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At a glance

It is a rare, progressive genetic disorder characterized by abnormal skeletal spine-type dwarfism associated with microcephaly and intellectual disability. Other clinical features include barrel-shaped chest with a short truck, genu valgum, and decreased joint mobility. In 11% of patients, there is atlantoaxial instability that can lead to spinal cord compression, weakness and paralysis.

Synonyms

Pseudo-Morquio Disease Type I; DMC Disease.

History

This medical condition was first described in 1962 by Dyggve, Melchior, and Clausen after studying three of eight siblings where the father was the mother’s paternal uncle. Because of physical appearance and the presence of mucopolysaccharides in the urine, originally the authors believed that it was a Morquio-Ullrich disease, now called Morquio Syndrome.

Incidence

The exact incidence remains unknown. Until this date, 90 cases have been reported in the literature. Seems to occur more frequently in Lebanon.

Genetic inheritance

It is inherited as autosomal recessive trait. Linkage studies localized the responsible genes to chromosome 18q12-21.1. This gene seems to be involved in normal skeletal development and brain function.

Pathophysiology

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.

Diagnosis

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.

Clinical aspects

Phenotypically, patients share some features of Morquio and Hurler Syndromes. In fact, the disorder initially was named Morquio-Ullrich disease. Affected individuals present dwarfism in association with a barrel-shaped chest with short trunk and long 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 ...

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