Diagnosis is based on the clinical examination and on laboratory findings showing leukopenia, severe lymphopenia with low CD3, CD4, and CD8 counts and variable B cell function and immunoglobulin levels. Neutropenia has also been reported. Hallmark diagnostic markers of PNP deficiency include hypouricemia, complete or near complete absence of PNP activity in red blood cell lysate and increased<unk>  or blood levels of inosine, guanosine and their deoxy forms. Diagnosis is confirmed by genetic screening of PNP. Differential diagnosis Differential diagnosis includes aplastic anemias, SCID, severe combined immunodeficiency due to adenosine deaminase deficiency, ataxia-telangiectasia, and viral meningoencephalitis.
Purine nucleoside phosphorylase deficiency
Dihydropyrimidine dehydrogenase deficiency
Adenine phosphoribosyltransferase deficiency
Dihydrofolate reductase deficiency
Mevalonate kinase deficiency
Guanidinoacetate methyltransferase deficiency
Methylenetetrahydrofolate reductase deficiency
Glutathione synthetase deficiency