Diastrophic Dysplasia: Diastrophic Dwarfism

Diastrophic Dysplasia (DTD) is a rare, inherited skeletal dysplasia (a condition of abnormal bone growth or development) affecting both females and males equally. It was first described in 1960 by French doctors, Dr M. Lamy and Dr P. Maroteaux, as Le nanisme diastrophique. DTD is a disorder of restricted growth, spinal curvature and abnormalities of the fingers and toes. Intelligence is normal. The average height of adults is 118 cm (males: 86-127 cm; females 104-122 cm). Respiratory complications can cause an increase in infant mortality, but individuals who survive infancy have a normal life span.

The incidence is thought to be 1 in 110,000 births and it is caused by mutations in the SLC26A2 (DTDST) gene on chromosome 5q31-q34.

The ways and severity that individuals with DTD are affected vary. The features of DTD include:

• shortening of the limbs but with a normal sized skull;
• small chest;
• protuberant abdomen;
• cleft palate in about 33% of cases
• swelling of the ears giving a 'cauliflower' appearance;
• joint contractures;
• shortening of the bones of the hands including hitchhiker thumbs (short bones cause the thumb to take up the typical hitchhiker position);
• club feet, varying from mild to severe due to bone abnormalities;
• progressive Scoliosis (sideways curvature of the spine), lumbar lordosis (forward curvature of the lower spine) and cervical kyphosis (outward curvature of the upper spine).

DTD is diagnosed by recognition of the clinical features of the disorder, radiographic (x-ray) findings and in some cases by molecular genetic testing of the SLC26A2 gene.

DTD is not a curable condition and treatment will be symptomatic for specific features. It important to maintain joint positioning and mobility as much as possible using physiotherapy and surgical correction for club feet to allow walking. This is often extremely difficult and ideally should be performed by a surgeon with experience of other children with diastrophic dysplasia. This is true of any surgical intervention in children with diastrophic dysplasia. Monitoring of abnormalities of the bones of the limbs and particularly of the spine is important since surgical intervention may be necessary. Progressive abnormality of the bones of the spine in the neck is an important complication and should be looked for specifically. This may also require surgical treatment. Surgical intervention to release joint contracture is not usually recommended since these tend to recur.

A range of support for families, based on the practical and psychological effects of being of short stature at school and in the wider community, is available. Families can obtain information about aids to ameliorate difficulties in access and operation of equipment from local and national statutory and support organisations.

DTD is inherited in autosomal recessive manner.

A range of testing is available. Where DTD is known in a family and the mutations in the SLC26A2 gene in the affected individual are known, chorionic villus sampling can be used at about 10-12 weeks or amniocentesis at about 15-18 weeks. Ultrasound examination may identify typical skeletal abnormalities.

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