Citrullinemia
Citrullinemia | |
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Other names | Citrullinuria |
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L-Citrulline | |
Specialty | Medical genetics |
Symptoms | Extreme sleepiness, no appetite, irritability, vomiting, muscle weakness, breathing problems. |
Citrullinemiais anautosomal recessiveurea cycle disorderthat causesammoniaand other toxic substances to accumulate in theblood.[1]
Two forms of citrullinemia have been described, both having different signs and symptoms, and are caused by mutations in different genes. Citrullinemia belongs to a class of genetic diseases calledurea cycledisorders. The urea cycle is a sequence of chemical reactions taking place in theliver.These reactions process excessnitrogen,generated whenproteinis used for energy by the body, to make urea, which is excreted by thekidneys.
Diagnosis
[edit]Type I
[edit]Type I citrullinemia (Online Mendelian Inheritance in Man(OMIM):215700,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 develop a lack of energy (lethargy), poor feeding,vomiting,seizures,and loss of consciousness. These medical problems can be life-threatening in many cases. A milder form of type I citrullinemia is less common in childhood or adulthood. Some people with gene mutations that cause type I citrullinemia never experience signs and symptoms of the disorder. Diagnosis of citrullinemia type I is elevated citrulline in the blood.[citation needed]
Type I citrullinemia is the most common form of the disorder, affecting about one in 57,000 births worldwide.Mutationsin theASSgenecause type I citrullinemia. Theenzymemade by this gene,argininosuccinate synthetase(EC6.3.4.5), is responsible for one step of the urea cycle. Mutations in theASSgene 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, leading to the characteristic features of type I citrullinemia.[citation needed]
Type II
[edit]The symptoms of type II citrullinemia (Online Mendelian Inheritance in Man(OMIM):605814andOnline Mendelian Inheritance in Man(OMIM):603471) usually appear during adulthood and mainly affect thecentral nervous system.[2]Characteristic features include confusion, abnormal behaviors (such as aggression, irritability, and hyperactivity), seizures, and coma. Diagnosis of type II includes measuring decreased citrulline level and an increase in ammonium ions. These symptoms can be life-threatening, and are known to be triggered by certain medications, infections, andalcoholintake in people with this type.[citation needed]
Type II citrullinemia may also develop in people who had aliverdisorder calledneonatal cholestasisduring infancy. This condition blocks the flow ofbileand prevents the body from processing certain nutrients properly. In many cases, the symptoms resolve within a year. Years or even decades later, however, some of these people develop the characteristic features of adult type II citrullinemia.[citation needed]
Type II citrullinemia is primarily found in theJapanesepopulation, where it occurs in an estimated one in 100,000 to 230,000 individuals. Type II has also been reported in people fromEast AsianandMiddle Easternpopulations. Mutations in theSLC25A13gene are responsible for type II citrullinemia. This gene makes a protein calledcitrin,which normally shuttles certain molecules in and out ofmitochondria.These molecules are essential for the urea cycle and are also involved in making proteins andnucleotides.Mutations inSLC25A13typically prevent the production of 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 symptoms of type II citrullinemia. Researchers have found many infants with neonatal intrahepatic cholestasis have the same mutations in theSLC25A13gene as adults with type II citrullinemia.
Treatment
[edit]There are multiple treatment methods. Low protein diets are intended to minimize production of ammonia. Arginine, sodium benzoate and sodium phenylacetate help to remove ammonia from the blood. Dialysis may be used to remove ammonia from the blood when it reaches critical levels. In some cases, liver transplant has been successful.[3]
See also
[edit]References
[edit]- ^Freedberg, et al. (2003).Fitzpatrick's Dermatology in General Medicine.(6th ed.). McGraw-Hill.ISBN0-07-138076-0.
- ^"Citrullinemia type II".Genetic and Rare Diseases Information Center.
- ^Yazaki M et al. First two cases of adult-onset type II citrullinemia successfully treated by deceased-donor liver transplantation in Japan
Further reading
[edit]- GeneReviews/NCBI/NIH/UW entry on Argininosuccinate Synthetase Deficiency; ASS Deficiency; Argininosuccinic Acid Synthetase Deficiency; CTLN1; Citrullinemia, Classic
- GeneReviews/NIH/UW entry on Citrin deficiency and Citrullinemia Type II
- The U.S. National Library of Medicine
- Citrin Foundation
- Citrin deficiency patient support