Immune thrombocytopenic purpura (ITP), also known as idiopathic thrombocytopenic purpura or immune thrombocytopenia, is a type of thrombocytopenic purpura defined as an isolated low platelet count with a normal bone marrow in the absence of other causes of low platelets. It causes a characteristic red or purple bruise-like rash and an increased tendency to bleed. Two distinct clinical syndromes manifest as an acute condition in children and a chronic condition in adults. The acute form often follows an infection and spontaneously resolves within two months. Chronic immune thrombocytopenia persists longer than six months with a specific cause being unknown. ITP is an autoimmune disease with antibodies detectable against several platelet surface structures. ITP is diagnosed by identifying a low platelet count on a complete blood count (a common blood test). However, since the diagnosis depends on the exclusion of other causes of a low platelet count, additional investigations (such as a bone marrow biopsy) may be necessary in some cases. In mild cases, only careful observation may be required but very low counts or significant bleeding may prompt treatment with corticosteroids, intravenous immunoglobulin, anti-D immunoglobulin, or immunosuppressive medications. Refractory ITP (not responsive to conventional treatment or constant relapsing after splenectomy) requires treatment to reduce the risk of clinically significant bleeding. Platelet transfusions may be used in severe cases with very low platelet counts in people who are bleeding. Sometimes the body may compensate by making abnormally large platelets.
Ornithine translocase deficiency, also called hyperornithinemia-hyperammonemia-homocitrullinuria (HHH) syndrome, is a rare autosomal recessive urea cycle disorder affecting the enzyme ornithine translocase, which causes ammonia to accumulate in the blood, a condition called hyperammonemia. Ammonia, which is formed when proteins are broken down in the body, is toxic if the levels become too high. The nervous system is especially sensitive to the effects of excess ammonia. Pathophysiology
Mutations in SLC25A15 cause ornithine translocase deficiency. Ornithine translocase deficiency belongs to a class of metabolic disorders referred to as urea cycle disorders. The urea cycle is a sequence of reactions that occurs in liver cells. This cycle processes excess nitrogen, generated when protein is used by the body, to make a compound called urea that is excreted by the kidneys. The SLC25A15 gene provides instructions for making a protein called a mitochondrial ornithine transporter. This protein is needed to move a molecule called ornithine within the mitochondria (the energy-producing centers in cells). Specifically, this protein transports ornithine across the inner membrane of mitochondria to the region called the mitochondrial matrix, where it participates in the urea cycle. Mutations in the SLC25A15 gene result in a mitochondrial ornithine transporter that is unstable or the wrong shape, and which cannot bring ornithine to the mitochondrial matrix.