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Autosomal recessive inherited form of short-limb
dwarfism associated with spine anomalies.
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Diastrophic Dwarfism; Diastrophic Nanism Syndrome.
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1:100,000 live births, with an approximately three times
higher incidence in Finland.
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Transmission is autosomal recessive, with a
broad phenotypical range. The responsible gene maps to 5q32-q33.1 (also
called SLC26A2).
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The defect on chromosome 5 affects the diastrophic
dysplasia sulfate transporter (DTDST) and leads to depletion of
intracellular sulfate and insufficient sulfation of sulfated macromolecules
such as cartilage matrix proteoglycans, which results in abnormally soft
cartilage with decreased resistance to stress.
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Made by the clinical findings and molecular genetic
testing.
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This form of rhizomelic (short-limb) dwarfism is
characterized by a proportionate shortening of the tubular bones, which are
approximately 50% of the normal length. Abduction of the thumbs results
from a short and oval-shaped first metacarpal bone, which gives it the
aspect of a “hitchhiker thumb.” Severe clubfoot deformity with luxation of
the big toes and ulnar deviation of the hands are typical. These findings,
which are present in prenatal ultrasonographs, make very likely the
diagnosis of diastrophic dysplasia. A patient may suffer from hyperlaxity
with recurrent dislocations of some joints, while other joints show
stiffness and contractures. During the first 2 to 5 weeks of life, more than
80% of patients suffer from swelling and inflammation of the ear cups
with subsequent calcification and “cauliflower”-like ears. The palate is
high arched and broad, and cleft palate (complete, partial or submucous,
double or bifid uvula) may occur in up to 25% of patients. The abnormally
soft cartilage is responsible for laryngotracheobronchomalacia and often
causes respiratory distress. Spinal deformities, such as mid-cervical
kyphosis with potential compression of the medulla, cervical spina bifida
occulta, and scoliosis (with lung volumes inversely correlated to the angle
of scoliosis) with decreased chest mobility, contribute to the respiratory
problems. In fact, respiratory failure is responsible for the increased
mortality in the first months of life. Although cervical kyphosis resolves
spontaneously in more than 90% of patients, progression to quadriplegia
and death has been reported. The median adult height in a Finnish study of
121 affected men and women was 135 cm (53.1 in) and 129 cm (50.8 in),
respectively. Most of the patients are mentally normal, but as a consequence
of the orthopedic problems, motor skills are delayed and their exercise
tolerance is reduced secondary to respiratory problems.
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The pulmonary situation should be
optimized as much as possible before surgery, and the need for postoperative
mechanical ventilation should be anticipated. A chest radiograph should be
obtained. Cervical spine anomalies are frequent and require a thorough
clinical and radiologic evaluation. Lateral flexion and extension radiograph
and/or MRI of the neck may be necessary to evaluate the grade of spinal
compression.
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Death as a result of anesthetic
complications has been described. If tracheal intubation is required,
either inline cervical stabilization or fiberoptic intubation is
recommended. ...