Skeletal Dysplasia

Skeletal dysplasias are rare genetic disorders that cause very short height and other growth differences. Experts almost always diagnose them during childhood.

These conditions happen because of DNA changes that affect how your child’s bones form and grow. Skeletal dysplasias (pronounced SKELL-et-ull dis-PLAY-zh-uhs”) fall under two main umbrellas:

• Osteochondrodysplasias: These are more general, affecting multiple or all bones in your body.
• Dysostoses: These affect one bone or a group of bones in the same area (like a hand or foot).

There are 771 types of skeletal dysplasias that experts recognize. Some are minor and manageable. Others can cause severe disability or even death.

A few of the main types of skeletal dysplasias include:

• Achondroplasia (short-limbed dwarfism): This is the most common skeletal dysplasia.
• Hypochondroplasia: This condition has a range of severity. When it’s severe, it causes short-limbed dwarfism. When it’s not severe, it can go undetected for years. Some children only get diagnoses during puberty because they don’t grow at the expected rates.
• Osteogenesis imperfecta (brittle bone disease): This disease has many subtypes, and they all involve disruptions that make your child’s bones weaker.
• Lethal skeletal dysplasias: These cause stillbirth or death shortly after birth. About half of all skeletal dysplasias fall under this type. The most common examples include thanatophoric dysplasia, achondrogenesis and osteogenesis imperfecta type II.

Symptoms of skeletal dysplasia

Skeletal dysplasias cause a wide range of symptoms and effects. Some are very specific and only happen with certain types of these conditions.

Common effects across the types of skeletal dysplasias include differences in your child’s:

• Height
• Head size and shape
• Length of their arms, legs, hands or feet
• Facial features (like nose shape or distance between their eyes)
• Limb shape
• Spine shape
• Hand and foot shape (like clubfoot)
• Bone strength
• Hair, teeth and nail growth

There are many other symptoms that are specific to certain types of skeletal dysplasia. Your healthcare provider can tell you more about them.

Skeletal dysplasia causes

Skeletal dysplasias happen because of DNA changes. Those changes are often ones your child inherited from one or both biological parents. But these changes can also be spontaneous. That’s when your child develops a change that doesn’t run in your family.

So far, researchers know of at least 552 genetic changes that can cause skeletal dysplasias. They can either cause skeletal dysplasia directly, changing the way your child’s bones form and grow. Or they can affect your child’s bones indirectly, disrupting processes that your child’s body uses for bone upkeep. That’s how metabolic diseases like hypophosphatasia cause skeletal dysplasia.

Some of the most common genetic changes that can cause skeletal dysplasias include those that affect:

• Bone growth genes: Changes to the FGFR3 gene cause achondroplasia, hypochondroplasia and thanatophoric dysplasia.
• Collagen genes: Examples include COL1A1, COL1A2, COL2A1 and COMP. Changes in these genes can cause various subtypes of brittle bone disease. They can also cause conditions like Steel syndrome, pseudoachondroplasia and achondrogenesis type II.
• Cartilage genes: These affect how your child’s body makes and maintains cartilage. DTDST is an example. It causes conditions like diastrophic dysplasia and achondrogenesis type I.

Complications of skeletal dysplasia

There are many possible complications from skeletal dysplasia. Some are very specific to certain types of the condition. Others are more common across multiple types.

Some of the possible complications include those related to your child’s brain and spine, chest and bone strength.

Your healthcare provider is the best person to tell you about the possible kinds of complications in your case.

How doctors diagnose skeletal dysplasias

Healthcare providers can diagnose skeletal dysplasias with various tests. These include:

• Imaging scans: Providers can see some skeletal dysplasias in a fetus with an ultrasound scan during pregnancy. Other imaging scans, like MRI or CT scans, may help during pregnancy, childhood or adulthood.
• A physical exam: Providers often suspect skeletal dysplasias because of effects they can see. Some are visible at birth. Others become visible later during childhood. Providers may take very detailed measurements to diagnose skeletal dysplasias.
• DNA tests: These tests check for known DNA changes that can cause skeletal dysplasias.

It usually takes a combination approach to diagnose skeletal dysplasias. That’s because of how many there are, how similar they can be and how many genetic changes can cause them. Your provider can explain more about the tests they recommend and why these may help.

How are skeletal dysplasias treated?

Skeletal dysplasia treatments can vary a lot, depending on the specific condition. Your child’s healthcare providers are your best source of information about your specific case.

Some examples of treatments for skeletal dysplasias include:

• Medicines: Growth hormone can treat some types of skeletal dysplasias. A drug called vosoritide (Voxzogo®) can sometimes treat achondroplasia. Bone-strengthening drugs may help the effects of brittle bone disease.
• Orthotics: These are devices that support your child’s body. Back braces for scoliosis are an example.
• Physical therapy: This can help your child improve strength and balance. And PT specialists can teach your child mobility techniques and exercises that may help.
• Surgery: Sometimes, the effects of skeletal dysplasias need surgery. These procedures may repair damage or try to prevent more of it.

What can I expect if I have a skeletal dysplasia?

What you and your child can expect from a skeletal dysplasia varies widely, partly because there are several hundred types. And even within specific types, the effects can range from minor to serious. Some skeletal dysplasias are deadly early on. Others may not affect your child’s life expectancy and only cause minimal differences in your daily life.

Your child’s healthcare team is the best source to tell you more about what to expect. They can explain what effect — if any — your child’s condition could have on your child’s life expectancy and quality of life.

Can a baby survive with skeletal dysplasia?

Sometimes, but it depends on the specific type and how severe it is. Some skeletal dysplasias are deadly before birth or shortly after. Others have little or no effect on how long you’re likely to live. Your child’s healthcare provider is the best one to tell you what to expect in your child’s case.

Is skeletal dysplasia the same as dwarfism?

No, they aren’t the same. The most common cause of dwarfism is achondroplasia, a type of skeletal dysplasia. But many other conditions that aren’t skeletal dysplasias can still cause dwarfism.