What is Hurler Syndrome?

Hurler syndrome is a rare genetic condition where affected individuals have a deficiency or absence of the enzyme called alpha-L-Iduronidase. The alpha-L-Iduronidase is a specific enzyme inside cell organelles called lysosomes that are mostly responsible for the breakdown of long chain molecules of sugar, called mucopolysaccharides or glycosaminoglycans. This deficiency often results to the accumulation of dermatan sulfate and heparan sulfate inside certain types of cells, causing the enlargement and dysfunction of these cells. As these cells are generally located in the organ systems of the body, there is often multiple organ involvement seen in Hurler syndrome.

It is one of the six types of mucopolysaccharidoses, which are a group of conditions having deficiencies in specific lysosomal enzymes with accumulation of harmful products inside the cells. Hurler syndrome, also called Mucopolysaccharidoses (MPS) type I, is usually characterized by progressive mental retardation, organ involvement, and physical deformities like dwarfism, claw hand, and spinal bone abnormalities. The eyes are frequently involved, showing signs of clouding of the cornea. Patients also often present with coarse facial features like gargoylism. Joint stiffness is often severe, resulting in limitations of movement.

The disorder is divided into three types, namely MPS type I-H or Hurler disease, MPS type I-S or Scheie disease, and MPS type I-H/S or Hurler-Scheie disease. Hurler disease is usually seen during infancy, and the disorder manifests with mental retardation, severe physical deformities, and enlargement of the spleen and liver. Scheie disease presents in adulthood, often with mild or less severe organ involvement and physical deformities, but without mental retardation. Intermediate MPS type I-H/S or Hurler-Scheie disease is a condition with manifestations and onset that lie between the two types, usually associated with severe organ involvements like cardiovascular disease and spleen and liver enlargements, but no mental retardation.

Hurler syndrome is passed to the next generation through an autosomal recessive pattern. Autosomal recessive inheritance means that the disease will manifest in the child when he gets both defective chromosomes or genes from each parent. If only one parent has a defective gene, the child who inherits that gene will become a carrier and usually will not manifest Hurler syndrome symptoms.

There are tests which can detect the disorder in affected individuals. These include urine testing for presence of mucopolysacchides, EKG, X-ray of the spine, and through genetic testing. Pregnant women who have a family history of mucopolysaccharidoses, can also undergo amniocentesis to detect if a fetus is carrying the defective gene as well. Treatment for Hurler syndrome includes stem cell transplantation and specific enzyme therapy.