Genetic Bone Disease
Genetic bone diseases are rare, but there are some common elements. Most bone diseases cause a change in the shape of the bones (bowing, shortening), change in bone strength (brittle), change in density (increased or decreased) and often a change in body proportion with normal-sized head but limbs that are shortened or uneven in size. Some genetic bone diseases cause abnormal growths or tumors to grow on the bones as well, and most diseases result in increased fractures and pain.
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Osteogenesis Imperfecta
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Osteogenesis imperfecta, also called "brittle bones" disease, comprises a group of seven disorders (Types I through VII) of the connective tissue with different clinical presentations and a range in severity. Typical symptoms include bones that easily fracture (sometimes a child is born with multiple fractures), muscle weakness, short stature, skeletal deformities and lax joints. Other frequent manifestations include hearing loss, blue sclerae of the eyes, weak blood vessels with frequent bleeding and weak discolored teeth.
Osteopetrosis
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Osteopetrosis comprises a group of similar disorders also called "marble bone diseases" because the body is not able to replace old bone cells with new; therefore, as new cells arise, the bones become thicker and change in shape, making them weak and crowding out the bone marrow so that production of blood cells is impaired. The growing bones in the skull may press on nerves, causing paralysis, and may distort facial features.
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Fibrous Dysplasia
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Fibrous dysplasia begins during fetal development with a genetic abnormality causing some abnormal bone-producing cells to produce an area of fibrous bone. The condition may be limited to two bones or many bones throughout the skeleton. As the child grows, the fibrous area expands, weakening the bone and resulting in pain and fractures. Fibrous dysplasia most commonly affects the bones of the thigh, shin, ribs, skull, pelvis and upper arms. The same abnormality often occurs in glands, causing hormonal imbalances. While caused by a genetic abnormality, there is no increased family risk.
Multiple Osteochondromas
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Multiple osteochondromas (also known as hereditary multiple exostoses) result in nonmalignant bone tumors that arise from the ends or flat surfaces of bones. Some people develop only two tumors while others develop hundreds. The tumors can cause compression of nerves, muscles and tendons and cause pain, deformity and lack of mobility. In up to 5 percent of those affected, the tumors convert to malignant chondrosarcomas.
Hypophosphatemia
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Hypophosphatemia is a metabolic bone disorder characterized by low levels of the enzyme alkaline phosphatase, preventing mineralization and hardening of bones and teeth. Children have an unusually shaped head and are often abnormally short and have bowed legs but enlarged joints. Symptoms vary widely but are more severe with onset during infancy. Adults are prone to fractures and early loss of teeth.
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