Jesse Gelsinger was the first person publicly identified as having died in a clinical trial for gene therapy. Gelsinger suffered from ornithine transcarbamylase deficiency, an X-linked genetic disease of the liver, the symptoms of which include an inability to metabolize ammonia – a byproduct of protein breakdown. The disease is usually fatal at birth, but Gelsinger had a milder form of the disease, in which the ornithine transcarbamylase gene is mutated in only part of the patient's cells, a condition known as somatic mosaicism. As his deficiency was partial, Gelsinger managed to survive on a restricted diet and special medications.