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Thursday, July 2, 2015
Inherited Disorders and Birth Defects
My grandson of nearly 2yrs of age has Hunter syndrome and myself and my daughter carry the gene. What does this mean for us?
Hunter syndrome (also called Mucoplysaccaridosis Type II is an inherited metabolic disorder. Individuals (usually boys) with Hunter syndrome are missing an enzyme called iduronate sulfatase. This enzyme is needed to break down certain metabolites or materials found in the cells throughout the body. When it is absent or in very low levels, the cells do not break down these metabolites and instead, the metabolites build up in the cells and are toxic. This leads to problems with the central nervous system, the heart, bones and other organs of the body as well as mental retardation. Because it takes some time for the tissues in the body to store these mucoploysaccarides - newborns usually do not show any problems. There is no cure, however, there may be treatments available for some of the different symptoms.
Hunter syndrome is inherited as an X-linked recessive disease. That means that the gene that causes Hunter syndrome is located on the X chromosome. Everyone has 46 chromosomes, the structures in our cells that carrier our genes. Two of the 46 chromosomes are the sex chromosomes - women have 2 X chromosomes and males have an X and a Y chromosome. Because women have 2 X chromosomes, the normal gene on one of the X chromosomes overshadows the effect of the changed (mutated) gene on the other X chromosome. Women are called carriers and they usually make enough of the enzyme so that they do not have the disease. However, because there is no similar gene on the Y chromosome in boys to overshadow the effect of the mutated (changed) gene on the X chromosome, boys are affected.
This means, that any woman (in your case, both you and your daughter) who is a carrier of the gene that causes Hunter syndrome has a 50-50 chance of having boys affected. There is also a 50-50 chance of having any daughters be carriers like the mother. There is carrier testing for available for families where there has been a boy born with Hunter syndrome as well as prenatal diagnosis to test for the disease during pregnancy.
If you and your daughter have not spoken to a geneticist or genetic counselor, I would highly recommend that you do so. They would be able to discuss the disease in much greater detail. You can locate a genetics center near you at the National Society of Genetic Counselors Resource center website listed below.
The Society for Mucopolysaccharide Diseases and the National MPS Society listed below also have materials available for families.
Anne Matthews, RN, PhD
Associate Professor of Genetics
School of Medicine
Case Western Reserve University