What Is Achondroplasia?

Overview

Achondroplasia is one of several conditions that causes altered bone growth and structure resulting in physical traits such as smaller limbs, shorter than average height, and altered skull shape. The joints, such as in the hand and limbs, are also affected resulting in difficulty with motor skills and mobility.¹

Achondroplasia is caused by a genetic mutation that can either be passed down from parent to child or arise at random. This means that anyone can be affected with achondroplasia, even without a precious family history of the condition.¹ 

Achondroplasia is a lifelong condition, so management and treatment will likely be needed throughout life. Treatment is especially pertinent for infants and young children due to the vast array of complications and developmental challenges they can face in their first years of life.²

Causes of achondroplasia

Achondroplasia is a genetic condition that develops during gestation and is present from birth.

There are two types of achondroplasia that can develop:

• Heterozygous achondroplasia - where one achondroplasia gene is passed on/develops causing typical symptoms and complications but with reduced infancy death.
• Homozygous achondroplasia - where both parents pass on an achondroplasia gene resulting in highly probable infant death due to the severity of complications.¹ 

The chances of which (if any) form of the condition your child may develop is dependent on which genes they inherit and other random genetic factors, for example:

• If either you or your partner, or both you and your partner, have achondroplasia, there is a 1 in 2 chance your child will be born with the heterozygous form of the condition.
• If you and your partner have both been diagnosed with achondroplasia there is a further 1 in 4 chance of becoming pregnant with a homozygous foetus. 
• If neither you nor your partner has achondroplasia there is still a chance of your child developing achondroplasia due to a random change in their genetic material before birth.¹ 

Signs and symptoms of achondroplasia

Achondroplasia causes the skeleton to form abnormally - called skeletal dysplasia. This causes distinct physical traits such as:

• Shorter than average height that becomes apparent with ageing 
• Shorter than average limb length (arms and legs)
• Small, displaced fingers
• Enlarged head/protruding forehead 
• Flat nose bridge ¹ 

Children and adults with achondroplasia will also usually have difficulties with mobility due to:

• Weak muscles 
• Stiff elbow joints
• Loose hip and knee joints 
• Spinal curvature which can cause tilted hips and/or hunched shoulders ¹ 
• Tibial bowing (where the tibia or shin bone becomes curved causing pain and abnormal walking movement)²  
• Spinal stenosis (where narrow spinal processes compress the spinal veins leading to leg pain)² 

Achondroplasia can also lead to several clinical complications such as:

• Obesity 
• Sleep apnoea 
• Cardiovascular disease 
• Ear infections and hearing loss 
• Chronic respiratory insufficiency (where problems such as reduced air capacity of the lungs and blockages in the upper respiratory system create breathing difficulties)
• Cervical medullary compression/foramen magnum stenosis (where the spinal cord nerves at the base of the skull can become damaged and lead to brain swelling)² 

Cranial medullary compression/foramen magnum stenosis poses a risk to the life of newborns and a small number of infant deaths have been recorded. The risk of sudden death due to spinal cord compression usually disappears after 1 year of age once good head control has been established, but care should still be taken throughout childhood to avoid neck injuries.¹

Management and treatment for achondroplasia

Managing and treating complications 

Achondroplasia management and treatment begin in infancy. If your baby is born with achondroplasia and shows signs of serious complications, they will most likely require surgical interventions, for example:

• Cervicomedullary decompression - used to relieve lethal pressure on the upper spinal cord by enlarging the base of the skull (foramen magnum).²
• Adenotonsillectomy - used to correct complications like breathing obstruction and hearing loss by removing the adenoids and tonsils from the mouth.²
• Fluid shunting - used to drain excess spinal fluid present in the brain (hydrocephalus).¹
• Spinal canal compression - used to alleviate the symptoms of spinal stenosis.³

While your child is an infant it is also extremely important to hold and place them in the correct way, including holding them and using baby equipment in a way that fully supports their head and neck (which are prone to flopping and pressurising the upper spinal cord).²

Baby equipment that should be strictly avoided includes slings, flimsy (umbrella) prams, (automatic) swings and car seats that don’t offer any head or neck support. Activities that pose a risk of head and neck injuries must also be regulated throughout life such as high-impact sports and activities that could cause a probable fall.⁴

Complications can arise at any point during infancy and throughout childhood so it is important to look out for any indications that your child may be suffering and alert your doctor so they can screen for and treat the specific issue.⁴ 

Managing and treating lifelong symptoms 

Achondroplasia also comes with a host of lifelong symptoms that will need to be managed to

improve quality of life. As children with achondroplasia age, it is important to monitor their height, weight and head circumference to make sure it is in keeping with normal development in achondroplasia.³ 

Achondroplasia causes symptoms and complications that lead to motor and mobility issues which also must be managed through means such as:

• Weight management with diet and exercise to reduce immobility related to obesity.² 
• Mobility aids like back braces and leg splints to help correct the bone structure and support weak muscles and joints.²
• Adaptations to the home, school and workplaces to allow independence and inclusion for children and accessibility for adults.⁴

Some also opt for the use of medications like growth hormone and bone surgeries to lengthen/strengthen limb bones and increase overall stature by adulthood.³ 

Diagnosis of achondroplasia

Achondroplasia can be diagnosed before and after the birth of a child, but the sooner the diagnosis, the better the care and treatment the baby can receive, and the lower the chance that complications will seriously affect them.¹ 

Foetuses are tested for achondroplasia by taking a blood sample from the mother and screening for a specific fragment of DNA. Doctors will also be able to distinguish whether the homozygous or heterozygous form of achondroplasia has developed.^1,5

Babies with achondroplasia can also be diagnosed by identification of physical traits specific to the disease with simple examination or scanning technology. Most traits are apparent from birth but can also develop at any later point.¹ 

FAQs

How can I prevent achondroplasia?

You should keep in mind that achondroplasia isn't something that can be prevented - rather it is down to random genetic determinants that are beyond our control. However, if you are worried about the chance of your child being born with achondroplasia there are some things to know:

• Genetic counselling - if you and/or your partner are affected with achondroplasia you should receive counselling from a specialist to help gain a better understanding of the risk of conceiving a child with achondroplasia and help you to decide whether having a biological child is something you want. 

• Foetal testing - if you choose to or become pregnant you can ask for the early-stage foetus to be tested while still in the womb or before the fertilised egg is implanted into the uterus (if IVF conception is used) which can determine the presence or non-presence of the achondroplasia gene (and the severity of the condition it could cause).

• Alternative routes - if you decide not to try for a biological child you can still opt to build a family in other ways such as sperm/egg donation or adoption.¹

How common is achondroplasia?

Achondroplasia affects approximately a quarter of a million people globally. Within families, it is unlikely that parents will conceive more than one child with achondroplasia.¹

Is achondroplasia hereditary?

Around one-fifth of cases of achondroplasia arise from inheriting the gene from one or both of your parents with the disease. However, most cases arise from parents where neither of them are affected with achondroplasia meaning most people with achondroplasia will have developed it due to a random change in their genetic material.¹ 

When should I see a doctor?

You should see a doctor if you or your partner has achondroplasia and are or are planning to become pregnant. This is because the risks to the mother and/or the baby with achondroplasia are substantial and must be mediated with special pregnancy, delivery and post-natal care.⁶ 

Summary

Achondroplasia is a genetic, lifelong condition - the severity of which is dependent on what type is inherited and what complications arise. Achondroplasia increases your risk of acquiring certain further health conditions, though each individual case is different. Treatment can be critical in infancy due to complications and potential threat to life, and management of achondroplasia and its associated symptoms must continue throughout childhood development. With timely diagnosis and proper disability support, babies and children with achondroplasia can expect to lead fulfilling lives into adulthood.