What is Morquio Syndrome?
Morquio syndrome is a familial variety of osseous dystrophy involving bones developed from cartilage that result in dwarfism, spine deformity and joint deformities with typical radiological changes in the vertebral bodies and limb bones but without the hepatosplenomegaly and mental deterioration seen in Hurler’s syndrome and without early corneal changes.
Inheritance of Morquio syndrome is autosomal recessive.
Clinical Features of Morquio Syndrome
At birth there is little or no abnormality to be found. The first symptoms usually appear at about the time of weight bearing. The most common presenting feature is short trunk and thoracolumbar kyphosis. As the time passes deformities develop in all the limbs
Dwarfing is marked and growth in height cases by the age of 10 years.
The head is normal or slightly enlarged. There is flat nose with a depressed bridge, a wide mouth with dysplastic teeth and head thrust forward and sunk between high shoulders. The sternum is pushed forward (pectus carinatum) and the chin seems to rest upon it.
The spine shows a moderate thoracolumbar scoliosis, and scoliosis may develop in some patients.
The limbs are relatively long and the joints hypermobile. There is often a degree of general muscular weakness. A minor fall or head injury may lead to death or quadriplegia whose characteristic is that it is mainly motor predominantly unilateral.
Impending paralysis can often be anticipated by examination for early neurological signs such as a positive Babinski’s sign in a child who complains of tiredness and difficulty in walking. The upper limbs show limited shoulder abduction and elbow extension.
Intelligence is normal in childhood but may deteriorate slightly later. Corneal opacities develop but are less severe and more difficult to detect than in Hurler’s syndrome. They can be seen on slit-lamp investigation.
The skin is thickened and hirsute. There are no visceral changes. Some deafness often develops.
Radiological Appearances in Morquio Syndrome
The vertebrae show a typical appearance. There is more obvious anterior projection than in Hurler’s syndrome and the tip of the projection is pointed or flame-shaped. The posterior borders of the vertebral bodies are concave.
The vertebral flattening increase with age. There is an overall kyphosis, aggravated by posterior displacement or wedging of one or two vertebrae in the thoracolumbar region. There is frequently odontoid dysplasia which may require tomography to show it. The ribs are broad and deformed at their anterior and posterior ends.
In the upper limbs, the metacarpals show the most typical changes. The bases of the metacarpals are conical and there appears to be a bit out of the base of the fifth metacarpal like that in other mucopolysaccharidoses.
The distal metacarpal metaphyses are wider than their adjacent epiphyses. The radial and ulnar growth plates are sloped towards each other and both bones are short, especially the ulna.
In the lower limbs, the hips are always affected. The acetabula are enlarged and irregular, the femoral necks are in valgus and the femoral heads flattened with fragmented epiphyses. The pelvis shows a narrow hour-glass inlet and the acetabula are enlarged, leading to subluxation in later years.
At the knees there is genu valgum with a medial spur at the proximal tibial metaphysis and some epiphysial irregularity and sclerosis of the metaphyses at the femoral and tibial growth plate margins. The skull shows minimal changes.
Differential Diagnosis of Morquio Syndrome
The presence of keratan sulphate in the urine is a feature of Morquio syndrome but its excretion may be inconstant after puberty. In infancy, there may be confusion with rickets, or, in later childhood, with renal rickets.
Treatment of Morquio Syndrome
Orthopaedic management is particularly concerned with problems of walking. If this is present, atlanto-axial fusion or fusion of the posterior arch of the axis to the occiput should be done, sometimes at an early age. If quadriplegia does develop, head traction or halo-pelvic traction needs to be applied and atlanto-axial fusion performed as soon as the child’s general condition allows. During anaesthesia, flexion or extension of the neck must be avoided.
Genu valgum is the commonest abnormality requiring treatment in the lower limbs. Progressive deformity can be corrected by supracondylar osteotomy, but recurrence may occur rapidly and ligamentous laxity may vitiate the result.
Marked joint instability may require the use of orthotic appliances to support the knees and feet. Many patients survive well into adult life but death usually occurs from cardiac or pulmonary failure before the age of 40.
There may be complications such as ear infections and herniae, defective vision or hearing and abdominal pains may need treatment.