Citrullinemia
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What is citrullinemia?Citrullinemia is an inherited disorder that causes ammonia and other toxic substances to accumulate in the blood. Two forms of citrullinemia have been described; they have different signs and symptoms and are caused by mutations in different genes. Type I citrullinemia (also known as classic citrullinemia) usually becomes evident in the first few days of life. Affected infants typically appear normal at birth, but as ammonia builds up in the body they experience a progressive lack of energy (lethargy), poor feeding, vomiting, seizures, and loss of consciousness. These medical problems are life-threatening in many cases. Less commonly, a milder form of type I citrullinemia can develop later in childhood or adulthood. This later-onset form is associated with intense headaches, partial loss of vision, problems with balance and muscle coordination (ataxia), and lethargy. Some people with gene mutations that cause type I citrullinemia never experience signs and symptoms of the disorder. Type II citrullinemia chiefly affects the nervous system, causing confusion, restlessness, memory loss, abnormal behaviors (such as aggression, irritability, and hyperactivity), seizures, and coma. In some cases, the signs and symptoms of this disorder appear during adulthood (adult-onset). These signs and symptoms can be life-threatening, and are known to be triggered by certain medications, infections, surgery, and alcohol intake in people with adult-onset type II citrullinemia. The features of adult-onset type II citrullinemia may also develop in people who as infants had a liver disorder called neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD). This liver condition is also known as neonatal-onset type II citrullinemia. NICCD blocks the flow of bile (a digestive fluid produced by the liver) and prevents the body from processing certain nutrients properly. In many cases, the signs and symptoms of NICCD resolve within a year. Years or even decades later, however, some of these people develop the characteristic features of adult-onset type II citrullinemia. How common is citrullinemia?Type I citrullinemia is the most common form of the disorder, affecting about 1 in 57,000 people worldwide. Type II citrullinemia is found primarily in the Japanese population, where it occurs in an estimated 1 in 100,000 to 230,000 individuals. Type II also has been reported in other populations, including people from East Asia and the Middle East. What genes are related to citrullinemia?Mutations in the ASS1 and SLC25A13 genes cause citrullinemia. Citrullinemia belongs to a class of genetic diseases called urea cycle disorders. The urea cycle is a sequence of chemical reactions that takes place in liver cells. These reactions process excess nitrogen that is generated when protein is used by the body. The excess nitrogen is used to make a compound called urea, which is excreted in urine. Mutations in the ASS1 gene cause type I citrullinemia. This gene provides instructions for making an enzyme, argininosuccinate synthetase 1, that is responsible for one step of the urea cycle. Mutations in the ASS1 gene reduce the activity of the enzyme, which disrupts the urea cycle and prevents the body from processing nitrogen effectively. Excess nitrogen (in the form of ammonia) and other byproducts of the urea cycle accumulate in the bloodstream. Ammonia is particularly toxic to the nervous system, which helps explain the neurologic symptoms (such as lethargy, seizures, and ataxia) that are often seen in type I citrullinemia. Mutations in the SLC25A13 gene are responsible for adult-onset type II citrullinemia and NICCD. This gene provides instructions for making a protein called citrin. Within cells, citrin helps transport molecules used in the production and breakdown of simple sugars, the production of proteins, and the urea cycle. Molecules transported by citrin are also involved in making nucleotides, which are the building blocks of DNA and its chemical cousin, RNA. Mutations in the SLC25A13 gene typically prevent cells from making any functional citrin, which inhibits the urea cycle and disrupts the production of proteins and nucleotides. The resulting buildup of ammonia and other toxic substances leads to the signs and symptoms of adult-onset type II citrullinemia. A lack of citrin also leads to the features of NICCD, although ammonia does not build up in the bloodstream of infants with this condition. How do people inherit citrullinemia?This condition is inherited in an autosomal recessive pattern, which means two copies of the gene in each cell are altered. Most often, the parents of an individual with an autosomal recessive disorder each carry one copy of the altered gene but do not show signs and symptoms of the disorder.
Source: National Institutes of Health
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Scientists at Shinshu University, Department of Internal Medicine target spinal cord disease
2007 MAR 27 -- New investigation results, "An autopsy case with adult onset type II citrullinemia showing myelopathy," are detailed in a study published in Journal of the Neurological Sciences. "Hepatic myelopathy is a rare neurological complication in patients with chronic liver failure and most patients who suffered from this disorder were demonstrated to have portal-systemic shunt. A 31-year-old man who was diagnosed as having adult-onset type II citrullinemia (CTLN2) and had a six-year history of recurrent hepatic encephalopathy showed progressive spastic paraparesis with no involvement of sensation and sphincter function," scientists writing in the Journal of the Neurological Sciences report. "Examinations of cerebrospinal fluid and spinal MRI were normal. He suddenly died of acute exacerbation of hepatic encephalopathy with severe brain edema. The pathology of the spinal cord disclosed a localized degeneration of both lateral columns, the lesion being more remarkable in the lower segments of the cord. These clinical and pathological findings of hepatic myelopathy have not been noted in the many patients with CTLN2 previously reported, and our patient is unique in developing hepatic myelopathy without porto-caval shunting," wrote K. Tazawa and colleagues, Shinshu University, Department of Internal Medicine. The researchers concluded: "Thus, repeated attacks of encephalopathy with hyperammonemia might secondarily have induced the myelopathy in this patient." Tazawa and colleagues published their study in the Journal of the Neurological Sciences (An autopsy case with adult onset type II citrullinemia showing myelopathy. Journal of the Neurological Sciences, 2007;253(1-2):77-80). Additional information can be obtained by contacting K. Tazawa, Shinshu University School of Medicine 3-1-1 Asahi, Dept. of Internal Medicine (Neurology), Matsumoto 390-8621, Japan. The publisher of the Journal of the Neurological Sciences can be contacted at: Elsevier Science BV, PO Box 211, 1000 AE Amsterdam, Netherlands. Keywords: Japan, Matsumoto, Spinal Cord Disease. This article was prepared by Life Science Weekly editors from staff and other reports. Copyright 2007, Life Science Weekly via NewsRx.com.
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