Ornithine transcarbamylase deficiency

Gene : OTC

What is ornithine transcarbamylase deficiency?

Ornithine transcarbamylase deficiency (OTC) is an inherited disorder characterized by damage to the nervous system due to the accumulation of toxic levels of ammonia in the bloodstream. This accumulation is due to a deficient enzyme called ornithine transcarbamylase. The more severe form of OTC is mostly seen in males with symptoms typically appearing the second or third day of life. These infants appear normal at birth and rapidly become very ill. Their muscle tone weakens, they may refuse to eat, and begin to hyperventilate as their body temperature drops. They may also have seizures. Once a diagnosis has been made, treatment begins right away that can stabilize ammonia levels in these infants, though episodes of increased levels of ammonia in the bloodstream can still easily occur in spite of adherence to a strict treatment. Typically a liver transplant is needed by six months of age for these infants affected with OTC. Brain damage is possible during these episodes, which can cause variable amounts of intellectual disability and decreased control over muscle movement. Some males, and even some females, may not have symptoms until later on in childhood, adolescence or adulthood. Symptoms tend to be milder and episodes of increased levels of ammonia occur less often. Females appear to be especially at risk in the postpartum period for levels of ammonia to rise. There is no cure for OTC. Treatment for OTC includes strict, life-long dietary and supplemental management. Some babies may require dialysis to help lower ammonia levels. In general, the more severe the symptoms and the number of episodes, the shorter the life expectancy is for individuals with OTC. OTC is caused by pathogenic variants in the OTC gene.

How is ornithine transcarbamylase deficiency inherited?

OTC is inherited in an X-linked recessive manner. This type of inheritance requires the presence of one copy of a pathogenic variant in the gene located on the X-chromosome for males to be affected. When the pathogenic variant is inherited from the unaffected carrier mother, the male child will have the genetic disease. There is a 50% chance that a baby will inherited the pathogenic variant from the mother; females who inherited the pathogenic variant will be carriers, males who inherited the pathogenic variant will be affected.

What does it mean to be a carrier?

There is much variability as to how affected a female carrier could be, from experiencing none of the symptoms associated with OTC to being severely affected. The risk to have a child affected with OTC is also increased. Testing of reproductive partners is recommended for carriers of OTC.

How common is ornithine transcarbamylase deficiency?

OTC is estimated to occur between 1 in 40,000 and 80,000 newborns.

Family References and Resources
Clinician References
What is Analyzed?
  • Full gene sequencing
Affected Systems

Brain

Muscle

Metabolic

Carrier Rates
Ethnicity
Detection Rate
Carrier Frequency
General Population 72% 1 in 1

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