hereditary multiple osteochondromas

Hereditary multiple osteochondromas is a skeletal condition in which two or more cartilage-capped bony growths (osteochondromas) develop near the ends of long bones, most often around the knees, shoulders, ankles, or wrists. Changes in the EXT1 or EXT2 genes interfere with normal bone growth, leading to these outgrowths that generally appear in childhood and may increase in number or size during the growth years. The disorder affects males and females and is usually noticed when a child begins walking or experiences painless bumps around joints. It is considered uncommon, affecting an estimated 1 to 9 per 100,000 people worldwide. Severity and symptoms vary widely between individuals, even within the same family.

The defining feature is the presence of multiple osteochondromas, which are typically painless but can become bothersome if they press on surrounding muscles, nerves, or blood vessels. Children are often brought to medical attention when parents notice hard bumps near joints or when the growths restrict normal movement. Over time, some individuals develop limb length differences, angular deformities of the forearm or legs, or short stature because the growth plates are affected. Pain, limitation of joint mobility, and functional motor difficulties can arise during rapid growth spurts or after minor trauma to an osteochondroma. Less commonly, bursitis, tendon irritation, or femoroacetabular impingement of the hip are reported. Not all individuals experience all features, and the number, size, and location of osteochondromas—and their impact on daily life—can differ considerably.

Hereditary multiple osteochondromas results from pathogenic variants in either the EXT1 or EXT2 gene. These genes provide instructions for proteins involved in the formation of heparan sulfate, a molecule essential for regulating normal bone growth at the growth plates. When one of these genes is altered, the signaling pathways that control how cartilage is molded into bone are disrupted, leading to the development of osteochondromas. Specific information about the inheritance pattern was not provided in the current data set, so families are encouraged to discuss personal recurrence risks and testing options with a genetic counselor. Even when a causative variant is identified, the severity of symptoms can vary (variable expressivity) among affected relatives.

Currently, management focuses on supportive care and symptom relief. Most individuals are followed by a multidisciplinary team that may include orthopedic surgeons, physical therapists, and pain specialists. Long-term care relies on regular surveillance to monitor growth of existing osteochondromas, detect new lesions, and identify complications such as nerve compression or joint restriction early. Surgical removal is considered when a growth causes pain, limits movement, or threatens nearby structures, while physical therapy can help maintain joint flexibility and muscle strength. Because no targeted or gene-based treatments are yet approved, treatment plans are individualized, and families should discuss available options and timing of interventions with their healthcare team.

Outcomes depend on the number, size, and location of osteochondromas as well as timely access to orthopedic care. Many individuals lead active lives, although some may experience chronic pain, joint stiffness, or require multiple surgeries during childhood or adolescence. Rarely, an osteochondroma can undergo malignant change later in life, so lifelong awareness and prompt evaluation of new or enlarging pain-ful masses are advised. Outcomes described in medical literature continue to evolve as standards of care improve. Families often find it helpful to connect with orthopedic specialists familiar with this condition and to seek genetic counseling for guidance on monitoring and family planning.

Clinical trials are underway exploring new treatment approaches aimed at modifying bone growth or alleviating complications. Individuals interested in participating can search ClinicalTrials.gov or consult their care team about eligibility.