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

Genetic Counseling

If you and your partner are newly pregnant, you may be amazed at the number and variety of prenatal tests available to you. Blood tests, urine tests, monthly medical exams, diet questionnaires, and family history tracking — each helps to assess the health of you and your baby, and to predict any potential health risks.

Unlike your parents, you may also have the option of genetic testing. These tests identify the likelihood of passing certain genetic diseases or disorders (those caused by a defect in the genes — the tiny, DNA-containing units of heredity that determine the characteristics and functioning of the entire body) to your children.

Some of the more familiar genetic disorders are:

If your history suggests that genetic testing would be helpful, you may be referred to a genetic counselor. Or, you might decide to seek out genetic counseling yourself.

But what do genetic counselors do, and how can they help your family?

What Is Genetic Counseling?

Genetic counseling is the process of:

  • evaluating family history and medical records
  • ordering genetic tests
  • evaluating the results of this investigation
  • helping parents understand and reach decisions about what to do next

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.

Genes are made up of DNA molecules, which are the simplest building blocks of heredity. They're grouped together in specific patterns within a person's chromosomes, forming the unique "blueprint" for every physical and biological characteristic of that person.

Humans have 46 chromosomes, arranged in pairs in every living cell of our bodies. When the egg and sperm join at conception, half of each chromosomal pair is inherited from each parent. This newly formed combination of chromosomes then copies itself again and again during fetal growth and development, passing identical genetic information to each new cell in the growing fetus.

Current science suggests that human chromosomes carry from 25,000 to 35,000 genes. An error in just one gene (and in some instances, even the alteration of a single piece of DNA) can sometimes be the cause for a serious medical condition.

Some diseases, such as Huntington's disease (a degenerative nerve disease) and Marfan syndrome (a connective tissue disorder), can be inherited from just one parent. Most disorders, including cystic fibrosis, sickle cell anemia, and Tay-Sachs disease, cannot occur unless both the mother and father pass along the gene.

Other genetic conditions, such as Down syndrome, are usually not inherited. In general, they result from an error (mutation) in the cell division process during conception or fetal development. Still others, such as achondroplasia (the most common form of dwarfism), may either be inherited or the result of a genetic mutation.

Genetic tests don't yield easy-to-understand results. They can reveal the presence, absence, or malformation of genes or chromosomes. Deciphering what these complex tests mean is where a genetic counselor comes in.

About Genetic Counselors

Genetic counselors are professionals who have completed a master's program in medical genetics and counseling skills. They then pass a certification exam administered by the American Board of Genetic Counseling.

Genetic counselors can help identify and interpret the risks of an inherited disorder, explain inheritance patterns, suggest testing, and lay out possible scenarios. (They refer you to a doctor or a laboratory for the actual tests.) They will explain the meaning of the medical science involved, provide support, and address any emotional issues raised by the results of the genetic testing.

Who Should See One?

Most couples planning a pregnancy or who are expecting don't need genetic counseling. About 3% of babies are born with birth defects each year, according to the Centers for Disease Control and Prevention (CDC) — and of the malformations that do occur, the most common are also among the most treatable. Cleft palate and clubfoot, two of the more common birth defects, can be surgically repaired, as can many heart malformations.

The best time to seek genetic counseling is before becoming pregnant, when a counselor can help assess your risk factors. But even after you become pregnant, a meeting with a genetic counselor can still be helpful. For example, sometimes babies have been diagnosed with spina bifida before birth. Recent research suggests that delivering a baby with spina bifida via cesarean section (avoiding the trauma of travel through the birth canal) can minimize damage to the spine — and perhaps reduce the likelihood that the child will need a wheelchair.

Experts recommend that all pregnant women, regardless of age or circumstance, be offered genetic counseling and testing to screen for Down syndrome.

It's especially important to consider genetic counseling if any of the following risk factors apply to you:

  • a standard prenatal screening test (such as the alpha fetoprotein test) yields an abnormal result
  • an amniocentesis yields an unexpected result (such as a chromosomal defect in the unborn baby)
  • either parent or a close relative has an inherited disease or birth defect
  • either parent already has children with birth defects or genetic disorders
  • the mother-to-be has had two or more miscarriages or babies that died in infancy
  • the mother-to-be will be 35 or older when the baby is born. Chances of having a child with Down syndrome increase with the mother's age: a woman has a 1 in 350 chance of conceiving a child with Down syndrome at age 35, a 1 in 110 chance at age 40, and a 1 in 30 chance at age 45.
  • you are concerned about genetic defects that occur frequently in certain ethnic or racial groups. For example, couples of African descent are most at risk for having a child with sickle cell anemia; couples of central or eastern European Jewish (Ashekenazi), Cajun, or Irish descent may be carriers of Tay-Sachs disease; and couples of Italian, Greek, or Middle Eastern descent may carry the gene for thalassemia, a red blood cell disorder.

Meeting With a Genetic Counselor

Before you meet with a genetic counselor in person, you'll be asked to gather information about your family history. The counselor will want to know of any relatives with genetic disorders, multiple miscarriages, and early or unexplained deaths. The counselor will also want to look over your medical records, including any ultrasounds, prenatal test results, past pregnancies, and medications you may have taken before or during pregnancy.

If more tests are necessary, the counselor will help you set up those appointments and track the paperwork. When the results come in, the counselor will call you with the news and often will encourage you to come in for a discussion.

The counselor will study your records before meeting with you, so you can make the best use of your time together. During the session, you'll go over any gaps or potential problem areas in your family or medical history. The counselor can help you understand the inheritance patterns of any potential disorders and help assess your chances of having a child with those disorders.

The counselor will distinguish between risks that every pregnancy faces and risks that you personally face. Even if you discover you have a particular problem gene, science can't always predict the severity of the related disease. For instance, a child with cystic fibrosis can have debilitating lung problems or, less commonly, milder respiratory symptoms.

After Counseling

Genetic counselors can help you understand your options and adjust to any uncertainties you face, but you and your family will have to decide what to do next.

If you've learned prior to conception that you and/or your partner are at high risk for having a child with a severe or fatal defect, your options might include:

  • pre-implantation diagnosis — when eggs that have been fertilized in vitro (in a laboratory, outside of the womb) are tested for defects at the 8-cell (blastocyst) stage, and only nonaffected blastocysts are implanted in the uterus to establish a pregnancy
  • using donor sperm or donor eggs
  • adoption
  • taking the risk and having a child
  • establishing pregnancy and have specific prenatal testing

If you've received a diagnosis of a severe or fatal defect after conception, your options might include:

  • preparing yourself for the challenges you'll face when you have your baby
  • fetal surgery to repair the defect before birth (surgery can only be used to treat some defects, such as spina bifida or congenital diaphragmatic hernia, a hole in the diaphragm that can cause severely underdeveloped lungs. Most defects cannot be surgically repaired.)
  • ending the pregnancy

For some families, knowing that they'll have an infant with a severe or fatal genetic condition seems too much to bear. Other families are able to adapt to the news — and to the birth — remarkably well.

Genetic counselors can share the experiences they've had with other families in your situation. But they will not suggest a particular course of action. A good genetic counselor understands that what is right for one family may not be right for another.

Genetic counselors can, however, refer you to specialists for further help. For instance, many babies with Down syndrome are born with heart defects. Your counselor might encourage you to meet with a cardiologist to discuss heart surgery, and a neonatologist to discuss the care of a post-operative newborn. Genetic counselors can also refer you to social workers, support groups, or mental health professionals to help you adjust to and prepare for your complex new reality.

Finding a Genetic Counselor

Working with a genetic counselor can be reassuring and informative, especially if you or your partner have known risk factors. Talk to your doctor if you feel you would benefit from genetic counseling. Many doctors have a list of local genetic counselors with whom they work. You can also contact the National Society of Genetic Counselors for more information.

Reviewed by: Louis E. Bartoshesky, MD, MPH
Date reviewed: June 2010
Originally reviewed by: Linda Nicholson, MS, MC