Citrullinemia

Citrullinemia

_L-Citrulline
Classification and external resources
Specialty	endocrinology
ICD-10	E72.2
ICD-9-CM	270.6
OMIM	215700 605814 603471
DiseasesDB	29676 34048
eMedicine	ped/406
MeSH	C10.228.140.163.100.175

Citrullinemia is an autosomal recessive urea cycle disorder that causes ammonia and other toxic substances to accumulate in the blood.^[1] Since the substances also accumulate in the urine, the disorder can also be called citrullinuria.

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 called urea cycle disorders. The urea cycle is a sequence of chemical reactions taking place in the liver. These reactions process excess nitrogen, generated when protein is used for energy by the body, to make urea, which is excreted by the kidneys.

Diagnosis

Type I

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.

Type I citrullinemia is the most common form of the disorder, affecting about one in 57,000 births worldwide. Mutations in the ASS gene cause type I citrullinemia. The enzyme made by this gene, argininosuccinate synthetase (EC 6.3.4.5), is responsible for one step of the urea cycle. Mutations in the ASS 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, leading to the characteristic features of type I citrullinemia.

Type II

The symptoms of type II citrullinemia (Online Mendelian Inheritance in Man (OMIM) 605814 and Online Mendelian Inheritance in Man (OMIM) 603471) usually appear during adulthood and mainly affect the central nervous system. Characteristic features include confusion, abnormal behaviors (such as aggression, irritability, and hyperactivity), seizures, and coma. These symptoms can be life-threatening, and are known to be triggered by certain medications, infections, and alcohol intake in people with this type.

Type II citrullinemia may also develop in people who had a liver disorder called neonatal cholestasis during infancy. This condition blocks the flow of bile and 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.

Type II citrullinemia is primarily found in the Japanese population, where it occurs in an estimated one in 100,000 to 230,000 individuals. Type II has also been reported in people from East Asian and Middle Eastern populations. Mutations in the SLC25A13 gene are responsible for type II citrullinemia. This gene makes a protein called citrin, which normally shuttles certain molecules in and out of mitochondria. These molecules are essential for the urea cycle and are also involved in making proteins and nucleotides. Mutations in SLC25A13 typically 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 the SLC25A13 gene as adults with type II citrullinemia.

Treatment

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.^[2]

References

↑ Freedberg, et al. (2003). Fitzpatrick's Dermatology in General Medicine. (6th ed.). McGraw-Hill. ISBN 0-07-138076-0.
↑ Yazaki M et al. First two cases of adult-onset type II citrullinemia successfully treated by deceased-donor liver transplantation in Japan

External links

Inborn error of amino acid metabolism (E70–E72, 270)

K→acetyl-CoA

Lysine/straight chain	Glutaric acidemia type 1 type 2 Hyperlysinemia Pipecolic acidemia Saccharopinuria
Leucine	3-hydroxy-3-methylglutaryl-CoA lyase deficiency 3-Methylcrotonyl-CoA carboxylase deficiency 3-Methylglutaconic aciduria 1 Isovaleric acidemia Maple syrup urine disease
Tryptophan	Hypertryptophanemia

G→pyruvate→citrate

Glycine	D-Glyceric acidemia Glutathione synthetase deficiency Sarcosinemia Glycine→Creatine: GAMT deficiency Glycine encephalopathy

G→glutamate→
α-ketoglutarate

Histidine	Carnosinemia Histidinemia Urocanic aciduria
Proline	Hyperprolinemia Prolidase deficiency
Glutamate/glutamine	SSADHD

G→propionyl-CoA→
succinyl-CoA

Valine	Hypervalinemia Isobutyryl-CoA dehydrogenase deficiency Maple syrup urine disease
Isoleucine	2-Methylbutyryl-CoA dehydrogenase deficiency Beta-ketothiolase deficiency Maple syrup urine disease
Methionine	Cystathioninuria Homocystinuria Hypermethioninemia
General BC/OA	Methylmalonic acidemia Methylmalonyl-CoA mutase deficiency Propionic acidemia

G→fumarate

Phenylalanine/tyrosine

Phenylketonuria	6-Pyruvoyltetrahydropterin synthase deficiency Tetrahydrobiopterin deficiency
Tyrosinemia	Alkaptonuria/Ochronosis Type I tyrosinemia Type II tyrosinemia Type III tyrosinemia/Hawkinsinuria
Tyrosine→Melanin	Albinism: Ocular albinism (1) Oculocutaneous albinism (Hermansky–Pudlak syndrome) Waardenburg syndrome
Tyrosine→Norepinephrine	Dopamine beta hydroxylase deficiency reverse: Brunner syndrome

G→oxaloacetate

Urea cycle/Hyperammonemia (arginine aspartate)	Argininemia Argininosuccinic aciduria Carbamoyl phosphate synthetase I deficiency Citrullinemia N-Acetylglutamate synthase deficiency Ornithine transcarbamylase deficiency/translocase deficiency

Transport/
IE of RTT

Other

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