Sorted By Test Name - Mayo Medical Laboratories

XAN
80313
soluble chimeric CD40-uIg antibody, substantiating a diagnosis of XL-HIGM. Females who are carriers
for this disease will show a typical bimodal pattern of CD40L expression, with 50% of the T cells lacking
any CD40L expression. In the case of aberrant protein function, a similar profile will be obtained with the
CD40-uIg antibody. CD69 is a marker for T-cell activation and serves as a positive control; in the absence
of induced CD69 expression on T cells, the presence of XL-HIGM cannot be assessed.
Reference Values:
Present
Clinical References: 1. Etzioni A, Ochs HD: The hyper IgM syndrome-an evolving story. Pediatr
Res 2004:56(4):519-525 2. Durandy A, Peron S, Fischer A: Hyper-IgM syndromes. Curr Opin Rheumatol
2006;18(4):369-376 3. Lee WI, Torgerson TR, Schumacher MJ, et al: Molecular analysis of a large cohort
of patients with the hyper immunoglobulin M (IgM) syndrome. Blood 2005;105(5):1881-1890 4. Seyama
K, Nonoyama S, Gangsaas I, et al: Mutations of the CD40 ligand gene and its effect on CD40 ligand
expression in patients with X-linked hyper IgM syndrome. Blood 1998;92:2421-2434
Xanthine and Hypoxanthine, Urine
Clinical Information: Xanthine and hypoxanthine are the precursors of uric acid, the end product of
purine metabolism. Two inborn errors of metabolism are characterized by elevated excretion of xanthine
and hypoxanthine. Isolated xanthine dehydrogenase (XDH, xanthine oxidase) deficiency: patients with
isolated XDH deficiency may remain asymptomatic, but nephrolithiasis due to the insolubility of
xanthine, may occur at any age. Some patients also develop a myopathy with crystalline xanthine deposits
in muscle. Combined deficiency of SDH and the related enzyme sulfite oxidase (SO): combined XDH/SO
deficiency is also characterized by nephrolithiasis, but more prominently by the symptoms of SO
deficiency (isolated SO deficiency also occurs) which include neonatal seizures, myoclonus, lens
dislocation, and severe mental retardation. This form of xanthinuria is caused by molybdenum cofactor
deficiency, which is required for the activity of both oxidases. Elevations of xanthine and hypoxanthine
and abnormally low levels of uric acid are found in both disorders, while in patients with XDH/SO
deficiency sulfites and sulfur-containing metabolites (S-sulfocysteine, thiosulfate, taurine) also
accumulate. Allopurinol, a xanthine oxidase inhibitor that prevents conversion of xanthine to uric acid, is
used to treat hyperuricemia.
Useful For: Diagnosis and confirmation of xanthinuria Evaluation of low serum or urine uric acids
Evaluation of allopurinol treatment in hyperuricemic disorders (eg, Lesch-Nyhan syndrome)
Interpretation: Abnormal concentrations of xanthine and hypoxanthine will be reported along with an
interpretation. The interpretation of an abnormal metabolite pattern will include an overview of the results
and of their significance, a correlation to available clinical information, possible differential diagnoses,
recommendations for additional biochemical testing and confirmatory studies (enzyme assay, molecular
analysis), name and phone number of contacts who may provide these studies at the Mayo Clinic or
elsewhere, and a number for one of the laboratory directors if the referring physician has additional
questions. Increased urinary xanthine and hypoxanthine with low urinary uric acid are characteristic of
xanthine oxidase deficiency. Increased urinary excretion of xanthine, hypoxanthine, and uric acid are
indicative of hyperuricemia disorders treated with allopurinol.
Reference Values:
HYPOXANTHINE
20-100 mcmol/24 hours
XANTHINE
20-60 mcmol/24 hours
Clinical References: Raivio KO, Saksela M, Lapatto R: Xanthine oxidoreductases-Role in human
pathophysiology and in hereditary xanthinuria. In The Metabolic and Molecular Bases of Inherited
Disease. 8th edition. Edited by CR Scriver, AL Beaudet, WS Sly, et al. New York, McGraw-Hill Book
Company, 2001, pp 2639-2652
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