PubMed · 14095235
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L GARCIADADONI. 1963-10-03. [UREMIC COMA].. https://pubmed.ncbi.nlm.nih.gov/14095235/
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Ornithine transcarbamylase (OTC) deficiency is an X-linked disorder and the most common inherited cause of hyperammonemia. Clinical manifestations are more severe in hemizygous males who often present in neonatal period. Heterozygous females may be asymptomatic until juvenile or adulthood. Fluctuating concentration of ammonia, glutamine and other excitotoxic amino acids result in a chronic or episodically recurring encephalopathy. The authors report a heterozygous female with OTC deficiency who presented with recurrent encephalopathy.
Ammonia, normally produced from catabolism of amino acids, is a deadly neurotoxin. As such, the concentration of free ammonia in the blood is very tightly regulated and is exceeded by two orders of magnitude by its physiologic derivative, urea. The normal capacity for urea production far exceeds the rate of free ammonia production by protein catabolism under normal circumstances, such that any increase in free blood ammonia concentration is a reflection of either biochemical or pharmacologic impairment of urea cycle function or fairly extensive hepatic damage. Clinical signs of hyperammonemia occur at concentrations > 60 micromol/L and include anorexia, irritability, lethargy, vomiting, somnolence, disorientation, asterixis, cerebral edema, coma, and death; appearance of these findings is generally proportional to free ammonia concentration, is progressive, and is independent of the primary etiology. Causes of hyperammonemia include genetic defects in the urea cycle ("primary") or organic acidemias ("secondary"), as well as genetic or acquired disorders resulting in significant hepatic dysfunction. Thus, because of the neurotoxic implications of hyperammonemia and the typical absence of other specific laboratory abnormalities, appearance of the clinical signs should trigger an emergent search for elevated blood ammonia concentration.
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