Dr. Wilhelm Kniest first described this condition in 1952 at the Children’s Hospital of the University of Jena. It was previously thought to be a variant of metatropic dysplasia, sometimes called Pseudometatropic or Metatropic dysplasia Type II. Kniest dysplasia is a rare form of cartilage dysplasia; the estimated incidence is less than 1 in 1,000,000 (4).
Kniest dysplasia results from a mutation in the gene coding for Collagen Type II (COL2A1) found on chromosome 12. Collagen Type II is a structural protein present in intervertebral discs, cartilage, and the eyeball (1).
Kniest dysplasia is a rare, severe form of cartilage dysplasia that causes short-stature, spine deformities, near-sightedness, and large, stiff joints.
Face and Skull
- large head relative to trunk
- round and flat face
- wide, prominent forehead and eyes
- fattened nose
- wide mouth
- depressed chin
- cleft palate present in 50 percent of patients
Trunk, Chest and Spine:
Arms and Legs:
What Are the X-Ray Characteristics?
The radiographic features of Kniest patients include broad and short femoral necks. Retarded ossification of capital femoral epiphyses usually appearing in ages 2-3 is typical. Ultimately, the epiphyses are large and flattened. Platyspondyly with anterior wedging of vertebral bodies is also characteristic.
In newborns, lumbar bodies exhibit coronal clefts. The ilia are broad ilia with hypoplasia of the basilar portions. By age 3, the pelvis has “dessert-cup” shape. The tubular bones are short with flared metaphyses and large, deformed epiphyses. Hand radiographs reveal osteoporosis, large carpal centers, and “bulb-like” interphalangeal joints with narrow joint spaces.
Kniest dysplasia is usually recognized at birth and can be detected via ultrasound. It is identified by its characteristic clinical and X-ray features. Radiographs especially help to differentiate Kniest dysplasia from other
type II collagenopathies. Clinical genetic testing by direct DNA analysis is also available.
Atlantoaxial instability should be ruled out in all children with Kniest syndrome at diagnosis (see SED for details). The instability results from the skull moving abnormally in relation to the first cervical vertebra (called the "atlas"). It can cause spinal cord compression and impingement. Lateral neck x-rays in flexion and extension should be performed before administering a general anesthetic to these children.
Kyphosis occurs at the thoracolumbar junction in addition to scoliosis. No definite conclusions have been reached regarding the management of
spinal deformities in Kniest children, but the same general principles of bracing apply to control the curve. Experience is limited on spine fusions in this group.
As with other disorders that affect type II collagen, such as SEDC, children with Kniest dysplasia develop serious eye problems, including severe myopia (near-sightedness), retinal detachment, and cataracts. This makes regular ophthalmologic follow-up a necessity. Eyes may also protrude.
Progressive conductive hearing loss is common due to repeated middle ear infections. This can be made worse by associated sensorineural deafness to high-pitched sounds.
Tracheomalacia (softening and collapse of the windpipe leading to breathing difficulties) and respiratory distress are common in neonates. Upper respiratory tract infections occur frequently leading to conductive hearing loss.
Cleft palate occurs in 50% of patients and oftentimes leads to middle ear infections and delayed onset of speech. It should be repaired once the infant is stable enough to withstand surgical procedures.
Due to eye complications, including severe myopia (near-sightedness), retinal detachment, and cataracts, regular ophthalmologic follow-ups are a necessity for Kniest Dysplasia.
Kniest dysplasia is characterized by early onset arthritis in multiple joints that significantly interferes with function. Joint replacement surgery may become necessary in the second decade due to disabling symptoms.
Generally all skeletal dysplasias warrant multidisciplinary attention. Regular assessment by an orthopedist, geneticist, pediatrician, dentist, neurologist, and physical therapist will provide the most comprehensive treatment.
- Jones, Kenneth L. Recognizable Patterns of Human Malformation. Philadelphia, PA: Elsevier Saunders. 2006.
- Scott, Charles I. Dwarfism. Clinical Symposium, 1988; 40(1);26-29.
- Spranger, Jurgen W. Brill, Paula W. Poznanski, Andrew. Bone Dysplasias: An Atlas of Genetic Disorder of Skeletal Development. Oxford: Oxford University Press. 2002.
- The Greenberg Center for Skeletal Dysplasias at John Hopkins University Type II Collagen Conditions Clinical Summaries
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