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The following points highlight the five major metabolic disorders in urea cycle. The disorders are: 1. Hyperammonemia Type I 2. Hyperammonemia Type II 3. Citrullinemia 4. Arginosuccinic Aciduria 5. Hyperargininemia.
Urea Cycle: Metabolic Disorder # 1. Hyperammonemia Type I:
a. This is a familial disorder.
b. This occurs due to the deficiency of the enzyme carbamoyl phosphate synthetase.
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c. It produces the symptoms of ammonia toxicity.
Urea Cycle: Metabolic Disorder # 2. Hyperammonemia Type II:
a. Patients suffer from a deficiency of ornithine transcarbamoylase.
b. The clinical finding is an elevation of glutamine in the blood, cerebrospinal fluid and urine.
c. There is enhanced synthesis of glutamine by the glutamine synthetase reaction for which tissue level of ammonia is increased.
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d. The mothers show hyperammonemia and intolerance to high protein diet.
Urea Cycle: Metabolic Disorder # 3. Citrullinemia:
a. Complete absence of arginosuccinate synthetase activity produces this condition.
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b. Large quantities of citrulline are excreted in the urine and plasma and CSF citrulline levels are elevated.
c. Citrulline and arginosuccinate act as alternative carriers of waste nitrogen, since they contain nitrogen used for urea synthesis.
d. Arginine feeding accelerates citrulline excretion in these patients.
e. Benzoate feeding diverts ammonium nitrogen to hippuric acid via glycine.
Urea Cycle: Metabolic Disorder # 4. Arginosuccinic Aciduria:
a. Arginosuccinic aciduria is caused due to the absence of arginosuccinase activity. This enzyme is also absent from brain, liver, kidney and erythrocytes of patients with this disease.
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b. The disease is characterized by the increased level of arginosuccinic acid in blood, CSF, and urine.
c. It is frequently associated with the occurrence of tufted hair.
d. The disease always appears by age 2 and generally terminates fatally early in life.
e. It needs measurement of erythrocyte arginosuccinase activity for confirmative diagnosis.
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f. Arginine and benzoate feedings accelerate nitrogen excretion in these patients.
Urea Cycle: Metabolic Disorder # 5. Hyperargininemia:
a. Low erythrocyte level of arginase causes this disease.
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b. The urinary amino acid pattern resembles that of lysine cystinuria.
c. A low protein diet results in the lowering of plasma ammonia and abolishes urinary lysine cystinuria.
