Kniest Syndrome - Cause, Diagnosis, and Treatment

Introduction:

Kniest syndrome is a rare genetic disorder, which is a type of skeletal dysplasia that affects the cartilage. It was first identified by Wilhelm Kniest, a German pediatrician. It is also called Swiss cheese cartilage dysplasia, metatropic dwarfism type 2, metatropic dysplasia type 2, and Kniest chondrodystrophy. Symptoms start to show up soon after birth or during infancy.

It has clinical features such as short stature, short extremities, large joint, cervical instability, eye problems such as myopia (nearsightedness), glaucoma (a disease that causes blindness due to optic nerve damage), and retinal detachment (layer of tissue which is present at the back of the eye is pulled away and causes vision problem), breathing problems due to weak windpipe, and facial abnormalities such as a round face, midface depression, prominent forehead, and cleft palate. Adult height is around 42 to 58 inches. This syndrome occurs due to a mutation in the type 2 collagen (COL2A1) gene, which gets inherited as an autosomal dominant pattern. Diagnosis is based on physical examination and medical history. Prenatal diagnosis is made through amniocentesis (a prenatal diagnostic procedure that uses amniotic fluid to access the genetic condition). Treatment is mainly supportive and involves multiple healthcare specialties. Individuals with Kniest syndrome have normal intelligence and can live normal lives.

What Is Kniest Syndrome?

Kniest syndrome is a genetic disorder due to a type 2 collagen (COL2A1) gene defect. It is an autosomal dominant disorder (a mutated gene from one parent can cause the disorder). It affects the cartilage, which becomes soft and crumbly and has a Swiss cheese appearance. It has skeletal and craniofacial anomalies along with breathing problems.

What Are the Clinical Features of Kniest Syndrome?

The clinical features of Kniest syndrome include skeletal and craniofacial abnormalities.

1. Skeletal Abnormalities: These include:

• Short stature or dwarfism.

• Joints such as hips and knees are big, bulgy, and stiff.

• Cervical instability.

• Bell-shaped chest.

• Kyphosis (forward curve of the spine) or scoliosis (sideways curve of the spine).

• Knobby fingers.

• Clubfeet (defect of the foot that is in inward shape).

• Misalignment of legs.

• Premature arthritis (early onset arthritis, which is characterized by swelling, pain, and stiffness in the joint).

• Small pelvis.

• Pectus carinatum (outward growth of the chest bone).

• Short legs.

• Prominent joints.

• Hip dislocation.

• Inguinal hernia or umbilical hernia (part of the organ is bulged out of its place because of weakened muscle and tissue which contains it).

• Breathing problems due to weakened windpipe.

• Respiratory distress due to dyspnea (shortness of breath).

2. Craniofacial Abnormalities: These include:

Eye Abnormalities:

• Cataract (opacity in the lens of the eye).

• Proptosis (protrusion of the eye).

• Wide-set eyes.

• Myopia (nearsightedness, where the near objects are seen clearly but not the far ones).

• Eye complications such as glaucoma (an eye disorder that causes blindness due to optic nerve damage) and retinal detachment.

Facial Abnormalities:

• Prominent forehead.

• Round face with small chin and flat nose.

• Midface depression.

• Celf palate (a slit in the roof of the mouth).

Ear Abnormalities:

• Long-term hearing loss due to recurrence infections.

• Recurrent otitis media (ear infection).

3. Other Abnormalities:

• Hypoplasia (less number of cells in an organ).

• Gait disturbance (difficulty in walking).

• Motor delay (delay in acquiring motor skills).

• Tracheomalacia (a condition where the trachea is flexible and soft, causing it to collapse during coughing, exhaling, or crying).

What Is the Cause of Kniest Syndrome?

Kniest syndrome occurs due to a mutation in COL2A1 (collagen type 2) gene, which is located on chromosome 12. COL2A1 gene provides information in the making of a protein called pro-alpha1chain, which is a component of type 2 collagen. Type 2 collagen provides strength and structure to the development of bone and connective tissues of muscles, organs, joints, and skin; it is found primarily in cartilage, in the vitreous, which is the clear gel that fills the eyeball, the central portion of the vertebral disc of the spine and the inner ear. A mutation in the COL2A1 gene deletes one or more nucleotide bases, therefore producing short pro-alpha1(II) chains which results in abnormal type II collagen molecules.

What Is the Diagnosis of Kniest Syndrome?

The diagnosis of Kniest syndrome includes:

• Kniest syndrome can be identified before birth through prenatal ultrasound, which shows short arms and legs. Prenatal genetic tests can be done through amniocentesis, which involves the sample from amniotic fluid, and chorionic villi sampling (CVS), which is done during the 10 and 12 weeks of pregnancy in which placental biopsy is used.

• Complete physical examination and medical history.

• X-ray of the spine is done to check for spine abnormalities such as kyphosis and scoliosis and the lower extremities.

• Radiographic features show dumbbell-shaped femora and coronal clefts of vertebrae.

• Arthrogram is done to evaluate the cartilage of joints such as knees, hips, and ankles.

• The histopathology of cartilages shows perilacunar foaminess, and collagen fibrils were arranged sparsely in the interterritorial matrix, which had an appearance of Swiss cheese.

• Genetic testing with a sample of blood or saliva can be done.

What Is the Differential Diagnosis of Kniest Syndrome?

The differential diagnosis of Kniest syndrome includes:

• Burton syndrome (a rare genetic disorder that causes myotonia [relaxation of muscles], chondrodysplasia [abnormal development of cartilage], and mask-like faces).

• Rolland-Desbuquois syndrome (a rare disease that causes abnormal bone growth development).

• Metatropic dysplasia type I (a skeletal disorder that causes extreme dwarfism with short legs and arms).

• Spondyloepiphyseal dysplasia is congenital (an inherited condition that affects bone growth and results in dwarfism).

• Morquio's disease (an autosomal recessive disorder that occurs due to N-acetylgalactosamine-6-sulfate sulfatase [GALNS] deficiency).

• Weissenbacher-Zweymuller dysplasia (a bone growth disorder that affects the skeletal system, causes hearing loss, and has distinctive facial features).

What Is the Treatment of Kniest Syndrome?

Treatment for Kniest syndrome includes multiple specialty team, which includes:

• An orthopedic surgeon who treats joint and bone problems.

• A neurosurgeon to treat spinal cord problems.

• An ophthalmologist to treat eye-related problems.

• An otolaryngologist to treat the hearing problem.

• A pulmonologist to treat breathing problems.

• A pediatrician.

• A physical therapist to help with joint motion and muscle strength.

• An occupational therapist to help with daily activities like eating and writing.

The treatment of Kniest syndrome includes:

• Routine monitoring.

• Placement of a halo and vest and cervical fusion in case of cervical instability.

• Placement of growing rods to control spine abnormalities and posterior spinal fusion after the growth is complete.

• Surgical realignment.

• Aqua therapy to improve muscle strength and movements.

• Osteotomy, a surgical procedure of cutting bone by reshaping and realigning the bone to relieve pressure on any part of the bone, is done in correct contracture, hip containment, and misalignment of bones.

• Clubfeet casting in case of clubfeet abnormalities.

Conclusion:

The prognosis of Kniest syndrome depends on the severity of the clinical features. Deafness and eye involvement are the major complications and require periodic surveillance. Besides all these, with appropriate treatment and follow-up, the person can have normal intelligence and normal life.