A 4-fold increase in renal type II arginase has been demonstrated in an affected patient. Death from arginase deficiency appears to be relatively infrequent, but again, reliable statistics are not available. As an autosomal recessive trait, the disease affects each gender equally. As an inherited disorder, the age of onset typically is during the neonatal period. Due to its atypical form of presentation, the disease may be easily missed in the neonatal period and only recognized in later infancy or early childhood.
Some cases likely go undiagnosed with clinical symptomatology attributed to cerebral palsy.
The history of delayed development, protein intolerance, and spasticity should direct the clinician's attention to arginase deficiency. Although a catastrophic neonatal presentation is very uncommon in arginase deficiency, dietary protein intolerance is an early sign and should not be overlooked. The typical presentation is that of an older infant whose development is delayed, has occasional episodes of vomiting and somnolence without apparent cause, is protein intolerant, and shows evidence of long-tract neurological impairment. A common clinical feature in this disorder is spasticity, and it is likely that the disease is underdiagnosed because many patients are categorized as cerebral palsy patients without effort to diagnose this disease. The multiple primary causes of hyperammonemia, specifically those due to urea cycle enzyme deficiencies, are somewhat variable in presentation, diagnostic features, and treatment.