Cytosine and orotic acid in urine of immunodeficient children

The authors describe procedures for determining cytosine and orotic acid in urine. They determine cytosine by cation-exchange analysis with either HCl or a pH 5.2 buffer as eluent. Orotic acid is first separated by an anion-exchange separative procedure; after lyophilization, the product is subjected to 'high-pressure' liquid chromatography for further separation and detection. Three children with severe combined immunodeficiency had increased levels of cytosine in the urine (23-160 mmol/mol creatinine); one child with severe combined immunodeficiency and two children with other immunodeficiencies had normal urinary levels (<2 mmol/mol creatinine). Orotic acid excretion in urine was normal (1-5 mmol/mol creatinine) in all of the immunodeficient children. The possible significance of the increased cytosine excretion in the three children with severe combined immunodeficiency is discussed.