Causes of Bone Disease: Genetic, Environmental, and Nutritional
Keeping the skeleton strong and healthy is a complex process. The amount, structure, composition, and position of the bones should all be correct. Any errors or changes in these can lead to bone disease. This article discusses the various causes of bone disease in humans.
Genetic Causes of Bone Disease
Certain diseases of the bones are genetic. Some individuals are born with inherently weak and thin bones. Some are born with bones that are excessively dense. Osteogenesis imperfecta is a genetic disease of the bones in which there is an abnormality in the collagen molecule. This leads to the production of a weak protein matrix in bones. Thus, people with osteogenesis imperfecta are prone to suffering multiple fractures from minimal stress.
In osteopetrosis, which is also an inherited condition present from birth, there is abnormal form of the osteoclasts (the bone cells that are responsible for resorbing bone). Therefore, the bones in these people are excessively dense. In other words, the remodeling process is flawed in osteopetrosis and osteoclasts do not resorb trabecular bone from the marrow space. People with osteopetrosis, therefore, have a marrow cavity which is not large enough for the normal formation of red and white blood cells. In addition, dense bones cannot undergo proper remodeling in order to repair micro-damage as a result of mechanical stress. Hence, the bones of people with osteopetrosis are weak and at risk of fracture even though they have a high bone mass.
In addition to osteogenesis imperfecta and osteopetrosis, there are other congenital disorders and genetic abnormalities that are causes of bone disease, deformities, abnormal growth, or anomalous size and shape of the skeleton.
Environmental Causes of Bone Disease
Besides genetic factors, there are certain modifiable environmental factors that are causes of bone disease. Calcium, phosphorus, and vitamin D are essential nutrients that must be obtained from diet or made in the skin for proper bone formation and maintenance of healthy bones. Nutritional deficiencies of these minerals and vitamins can lead to weak bones that are poorly mineralized. Deficiency of vitamin D in children leads to a disease called rickets which is characterized by markedly weak bones, risk of fracture, bowing (curving) of the long bones, and other characteristic deformities and disfigurements due to epiphyseal cartilage overgrowth. Deficiency of vitamin D in adults leads to a condition called osteomalacia in which the bones are soft and prone to deformity and fracture.
Hormonal Causes of Bone Disease
Besides congenital disorders and nutritional causes of bone disease, several hormonal disorders can have an effect on the skeleton. Any under- or overactivity of the hormones that regulate bone metabolism or any error in the interaction of these hormones with each other can lead to bone disease. Hyperparathyroidism is a condition in which the parathyroid glands are overactive and produce an excess amount of parathyroid hormone. This leads to an excessive breakdown of bone and consequently an increased risk of fracture. When the hyperparathyroidism is particularly severe, the bones develop large cystic holes and are extremely fragile.
If there is a deficiency of the growth hormone or insulin-like growth factor-1, then proper growth of the skeleton does not take place and the individual has a short stature. Sex hormones are produced by the gonads (sex glands) – the testes in men and the ovaries in women. In a condition known as hypogonadism, the gonads do not produce enough sex hormones. Children and young adults with hypogonadism may suffer from severe osteoporosis due to insufficient testosterone and estrogen in their bodies.
Abnormally high cortisol production by the adrenal glands leads to Cushing’s syndrome, which is a collection of signs and symptoms including bone loss. Glucocorticoids (synthetic cortisol) are used to treat many diseases, and the use of these drugs is the most common secondary cause of bone disease. In children, high doses of glucocorticoids stunt the growth of bones. In adults, glucocorticoids lead to a decrease in bone formation and an increase in bone resorption with a resultant thinning of bones and high risk of fracture.
Localized Causes of Bone Disease
There are several causes of bone disease that affect a localized area of the skeleton rather than all the bones in the body. In patients with arthritis, inflammation of the affected joint leads to bone loss because inflammatory white cells produce resorbing factors locally. Severe bacterial infections of the gums are associated with inflammation and periodontal disease with degradation of the bone surrounding the affected teeth. Osteomyelitis (infection of the bone) can likewise produce bone loss at the affected site. Localized bone loss at the site of infection and inflammation is the result of direct damage from bacterial byproducts as well as from resorbing factors produced by white cells fighting the infection.
Poorly Understood Causes of Bone Disease
Paget’s disease of the bone is a condition in which there is an unregulated formation of large osteoclasts that are highly active. This results in abnormal resorption of bone. The exact causes of bone disease in this case, i.e., Paget’s disease, is not known, but it is believed that genetic as well as environmental factors (perhaps a viral infection) are responsible. In response to the increase in bone resorption, osteoblasts increase bone formation to try and repair the damage. However, this results in a disorderly alignment of minerals and collagen in the new bone matrix which is characteristically “woven” in appearance. Thus, Paget’s disease of the bone is associated with disruption in the normal bone architecture, weak bones, and improper positioning of new bone with the potential for deformities and fractures, even though on X-ray the bones appear dense.
Continuing Education for Radiologic Technologists
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