Short-spine-type dwarfism associated with mental
retardation and skeletal abnormalities.
Only 58 cases have been reported in the literature.
Seems to occur more frequently in Lebanon.
Autosomal recessive. Linkage studies localized
the responsible genes to chromosome 18q12-21.1. This gene seems to be
involved in normal skeletal development and brain function.
Electron microscopy of chondrocytes shows dilated
cisternae of rough endoplasmic reticulum, containing fine granular or
amorphous material. Protein accumulation within the rough endoplasmic
reticulum has been hypothesized to be secondary to an enzyme defect that has
not been characterized.
Clinically, thoracic deformities in the form of barrel
chest become visible in the first 18 months of life. Radiographs of the
iliac crests show a characteristic, lace-like appearance, which is caused by
an irregular pattern in the bone tissue deposits at the osteochondral
junction. Abnormal enchondral ossification and absent columnarization of
chondrocytes are found in the growth plates. The vertebral bodies are
characteristic, presenting with double-hump endplates associated with a
central constriction (platyspondyly). These signs usually are present by age
4 years and become more prominent with increasing age.
Phenotypically, patients share some features of
Morquio and Hurler syndromes. In fact, the disorder initially was named
Morquio-Ullrich disease. Affected patients present with dwarfism because of
both short trunk and short limbs. The mean adult height is approximately 130
cm (51.2 in). They also have a coarse facies, although the degree is highly
variable, ranging from almost normal to very severe, where the bulky jaws
and microcephaly are striking. The neck is short. Patients have a variable
degree of odontoid hypoplasia, which may lead to atlantoaxial instability
and place them at risk for complications related to spinal cord compression.
The chest is barrel shaped, and malalignment of the spine with
kyphoscoliosis is common. The hands and feet are broad, and the fingers
might be clawed. Dislocation of hips and shoulders are common (secondary to
dysplastic joints). Although mental retardation is present, general health
is otherwise good and survival into adulthood is the rule.
Short stature in association with
the spine deformity leads to restrictive lung disease so pulmonary function
tests are recommended, although cooperation may be limited. Blood gas
analysis and echocardiography (cor pulmonale) may be warranted, depending on
the results of the lung function tests. Obtain flexion and extension
radiographs or CT scans of the cervical spine to rule out atlantoaxial
instability. Anxiolytic or sedative premedication may be helpful in the
presence of mental retardation.
Difficult tracheal intubation is likely
(even without atlantoaxial instability) because of the presence of a short
neck, prominent, big jaws, macroglossia, and limited mouth opening. Tracheal
intubation should be performed either fiberoptically or, if possible,
conventionally with inline stabilization of the cervical spine. Restrictive
lung disease may render ventilation and oxygenation more challenging and may
preclude the use of neuraxial regional anesthesia. Proper patient
positioning is difficult because of atlantoaxial instability, dislocations