Sorted By Test Name - Mayo Medical Laboratories

ARST
8778
Interpretation: Normally, humans consume 5 to 25 mcg of arsenic each day as part of their normal
diet; therefore, normal urine arsenic output is 200 mcg/g, after which it will decline to 1,000 mcg/g indicates significant exposure. The highest value
observed at Mayo Clinic was 450,000 mcg/L in a patient with severe symptoms of gastrointestinal
distress, shallow breathing with classic "garlic breath," intermittent seizure activity, cardiac arrhythmias,
and later onset of peripheral neuropathy.
Reference Values:
0-35 mcg/g Creatinine
Reference values apply to all ages.
Clinical References: 1. Fillol CC, Dor F, Labat L, et al: Urinary arsenic concentrations and
speciation in residents living in an area with naturally contaminated soils. Sci Total Environ 2010 Feb
1;408(5):1190-1194 2. Caldwell K, Jones R, Verdon C, et al: Levels of urinary total and speciated arsenic
in the US population: National Health and Nutrition Examination Survey 2003-2004. J Expo Sci Environ
Epidemiol 2009 Jan;19(1):59-68
Arylsulfatase A, Fibroblasts
Clinical Information: Metachromatic leukodystrophy (MLD) is a lysosomal storage disorder caused
by a deficiency of the arylsulfatase A enzyme, which leads to the accumulation of galactosyl sulfatide
(cerebroside sulfate) in the white matter of the central nervous system and in the peripheral nervous
system. Galactosyl sulfatide and, to a smaller extent, lactosyl sulfatide, also accumulate within the kidney,
gallbladder, and other visceral organs, and are excreted in excessive amounts in the urine. The 3 clinical
forms of MLD are late-infantile, juvenile, and adult, depending on age of onset. All result in progressive
neurologic changes and leukodystrophy demonstrated on magnetic resonance imaging. Late-infantile
MLD is the most common (50%-60% of cases) and typically presents between 1 to 2 years of age with
hypotonia, clumsiness, diminished reflexes, and slurred speech. Progressive neurodegeneration occurs
with a typical disease course of 3 to 10 years. Juvenile MLD (20%-30% of cases) is characterized by
onset between 4 to 14 years. Typical presenting features are behavior problems, declining school
performance, clumsiness, and slurred speech. Neurodegeneration occurs at a somewhat slower and more
variable rate than the late-infantile form. Adult MLD (15%-20% of cases) has an onset after puberty and
can be as late as the fourth or fifth decade. Presenting features are often behavior and personality changes,
including psychiatric symptoms; clumsiness, neurologic symptoms, and seizures are also common. The
disease course has variable progression and may occur over 2 to 3 decades. The disease prevalence is
estimated to be approximately 1 in 100,000. MLD is an autosomal recessive disorder and is caused by
mutations in the ARSA gene coding for the arylsulfatase A enzyme. This disorder is distinct from
conditions caused by deficiencies of arylsulfatase B (Maroteaux-Lamy disease) and arylsulfatase C
(steroid sulfatase deficiency). Extremely low arylsulfatase A levels have been found in some clinically
normal parents and other relatives of MLD patients. These individuals do not have metachromatic
deposits in peripheral nerve tissues, and their urine content of sulfatide is normal. Individuals with this
"pseudodeficiency" have been recognized with increasing frequency among patients with other apparently
unrelated neurologic conditions as well as among the general population. This has been associated with a
fairly common polymorphism in the arylsulfatase A gene, which leads to low expression of the enzyme
(5%-20% of normal). These patients can be difficult to differentiate from actual MLD patients. Additional
studies, such as molecular genetic testing of ARSA, urinary excretion of sulfatides (CTSA/81979
Ceramide Trihexoside/Sulfatide Accumulation in Urine Sediment, Urine) and/or histological analysis for
metachromatic lipid deposits in nervous system tissue are recommended to confirm a diagnosis. Current
treatment options for MLD are usually focused on managing disease manifestations such as seizures.
Bone marrow transplantation remains controversial, and the effectiveness of enzyme replacement therapy
may be limited due to difficulties crossing the blood-brain barrier. Other treatments under ongoing
investigation include hematopoietic stem cell transplantation and fetal umbilical cord blood
transplantation.
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