Be warned, readers, I am about to drop some science on you. Feel free to skip this post if chemistry isn’t your thing. On the other hand, I do refer to the classic television show “I Love Lucy,” so there may in fact be something for everyone.
Disclaimer: No information in this post, or in this entire blog, in fact, should be used to diagnose or treat a urea cycle disorder. I am not an expert, and my explanations are based on my best understanding from my discussions with Jacob’s doctors and my own research.
the ammonia molecule
That being said, here goes. When we digest protein, we produce nitrogen as a waste product in the form of ammonia. Our liver removes the ammonia from our blood through a chemical process called the urea cycle. A normal urea cycle converts the ammonia into urea, which harmlessly leaves our body when we pee. There are several enzymes involved in making this happen. Jacob’s condition, citrullinemia, is also known as ASS, or argininosuccinate synthase deficiency, because his body does not effectively produce that particular enzyme. Need a visual? Did you ever see the I Love Lucy episode with the chocolates? Think of Lucy as that enzyme. Some chocolates (ammonia) get wrapped (processed into urea), but mostly they stack up and his body doesn’t know what to do with them. Left untreated, his urea cycle would be unable to keep up with the demands placed on it, and his ammonia levels would become dangerous.
While Jacob was in the hospital, he underwent tests every 8-12 hours to determine his ammonia levels. The test requires a venous blood draw that must be immediately placed on ice and processed within an hour of the blood draw at most, but ideally within 20 minutes. This was the hardest part of his stay in the NICU. Jacob’s blood clots quickly, so it would often take several tries for the nurses to get enough blood from his little veins. Occasionally, the lab would not process the blood fast enough, and he would have to go through the whole thing again. It took several weeks after his discharge for the bruises to fade. Once properly processed, the lab results would tell us how well Jacob was tolerating the amount of protein he was taking in via formula and breast milk. Normal ammonia levels vary by age, and different hospitals often have different acceptable results. According to WebMD, normal results for children range from 40-80 micrograms per deciliter (μg/dL). Jacob’s highest level, at 4 days old, was in the 70s. After he was admitted to the NICU and started on his special diet, his levels hovered in the high 30s to low 40s. Though we can’t be sure, these numbers encourage us that he never sustained any brain damage due to high ammonia levels. Ammonia levels over 200 μg/dL for more than 2 hours would put a child at serious risk for brain damage.
Managing Jacob’s protein intake will be our primary way of preventing high ammonia levels. We will have to be especially vigilant when he gets sick (cold, flu, etc). When we are sick, our bodies actually break down existing lean tissue. Our liver then processes that protein the same way it does when we drink a glass of milk. So, when Jacob is sick, there will be additional demands on his liver from his body’s natural response to illness. Jacob’s “sick day formula” has almost no protein in order to compensate, but he is still likely to end up in the hospital if the illness becomes prolonged.