What Is Multiple Hereditary Exostosis?

Medically Reviewed by Mahammad Juber, MD on September 21, 2022
Written by Martin Taylor
4 min read

Multiple hereditary exostosis is a rare genetic condition typically passed down from parent to child. A mutated gene can also cause the disease. 

If a parent has multiple hereditary exostosis, then their child has a 50% chance of developing the same condition. You can also take genetic tests before pregnancy to determine if you’re at a higher risk for the condition. 

Multiple hereditary exostosis is a disorder that causes bony bumps, called exostoses, to grow on your bones. The bumps are noncancerous but come with other challenges. For instance, these bumps on your bones make moving hard if they’re located near a joint.

The exostoses vary in size, number, and location, but they’re typically found on the: 

  • Legs
  • Arms
  • Fingers
  • Toes
  • Shoulders
  • Pelvis

Bumps will continue to grow during childhood. Their growth doesn’t typically stop until your child is fully grown.

The exostoses are defined in two ways: sessile or pedunculated. 

Sessile exostoses. These types of bumps are permanently attached to the bone. 

Pedunculated exostoses. A narrow stem connects these types of bumps. 

Multiple hereditary exostosis is not diagnosed prior to age three or four. That’s when the first bumps start appearing, and they may become even more prominent as your child gets older and continues to grow.

You may be able to identify someone with multiple hereditary exostosis based on their short statures and bowed arms or legs. Someone with multiple hereditary exostosis may also have stiff elbows, forearms, and hips. 

One of the main symptoms of this genetic disorder is chronic pain due to the growing bumps. The exostoses can make it hard for someone to walk, run, or extend their arms.

Multiple hereditary exostoses can also cause other problems like: 

  • Pressure on your tendons and nerves
  • Deformities in your arms and legs
  • Differences in the length of your arms or legs
  • Cancerous growths within the bumps

Multiple hereditary exostoses are frequently caused by a genetic condition passed from parent to child. A genetic mutation can also result in a mutated gene, resulting in the condition. However, only about 10% of cases stem from a mutated gene rather than genetic inheritance. 

If you or your spouse has multiple hereditary exostosis, your child has a 50% chance of inheriting the illness. 

Sex doesn’t play a role in how likely the child is to develop the condition. 

In some cases, children with multiple hereditary exostosis don’t have a decreased range of motion or function and can go without treatment. However, once the bumps become painful or impact how easily they can move, they’ll need a treatment plan. 

Surgery is typically the best treatment for this condition. In most cases, the bumps can be removed with surgery. If the bumps are making arms or legs bowed, then removing them can help straighten out the bones as your child continues to grow. 

If they are left untreated for too long, though, just removing the bumps isn’t enough. Your child may need surgery to straighten or lengthen their damaged bones.

Hemiepiphysiodesis is a surgical procedure that targets your child’s growth plates. This surgery is mostly performed on the lower extremities and wrists to correct bones that aren’t aligned. This helps straighten your child’s bones so they can grow correctly as they age.

There are nonsurgical treatments as well. If a child receives their diagnosis early enough, your doctor can monitor and manage the effects of the condition on your child. This treatment requires much observation and regular X-rays to monitor the changes in the exostoses growth. 

If the bumps become problematic, then surgery will be required.

This condition starts during childhood and is a lifelong condition. However, most people with multiple hereditary exostosis have an average life expectancy. With an early diagnosis, proper care, and treatment, your child can live a long healthy life. 

In very rare cases, though, this condition can become cancerous. This complication is called chondrosarcoma and occurs between ages 20 and 50. Cancerous growths only appear once your child and the bumps are fully grown.

There’s about a 2% to 5% chance of the exostoses becoming cancerous. Talk to your doctor if:

  • New tumors are growing after your child is done with puberty
  • The exostoses become painful
  • The cartilage cap on the bump is thicker than 2 cm. 

Osteochondromas are the bumps that accompany multiple hereditary exostosis. These tumors grow as the child does and should stop following puberty.

Osteochondroma is a common benign tumor found in the bone. There are no symptoms accompanying an osteochondroma, and it may only be found if a child has a noticeable bump or says they’re feeling pain in the area. In some cases, a child may never even know they have an osteochondroma. 

Multiple hereditary exostosis is a condition that occurs during childhood. In some cases, it can be painful; in others, it may go unnoticed for the entirety of your child's life. Though this is a lifelong condition, life expectancy and quality of life can still be good for your child. They will simply need proper treatment and preventative care to help them manage the condition.