Kniest Dysplasia - Causes, Symptoms and Treatment

Kniest dysplasia is a disorder of bone growth. This condition is characterized by short stature (dwarfism), enlarged joints and other skeletal abnormalities, and problems with vision and hearing. People with this condition have short stature from birth, with a short trunk and shortened limbs. Adult height ranges from 42 inches to 58 inches. Progressive joint enlargement and pain restrict movement of the joints, which limits activity and interferes with standing and walking. These joint problems can also lead to arthritis.

Kniest dysplasia is one of several forms of dwarfism that is caused by a change (mutation) in a gene known as COL2A1. This gene is involved in the production of a particular protein that forms type 2 collagen, which is essential for the normal development of bones and other connective tissue. Changes in the composition of type 2 collagen lead to abnormal skeletal growth and, thus, to a variety of dwarfing conditions known as skeletal dysplasias.

Causes of Kniest dysplasia

The patients develop marked dorsal kyphosis or kyphoscoliosis and lumbar lordosis. Radiographs reveal shortened tubular bones with flared ends, delayed epiphyseal development, and fragmented, flattened and squared epiphyses in the hands. Swellings resembling Heberdens nodes and Bouchards nodes may also be seen. Pelvic abnormalities include broad and short femoral necks, marked coxa vara and hip contractures.

Skeletal dysplasia is a heterogeneous group of disorders characterized by abnormalities of cartilage and bone growth. Their modes of inheritance are heterogeneous (ie, autosomal recessive, autosomal dominant, X-linked recessive, or X-linked dominant.

Kniest dysplasia is one of a spectrum of skeletal disorders caused by mutations in the COL2A1 gene. The protein made by this gene forms type II collagen, a molecule found mostly in cartilage and in the clear gel that fills the eyeball (the vitreous). Mutations in the COL2A1 gene that cause Kniest dysplasia interfere with the assembly of type II collagen molecules, which prevents bones from developing properly and causes the signs and symptoms of the disorder.

Symptoms of Kniest dysplasia

People with Kniest dysplasia have round, flat faces with prominent and wide-set eyes. Some infants are born with an opening in the roof of the mouth (a cleft palate). Infants may also have breathing problems due to weakness of the windpipe. Severe nearsightedness (myopia) is common, as are other eye problems that can lead to blindness. Hearing loss resulting from recurrent ear infections is also possible.

Three women with dwarfism and skeletal defects characteristic for Kniest's dysplasia are described. In two of the patients (from two generations of one family) there are only skeletal defects. In the third patient they are combined with other symptoms pertaining to the tendons, the sclerae, the eye lenses, the retinal vessels and loss of hearing. This allows the conclusion of genetic variations of the disease--such pertaining to the skeleton and others, where the inferiority of collagen is not limited to the skeleton.

Treatment for Kniest dysplasia

Surgical treatment, but close ophthalmological follow up will be necessary for their favorable prognosis. The literature on vitreoretinal degeneration such as Wagner's disease or Stickler syndrome may indicate the relation of Kniest dysplasia to similar diseases. Because they might have different clinical courses and visual prognosis according to the original biosynthetic disorders, we emphasized the importance of orthopedic diagnosis regarding such vitreoretinal degeneration with constitutional bone diseases.

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