Metatropic Dysplasia

The word “Metatropic” is derived from the Greek word “Metatropos”, meaning "changing form." Clinically, this dysplasia is one that progresses over time. Metatropic dysplasia is a rare disorder. Because it is so uncommon, the exact incidence is not known.

 
How Metatropic Dysplasia Is Inherited

Metatropic dysplasia has an autosomal dominant inheritance.
This means that those with metatropic dysplasia have a 50/50 chance of passing this condition on to their children, either males or females. Metatropic dysplasia can also happen for the first time in a child; in cases when both parents are of typical stature, the chance to have another child with metatropic dysplasia is low (2-3%).

 
Causes of Metatropic Dysplasia

A change in a gene called TRPV4.

 
Physical Characteristics

Initially, individuals have shortened limbs with a relatively average-sized trunk (short-limbed dwarfism). As the child gets older and the condition progresses, kyphoscoliosis of the spine develops that decreases trunk height (short-trunk dwarfism). Apparent shortening of the limbs also occurs over time, due to progressive joint contractures.

Face & Skull
Trunk, Chest, & Spine:
  • Small and narrow chest
  • Pectus carinatum (chestbone sticking out more than average) or pectus excavatum (depressed breast bone)
  • Severe kyphoscoliosis
  • In infancy, “coccygeal tail” can be apparent, which is a prolongation of the normal tailbone consisting of cartilage material
Arms & Legs:
  • Signficantly shortened limbs with a characteristic dumbbell shape bone
  • Enlarged joints
  • Progressive joint contractures during childhood
What are the X-ray characteristics?

The radiographic features of Metatropic Dysplasia include small, flat, diamond-shaped vertebral bodies in early infancy due to defective ossification.

Later, platyspondyly and anterior wedging of vertebral bodies are characteristic. Appearance of a hump-like build-up of bone in both the central and posterior portions of vertebral end plates in the lower posterior and upper lumbarspine. The thorax is narrow and ribs are short in both infancy and early childhood. Limbs are also short with marked metaphyseal flare and epiphyseal dysplasia. Deformed capital femoral epiphyses. Hyperplasia of proximal femoral metaphyses. The capital femoral epiphyses are typically deformed. Hyperplasia of proximal femoral metaphyses is usually observed.

Finally, hypoplasia of basilar pelvis with crescent-shaped iliac crests and low-set anteriosuperior iliac spines is characteristic.

 
Making the Diagnosis

Metatropic dysplasia is diagnosed by its characteristic clinical features such as the coccygeal tail, normal facies, spinal issues, and limb shape. Radiographic features help with diagnosis and genetic testing can also help confirm a diagnosis.

Being a rare disorder with few reports in the medical literature, consultation with an experienced clinical geneticist may be required before a diagnosis is made.

 
Musculoskeletal Problems

Metatrophic Dyplasia varies in severity. Some infants die from severe respiratory problems whereas others survive with only minor changes.

Neck

Atlantoaxial instability is almost universally present in metatropic dysplasia. X-rays of the neck should be performed at diagnosis and at periodical intervals thereafter. Progressive instability in this region will lead to spinal cord compression and is potentially life threatening. Signs of cord compression have been listed elsewhere.

If instability is progressive or symptomatic, early surgical fusion of the affected bones is essential. In cases of diagnostic doubt, further information can be obtained by means of an MRI scan (with flexion-extension views and CSF flow studies). It allows accurate determination of the degree of spinal cord compression and space available for the cord.

Spinal fusion may be supplemented by instrumentation (metal implants) to support the bones until the fusion mass consolidates. Usually extra bone is taken from a rib or from the pelvis to help the healing process. Immobilization of the neck is achieved by a halo vest or body cast, for at least 3 months.

Spine

Kyphoscoliosis is commonly seen in early childhood. It is often severe and rapidly progressive. Spinal curves should be diagnosed early and followed-up at regular intervals. Bracing may be of some benefit in younger children with smaller curves (400 to 500).

The timing of spinal decompression and fusion for scoliosis in metatropic dysplasia is dependent upon the severity of the curve, curve progression, age and risk of injury to the spinal cord. Instrumentation of the spinal fusion may not be possible due to the size and structure of the vertebral column. Prolonged immobilization in a halo body cast may be necessary
following surgery.

The status of the respiratory system may dictate the timing of surgery, especially in the younger, more severely affected children. In the lower back, spinal stenosis may occur requiring decompression and spinal fusion.

Limb Deformities

The limbs are short with significant joint contractures. The treatment of bony deformities and joint contractures is dictated by walking ability, amount of functional compromise and symptoms. Common problems include hip and knee flexion contractures and genu valgus. Some individuals may have signs of ligamentous laxity. Premature degenerative arthritis invariably occurs, requiring joint replacement surgery.

 
Problems Elsewhere in the Body
Respiratory Problems

Respiratory problems are the result of a poorly developed, stiff rib cage. Prolonged breathing difficulties may warrant a tracheostomy and long-term ventilatory support. This is a frequent cause of death in infancy.

Other serious but preventable causes of breathing impairity are spinal cord compression and hydrocephalus. Lung function tests and sleep studies are frequently used to diagnose breathing problems in skeletal dysplasias. Regular review by a pulmonologist is recommended.

Hydrocephalus

Hydrocephalus has been reported in metatropic dysplasia. Regular measurement of head circumference will facilitate early diagnosis. Headache, vomiting, visual disturbances, and loss of consciousness are signs of increased pressure around the brain.

 
What to Look For

In metatropic patients, any change in walking ability, endurance or
breathing should merit further assessment by a physician to rule out
spinal cord compression. Specific neurological symptoms such as
tingling or numbness in the arms or legs, weakness, shooting leg or
arm pain, or problems controlling bladder/bowel function should be investigated further.

One should also watch out for progressive curvature of the spine.
Headache, vomiting, visual disturbances, and loss of consciousness
are signs of increased pressure around the brain; possibly due to
worsening hydrocephalus.

 
References
  1. Jones, Kenneth L. Recognizable Patterns of Human Malformation. Philadelphia, PA: Elsevier Saunders. 2006.
  2. Krakow D, Vriens J, Camacho N, Luong P, Deixler H, Funari TL, Bacino CA, Irons MB, Holm IA, Sadler L, Okenfuss EB, Janssens A, Voets T, Rimoin DL, Lachman RS, Nilius B, Cohn DH. Mutations in the gene encoding the calcium-permeable ion channel TRPV4 produce spondylometaphyseal dysplasia, Kozlowski type and metatropic dysplasia. Am J Hum Genet. 2009 Mar;84(3):307-15.
  3. Scott, Charles I. Dwarfism. Clinical Symposium, 1988; 40(1):17-18
  4. Spranger, Jurgen W. Brill, Paula W. Poznanski, Andrew. Bone Dysplasias: An Atlas of Genetic Disorder of Skeletal Development. Oxford: Oxford University Press. 2002.

Trusted Insights from Nemours' KidsHealth

Dwarfism

There's been a lot of discussion over the years about the proper way to refer to someone with dwarfism. Many people who have the condition prefer the term "little person" or "person of short stature." For some, "dwarf" is acceptable. For most, "midget" definitely is not.

But here's an idea everyone can agree on: Why not simply call a person with dwarfism by his or her name?

Being of short stature is only one of the characteristics that make a little person who he or she is. If you're the parent or loved one of a little person, you know this to be true.

But here are some facts that other people may not realize about dwarfism and those who have it.

Dwarfism:

  • is characterized by short stature. Technically, that means an adult height of 4 feet 10 inches or under, according to the advocacy group Little People of America (LPA).
  • can be caused by any one of more than 300 conditions, most of which are genetic. The most common type, accounting for 70% of all cases of short stature, is called achondroplasia.
  • can and most often does occur in families where both parents are of average height. In fact, 4 out of 5 of children with achondroplasia are born to average-size parents.

Dwarfism isn't:

  • an intellectual disability. A person who has dwarfism is typically of normal intelligence.
  • a disease that requires a "cure." Most people with one of these conditions live long, fulfilling lives.
  • a reason to assume someone is incapable. Little people go to school, go to work, marry, and raise children, just like their average-size peers.

What Causes Short Stature?

More than 300 well-described conditions are known to cause short stature in a child. Most are caused by a spontaneous genetic change (mutation) in the egg or sperm cells prior to conception. Others are caused by genetic changes inherited from one or both parents.

Similarly, depending on the type of condition causing the short stature, it is possible for two average-size parents to have a child with short stature, and is also possible for parents who are little people to have an average-size child.

What prompts a gene to mutate is not yet clearly understood. The change is seemingly random and unpreventable, and can occur in any pregnancy. If parents have some form of dwarfism themselves, the odds are much greater that their children will also be little people. A genetic counselor can help determine the likelihood of passing on the condition in these cases.

Dwarfism has other causes, including metabolic or hormonal disorders in infancy or childhood. Chromosomal abnormalities, pituitary gland disorders (which influence growth and metabolism), absorptive problems (when the body can't absorb nutrients adequately), and kidney disease can all lead to short stature if a child fails to grow at a normal rate.

Types of Short Stature

Most types of dwarfism are known as skeletal dysplasias, which are conditions of abnormal bone growth. They're divided into two types: short-trunk and short-limb dysplasias. People with short-trunk dysplasia have a shortened trunk with more average-sized limbs, whereas those with short-limb dysplasia have an average-sized trunk but shortened arms and legs.

By far, the most common skeletal dysplasia is achondroplasia, a short-limb dysplasia that occurs in about 1 of every 15,000 to 40,000 babies born of all races and ethnicities. It can be caused by a spontaneous mutation in a gene called FGFR3, or a child can inherit a change in this gene from a parent who also has achondroplasia.

People with achondroplasia have a relatively long trunk and shortened upper parts of their arms and legs. They may share other features as well, such as a larger head with a prominent forehead, a flattened bridge of the nose, shortened hands and fingers, and reduced muscle tone. The average adult height for someone with achondroplasia is a little over 4 feet.

Diastrophic dysplasia is a different form of short-limb dwarfism. It occurs in about 1 in 100,000 births, and is also sometimes associated with cleft palate, clubfeet, and ears with a cauliflower-like appearance. People who have this diagnosis tend to have shortened forearms and calves (this is known as mesomelic shortening).

Spondyloepiphyseal dysplasias (SED) refers to a group of various short-trunk skeletal conditions that occurs in about 1 in 95,000 babies. Along with achondroplasia and diastrophic dysplasia, it is one of the most common forms of dwarfism. In some forms, a lack of growth in the trunk area may not become apparent until the child is between 5 and 10 years old; other forms are apparent at birth. Kids with this disorder also might have clubfeet, cleft palate, and a barrel-chested appearance.

In general, dwarfism caused by skeletal dysplasias results in what is known as disproportionate short stature — meaning the limbs and the trunk are not the same proportionally as those of typically-statured people.

Metabolic or hormonal disorders typically cause proportionate dwarfism, meaning a person's arms, legs, and trunk are all shortened but remain in proportion to overall body size.

Diagnosis

Some types of dwarfism can be identified through prenatal testing if a doctor suspects a particular condition and tests for it.

But most cases are not identified until after the child is born. In those instances, the doctor makes a diagnosis based on the child's appearance, failure to grow, and X-rays of the bones. Depending on the type of dwarfism the child has, diagnosis often can be made almost immediately after birth.

Once a diagnosis is made, there is no "treatment" for most of the conditions that lead to short stature. Hormonal or metabolic problems may be treated with hormone injections or special diets to spark a child's growth, but skeletal dysplasias cannot be "cured."

People with these types of dwarfism can, however, get medical care for some of the health complications associated with their short stature.

Some forms of dwarfism also involve issues in other body systems — such as vision or hearing — and require careful monitoring.

Possible Complications and Treatments

Short stature is the one quality all people with dwarfism have in common. After that, each of the many conditions that cause dwarfism has its own set of characteristics and possible complications.

Fortunately, many of these complications are treatable, so that people of short stature can lead healthy, active lives.

For example, a small percentage of babies with achondroplasia may experience hydrocephalus (excess fluid around the brain). They may also have a greater risk of developing apnea — a temporary stop in breathing during sleep — because of abnormally small or misshapen anatomy or, more likely, because of airway obstruction by the adenoids or the tonsils. Occasionally, a part of the brain or spinal cord is compressed. With close monitoring by doctors, however, these potentially serious problems can be detected early and surgically corrected.

As a child with dwarfism grows, other issues may also become apparent, including:

  • delayed development of some motor skills, such as sitting up and walking
  • a greater susceptibility to ear infections and hearing loss
  • breathing problems caused by small chests
  • weight problems
  • curvature of the spine (scoliosis, kyphosis, and/or lordosis)
  • bowed legs
  • trouble with joint flexibility and early arthritis
  • lower back pain or leg numbness
  • crowding of teeth in the jaw

Proper medical care can alleviate many of these problems. For example, surgery often can bring relief from the pain of joints that wear out under the stress of bearing weight differently with limited flexibility.

Surgery also can be used to improve some of the leg, hip, and spine problems people with short stature sometimes face.

Nonsurgical options may help, too — for instance, excessive weight can worsen many orthopedic problems, so a nutritionist might help develop a healthy plan for shedding extra pounds. And doctors or physical therapists can recommend ways to increase physical activity without putting extra stress on the bones and joints.

Helping Your Child

Although types of dwarfism, and their severity and complications, vary from person to person, in general a child's life span is not affected by dwarfism. Although the Americans with Disabilities Act protects the rights of people with dwarfism, many members of the short-statured community don't feel that they have a disability.

You can help your child with dwarfism lead the best life possible by building his or her sense of independence and self-esteem right from the start.

Here are some tips to keep in mind:

  • Treat your child according to his or her age, not size. If you expect a 6-year-old to clean up his or her room, don't make an exception simply because your child is small.
  • Adapt to your child's limitations. Something as simple as a light switch extender can give a short-statured child a sense of independence around the house.
  • Present your child's condition — both to your child and to others — as a difference rather than a hindrance. Your attitude and expectations can have a significant influence on your child's self-esteem.
  • Learn to deal with people's reactions, whether it's simple curiosity or outright ignorance, without anger. Address questions or comments as directly as possible, then take a moment to point out something special about your child. If your child is with you, this approach shows that you notice all the other qualities that make him or her unique. It will also help prepare your child for dealing with these situations when you're not there.
  • If your child is teased at school, don't overlook it. Talk to teachers and administrators to make sure your child is getting the support he or she needs.
  • Encourage your child to find a hobby or activity to enjoy. If sports aren't going to be your child's forte, then maybe music, art, computers, writing, or photography will be.
  • Finally, get involved with support associations like the Little People of America. Getting to know other people with dwarfism — both as peers and mentors — can show your child just how much he or she can achieve.

Reviewed by: Angela L. Duker, MS, CGC
Date reviewed: March 2011