Mayo Test Catalog, (Sorted By Test Name) - Mayo Medical ...

FXIST
88538
XHIM
82964
males most likely do not have a clone of cells with an abnormal complement of sex chromosomes, but the
presence of an abnormal clone of cells is not completely ruled out.
Reference Values:
XX in females; XY in males
Clinical References: Babovic-Vuksanovic D, Michels VV, Law ME, et al: Guidelines for buccal
smear collection in breast-fed infants. Am J Med Genet 1999;84:357-360
X-Inactivation (XIST), Xq13.2 Deletion, FISH
Clinical Information: Turner syndrome is characterized by ovarian hypofunction, short stature,
loose skin folds at the back of the neck, and cubitus valgus (elbow deformity) and results from complete
or partial monosomy of the X chromosome. Phenotypic expression of Turner syndrome patients is
largely dependent on the patientâ€s karyotype and identification of sex chromosomes mosaicism
plays a key role in clinical management. In mosaicism, 2 or more populations of cells with different
karyotypes are present (eg, 45,X/46,XX). Additionally, mental retardation is more common in patients
with a small ring chromosome derived from an X chromosome with a deletion of the X-inactivation
center (XIST) at Xq13.2. Fluorescence in situ hybridization (FISH) studies are highly specific and do
not exclude other chromosome abnormalities, we recommend that patients suspected of having Turner
syndrome also have conventional chromosome studies (CMS/8696 Chromosomes Analysis, for
Congenital Disorders, Blood) performed to rule out other chromosome abnormalities or translocations.
Useful For: As an aid in the diagnosis of Turner syndrome, in conjunction with CMS/8696
Chromosomes Analysis, For Congenital Disorders, Blood To characterize marker chromosomes that are
derived from the X chromosome
Interpretation: Any individual with a normal signal pattern (signal on each normal X homolog) in
each metaphase is considered negative for a deletion in the region tested by this probe. Any patient with
a FISH signal pattern indicating loss of the XIST critical region will be reported as having a deletion of
the regions by this probe.
Reference Values:
An interpretive report will be provided.
Clinical References: 1. Van Dyke DL, Wiktor A, Palmer CG, et al: Ullrich-Turner syndrome with
a small ring X chromosome and presence of mental retardation. Am J Med Genet 1992;43:996-1005 2.
Sybert VP, McCauley E: Turnerâ€s syndrome. N Engl J Med 2004;351:1227-1238
X-Linked Hyper IgM Syndrome, Blood
Clinical Information: CD154 (CD40 ligand: CD40L) is required for the interaction of T cells and
B cells as part of the normal adaptive immune response. Activation of T cells leads to the expression of
the CD40L molecule on the cell surface. CD40L binds the CD40 receptor that is always present on B
cells, monocytes, and macrophages (regardless of environmental conditions). This interaction of CD40L
with CD40 is important in B-cell proliferation, differentiation, and class-switch recombination (isotype
class-switching). Patients with X-linked hyper-IgM (XL-HIGM) syndrome have defective CD40L
expression on their activated helper CD4 T cells.(1,2) This leads to defective B-cell responses and the
absence of immunoglobulin class-switching. These features are typified in these patients by a profound
reduction or absence of isotype class-switched memory B cells (CD19+CD27+IgM-IgD-) with low or
absent secreted IgG and IgA, and normal or elevated serum IgM levels.(1,2) Due to the impairment of
T-cell function and macrophage activation, XL-HIGM patients are particularly prone to opportunistic
infections with Pneumocystis jiroveci, Cryptosporidium, and Toxoplasma gondii.(1) To date, more than
100 unique mutations of CD40LG, the gene that encodes CD40L, have been described, affecting the
intracellular, transmembrane and, more commonly, extracellular domain containing the CD40-binding
region. A defect in surface expression of CD40L on activated CD4 T cells can be demonstrated using an
anti-CD40L antibody and flow cytometry.(3,4) Since certain CD40LG mutations can maintain surface
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