Kniest dysplasia or kniest syndrome is a kind of skeletal dysplasia that is very rare in its occurrence. Caused by an autosomal dominant gene abnormality, this disorder or condition was first termed as Kniest dysplasia by the German paediatrician Wilhelm Kniest, in the year 1952. Previously, this type of dysplasia was considered to be Pseudometatropic or Metatropic dysplasia Type II. However, it was since 1952 that this kind of dysplasia is clearly recognised as separate from other kinds of dysplasias. Kniest dysplasia or kniest syndrome is as rare a disease as occurring in only one person per 1,000,000 live births and affects male as well as female child equally.
What is Kniest Dysplasia or Kniest Syndrome?
Kniest dysplasia or kniest syndrome is a rare genetic bone growth disorder or a malformation in the development of at least one bone in the body, characterized by dwarfism or short stature and other problems associated with hearing and vision.
It needs to be understood that not all kind of bone or skeletal development malformation lead to a short stature. Bone growth is an extremely complex process that can be disrupted by different causes, leading to 200 different forms of skeletal dysplasia. Some are associated with defects in bone formation during childhood or even foetal development and some are associated with hormonal imbalance. When it is associated with gene mutation defects, it is known as Kniest dysplasia or Kniest syndrome.
Symptoms of Kniest dysplasia or Kniest Syndrome:
The symptoms of Kniest dysplasia or kniest syndrome vary during childhood and adulthood. The symptoms of Kniest dysplasia or kniest syndrome during childhood include –
- Short limbs
- Swollen, stiff or deformed joints
- Brittle bone cartilage
- Shortened body trunk, short neck, making a barrel-chested appearance
- Hearing loss and vision problems
- Clubfoot and other foot deformities
- Inguinal hernia – bulging of internal organs into the abdomen opening
- Bulging or wide-set eyes
- Respiratory issues
- Round and flat face
- Cleft palate
- Hip dysplasia - misaligned or crooked hip joints.
As the child grows up with Kniest dysplasia or kniest syndrome, the symptoms that he or she expresses, include –
- Joint contractions, which are progressively more swollen and worse
- Worse spinal curvature
- Hearing and visionary difficulties get worse with time
- 42 - 58 inches of adult height.
However, the intelligence remains unaffected in Kniest dysplasia or kniest syndrome.
Mechanism of Gene Mutation Associated with Kniest Dysplasia or Kniest Syndrome:
Kniest dysplasia or kniest syndrome is caused due to COL2A1 gene mutations. The function of this gene is to provide the instruction for forming the type II collagen, which is a type of protein. The type II collagen is a basic component for bone formation and is found in the clear gel which fills the eyeball and the cartilage that forms the inner ears and eyes. This cartilage plays a very significant role in making up the early skeletal development with this tough, flexible tissue. Hence, as the main component of this cartilage, type II collagen has a very important purpose. The cartilage is present in the external ears and nose and protects the ends of bones. Most of the time, it gets converted into bone during normal bone formation process.
There are different other kinds of collagens, nearing about 25 in number. However, the Kniest syndrome is associated only with those genes that instruct the type II collagen formation. During normal bone formation, the type II collagen works as a connective tissue forming the body's supportive framework. In Kniest dysplasia or kniest syndrome, the COL2A1 gene interferes with the type II collagen molecules assembly. In this disorder, the gene fails to properly instruct the formation of type II collagen and hence, abnormal collagen prevents connective tissues and bones to develop and form the bone structure properly.
Causes and Risk Factors of Kniest Dysplasia or Kniest Syndrome:
Kniest dysplasia or kniest syndrome is an autosomal dominant gene inheritance disorder that means that if the child carries even a single copy of the altered gene in each cell, it will be sufficient enough to cause this disorder. However, the chance of developing Kniest dysplasia or kniest syndrome in each of the children of an affected parent is 50%. Although it can be inherited, if even a single parent is affected with Kniest dysplasia or kniest syndrome; it can also occur with no history of this disorder in the family.
The cause of the gene mutation has no specific or apparent reason. If one receives a normal gene and an abnormal gene responsible for the disease, the person will be a carrier of Kniest dysplasia, but will not show symptoms. If both the parents are carriers of these abnormal genes responsible for Kniest dysplasia or kniest syndrome and both pass the defective gene, the chance for an affected child is 25% with each pregnancy and in 50% cases of each pregnancy, there is a chance that the child will also be a carrier. As a result, the chance for the child to receive normal genes from both the parents is also 25%.
Diagnosis and Tests for Kniest Dysplasia or Kniest Syndrome:
Starting with a thorough medical history of the individual with the symptoms, the tests for this disorder gradually proceeds towards –
- X-rays for testing the position of the bones and the disorders
- MRI scan to test the structures within the bones
- CT scan to produce cross-sectional images
- Genetic testing to diagnose the gene mutations, by collecting sample of the child's saliva or blood
- EOS imaging to collect 3-dimensional images of the child's bone structure.
Although all these diagnostic tests are run once the child is born and is seen to have some abnormal bone structure and development, there are procedures that can diagnose Kniest dysplasia or kniest syndrome in the child right within the womb of the mother.
Tests to Diagnose Kniest Dysplasia or Kniest Syndrome in Prenatal Stage:
If parents, who have Kniest dysplasia or kniest syndrome and wish to have children, want to know the possibility of their children acquiring this disorder, there are tests that can recognise some of the mutations. Amniocentesis and CVS are the diagnostic tests that can identify the known Kniest mutations. Sometimes, some of the bone anomalies in the foetus can be identified by sonograms in the end of the second trimester. Hence, it is very important and helpful for the would-be parents to see a genetic counsellor to know for the possible gene mutations.
Complications of Kniest Dysplasia or Kniest Syndrome:
Short stature is a common complication that children as well as adults with Kniest dysplasia or kniest syndrome have. All the complications associated with short stature are also present in them. However, with advancement of treatment, these additional and associated complications can well be managed. Hearing and visual difficulties and complications are common in them. Some of the children with Kniest dysplasia or kniest syndrome also have hydrocephalus or excessive fluid around the brain. A gradual development of apnea or a temporary stop in breathing during sleep is also a possible complication that is seen to occur in many. This is a result of the airway obstruction by the adenoids or the tonsils caused by the abnormally small bone anatomy. However, with early detection and surgical correction, all these complications can be managed.
What becomes more serious problem and complication for these children, as they grow into dwarf adults are –
- ear infections and hearing loss
- weight problems
- breathing problems
- crowding of teeth
- early arthritis and trouble with joint flexibility
- curvature of the spine, bowed legs
- lower back pain
- late development of motor skills like walking and sitting up at older ages than an average-sized child
- leg numbness.
However, with proper therapy and guidance of the medical caregiver, these difficulties can be lessened to a great extent, making sure that the individual receives a better life and increase physical activity.
Treatment and Management of Kniest Dysplasia or Kniest Syndrome:
There is no possible treatment for Kniest dysplasia or kniest syndrome. However, for some of the symptoms associated with this disorder, there is a possible treatment that can help the child get rid of those difficulties and complications right at the very tender age. These management techniques include physical and occupational therapies, surgeries, psychological assistance and general care giving.
The general orthopaedic conditions such as hip dysplasia, scoliosis, craniofacial anomalies, limb shortening and joint stiffness are some of the common difficulties associated with Kniest dysplasia or kniest syndrome can be treated with surgical assistance at the very young and tender age of the child. Cleft palate and club foot symptoms can also be treated with surgery.
However, each child has a different set of complications and depending on these complications, the proper treatment and management programs are chosen. It is always better to visit the specialists for specific problems and to treat them well. Kniest dysplasia or kniest syndrome is not a life threatening problem and hence, with proper care and health management, a better life can be given to the individuals. You need to consult –
- A plastic surgeon for craniofacial or hand anomalies
- An ophthalmologist for vision problems
- Physical and occupational therapists to expand physical dexterity and skill of your child
- An orthopaedist for any bone-, muscle- and joint-related issues
- An audiologist for any hearing issues
- A Psychologist for dealing with social issues that the child face.
Regular visit of the experts for follow up care is a very useful way of making assured that the child is getting the best care and treatment. Understanding the difficulties of the child and making the home atmosphere suitable for them is also a part of the management and care.