MPS 1H (also known as Hurler Syndrome) is an inherited lysosomal storage disorder caused by the deficiency of an enzyme called alpha-L-iduronidase. This defiency results in the body being unable to metabolise complex carbohydrates called mucopolysaccharides, these are required to breakdown certain substances in the body known as glycosaminoglycans (commonly referred to as GAGs). GAGS are complex substances produced by the body that are found in all types of connective tissue. Connective tissue provides structural support to organs and tissues and makes up the cartilage of growing bones, joints, and heart valves. Without sufficient quantities of this enzyme, GAGs accumulate in virtually all organs of the body, causing progressive disease.
This increased accumulation, in time, leaves the child with various physical and neurological disabilities as well as severe mental impairment, loss of hearing, and potential blindness. Sadly, if left untreated, the life expectancy of a child with MPS1-H is only 5-10 years.
This disease has symptoms that usually present between the ages of 6 months to 2 years. The common presenting symptoms include a general muscle weakness, a delay in development, clouding of the cornea, an enlarged liver (hepatomegaly) and spleen (splenomegaly) and a gibbus, or curve, in the lower back. Commonly coarse facial features do develop. These include a depressed nasal bridge, a large tongue (macroglossia), large lips, widely spaced teeth and a prominent forehead. With this disease there can be umbilical or inguinal hernias, recurrent urine and upper respiratory infections, noisy breathing, persistent nasal discharge and possibly hydrocephalus, which can lead to seizures. There is usually stiffness in the joints and an associated loss in the range of mobility. Additionally in some cases there can be a build up of carbohydrate deposits in the heart that can affect the functioning of values. Overall an individual will tend to show a poor rate of growth and mental development will reach a peak at about 2 years then progressively deteriorate due to build up of deposits in the brain.
There is no cure for Hurler Syndrome. To date, the only treatment is a bone marrow or a cord blood transplant. If a child undergoes a successful transplant, many aspects of the disease are halted. However, proof of stabilizing the disease in the bones still remains to be seen. The oldest Hurler survivor of a bone marrow transplant is in his early twenties. It has been noted that the transplant should be carried out before the child's second birthday and that younger a child is when they undergo a transplant, the better off he or she will be long-term. Enzyme replacement therapy for this condition has recently been approved for use in the USA and Europe. This therapy has been shown to help with the skeletal and stamina aspects of Hurlers although it does not transfer to the brain.
Hurler's Syndrome is inherited from the genes of the parents. For a child to have the condition a gene with the disease must be inherited from both parents, this is called autosomal recessive inheritance.