures and thus a higher calcium concentration in the blood. As a result, bone flexibility decreases making the bone more amenable to fractures.

Navicular syndrome, often called navicular disease, is a syndrome of lameness problems in horses. It most commonly describes an inflammation or degeneration of the navicular bone and its surrounding tissues, usually on the front feet. It can lead to significant and even disabling lameness.

Cranio–lenticulo–sutural dysplasia (CLSD, or Boyadjiev-Jabs syndrome) is a neonatal/infancy disease caused by a disorder in the 14th chromosome. It is an autosomal recessive disorder, meaning that both recessive genes must be inherited from each parent in order for the disease to manifest itself. The disease causes a significant dilation of the endoplasmic reticulum in fibroblasts of the host with CLSD. Due to the distension of the endoplasmic reticulum, export of proteins (such as collagen) from the cell is disrupted.

The production of SEC23A protein is involved in the pathway of exporting collagen (the COPII pathway), but a missense mutation causes and underproduction of SEC23A which inhibits the pathway, affecting collagen secretion. This decrease in collagen secretion can lead to the bone defects that are also characteristic of the disease, such as skeletal dysplasia and under-ossification. Decreased collagen in CLSD-affected individuals contributes to improper bone formation, because collagen is a major protein in the extracellular matrix and contributes to its proper mineralization in bones. It has also been hypothesized that there are other defects in the genetic code besides SEC23A that contribute to the disorder.