How UCDs are passed on in the family
Urea cycle disorders (UCDs) are passed down through a family’s genes because people in the same immediate or extended families have some of the same genes. This may include the gene that causes ornithine transcarbamylase deficiency or OTC deficiency. If one person in your family has OTC deficiency, there could be others who are affected as well.
OTC deficiency is the most common type of UCD. It is typically passed from a mother to her child through the X chromosome. Women who pass on the OTC gene are often called “OTC carriers,” and learn this when their child is diagnosed. A mother who is an OTC “carrier” has one unaffected gene and one OTC gene. If you’re a woman with a child who has OTC deficiency, you may be a carrier of OTC deficiency as well.
If your child has OTC deficiency, contact your doctor to receive a genetic test that will determine if you are a “carrier.”
The OTC Family Tree, which you can download here can help you see who in your family may be at risk for OTC deficiency. Take a few minutes to fill it out, then review it with your doctor or genetic counselor to see who in your family should be tested for the OTC gene.
Symptoms every OTC carrier should know
OTC carriers can have symptoms.
Symptoms such as migraines, vomiting, and exhaustion may be signs of high levels of ammonia in your blood. Over time, high ammonia levels can lead to brain damage.
Use this interactive OTC Symptom Assessor to review other UCD symptoms and see if they apply to you. If you have symptoms, talk with a specialist and share your completed symptom survey with him or her.
Talk to your family about OTC deficiency
If your child has been diagnosed with OTC deficiency, or if you learned that you are an OTC carrier, other people in your family might also be affected. It’s important to let your family members know and to give them as much information as you can about OTC and UCDs.
Starting this conversation with family members might not be easy or comfortable, but talking openly with your family about your experiences and answering their questions can give them a better understanding of the risk. You can explain what being an OTC carrier can mean to their health and suggest that they may want to get a genetic test as well.
If you don’t feel comfortable talking to them in person, you can take other approaches. Getting on the phone or writing a letter or email are also good options. You can compose your thoughts and include any important information. Then, you can follow up with an in-person conversation.
Use our "Talking to Your Family" guide for talking points and a sample letter to help you get started.
Separating Myths From Facts
MYTH: Carriers are not affected by OTC deficiency.
FACT: Many carriers experience OTC symptoms.
Some OTC carriers experience symptoms for some time before they even know they are carriers or that it is damaging their health.
MYTH: Carriers cannot have an episode of hyperammonemia.
FACT: Not true!
Even people with mild OTC can experience hyperammonemia (too much ammonia) at any age.
MYTH: What’s happening to you is normal and you just have to live with it.
FACT: You don’t have to live with things like nausea, migraines, or exhaustion.
There are things you can do to help keep these symptoms under control. An OTC management plan may help!
MYTH: It’s all in your head.
FACT: Elevated ammonia that’s not high enough to cause a crisis can still cause symptoms and damage to the brain.
Carriers may have less severe OTC, which means they may not experience hyperammonemic crises often or even ever. BUT this doesn’t mean carriers don’t experience high levels of ammonia!
MYTH: Genetic testing for UCDs is expensive and complicated.
FACT: The cost of a genetic test varies, and health insurance may cover some or all of the cost.
There are also programs available to help people afford a genetic test. The UCD Genetic Testing Program provides access to genetic testing for people suspected of having OTC and their family members at no cost.