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At a glance

Genetic disorder leading to skeletal dysplasia.

Synonym

Kniest-like Dysplasia with Pursed Lips and Ectopia Lentis.

Incidence

Only three cases reported in the literature.

Genetic inheritance

First described in two siblings, one male and, one female. A second case in a 2-year-old girl was subsequently reported. The mode of inheritance is uncertain, but autosomal recessive or gonadal mosaicism seems most likely.

Pathophysiology

An iliac bone biopsy reveals markedly abnormal cartilage matrix in certain areas with large clumps of aggregated collagen fibrils. The growth plates are shorter than normal, however, the resultant calcified cartilage and bone trabeculae appear normal. Electron microscopy confirms the presence of broad-banded, aggregated collagen fibers, 10 to 30 times broader than normal that are scattered throughout the cartilage matrix.

Diagnosis

Based on the characteristic clinical and radiologic findings. The analysis of bone biopsy specimens reveals the distinctive abnormalities in the cartilage matrix.

Clinical aspects

Characterized by short stature (<3rd percentile), bowing of the lower extremities with normal or mildly shortened length (upper extremities are normal), talipes equinovarus, stiffness and contractures of several large joints (shoulders, elbows, hips, and knees), and swelling of wrists and knees. Mild craniofacial disproportions with the facial bones being small compared to the skull size and short neck have been described. Other features may include microstomia, pursed lips, high-arched palate, upslanting of the palpebral fissures, bilateral epicanthal folds, ectopia lentis, and myopia. The chest may become bell-shaped with flaring of the lower ribs. Radiologic findings include mainly thoracic platyspondyly and cervical kyphosis with hypoplastic cervical vertebral bodies resulting in decreased neck mobility (extension and rotation), thoracolumbar kyphoscoliosis, pectus carinatum, wide short ribs, an increased lumbosacral angle, bowing and mild shortening of the lower limbs, dumbbell-shaped long bones with short diaphyses, flared metaphyses and metaphyseal sclerosis, delayed ossification of the femoral heads and dysplastic femoral necks, broad and short pelvis with narrow sacrosciatic notches, flattened and hypoplastic acetabular roofs, and wide pubic and ischial bones. Mild brachydactyly may be observed. Unlike Kniest dysplasia, coronal clefts of the vertebrae are absent. Psychomotor development appears normal for age.

Precautions before anesthesia

Preoperative assessment should include careful assessment of the airway to determine the potential for difficult airway management (microstomia, cervical kyphosis, and limitation of neck movements). Radiologic investigation to assess neck stability may be required in the presence of cervical vertebral dysplasia. Anticholinergic premedication to decrease secretions can be of value in the younger age group, particularly if difficult airway management and/or fiberoptic intubation is anticipated. Using lung function tests to assess respiratory function in older patients may be beneficial, although chest deformation seems not to be a constant finding.

Anesthetic considerations

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