Our body contains long chains of sugar called as glycosaminoglycans (GAGs). These GAGs must be broken down so that they can be used for development of bones, connective tissues, etc. and they are usually broken down by an enzyme named iduronate-2-sulfatase (I2S).
In Hunter syndrome, there is deficiency or absence of this enzyme I2S. Because of this the GAGs are not broken down and eventually they start accumulating in the cells and tissues. Proper development of bones and tissues is hampered due to lack of GAGs. Hence, Hunter syndrome is a genetic disorder that shows multisystem involvement.
How To Prevent Hunter Syndrome?
Hunter syndrome can be prevented with the help of PGD (Pre-implantation Genetic Diagnosis). PGD is a procedure that is used before the implantation of embryo. This method is very useful for preventing Hunter syndrome. (1)
Steps Involved In PGD-
- In vitro fertilization- First the embryos are prepared in the laboratory. Embryos are prepared by egg retrieval and then fertilization.
- Few cells are now removed microsurgically from the embryos that are 5 days old. After cell removal, the embryos are frozen.
- These cells that are removed are used to check if the DNA of the cells contains the abnormal gene or not. This step takes seven days.
- If the cells are found to be free of abnormal chromosomes, the remaining embryos are then placed in the uterus. After insertion of embryos, you have to wait for implantation and this is when the pregnancy turns positive.
- If the cells are found to contain the abnormal, disease causing genes then these embryos are destroyed.
Advantages Of PGD-
- With the help of PGD, almost 100 genetic disorders can be tested.
- This process is done before implantation of the embryo and so the couple can make a decision if they want to continue the pregnancy or not.
- This procedure makes it possible for the couple to produce their own biological children even after father suffering from Hunter syndrome or mother being the carrier.
Disadvantages Of PGD-
This procedure can detect the genetic disorder before implantation but in some cases the disorder may be undiagnosed, so regular tests are to be done during pregnancy.
Sometimes the patient may show the symptoms at the middle age and hence it may remain undiagnosed.
There is no way to prevent Hunter syndrome once the mother has given birth. If the first child is diagnosed with Hunter syndrome then the couple must consult a genetic counselor before planning for second pregnancy. If the father is already diagnosed then preventive measure must be taken before having first child.
Complications Of Hunter Syndrome
Cardiovascular Complications– Improper blood supply to the organs due to thickening of heart tissue and this causes improper functioning of the valves of heart. Gradually the heart cannot function leading to heart failure. The patient also suffers from hypertension due to thickening of major blood vessels like aorta.
Respiratory Complications– Breathing difficulty due to macroglossia, thickened nasal passages and gums. Respiratory tract infections and pneumonia are very common. Due to obstructed airways, the patient experiences sleep apnea. Sleep apnea refers to a condition due to which there is intermittent disturbance of breathing during sleep.
Nervous System Complications– There is thickening of the membranes that cover the spinal cord and this leads to scarring. Due to this there is spinal cord compression. This results in fatigue and weakness of the lower limbs. When the disease is more severe, the patient shows behavioral abnormalities. Children may find difficulty concentrating. Seizures are also common in patients with Hunter syndrome.
Skeletal Complications– Due to accumulation of GAGs in the connective tissue there is problem in proper growth of bones causing stunted growth of child. Physical malformations are also common. Irregular shape of vertebrae, arms, ribs, etc. is seen. All these abnormalities related to bones in Hunter syndrome are collectively called as dysostosis multiplex.
Hunter syndrome or mucopolysaccharidosis type II can be prevented with the help of a diagnostic technique called Pre-implantation Genetic Diagnosis (PGD). This is a special test where the embryo is prepared in vitro first. Then few cells from the embryo are collected and testes for the presence abnormal chromosome are done. This is the best method to prevent Hunter syndrome.