A heterogeneous inherited chondrodystrophic growth
disorder associated with disproportionate short stature and limbs, marked
joint deformities, and early-onset osteoarthritis.
In 1969, Hall and Dorst suggested a classification into
four types: two dominant (formerly designated types I and III) and two
recessive (formerly designated II and IV).
4:1,000,000 live births; one of the most frequent of the
Both autosomal dominant of gonadal mosaicism
and autosomal recessive inheritance has been reported. Gene map locus is
It results as T mutations in the gene for
cartilage oligomeric matrix protein (COMP). COMP produces soft cartilage,
which deforms markedly under stress. Accumulation of a noncollagenous
protein in the rough endoplasmic reticulum of chondrocytes and the absence
of a proteoglycan “population” from the cartilage suggest that an
abnormally synthesized or processed protein core is not properly transferred
to the Golgi system. The structurally abnormal COMP is expressed in tendon
explains the loose joints that are a consistent feature of
Clinically characterized by marked shortening
of the limbs with a normal head and face (which makes the difference with
achondroplasia). Radiologically, all long bones are short with widened
metaphyses and fragmentation, and irregularities of the developing
epiphyses. In childhood, platyspondyly is characteristic, with anterior
tonguing as a result of delayed ossification of the annular epiphyses; after
puberty, the vertebrae become more normal in appearance. Cytoplasmic
metachromasia of fibroblasts is seen under microscopy.
Patients appear normal at birth and growth
retardation is seldom recognized until the second year of life when the body
proportions may resemble classical achondroplasia. Skeletal lesions occur as
a result of stresses on soft epiphyseal cartilage. Thus, at sites such as
the anterior vertebral margins, and the wrists, ankles, and knee joints,
there may be severe cartilaginous deformity. Sites not subjected to
excessive stress, such as the base of skull, face, sacrum, and central
portions of the vertebrae, appear relatively normal. Unlike achondroplasia,
head size is normal for age and the face appears normal. Intelligence is not
affected. Lumbar lordosis, kyphosis, and scoliosis may all occur. Waddling
gait. There may be atlantoaxial dislocation and odontoid hypoplasia. The
fingers are hyperlax and short, and do not show the trident configuration
typical of achondroplasia. Ligamentous laxity contributes to the leg
deformities (from genu varum to genu valgum). Chronic compression myelopathy
of the cervical cord as a consequence of chronic atlantoaxial dislocation
has been reported. Extraskeletal complications are uncommon. Adult height
ranges from 80 to 130 cm (31.5 to 51.2 inches).
Evaluation of the stability of the
atlantoaxial joint should be made (history, neurologic examination,
radiographic examination including flexion/extension views, CT, MRI).
Document any preoperative neurologic deficit. Thoracic dystrophy and
kyphoscoliosis are present and a detailed cardiopulmonary assessment should
be made (chest radiograph, echocardiography, and lung function tests).
Careful positioning of the patient is
important to prevent injury to ...