How MPS I is passed on
The genes that control the production of the enzymes that breakdown GAG (glycosaminoglycans) are passed from parent to child. In people with MPS I disease, one of these genes is faulty. As a result, not enough of the enzyme is produced or the available enzyme do not function properly.
MPS I disease is referred to as an autosomal recessive disorder. A person is born with the disease by inheriting two faulty MPS I genes, one from each parent. When only one MPS I gene is passed on to a person, he or she will not develop MPS I disease, but will become a carrier. A carrier can pass a mutated MPS I gene to his or her children.
The odds of passing on MPS I genes
When both parents are carriers, there is a 25% chance that each child will inherit two faulty genes and be born with MPS I disease. It is equally likely that the child will inherit two normal genes and be unaffected. With each pregnancy, there is a 50% chance that the child will receive just one mutated gene and become an unaffected carrier for the disease. The diagram below shows how the MPS I gene may be passed from one generation to the next.
Legend:
M - gene that properly controls production of the enzymes that breakdown GAG
MR -faulty gene, one that does not properly control production of the enzymes that breakdown GAG
Possible Outcomes When Both Parents Are Carriers:
- The child inherits two healthy copies of the gene, one from each parent (unaffected child).
- The child inherits one faulty copy of the gene from mother, one healthy gene from father (carrier child).
- The child inherits one faulty copy of the gene from father, one healthy copy of the gene from mother (carrier child).
- The child inherits two faulty copies of the gene, one from each parent (affected child).
Families affected by MPS I may wish to consult with their doctor or genetic counselor to discuss issues of genetic inheritance and family planning.
Prenatal Diagnosis: It is possible for parents who have a child with MPS I to have tests during a subsequent pregnancy to find out whether the baby being carried is affected. It is important to consult with a doctor as soon as the pregnancy is suspected to have tests arranged.
A genetic counselor may be a valuable resource to help you understand how MPS I is inherited in families. He or she may also provide guidance to families for diagnostic, medical, and support services. For more information about genetic counseling, please click here.
