Ornithine Transcarbamylase Deficiency, or OTCD is a rare, genetic condition that can impact infants, children and adults. It is a condition whereby the body does not produce enough of, or any OTC enzyme responsible for breaking down protein into urea through a process called urea cycle. This process happens mainly in the liver. The lack or absence of the OTC enzyme poses a serious risk for elevated ammonia levels in the blood, known as hyperammonemia. Since ammonia is a neurotoxin, it can lead to devastating consequences in the body.
OTCD is an X-linked disorder. This means that only one parent needs to have the mutation to pass it on to their child. Affected women have a 50% chance of passing on a mutated OTC gene to their daughters and sons. All men with an OTC gene mutation will pass the genetic error to their daughters, but not to their sons because boys have only one X chromosome (received from the mother) and one Y chromosome (received from the father).
The most severe form of OTCD is diagnosed during the first 28 days of life. This is referred to as ‘early onset.’ People diagnosed with ‘later onset’ OTCD are usually less severely impacted because they may have more enzymatic activity; however, that is not always the case. More research is surfacing to correlate specific mutations with disease severity, regardless of ‘early’ versus ‘later’ onset diagnosis.
Unfortunately, it is common for individuals with OTCD to be misdiagnosed. Without receiving an accurate diagnosis and proper, timely treatment, individuals with this condition may die (particularly during an acute crisis). OTCD can also lead to coma and brain damage in both adults and children. This can happen rather quickly. Furthermore, individuals impacted by OTCD are at risk for seizures, developmental delays and movement disorders such as dystonia. With recurrent crisis episodes, this risk increases.
Some people with OTCD may never show any symptoms. This is mostly applicable to women, but not always, because they have two copies of the gene (correct and altered copy), one on each X chromosome. Over 500 different variants (genetic errors) have been identified in the OTC gene. Some studies have established a predictability model for specific OTC variants. This demonstrates a relationship between specific mutations, severity and clinical outcomes for OTCD patients. For more information, check out the Resources page.
It is estimated that about 1/14,000 to 1/77,000 people are impacted by OTC Deficiency worldwide. This is anywhere from 100,000 to half a million people around the world. It is hard to know the exact number because this condition often goes misdiagnosed and it is not captured in newborn screening testing in Ontario. It is offered as part of newborn screening in some States across the US.
Genetic Variants have been identified in the OTC gene
OTCD is the most common Urea Cycle Disorder, making up more than half of all UCD cases
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