OMIM ID:
Maroteaux-Lamy Syndrome (MPS VI)
Alternate Names
Defective Genes
Clinical Characteristics
Ocular Features
Corneal clouding is the cardinal ocular feature and is often visible by 5 years of age. Several adult patients have had glaucoma with both open and closed angles. The mechanism is unknown. Optic nerve compression or secondary edema can cause a relatively sudden loss of vision.
Systemic Features
The lysosomal accumulation of glycosaminoglycans is responsible for the widespread signs and symptoms found in this disease. Bone destruction in shoulders, hips and skull is often seen by the second decade of life and may become evident later in the knees and spine. Early growth may be normal but eventually slows resulting in short stature. Dysplasia of bones comprising these joints leads to stiffness and restricted movement. The face is dysmorphic with coarse features. Bone dysplasia and facial dysmorphism may be seen at birth. Myelopathy and even tetraplegia can result from vertebral compression. Intelligence is often normal although more severely affected individuals may have some cognitive defects. Hepatosplenomegaly is common and compromised respiratory function can result in reduced physical stamina. The tongue is usually enlarged. Accumulation of dermatan sulfate in heart valves may produce insufficiency or restriction of outflow.
Genetics
Inheritance
MPS VI is a lysosomal storage disease inherited in an autosomal recessive pattern. The responsible mutations lie in ARSB (5q11-q13), the gene that encodes the enzyme arylsulfatase B. The phenotype results from defective dermatan sulfate breakdown with lysosomal accumulation.
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.