OMIM ID:
Morquio Syndrome (MPS IVA)
Alternate Names
Defective Genes
Clinical Characteristics
Ocular Features
Corneal clouding in the form of fine deposits in the stroma is the major ocular manifestation but it may not be noted for several years after birth. Penetrating keratoplasty is rarely needed. Glaucoma occurs rarely.
Systemic Features
There is wide variation in the clinical disease in this disorder and some have grouped cases into severe, intermediate and mild categories. Onset is about 2 years of age and three-quarters of patients are diagnosed by the age of 6 years. Intelligence is usually normal and the central nervous system is spared similar to MPS IVB. However, the skeletal dysplasia can lead to neurologic complications. In particular, odontoid hypoplasia raises the risk of atlantoaxial dislocation and spinal cord damage. The maxillary teeth are often abnormal with wide spacing and a flared appearance. Truncal dwarfism is characteristic but the facies are often more fine-featured than in other mucopolysaccharidoses. Lifespan is shortened in most patients.
Genetics
Inheritance
This is an autosomal recessive disorder resulting from mutations in the GALNS gene (16q24.3) encoding galactosamine-6-sulfate sulfatase. Keratan sulfate and chondroitin-5-sulfate accumulates in lysosomes. Urinary keratin sulfate excretion is increased.
A clinically similar disease, Morquio syndrome B (253010), is caused by a different mutation.
Pedigree
Autosomal recessive
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.