Glycogen storage disease ixa
How did my child get glycogen storage disease IXa?
Glycogen storage disease type IXa (GSD IXa) is an X-linked disorder. An X-linked disorder is when the genetic change is on the X chromosome. Females have two copies of the X chromosome, while males have one X and one Y. Because males only have one copy of the X chromosome, if there is a genetic change that is medically significant in a particular gene on the X-chromosome, they will be affected. Females, on the other hand, have two X chromosomes. If there is genetic change on one X-chromosome, there is a second copy which still works. Females are usually "carriers" of X-linked disorders such as GSD IXa. A carrier is someone who does not have GSD IXa, but can pass on the genetic change to their children. Some females that have a genetic change for GSD IXa can have milder features of the diagnosis that may go undetected by a medical professional or not cause any significant health issues.
If a female carrier of GSD IXa has children, there is a 50% chance her sons will be affected and a 50% chance her daughters will be carriers. This applies to each pregnancy and does not mean that if a female carrier has a son with GSD IXa, that other male pregnancies will not be at a 50% risk to have inherited this same change.
More Inheritance Content
Am I a carrier for glycogen storage disease IXa?
Female carriers of glycogen storage disease type IXa (GSD IXa) have one copy of the PHKA1 gene without a change and one copy of the PHKA1 gene with a change. Because carriers have one normal copy of the gene, They may not have any of the medical issues associated with GSD IXa or only have mild features. It is possible though, for a carrier to pass on the PHKA1 gene with a change to her children. If you have a family history of GSD IXa your doctor or genetic counselor can order a blood test to see if you are a carrier of GSD IXa.
If a female carrier of GSD IXa has children, there is a 50% chance her sons will be affected and a 50% chance her daughters will be carriers. Since men only have one copy of the PHKA1 gene, they cannot be carriers. Males with GSD IXa will always pass on their gene change to their daughters and will not pass their gene change on to their sons at all. This is because males will only pass on their X-chromosomes to their daughters and will only pass on their Y-chromosome to their sons. Therefore, all the daughters of a male that has GSD IXa will be carriers. Males that do not have the disease themselves, cannot pass it on to their children.
Can I have healthy children if I have glycogen storage disease IXa?
People with glycogen storage disease type IXa (GSD IXa) can have unaffected children, children who are carriers, or children who have GSD IXa. If you have GSD IXa and are considering having children, speak with your doctor or genetic counselor about the chances of having a child with GSD IXa.
Males that have GSD IXa will only pass on their Y-chromosome to their sons and therefore, their male children will not be at an increased chance to have GSD IXa. Males with GSD IXa will always pass on their X-chromosome to their daughters. Therefore, all daughters of a male that has GSD IXa will be at least a carrier for GSD IXa. These daughters may or may not exhibit features of GSD IXa depending on which copy of their X-chromosome is active in each of the cells in their bodies.
Can you test for glycogen storage disease IXa prenatally?
It is possible to test a pregnancy for glycogen storage disease type IXa (GSD IXa) by amniocentesis or by chorionic villi sampling (CVS). Amniocentesis uses a needle guided by ultrasound to find a pocket of amniotic fluid away from the baby to take some cells for examination. Looking at the genetic information in these cells will allow the laboratory to determine if the pregnancy has GSD IXa or not. Amniocentesis is available after 16 weeks of pregnancy. It is only available if the gene change for GSD IXa is known.
Chorionic villi sampling (CVS) testing is available between 10-13 weeks of pregnancy. This testing involves taking a biopsy or a piece of the placental tissue by an ultrasound guided biopsy. The placental tissue can then be used to look for the previously identified GSD IXa gene change.
Amniocentesis and chorionic villi sampling both include a risk for miscarriage, infection and bleeding. These risks and the benefits and limitations to completing this testing can be reviewed with a high risk pregnancy doctor and/or genetic counselor.
If you would like to do testing while you are pregnant it is important that you talk to your doctor about it as soon as you know you are pregnant or before becoming pregnant.
Is there a way to prevent GSD IXa?
Preimplantation genetic diagnosis (PGD) in vitro fertilization (IVF) is a form of genetic testing that can take place before a pregnancy. This is a form of in vitro fertilization in which the sperm and egg cells of a parent are obtained during a round of IVF. Fertilized embryos are then created in a lab. During the very early stages of development of the fertilized embryo, a few cells are obtained to test for the known genetic change in a family for GSD IXa. Only those fertilized embryos that do not have GSD IXa are then transferred and afforded the opportunity to become a successful and viable pregnancy.