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F9INH
83103
lysosomes of both peripheral and visceral tissues. Severity and onset of symptoms are dependent on the
residual alpha-Gal A activity. Males with 1% alpha-Gal A activity may present with a variant form of Fabry
disease. The renal variant generally has onset of symptoms in the third decade. The most prominent
feature in this form is renal insufficiency and, ultimately, end-stage renal disease. Individuals with the
renal variant may or may not have other symptoms of classic Fabry disease. Individuals with the cardiac
variant are often asymptomatic until they present with cardiac findings such as cardiomyopathy or mitral
insufficiency later in life. The cardiac variant is not associated with renal failure. Female carriers of Fabry
disease can have a clinical presentation ranging from asymptomatic to severely affected. Measurement of
alpha-Gal A activity is not generally useful for identifying carriers of Fabry disease, as many of these
individuals have normal levels of alpha-Gal A. Mutations in the GLA gene result in deficiency of
alpha-Gal A. Most of the mutations identified to date are family-specific. Full sequencing of the GLA
gene identifies over 98% of the sequence variants in the coding region and splice junctions. Full gene
sequencing of the GLA gene is available by ordering FABMS/88264 Fabry Disease Full Gene Analysis.
Site-specific testing (this test) for mutations that have already been identified in an affected patient is
useful for confirming a suspected diagnosis in a family member. It is also useful for determining whether
at-risk individuals are carriers of the disease and, subsequently, at risk for having a child with Fabry
disease The following algorithms are available in Special Instructions: -Fabry Disease: Newborn
Screen-Positive Follow-up -Fabry Disease Testing Algorithm
Useful For: Diagnostic confirmation of Fabry disease when a familial mutation has been previously
identified Carrier screening of at-risk individuals when a mutation in the GLA gene has been identified in
an affected family member Prenatal testing when 2 familial mutations have been previously identified in
an affected family member
Interpretation: All detected alterations will be evaluated according to American College of Medical
Genetics and Genomics (ACMG) recommendations.(1) Variants will be classified based on known,
predicted, or possible pathogenicity and reported with interpretive comments detailing their potential or
known significance.
Reference Values:
An interpretive report will be provided.
Clinical References: 1. Richards CS, Bale S, Bellissimo DB, et al: ACMG recommendations for
standards for interpretation and reporting of sequence variations: Revisions 2007. Genet Med
2008:10(4):294-300 2. Germain DP: Fabry disease. Orphanet J Rare Dis. 2010 Nov 22;5:30 3. Wang RY,
Lelis A, Mirocha J, Wilcox WR: Heterozygous Fabry women are not just carriers, but have a significant
burden of disease and impaired quality of life. Genet Med 2007 Jan;9(1):34-35 4. Hwu WL, Chien YH,
Lee NC, et al: Newborn screening for Fabry disease in Taiwan reveals a high incidence of the later-onset
GLA mutation c.936+919G->A (IVS4+919G->A). Hum Mutat 2009;30:1397-1405
Factor IX Inhibitor Evaluation
Clinical Information: Factor IX inhibitors arise in patients with severe hemophilia B after factor IX
transfusion. Patients with factor IX inhibitors may also develop anaphylactic reactions in response to
factor IX infusions. Acquired factor IX inhibitors, occurring in previously healthy people, are exceedingly
rare.
Useful For: Detection and titering of coagulation inhibitor to the specific factor requested, primarily
factor IX in patients with hemophilia B
Interpretation: Normally, there is no inhibitor (ie, negative result). If the screening assays indicate the
presence of an inhibitor, it will be quantitated and reported in Bethesda (or equivalent) units.
Reference Values:
FACTOR IX ACTIVITY ASSAY
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