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.
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%).
A change in a gene called TRPV4.
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.
Trunk, Chest & Spine:
- Small and narrow chest
- Pectus carinatum (chest bone 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:
- Significantly 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 lumbar spine. 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.
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.
Metatrophic Dysplasia varies in severity. Some infants die from severe respiratory problems whereas others survive with only minor changes.
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.
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
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.
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.
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 impairment 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 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.
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
- Jones, Kenneth L. Recognizable Patterns of Human Malformation. Philadelphia, PA: Elsevier Saunders. 2006.
- 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.
- Scott, Charles I. Dwarfism. Clinical Symposium, 1988; 40(1):17-18
- Spranger, Jurgen W. Brill, Paula W. Poznanski, Andrew. Bone Dysplasias: An Atlas of Genetic Disorder of Skeletal Development. Oxford: Oxford University Press. 2002.
From Nemours' KidsHealth
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Genetic tests are done by analyzing small samples of blood or body tissues. They determine whether you, your partner, or your baby carry genes for certain inherited disorders.
Genetic testing has developed enough so that doctors can often pinpoint missing or defective genes. The type of genetic test needed to make a specific diagnosis depends on the particular illness that a doctor suspects.
Many different types of body fluids and tissues can be used in genetic testing. For deoxyribonucleic acid (DNA) screening, only a very tiny bit of blood, skin, bone, or other tissue is needed.
Genetic Testing During Pregnancy
For genetic testing before birth, pregnant women may decide to undergo amniocentesis or chorionic villus sampling. There is also a blood test available to women to screen for some disorders. If this screening test finds a possible problem, amniocentesis or chorionic villus sampling may be recommended.
Amniocentesis is a test usually performed between weeks 15 and 20 of a woman's pregnancy. The doctor inserts a hollow needle into the woman's abdomen to remove a small amount of amniotic fluid from around the developing fetus. This fluid can be tested to check for genetic problems and to determine the sex of the child. When there's risk of premature birth, amniocentesis may be done to see how far the baby's lungs have matured. Amniocentesis carries a slight risk of inducing a miscarriage.
Chorionic villus sampling (CVS) is usually performed between the 10th and 12th weeks of pregnancy. The doctor removes a small piece of the placenta to check for genetic problems in the fetus. Because chorionic villus sampling is an invasive test, there's a small risk that it can induce a miscarriage.
Why Doctors Recommend Genetic Testing
A doctor may recommend genetic counseling or testing for any of the following reasons:
- A couple plans to start a family and one of them or a close relative has an inherited illness. Some people are carriers of genes for genetic illnesses, even though they don't show, or manifest, the illness themselves. This happens because some genetic illnesses are recessive — meaning that they're only expressed if a person inherits two copies of the problem gene, one from each parent. Offspring who inherit one problem gene from one parent but a normal gene from the other parent won't have symptoms of a recessive illness but will have a 50% chance of passing the problem gene on to their children.
- A parent already has one child with a severe birth defect. Not all children who have birth defects have genetic problems. Sometimes, birth defects are caused by exposure to a toxin (poison), infection, or physical trauma before birth. Often, the cause of a birth defect isn't known. Even if a child does have a genetic problem, there's always a chance that it wasn't inherited and that it happened because of some spontaneous error in the child's cells, not the parents' cells.
- A woman has had two or more miscarriages. Severe chromosome problems in the fetus can sometimes lead to a spontaneous miscarriage. Several miscarriages may point to a genetic problem.
- A woman has delivered a stillborn child with physical signs of a genetic illness. Many serious genetic illnesses cause specific physical abnormalities that give an affected child a very distinctive appearance.
- The pregnant woman is over age 34. Chances of having a child with a chromosomal problem (such as trisomy) increase when a pregnant woman is older. Older fathers are at risk to have children with new dominant genetic mutations (those caused by a single genetic defect that hasn't run in the family before).
- A standard prenatal screening test had an abnormal result. If a screening test indicates a possible genetic problem, genetic testing may be recommended.
- A child has medical problems that might be genetic. When a child has medical problems involving more than one body system, genetic testing may be recommended to identify the cause and make a diagnosis.
- A child has medical problems that are recognized as a specific genetic syndrome. Genetic testing is performed to confirm the diagnosis. In some cases, it also might aid in identifying the specific type or severity of a genetic illness, which can help identify the most appropriate treatment.
A Word of Caution
Although advances in genetic testing have improved doctors' ability to diagnose and treat certain illnesses, there are still some limits. Genetic tests can identify a particular problem gene, but can't always predict how severely that gene will affect the person who carries it. In cystic fibrosis, for example, finding a problem gene on chromosome number 7 can't necessarily predict whether a child will have serious lung problems or milder respiratory symptoms.
Also, simply having problem genes is only half the story because many illnesses develop from a mix of high-risk genes and environmental factors. Knowing that you carry high-risk genes may actually be an advantage if it gives you the chance to modify your lifestyle to avoid becoming sick.
As research continues, genes are being identified that put people at risk for illnesses like cancer, heart disease, psychiatric disorders, and many other medical problems. The hope is that someday it will be possible to develop specific types of gene therapy to totally prevent some diseases and illnesses.
Gene therapy is already being studied as a possible way to treat conditions like cystic fibrosis, cancer, and ADA deficiency (an immune deficiency), sickle cell disease, hemophilia, and thalassemia. However, severe complications have occurred in some patients receiving gene therapy, so current research with gene therapy is very carefully controlled.
Although genetic treatments for some conditions may be a long way off, there is still great hope that many more genetic cures will be found. The Human Genome Project, which was completed in 2003, identified and mapped out all of the genes (about 25,000) carried in our human chromosomes. The map is just the start, but it's a very hopeful beginning.
Reviewed by: Larissa Hirsch, MD
Date reviewed: September 26, 2016