Morquio's disease and mucopolysaccharide excretion

Mucopolysaccharidosis: What Pediatric Rheumatologists and Orthopedics Need to Know

Mucopolysaccharidosis (MPS) is a group of disorders caused by the reduced or absent activity of enzymes involved in the glycosaminoglycans (GAGs) degradation; the consequence is the progressive accumulation of the substrate (dermatan, heparan, keratan or chondroitin sulfate) in the lysosomes of cells belonging to several tissues. The rarity, the broad spectrum of manifestations, the lack of strict genotype-phenotype association, and the progressive nature of MPS make diagnosing this group of conditions challenging. Musculoskeletal involvement represents a common and prominent feature of MPS. Joint and bone abnormalities might be the main clue for diagnosing MPS, especially in attenuated phenotypes; therefore, it is essential to increase the awareness of these conditions among the pediatric rheumatology and orthopedic communities since early diagnosis and treatment are crucial to reduce the disease burden of these patients. Nowadays, enzyme replacement therapy (ERT) and hematopoietic stem cell transplantation (HSCT) are available for some MPS types. We describe the musculoskeletal characteristics of MPS patients through a literature review of MPS cases misdiagnosed as having rheumatologic or orthopedic conditions.

A case of mucopolysaccharidosis IV with lower leg paresis due to thoraco-lumbar kyphoscoliosis

We treated a patient of type IV mucopolysaccharidosis (Morquio's disease) with lower leg paresis due to kyphoscoliosis. A 65-year-old woman presented with Morquio's disease. A lateral radiograph demonstrated the classic bullet-shaped vertebrae and a 65 degrees thoraco-lumbar kyphosis. After the age of 60, she suffered from numbness in both lower legs and walking disturbance. Bilateral patellae-tendon reflexes were exaggerated. MRI showed compression of the spinal cord around T12 to L2 with a highlighted area of change inside the spinal cord. Myelography and computed tomography after the myelography showed narrowing of the sub-arachnoidal space and deformation of the spinal cord around the T12 to L2 levels. Severe vertebral osteoporosis made it necessary to first perform posterior correction of the kyphosis and fusion. The curve was stabilised with the Luque method from T7 to L4. Her neurological condition markedly recovered, but 1 year after surgery her neurological condition again began to deteriorate, resulting in walking disturbance. For this reason, anterior decompression and fusion through a lateral thoracotomy was undertaken. Decompression of the spinal cord and a bone graft from the iliac crest were attained. The patient's neurological condition again improved, but not as much as immediately after the first operation.

Spinal manifestations of skeletal dysplasias

Skeletal dysplasias, disorders of abnormal bone and cartilage development, are a heterogeneous group, each disorder with its own genetics, prevalence, prognosis, and treatment. More than 150 distinct conditions have been identified. Despite their obvious differences, the osteochondrodysplasias share many clinical and radiographic features. These patients present to the orthopedic surgeon for evaluation of disproportionate short stature, which may be apparent at birth or manifest itself only with further growth. This article discusses bone dysplasias commonly associated with spinal abnormalities. Spinal pathology can lead to deformity, neurologic sequelae, pain, and cardiopulmonary compromise and further contribute to short stature.

Megalencephaly: definition and classification

The various definitions and classifications of megalencephaly are reviewed, and numerous diseases and syndromes associated with megalencephaly are listed. A new definition of megalencephaly based on quantitative radiographic features is proposed. We define megalencephaly as a brain volume which exceeds the mean by more than twice the standard deviation. Furthermore, a modified etiopathogenic classification of megalencephaly results in three main groups, viz anatomic, metabolic and dynamic megalencephaly. The clinical pictures in these main groups of megalencephaly, and the largest subgroup of anatomic megalencephaly, familial anatomic megalencephaly, appear to be quite different.

Morquio B syndrome: a primary defect in beta-galactosidase

Fibroblasts from patients with Morquio B syndrome contain normal numbers of beta-galactosidase molecules with normal turnover but strongly reduced activity per enzyme molecule. Various substrate affinities are abnormal: the Km for methylum belliferyl (MU)-beta-galactoside is 4-10-fold elevated and affinity for keratan sulphate and oligosaccharides, isolated from Morquio B urine, was not detectable. In contrast, these substrate affinities are normal for beta-galactosidase in adult type GM1-gangliosidosis fibroblasts. Cell hybridization studies demonstrate that Morquio B syndrome and infantile and adult type GM1-gangliosidosis belong to the same complementation group. From these results we conclude that Morquio B syndrome is caused by a mutation in the structural gene for beta-galactosidase, which is allelic to the mutations in infantile and adult type GM1-gangliosidosis. Urinary excretion of keratan sulphate and oligosaccharides is abnormal in Morquio B syndrome but normal in adult type GM1-gangliosidosis. The catalytic properties of beta-galactosidase in Morquio B syndrome and GM1-gangliosidosis provide a possible explanation for the distinct clinical manifestations in these disorders.

X-linked Dyggve-Melchior-Clausen syndrome

Ten affected males studied from four generations of a Colombian family with Dyggve-Melchior-Clausen (DMC) syndrome are described. The ages of the affected males varied from 13 to 50 years and they presented with typical clinical and radiological manifestations of the syndrome. The association of normal intelligence and a clear X-linked recessive inheritance in this family is evidence of heterogeneity in the Dyggve-Melchior-Clausen syndrome. In agreement with previous reports for DMC dwarfism, this new form has normal mucopolysaccharide excretion.

Heterogeneity of Dyggve-Melchior-Clausen dwarfism

Sibs with apparent Dyggve-Melchior-Clausen (DMC) dwarfism and normal intelligence are described. Three other familial and 3 sporadic cases with DMC dwarfism and normal intelligence are known. Twelve familial and 9 sporadic cases are known with the usual combination of DMC dwarfism and severe mental retardation. Since the two conditions appear to breed true they seem to be genetically different. We propose to name the former "Smith-McCort dwarfism" to clearly distinguish it from the DMC syndrome in which mental retardation is a constituent part. Both conditions are inherited as autosomal recessive traits. Spinal cord compression due to atlantoaxial instability is a serious and preventable complication of both disorders.

Oral manifestations of Morquio's syndrome

The clinical and laboratory findings in two siblings affected with Morquio's syndrome are described. The oral findings, consisting of disturbances in the structure of the enamel in both deciduous and permanent teeth, resemble those of amelogenesis imperfecta, Type 1. Preformed crowns are recommended as the initial treatment, in order to avoid loss of vertical height. The dentist's familiarity with the oral manifestations of Morquio's disease may contribute to the early detection of this condition.