Urocanic aciduria is an autosomal recessive metabolic disorder caused by a deficiency of the enzyme urocanase. It is a secondary disorder of histidine metabolism. Symptoms and signs
Urocanic aciduria is thought to be relatively benign. Although aggressive behavior and mental retardation have been reported with the disorder, no definitive neurometabolic connection has yet been established. Genetics
Urocanic aciduria has an autosomal recessive inheritance pattern, which means the defective gene is located on an autosome, and two copies of the gene – one copy inherited from each parent – are required in order to be born with the disorder. The parents of an individual with an autosomal recessive disorder both carry one copy of the defective gene, but are usually not affected by the disorder. Pathophysiology
The amino acid histidine, when catalyzed by the enzyme histidase, forms urocanic acid. Disruptions in this pathway, caused by a deficiency of histidase, is the underlying cause of histidinemia. This results in reduced levels of skin and serum urocanic acid, the primary indicator of insufficient histidase activity.In urocanic aciduria, increased urocanic acid in the urine indicates a deficiency of the enzyme urocanase.With normal to only slightly elevated levels of histidine present in the liver during urocanic aciduria, the only true metabolic indicator of the disorder can be found in the urine. Diagnosis
Treatment
See also
Inborn errors of metabolism
Imidazole
Aromatic amino acids
Recessive disorders

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Periodic breathing is clusters of breaths separated by intervals of apnea or near-apnea. As opposed to normal breathing which is usually regular, periodic breathing is defined as three or more episodes of central apnea lasting at least 4 seconds, separated by no more than 30 seconds of normal breathing.Periodic breathing was originally thought to arise from serious neurologic or cardiovascular disease and therefore to carry a poor outlook. It is now known that periodic breathing also tends to occur during sleep, it can occur in healthy persons, and the apnea in periodic breathing is usually central sleep apnea rather than obstructive sleep apnea. Periodic breathing during sleep occurs typically in adult patients with congestive heart failure. Periodic breathing is also a normal variation of breathing found in premature and full term infants. It occurs when the infant has pauses in breathing for no more than 10 seconds at a time followed by a series of rapid, shallow breaths. Then the breathing returns to normal without any stimulation or intervention. These pauses in breathing may be accompanied by minor oxygen desaturation and bradycardia. It usually occurs when the infant is sleeping deeply, but may occur with light sleep or even when awake. Studies have shown that 78% of healthy full-term infants experience episodes of periodic breathing in the first two weeks of life, which typically resolves in the first six months of life. == References ==