Developmental abnormalities in Morquio syndrome are usually detected late in the first year of life or later and may include deformities of the chest (flaring of the lower ribs or abnormal prominence of the breastbone), loose joints, abnormally short neck, or joint deformities such as knock-knees. Affected children have a characteristic facial appearance that may include an enlarged head, broad mouth, prominent cheekbones, an unusually small nose, widely spaced and thinly enameled teeth, and widely separated eyes with subtle corneal clouding. The liver and spleen may be mildly enlarged. Children with Morquio syndrome show marked growth retardation from early in life. The elbows, wrists, hips, knees and other large joints are abnormally flexible, causing overall instability. Early development and intelligence are typically normal. High frequency hearing impairment is common.
Skeletal X-rays typically show marked flattening of the vertebra. The long bones of the arms and legs are characteristically shorter and thicker than normal. The skull is large for the rest of the body. The connection between the first and second vertebrae in the neck is poorly developed and this abnormality can be life threatening. A trivial injury may cause the two vertebrae to slip on each other and compress the spinal cord. Surgery to stabilize the upper cervical spine, usually by spinal fusion, can be lifesaving but life expectancy is decreased somewhat despite surgery. The deformity of the chest causes a strain on the heart and lungs, which may eventually cause respiratory failure.
Morquio syndrome is an autosomal recessive genetic disorder in which a deficiency of lysosomal N-acetylgalactosamine-6-sulfatase in type A of the disorder, and a deficiency of lysosomal beta-galactosidase in type B, leads to an accumulation of keratan sulfate in the cells and tissues of the body. The two types never occur together in the same family.
Genetic diseases are determined by the combination of genes for a particular trait that are on the chromosomes received from the father and the mother.
Recessive genetic disorders occur when an individual inherits the same abnormal gene for the same trait from each parent. If an individual receives one normal gene and one gene for the disease, the person will be a carrier for the disease, but usually will not show symptoms. The risk for two carrier parents to both pass the defective gene and, therefore, have an affected child is 25% with each pregnancy. The risk to have a child who is a carrier like the parents is 50% with each pregnancy. The chance for a child to receive normal genes from both parents and be genetically normal for that particular trait is 25%. The risk is the same for males and females.
Morquio syndrome affects males and females equally often. Estimates of birth prevalence range from 1/40,000 to 1/200,000 births. Morquio syndrome type A occurs more often than type B.
As a group, lysosomal storage diseases (of which the mucopolysaccharidoses are a subgroup) are believed to have an estimated frequency of about one in every 5,000 live births. Although the individual diseases are rare, the group together affects many people around the world.
Excessive amounts of keratan sulfate in the urine will usually be present. The diagnosis is confirmed with the finding of a deficiency of N-acetylgalactosamine-6-sulfatase (type A) or beta-galactosidase (type B) in blood or skin cells. Prenatal diagnosis of Morquio syndrome is possible through amniocentesis or sampling of tissue from the placenta (chorionic villus sampling).
In 2014, The U.S. Food and Drug Administration (FDA) approved Vimizim (elosulfase alfa), as the first FDA-approved treatment for Morquio A syndrome. Vimizim, marketed by BioMarin Pharmaceutical Inc., is an enzyme replacement therapy for the missing GALNS enzyme.
Other treatment of Morquio syndrome is symptomatic and supportive. Surgery to decompress and fuse the bones of the upper neck to the base of the skull can prevent destabilization of the cervical vertebrae and potential damage to the spinal cord.
Genetic counseling may be of benefit for affected individuals and their families.
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Tomatsu S, et al. Mucopolysaccharidoses IVA (Morquio A): identification of novel common mutations in the N-acetylgalactosamine-6-sulfate sulfatase (GALNS) gene in Italians patients. Hum Mutat. 2004;24:187-8.
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FROM THE INTERNET
McKusick VA, ed. Online Mendelian Inheritance in Man (OMIM). Baltimore, MD: The Johns Hopkins University; Entry No. 253000; Last Update: 2/28/03, Entry No. 253010: Last Update: 5/1/02.
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