Achondroplasia

Achondroplasia is the most common skeletal dysplasia. Although the exact incidence is not known estimates range from 1 in 15,000 to 1 in 26,000 births. The name literally means failure or lack of cartilage formation. This is not strictly true as cartilage formation does occur in the growth plates of patients with achondroplasia.

 
How Achondroplasia Is Inherited
A child with achondroplasia stands next to his brother.

Achondroplasia is inherited in an autosomal dominant manner, but about 75% of patients with achondroplasia represent new mutations. These new mutations typically arise from the father during sperm formation. Paternal age greater than 35 years has been found to be a risk factor (3,4).

 
Causes of Achondroplasia

Achondroplasia is caused by a mutation in the fibroblast growth factor receptor-3 (FGFR-3) gene (3). Mutations which change the amino acid glycine to arginine at position 380 of the FGFR-3 protein account for >97% of all reported cases of achondroplasia. Normally the FGFR-3 protein functions as "brake" for endochondral bone growth. This typical G380R mutation actually increases the ability of the FGFR-3 protein to slow bone growth and causes the features of achondroplasia. This type of change associated with an increased ability is termed a "gain-of-function" mutation (4).

 
Physical Characteristics

Achondroplasia causes disproportionate short stature. Specifically the limbs are disporportionately small when compared to the trunk. Within the limbs the proximal segment is shorter causing rhizomelia. The average adult height is 52" in men and 49" in women with achondroplasia. Achondroplasts have average intelligence and can lead very rich and productive lives.

Face & Skull:
  • The head circumference may be larger than average.
  • The forehead tends to be prominent. This is termed frontal bossing.
  • The nasal bridge tends to be depressed and the nostrils are upturned.
  • The mid-face is underdeveloped, which is termed maxillary hypoplasia.
  • The foramen magnum, which is the opening in the skull base through which the spinal cord passes, is smaller then average.
An infant with achondroplasia.
Trunk, Chest, & Spine:
  • Thoraco-lumbar kyphosis (TLK) is present in most infants with achondroplasia and is a normal finding. It can be seen represented in the drawing on the right as the prominence in the lower back(5).
  • The TLK is replaced in later childhood by lumbar lordosis or sway back.
  • TLK is thought to be caused by the large head size and poor muscular tone in children who are not yet walking. It improves without treatment in 90% of affected children as they begin to walk.
  • The chest usually is broad and flat. The abdomen and buttocks
    are prominent.
  • The spinal canal is smaller than average in achondroplasia.
An infant with achondroplasia.
Arms & Legs:
  • There is marked ligamentous laxity or loose joints.
  • Despite the loose joints, typically the elbows cannot be fully extended. Less commonly the elbow joint may be out of place. This rarely causes symptoms or loss of function.
  • In infancy and early childhood there is extra space between the 3rd and 4th fingers. This is termed trident hand and disappears spontaneously in later childhood. The drawing below demonstrates the trident (5).
  • The fingers are short and broad giving rise to a stubby appearance.
An x-ray showing the characteristics of achondroplasia.
What are the x-ray characteristics?

Long bones are relatively plump and short. Proximal humerus and femur in infancy have distinctive rectangular or translucent ovals that change by 2 years. Fibulas tend to be longer than tibias.

Spacing between vertebral pedicles decreases rather than increases in the lumbar spine as you move from head to pelvis.

The pelvis is short and broad with wide, non-flaring iliac wings.

 
Making the Diagnosis

For parents of average stature, achondroplasia is sometimes detected by the presence of short limbs on routine prenatal ultrasound performed after 22 weeks. In this situation, the diagnosis can then be confirmed by molecular genetic testing techniques using fetal DNA obtained through amniocentesis. Cesarean section is recommended to deliver babies with achondroplasia, due to their large head size and risk of compression of the brain during the course of a vaginal delivery.

For parents who have achondroplasia or average-statured parents with a previously born child with achondroplasia, amniocentesis or chorionic villus sampling (CVS) can be performed. Using cells obtained by these techniques, DNA testing can then be performed and used to identify homozygous/ heterozygous achondroplasia in the pregnancy.

Most neonates with achondroplasia have average lengths and weights at birth. It is our belief that as many as 15% of children with achondroplasia are not recognized at birth.

In the neonate, infant, older child or adult, the diagnosis of achondroplasia can be made by an experienced physician (usually a clinical geneticist) on the basis of physical and radiologic examinations.

Sequencing of the FGFR-3 gene can be done in all patients, but is only required in unusual cases or cases of doubt.

 
Associated Medical Problems
An x-ray shows an achondroplasia patient’s foramen magnum.

Foramen magnum stenosis: As mentioned above, essentially all children with achondroplasia have a smaller than average foramen magnum. The foramen magnum is the opening through which the spinal cord leads the head to travel down the spinal column. For the vast majority of children this does not present a problem. There are, however approximately 5% or fewer of children with achondroplasia in whom this opening is so small that there is not adequate room for the spinal cord to function properly. These children have what is termed cord compression or compressive myelopathy. This is a very serious medical problem and requires surgical correction. Cord compression due to foramen magnum stenosis has been implicated as the cause of sudden death in a very small proportion of infants with achondroplasia. As with all surgeries performed on Little People, we suggest that care be taken to assure that the physician has experience not only with the procedure, but also performing the procedure on Little People.

Hydrocephalus: Enlargement of head circumference occurs invariably in achondroplasia but does not require treatment unless pressure within the skull (intracranial pressure) increases and interferes with brain function. Standard charts for normal head circumference throughout childhood in achondroplasia are available. If there is any deviation from average, an opinion should be obtained from a neurosurgeon regarding the need for a ventriculo-peritoneal shunt (a tube that drains excess fluid from the brain into the abdominal cavity).

Sleep apneas or Sleep-disordered breathing - 2 types: Sleep disordered breathing is common in achondroplasia with studies demonstrating a very wide range of affected children ranging from 22% - 85%. As many as 20% of children could be severely affected (6). There are 2 types of apneas or disordered breathing and they will be discussed separately.

  • Obstructive apnea - results from the blockage of airflow into and out of the lungs with normal respiratory drive. This is the most common type of apnea in achondroplasia because of the mid-face hypoplasia and hypotonia of the pharyngeal muscles. The end result is a "smaller pipe" for the air to travel through. Many children with achondroplasia adopt an open mouth habitus with the tongue resting on the lower lip to create maximum airway space. This commonly manifests as snoring and causes disturbed sleep. Symptoms can include tiredness, irritability, daytime sleeping, etc.Treatment for obstructive apnea can include weight reduction measures, adenoidectomy-tonsillectomy, continuous positive airway pressure (CPAP) or bilevel positive airway pressure (BiPAP) at night by nasal mask to keep the airways open. A tracheostomy may be necessary in the most severe cases.
  • Central apnea - results from failure of the respiratory centers in the brain to properly control the process of breathing. In the brainstem, the respiratory centers are in close proximity to the foramen magnum. Therefore, if the foramen magnum is compressing the spinal cord central apnea can result.
 
Musculoskeletal Problems
An x-ray of the legs of a child with achondroplasia.

Genu Varum is more common than genu valgus in achondroplasia. Knock-knees do not need treatment because they do not progress. Bowlegs however can result in symptoms around the knee such as pain and restricted walking ability. Pain around the knee due to bowing should be distinguished from knee pain due to spinal stenosis. A child with achondroplasia and genu varum with associated x-rays is shown below.

Some experts believed that relative overgrowth of the fibula compared to the tibia causes the knee to bend inwards. Therefore, surgery in the past relied on stopping growth in the fibula (epiphyseodesis) or removing a portion of the fibula.

A more recent analysis of this problem has shown that the bend occurs in the lower part of the femur and the upper part of the tibia. In addition, the tibia is twisted along its axis (internal tibial torsion). A few questions need to be answered through long-term studies before treatment can be advocated for genu varum.

  • Does genu varum in achondroplasia affect long-term function?
  • Does it pose an increased risk for knee arthritis in future?
  • How does surgical correction influence natural history?

We are still in the process of addressing these issues and definite answers may not be available immediately. Symptomatic knee arthritis is not a frequent problem in adults with achondroplasia and this is perhaps a reassuring fact for parents. The current recommendation is to undergo surgery only in the presence of bothersome symptoms or if there is severe deformity. Bracing is not advocated because it is difficult to exert enough corrective forces on the bones in the presence of ligamentous laxity.

Spinal stenosis in the lumbar spine is very common in young adults with achondroplasia, though it can occur at any age. The narrow spinal canal found in achondroplasia and the normal size of the spinal cord and cauda equina (nerve bundle at the base of the spine) mean that there is less room for the spinal cord in the achondroplastic spine. In some patients, this narrowing of the vertebral canal results in compression of the nerves. Symptoms include activity-related leg pain that is relieved on squatting down, tingling, pins and needles, or numbness in the feet (paraesthesias), weakness of the legs or rarely, disturbances in control of bladder or bowel function (incontinence). X-rays, CT and MRI scans of the lower spine, confirm the diagnosis. We believe that obesity greatly increases the risk of this problem developing.

A newborn with muskoskeletal problems due to achondroplasia.

Fixed TLK: As mentioned above, most infants with achondroplasia have a TLK and this is normal. In the vast majority of patients, as the child begins to walk, the TLK will spontaneously resolve without treatment. In some children however, the TLK will become fixed or permanent. Prolonged unsupported sitting likely predisposes this to occur. Bracing can be done to treat this problem and, if severe enough, surgery may be required. Typically, when a child is laid on their belly, the thoraco-lumbar region will flatten and indicate that the TLK is flexible. When, however a child is placed face down and a hump in the spine is seen, as pictured below, the TLK is said to be fixed and treatment will be required (5).

 
Problems Elsewhere in the Body
Obesity

Obesity is a common problem in children and adults of all statures, but especially with achondroplasia. Continuous monitoring for obesity is the first step in maintaining an ideal body weight. The problem is compounded if the weight and height charts which were prepared for average-statured children are used for children with achondroplasia. A weight-for-height chart is available specifically for children with achondroplasia and is a useful guide for weight management. Attention to weight issues in childhood is very important as we believe that obesity will significantly increase the risk for spinal problems in young adults or adults with achondroplasia. Equally important to dietary management is attention to physical activities and appropriate exercise.

Pregnancy

Females with achondroplasia may require a cesarean section for delivery due to the reduced size and shape of the pelvis.

ENT

The mid-face is underdeveloped in achondroplasia. This causes several problems in the ear, nose and throat region.

This hypoplasia can lead to overcrowding of the teeth and malocclusion. These problems may also contribute to articulation/speech defects. Sometimes children may have tongue thrust which affects speech clarity.

The Eustachian tube is a normal connection between the middle ear and the upper throat. In achondroplasia, the anatomy of this tube is distorted and persistent fluid in the middle ear can occur. Over the long term, this leads to conductive hearing loss. Hearing should be checked frequently during the growing years. Deafness can also result from poorly formed middle ear bones or due to compression of the brain stem at the foramen magnum. Ear infections are easily treated, and the use of middle ear tubes is common. Because of anatomical differences, we suggest that care be taken to assure that the physician has experience not only with the procedure, but also performing the procedure on Little People.

 
What to Watch For

Given the differences in head size relative to body size in achondroplasia and average children, it is inappropriate to use the average developmental charts to assess an a child with achondroplasia. There are developmental charts for children with achondroplasia and it is critical that these be used.

We often see children with poor head control at several months of age be referred for physical therapy because this is expected for an average-sized child. This should not be done. Infants with achondroplasia receiving physical therapy will not develop head or trunk control at a more rapid rate. Furthermore, the typical exercises done greatly increase the risk for cord compression related to foramen magnum stenosis.

Extreme care should be taken in the position and handling of infants so as to minimize the occurrence of sudden abnormal head and neck motion. The avoidance of soft swings, umbrella strollers and jumpers is recommended. No backpack carriers or front-pack carriers should be used until the child gains complete and total head control.

Properly installed rear-facing car seats with neck support when traveling in a car are important safety measures. This practice should be continued until the child is 20 pounds regardless of age.

Head size should be monitored carefully at least every three months and at most most, monthly in the first few years of life.

We believe that the parents should become comfortable with feeling the anterior fontanelle or soft spot located on top of the infants skull. The fontanelle should be soft and flat. If the fontanelle becomes hard (like a table top) or bulging when the child is at rest, then this should be brought to immediate medical attention.

Diminishing motor milestones, decreased endurance, apnea or any neurological symptoms should be quickly evaluated by an experienced physician.

Speech delay may indicate underlying conductive hearing loss.

Sleep disturbance may indicate cord compression or obstructive sleep apnea and should be brought to an experienced physicians attention immediately.

 
References
  1. Smith's Recognizable Patterns of Human Malformation. Ed. Jones KL. 6th edition. Elsevier Saunders. 2005.
  2. Hunter AG, Bankier A, Rogers JG, Sillence D, Scott CI Jr. Medical complications of achondroplasia: a multicentre patient review. J Med Genet. 1998 Sep;35(9):705-12.
  3. Trotter TL, Hall JG; American Academy of Pediatrics Committee on Genetics. Health supervision for children with achondroplasia. Pediatrics. 2005 Sep;116(3):771-83.
  4. Wilkin DJ, Szabo JK, Cameron R, Henderson S, Bellus GA, Mack ML, Kaitila I, Loughlin J, Munnich A, Sykes B, Bonaventure J, Francomano CA. Mutations in fibroblast growth-factor receptor 3 in sporadic cases of achondroplasia occur exclusively on the paternally derived chromosome. Am J Hum Genet. 1998 Sep;63(3):711-6.
  5. Scott, Charles I. Dwarfism. CIBA Clinical Symposia, 1988. All drawings were done by Dr. Frank Netter and are used with permission from Novartis AG.
  6. Mogayzel PJ Jr, Carroll JL, Loughlin GM, Hurko O, Francomano CA, Marcus CL. Sleep-disordered breathing in children with achondroplasia. J Pediatr. 1998 Apr;132(4):667-71.

Trusted Insights from Nemours' KidsHealth

Relaxation Techniques for Children With Serious Illness

Managing Stress

Nothing about serious illness is easy, but one of the hardest things for parents may be watching their child struggle with pain, stress, and anxiety.

Despite what we may sometimes tell ourselves, stress is not just "in our heads." The stress response — also called the flight-or-fight response — causes a rush of adrenaline and other hormones that trigger physical changes in the body: your heart races, your blood pressure rises, you breathe faster, your digestion slows, and your pupils dilate. Chronic stress takes a toll on the body as well as the mind.

The good news is that using a variety of mind-body relaxation techniques can help short-circuit the flight-or-fight response. Relaxation techniques not only can lessen a child's physical symptoms, they can also help him or her (and you!) regain a sense of control and confidence over a situation, helping everyone find moments of peace amid the chaos and isolation of illness and medical treatment.

Techniques That Can Help

These techniques are designed for parents and kids to practice together. Most can be done in a few minutes wherever you are, whether that's a quiet place or a crowded hospital, without any special tools.

However, it's important to note that these techniques should be used as a complement to conventional medical treatment for anxiety and pain, and not as a replacement — doing so could do a child more harm than good.

If your child is suffering from anxiety or pain, ask your doctor what can be done to help. And always check with your health care team to make sure that your child's symptoms are related to stress and not a different medical problem.

Focused Breathing

Pain and stress can leave a child breathing faster and shallower, or even holding his or her breath — all of which can actually keep the stress response going and heighten the intensity of pain. Paying attention to breathing can help calm the mind.

Try this exercise with your child:

  • Step 1. Sit or lie comfortably and put one hand on your stomach, the other on your chest.
  • Step 2. Close your eyes and try to relax all of your muscles, one by one, from the tips of your toes to the top of your head. Don't forget to relax the muscles in your face, neck, and jaw; you may be storing a lot of tension there.
  • Step 3. Breathe deeply and regularly for several minutes— and try to make your stomach (abdomen) rise and fall, not only your chest. This will help you deepen your breath.
  • Step 4. Pay attention to each breath; try to turn all your thoughts to each inhale … exhale. As you breathe out, imagine the tension leaving your body with the breath.

At first, it may be difficult for you and your child to focus on breathing. Distracting thoughts are normal — but rather than following a thought and letting it consume you, try to let it drift out of your mind, like a balloon.

Relaxation Response Method

This technique asks a person to focus on breathing and quiet the mind to create a sense of calmness and well-being. And by repeating a word, phrase, or prayer during the exercise, the mind is able to stay focused more easily. When practicing this, it's normal for thoughts to pop into the mind. Tell your child to disregard them and just focus on the word or phrase he or she is repeating.

Resembling an Eastern form of meditation, this technique — called the relaxation response — was popularized and put into Western practice in the 1970s by Herbert Benson, MD. To elicit the relaxation response, follow Steps 1-4 above, and then:

  • Step 5. Pick a focus word, phrase, sound, or prayer such as "om," "one," or "peace."
  • Step 6. As you breathe, say the focus word silently to yourself as you exhale.
  • Step 7. Continue for 5 or 10 minutes, ideally building up to 10 to 20 minutes for each session.
  • Step 8. When you're finished, do not stand up immediately. Continue sitting quietly for a bit, letting other thoughts back into your mind. Open your eyes, but stay sitting for another minute before getting up.

When practicing, go at your own pace. Don't feel like you have to achieve a deep level of relaxation right away. Often, feelings of calmness and well-being are felt later on or at times of crisis.

To achieve ongoing results, try to practice the technique with your child once or twice daily, but not within 2 hours after eating, as digestion can interfere with the relaxation response. Some people find that the best time to meditate is first thing in the morning, before breakfast.

Guided Imagery

A growing body of medical research suggests that imagery also can help lessen pain and anxiety, and promote positive feelings. In fact, studies have found that people who practice guided imagery during chemotherapy feel more relaxed and positive about their chemo experience than those who don't use the technique.

Guided imagery (also called "visualization") often works best when a person starts with a few minutes of focused breathing. Here's how it works: With eyes closed, imagine a safe place or a location you once visited that brought a feeling of contentment and joy. Hold on to the image of that place for a while, trying to picture all the sights and sounds:

  • What does the ground beneath you feel like? Is it weather warm or a chilly? Is there a breeze?
  • Are there any animal noises in the distance, or nature sounds (like running water) that you could hear?

Getting as descriptive as possible about this safe place will help you and your child get "into" the moment and feel relaxed.

Some children find this exercise more helpful when they are "guided" by a parent, another live instructor, or with a guided imagery CD or DVD.

As with meditation, distracting thoughts will float into the mind as you practice guided imagery. Acknowledge these thoughts, and then let them drift away while you move your attention back to the images in your mind and sounds you hear.

Music Therapy

Just as pleasant images can calm the mind and soothe the body, so can music. Kids who undergo music therapy — the research-based use of music to lift moods and promote mental and physical well-being — have been found to have lowered heart rates and blood pressure, and improved anxiety.

Many hospitals provide a licensed, trained music therapist who can work individually with kids to develop a customized treatment plan that engages them in:

  • active play that includes listening to music
  • dancing or moving the body to music
  • playing instruments or improvising on them
  • singing along

To participate in music therapy, your child doesn't need to read music or have any special musical talents. And the best part is that you can practice music therapy at home. By choosing music that both you and your child enjoy — and setting aside time to listen, dance, sing, or experiment with an instrument together — you, too, can teach your child the joys of music.

Energy Therapy

Energy therapy is based on the theory of bioelectromagnetics, the belief that the electrical currents in all living organisms produce magnetic energy fields that extend beyond the body. Proponents of this therapy believe that gentle, light touch or above-the-body hand movements can redirect energy to places where it's needed in an effort to bring energy into "balance" or harmony.

While the principles of energy therapy have not been scientifically proven, practitioners say it promotes healing and helps kids feel more relaxed, less anxious, and less bothered by pain.

Many different types of energy therapy are practiced all over the world, including therapeutic touch, healing touch, Reiki and Johrei (from Japan), and Qi gong (from China).

In the United States, some hospitals offer therapeutic or healing touch as a complement to standard treatments for anxiety, pain, or other medical problems.

And some nurses, doctors, or other health care providers are certified in healing touch techniques. They may be able to offer this service to your child, or teach you how to practice healing touch at home.

Massage Therapy

If you like to take a more hands-on approach to soothing and comforting your child, you might prefer massage. The benefits of massage are well known, offering muscle relaxation and increased blood flow and oxygen to body parts to help alleviate stress and ease pain.

But some types of massage are not recommended for certain types of conditions, so check with your doctor first before massaging your child or taking your child to a massage therapist.

The most common forms of massage used in complementary medicine include:

  • Swedish massage. Therapists use their hands to move muscles and joints with long, gliding strokes, tapping movements, friction (made by moving hands quickly) and kneading. Massage oils may be used, so be sure to tell the therapist about any allergies or sensitivities to ingredients that your child may have.
  • Deep-tissue massage. Many of the same techniques are used as in Swedish massage, only therapists apply more pressure to specific areas, concentrating on the deeper layers of muscles and connective tissue.
  • Trigger-point massage. Like deep-tissue massage, this technique massages deeper layers of tissue, focusing on what therapists call trigger points ("knots") within the connective tissue or muscles that are usually painful when pressed.

Many hospitals have massage therapists on hand to offer massages to both patients and their family members, so find out if massage therapy is offered at your hospital.

Learn More

These are just a few of the many methods designed to help patients and families cope with pain and anxiety. Many people find that yoga, stretching, or light, gentle exercise also helps to quiet the mind and sooth the body.

To learn more about relaxation techniques, talk to your child's health care team.

Reviewed by: Larissa Hirsch, MD, and Walle Adams-Gerdts, RN, BA, HTCP/I
Date reviewed: April 2011