Sorted By Test Name - Mayo Medical Laboratories

SLO
81595
are specific for lupus erythematosus (LE) and occur in approximately 30% of LE patients. The levels of
Sm antibodies remain relatively constant over time in patients with LE and are usually found in patients
that also have RNP antibodies.(1,2) Sm is 1 of 4 autoantigens commonly referred to as extractable nuclear
antigens (ENAs). The other ENAs are RNP, SS-A/Ro, and SS-B/La. Each ENA is composed of 1 or more
proteins associated with small nuclear RNA species (snRNP) ranging in size from 80 to approximately
350 nucleotides. Antibodies to ENAs are common in patients with connective tissue diseases (systemic
rheumatic diseases) including LE, mixed connective tissue disease, Sjogren's syndrome, scleroderma
(systemic sclerosis), and polymyositis/dermatomyositis. See Connective Tissue Disease Cascade (CTDC)
in Special Instructions and Optimized Laboratory Testing for Connective Tissue Diseases in Primary
Care: The Mayo Connective Tissue Diseases Cascade in Publications.
Useful For: Evaluating patients with signs and symptoms of a connective tissue disease in whom the
test for antinuclear antibodies is positive
Interpretation: A positive result for anti-Sm antibodies is consistent with a diagnosis of lupus
erythematosus.
Reference Values:
or =1.0 U (positive)
Reference values apply to all ages.
Clinical References: 1. Homburger H, Larsen S: Detection of specific antibodies. In Clinical
Immunology: Principles and Practice. 1st edition. Edited by R Rich, T Fleisher, B Schwartz, et al. St.
Louis, Mosby-Year Book, 1996, pp 2096-2109 2. Kotzin B, West S: Systemic lupus erythematosus. In
Clinical Immunology Principles and Practice. 2nd edition. Edited by R Rich, T Fleisher, W Shearer, et al.
St. Louis, Mosby-Year Book, 2001, pp 60.1-60.24
Smith-Lemli-Opitz Screen, Plasma
Clinical Information: Cholesterol plays an essential role in many cellular and developmental
processes. In addition to its role as a membrane lipid, it is the precursor to numerous molecules that play
an important role in cell growth and differentiation, protein glycosylation, and signaling pathways. The
biosynthesis of cholesterol and its subsequent conversion to other essential compounds is complex,
involving a number of intermediates and enzymes. In addition to an accumulation of specific
intermediates, defects in this pathway may result in a deficiency of cholesterol. Clinical findings common
to cholesterol biosynthesis disorders include congenital skeletal malformations, dysmorphic facial
features, psychomotor retardation, and failure to thrive. Smith-Lemli-Opitz syndrome (SLOS) is an
autosomal recessive disorder caused by mutations in the DHCR7 gene leading to a deficiency of the
7-dehydrocholesterol reductase enzyme. It is characterized by markedly increased plasma concentrations
of 7-dehydrocholesterol (7-DHC) and 8-DHC levels. Clinical features can include microcephaly, growth
retardation, developmental delay, dysmorphic facial features, cleft palate, limb abnormalities (especially
2-3 syndactyly of the toes and postaxial polydactyly), and heart and kidney malformations. Severity of
SLOS ranges from severe to mild. Some mildly affected individuals may only have 2 to 3 toe syndactyly
and mild cognitive impairment. The reported incidence is between 1:10,000 and 1:60,000, but it may be
more prevalent due to underdiagnosis of mildly affected individuals. Other disorders of cholesterol
biosynthesis, including desmosterolosis (desmosterol reductase deficiency) and sitosterolemia, may
present with similar manifestations. These disorders can be detected biochemically by performing a
quantitative profile of plasma sterols (STER/82079 Sterols, Plasma).
Useful For: Diagnosis of Smith-Lemli-Opitz syndrome (7-dehydrocholesterol reductase deficiency)
Interpretation: Elevated plasma concentrations of 7-dehydrocholesterol (7-DHC) and 8-DHC are
highly suggestive of a biochemical diagnosis of Smith-Lemli-Opitz (SLO). Mild elevations of these
cholesterol precursors can be detected in patients with hypercholesterolemia and patients treated with
haloperidol. However, the 7-DHC to cholesterol ratio is only elevated in SLO patients.
Reference Values:
Negative (reported as positive or negative)
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