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At a glance

Autosomal recessive inherited form of short-limb dwarfism associated with spine anomalies. It is characterized by an unusual clubfoot with twisting of the metatarsals, inward- and upward-turning foot, tarsus varus, and adductly inverted appearances. Other clinical features include a scoliosis, the “hitchhiker thumbs” sign and in 50% of affected individuals a cleft palate. Most newborns develop cauliflower-like ears as a result of cystic malformations of the upper part of the ears. Diastrophic dysplasia is often misdiagnosed for Atelosteogenesis Type 2 (see “Other conditions to be considered”); however, diastrophic dysplasia tends to be less severe.

N.B.: “Diastrophism” is used to describe the twisting of an extremity.

Synonyms

Diastrophic Dwarfism; Diastrophic Nanism Syndrome.

Incidence

The incidence is established at 1:100,000 live births, with an approximately three times higher incidence in Finland where 1 to 2% of the general population are carriers. It is estimated at one in every 500,000 births in the United States making it the third largest type of dwarfism. A total of 183 cases have been reported in the medical literature, with a prevalence ratio of 1:30,000. It is observed mostly in the white populations.

Genetic inheritance

Transmission is autosomal recessive, with a broad phenotypical range. The responsible gene has been identified to 5q32-q33.1. It is due to mutations in the SLC26A2 gene.

Pathophysiology

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.

Diagnosis

Made by the clinical findings and molecular genetic testing.

Clinical aspects

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 ...

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