Osteochondromas or osteocartilaginous exostoses are the most common benign tumors of the bones.

The tumors take the form of cartilage-capped bony projections or outgrowth on the surface of bones (exostoses). It is characterized as a type of overgrowth that can occur in any bone where cartilage forms bone. Tumors most commonly affect long bones in the leg, pelvis, or scapula (shoulder blade). Development of osteochondromas take place during skeletal growth between the ages of 13 and 15 and ceases when the growth plate fuses at puberty. They arise within the first three decades of life affecting children and adolescents.

Osteochondromas occur in 3% of the general population and represent 35% of all benign tumors and 8% of all bone tumors. Majority of these tumors are solitary non-hereditary lesions and approximately 15% of osteochondromas occur as hereditary multiple osteochondromas (HMOs). They can occur as a solitary lesion (solitary osteochondroma) or multiple lesions within the context of the same bone (Multiple Osteochondroma). Osteochondromas do not result from injury and the exact cause remains unknown. Recent research has indicated that multiple osteochondromas is an autosomal dominant inherited disease. Germ line Mutations in "EXT1" and "EXT2" genes located on chromosomes 8 and 11 have been associated with the cause of the disease.

The treatment choice for osteochondroma is surgical removal of solitary lesion or partial excision of the outgrowth, when symptoms cause motion limitations or nerve and blood vessel impingements.

Limited normal functions and movements are caused by osteochondromas growing slowly and inwardly. The majority of osteochondromas are symptomless and are found incidentally. Each individual with osteochondroma may experience symptoms differently and most of the time individuals will experience no symptoms at all. Some of the most common symptoms are a hard immobile painless palpable mass, adjacent muscle soreness, and pressure or irritation with heavy exercising.

Major symptoms arise when complications such as fractures, bone deformity or mechanical joint problems occur. If the occurrence of an osteochondroma is near a nerve or a blood vessel, the affected limb can experience numbness, weakness, loss of pulse or color change. Periodic changes in the blood flow can also take place. Approximately 20% of patients experiencing nerve compression commonly acknowledge vascular compression, arterial thrombosis, aneurysm, and pseudoaneurysm. Formation of pseudoaneurysm and venous thrombosis lead to claudication, pain, acute ischemia, and symptoms of phlebitis. If the tumor is found under a tendon, it can cause pain during movement causing restriction of joint motion. Pain can also occur due to bursal inflammation, swelling or fracture at the base of the tumor stalk. Some of the clinical signs and symptoms of malignant osteochondroma are pain, swelling, and mass enlargement.

Some parents of children with MHE have observed autism-like social problems in their children. To explore those observations more deeply, a 2012 study by the Sanford-Burnham Medical Research Institute used a mouse model of MHE to observe cognitive function. The findings indicated that the mutant mice endorsed three autistic characteristics: social impairment, impairments in ultrasonic vocalization, and repetitive behavior.

HME is an autosomal dominant hereditary disorder. This means that a patient with HME has a 50% chance of transmitting this disorder to his or her children. Most individuals with HME have a parent who also has the condition, however, approximately 10% -20% of individuals with HME have the condition as a result of a spontaneous mutation and are thus the first person in their family to be affected.

HME has thus far been linked with mutations in three genes.

- EXT1 which maps to chromosome 8q24.1

- EXT2 which maps to 11p13

- EXT3 which maps to the short arm of Chromosome 19 (though its exact location has yet to be precisely determined)

Mutations in these genes typically lead to the synthesis of a truncated EXT protein which does not function normally. It is known that EXT proteins are important enzymes in the synthesis of heparan sulfate; however the exact mechanism by which altered synthesis of heparan sulfate that could lead to the abnormal bone growth associated with HME is unclear. It is thought that normal chondrocyte proliferation and differentiation may be affected, leading to abnormal bone growth. Since the HME genes are involved in the synthesis of a glycan (heparan sulfate), HME may be considered a congenital disorder of glycosylation according to the new CDG nomenclature suggested in 2009.

For individuals with HME who are considering starting a family, preimplantation genetic testing and prenatal diagnosis are available to determine if their unborn child has inherited the disease. HME has a 96% penetrance, which means that if the affected gene is indeed transmitted to a child, the child will have a 96% of actually manifesting the disease, and 4% chance of having the disease but never manifesting it. It should be noted that the 96% penetrance figure comes from one study. Other studies have observed both incomplete and variable penetrance but without calculating the % penetrance, e.g. In both the aforementioned studies the symptomless individuals carrying the faulty gene were predominantly female, leading to speculation that incomplete penetrance is more likely to be exhibited in females. Indeed, other work has shown that boys/men tend to have worse disease than females, as well as that the number of exostoses in affected members of the same family can vary greatly. It is also possible for females to be severely affected.

Symptoms are more likely to be severe if the mutation is on the "ext1" gene rather than "ext2" or "ext3"; "ext1" is also the most commonly affected gene in patients of this disorder.

Hereditary multiple exostoses (HME), also called hereditary multiple osteochondromas (HMO), is a condition that is estimated to affect 1 in 50,000 individuals. Multiple benign or noncancerous bone tumors develop in the affected individuals. The number and location vary among affected patients. Most people seem unaffected at birth; however, by the age of 12 years, they develop multiple exostoses.

Multiple epiphyseal dysplasia (MED) encompasses a spectrum of skeletal disorders, most of which are inherited in an autosomal dominant form. However, there is an autosomal recessive form.

Associated genes include COL9A1, COL9A2, COL9A3, COMP, and MATN3.

Types include:

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.

Fairbank's disease or multiple epiphyseal dysplasia (MED) is a rare genetic disorder (dominant form: 1 in 10,000 births) that affects the growing ends of bones. Long bones normally elongate by expansion of cartilage in the growth plate (epiphyseal plate) near their ends. As it expands outward from the growth plate, the cartilage mineralizes and hardens to become bone (ossification). In MED, this process is defective.

Evidence for exostosis found in the fossil record is studied by paleopathologists, specialists in ancient disease and injury. Exostosis has been reported in dinosaur fossils from several species, including "Acrocanthosaurus atokensis", "Albertosaurus sarcophagus", "Allosaurus fragilis", "Gorgosaurus libratus", and "Poekilopleuron bucklandii".

There is no cure. Maintaining a healthy lifestyle by exercising and avoiding smoking can help prevent fractures. Treatment may include care of broken bones, pain medication, physical therapy, braces or wheelchairs, and surgery. A type of surgery that puts metal rods through long bones may be done to strengthen them.

Bone infections are treated as and when they occur with the appropriate antibiotics and antiseptics.

NBCCS has an incidence of 1 in 50,000 to 150,000 with higher incidence in Australia. One aspect of NBCCS is that basal-cell carcinomas will occur on areas of the body which are not generally exposed to sunlight, such as the palms and soles of the feet and lesions may develop at the base of palmar and plantar pits.

One of the prime features of NBCCS is development of multiple BCCs at an early age, often in the teen years. Each person who has this syndrome is affected to a different degree, some having many more characteristics of the condition than others.

Surgical excision is common and is a very effective mode of treatment.

Oral phosphate, 9, calcitriol, 9; in the event of severe bowing, an osteotomy may be performed to correct the leg shape.

Trevor disease, also known as Fairbank's disease and Trevor's disease, is a congenital bone developmental disorder. There is 1 case per million population. The condition is three times more common in males than in females.

This disorder is rare, and is characterised by an asymmetrical limb deformity due to localized overgrowth of cartilage, histologically resembling osteochondroma. It is believed to affect the limb bud in early fetal life. The condition occurs mostly in the ankle or knee region and it is always confined to a single limb. This usually involves only the lower extremities and on medial side of the epiphysis. It is named after researcher David Trevor.

They tend to be painful due to the pressure applied to the nail bed and plate. They can involve destruction of the nail bed. These lesions are not true osteochondromas, rather it is a reactive cartilage metaplasia. The reason it occurs on the dorsal aspect is because the periosteum is loose dorsally but very tightly adherent volarly.

Subungal malignant melanomas can also occur in canines.

They are distinct from subungual osteochondroma.

The cause of fibular hemimelia is unclear. Purportedly, there have been some incidents of genetic distribution in a family; however, this does not account for all cases. Maternal viral infections, embryonic trauma, teratogenic environmental exposures or vascular dysgenesis (failure of the embryo to form a satisfactory blood supply) between four and seven weeks gestation are considered possible causes.

In an experimental mouse model, change in the expression of a homeobox gene led to similar, but bilateral, fibular defects.

Children with NF-1 can experience social problems, attention problems, social anxiety, depression, withdrawal, thought problems, somatic complaints, learning disabilities and aggressive behavior. Treatments include psychotherapy, antidepressants and cognitive behavioral therapy.

Treatment is usually supportive treatment, that is, treatment to reduce any symptoms rather than to cure the condition.

- Enucleation of the odontogenic cysts can help, but new lesions, infections and jaw deformity are usually a result.

- The severity of the basal-cell carcinoma determines the prognosis for most patients. BCCs rarely cause gross disfigurement, disability or death .

- Genetic counseling

Within the CNS, NF-1 manifests as a weakness of the dura, which is the tough covering of the brain and spine. Weakness of the dura leads to focal enlargement terms dural ectasia due to chronic exposure to the pressures of CSF pulsation.

Acetazolamide has shown promise as a treatment for this condition.

A bone tumor (also spelled bone tumour) is a neoplastic growth of tissue in bone. Abnormal growths found in the bone can be either benign (noncancerous) or malignant (cancerous).

Average five-year survival in the United States after being diagnosed with bone and joint cancer is 67%.

Treatment of bone tumors is highly dependent on the type of tumor.

X-linked hypophosphatemia (XLH), also called X-linked dominant hypophosphatemic rickets, X-linked vitamin d-resistant rickets, is an X-linked dominant form of rickets (or osteomalacia) that differs from most cases of rickets in that ingestion of vitamin D is relatively ineffective. It can cause bone deformity including short stature and genu varum (bow leggedness). It is associated with a mutation in the PHEX gene sequence (Xp.22) and subsequent inactivity of the PHEX protein. The prevalence of the disease is 1:20000. The leg deformity can be treated with Ilizarov frames and CAOS surgery.

Schimmelpenning syndrome appears to be sporadic rather than inherited, in almost all cases. It is thought to result from genetic mosaicism, possibly an autosomal dominant mutation arising after conception and present only in a subpopulation of cells. The earlier in embryological development such a mutation occurs, the more extensive the nevi are likely to be and the greater the likelihood of other organ system involvement.

YVS has been described relatively recently in the 1980s and since then less than 15 cases have been reported around the world. Many of the infants did not survive beyond one year of age.