Extensive analysis of mosaicism in a case of Turner syndrome: the experience of 287 cytogenetic laboratories. College of American Pathologists/American College of Medical Genetics Cytogenetics Resource Committee.

OBJECTIVE: To assemble and interpret karyotype data provided as part of the College of American Pathologists/American College of Medical Genetics Cytogenetics Proficiency Testing Program. DATA SOURCES, EXTRACTION, AND SYNTHESIS: The Cytogenetics Resource Committee requested data on all cells analyzed in a 1994 whole-blood specimen challenge. In that study, 287 participating laboratories analyzed a total of 14297 cells derived from a sample drawn from an adult donor with Turner syndrome. This individual had previously been found to have mosaicism, including cell lines with X structural anomalies along with monosomy X, making this an excellent challenge for a multicenter cytogenetic survey. RESULTS AND CONCLUSIONS: Analysis of the data from this extensive study revealed mosaicism of up to 10 different sex chromosome complements involving the X chromosome with and without a small ring X or a derivative X chromosome. In the routine cytogenetic analysis performed by the participating laboratories, cell lines observed, in decreasing order of prevalence, included 45,X (n = 8357 cells), 46,X,r(X) (n = 3597), 46,X,der(X)t(X;X) (n = 2237), 46,XX (n = 93), 47,X,r(X),r(X) (n = 5), 47,X,der (X)t(X;X),der(X)t(X;X) (n = 3), 47,XX,r(X) (n = 2), and one observation each of 47,XX,der(X)t(X;X), 47,X,der(X)t (X;X),r(X), and 47,XXX. Our molecular cytogenetic data, as well as detailed analysis of G-banded chromosomes, suggest the nomenclature for these 2 abnormal X chromosomes as r(X)(p11.3q21.3) and der(X)t(X;X)(p11.3;q21.3), and we discuss models for the concomitant formation of these 2 entities. Both the degree of analysis and the extensive mosaicism that was discovered in this study are exceptional, and similar reported cases as well as possible mechanisms for the observed X chromosome instability are reviewed.

Acanthosis nigricans.

Acanthosis nigricans is a lesion affecting localized areas of the skin in persons with obesity and/or hyperinsulinemia. Roughening of the skin correlates with histological papilomatosis and the apparent darkening is due to hyperkeratosis. Biochemical mechanisms for developing this hyperplastic lesion are unclear, but likely involve local cutaneous growth factors. Cross sectional surveys of unselected populations have demonstrated that young children have low prevalences of obesity and acanthosis nigricans, but the prevalences of both increase with increasing age until plateaus are reached after the age of ten. Nearly 40% of Native American teenagers have acanthosis nigricans, whereas about 13% of African American, 6% of Hispanic, and less than 1% of white, non-Hispanic children aged 10-19 have clinically apparent acanthosis nigricans. We conclude that the presence of this skin lesion is a clinical surrogate of laboratory-documented hyperinsulinemia. Acanthosis nigricans identifies a subgroup within an ethnic group who have the highest insulin concentration, the most severe insulin resistance, and thus the highest risk for the development of type 2 diabetes.

Impaired metabolic function and signaling defects in phagocytic cells in glycogen storage disease type 1b.

Patients with glycogen storage disease (GSD) type 1b (1b), in contrast to patients with GSD type 1a (1a), are susceptible to recurrent bacterial infections suggesting an impairment in their immune system. In this study, phagocytic cell (neutrophil and monocyte) respiratory burst activity, as measured by superoxide anion generation, oxygen consumption, and hexose monophosphate shunt activity, was markedly reduced in both neutrophils and monocytes from GSD 1b patients as compared with either GSD 1a patients or healthy adult control cells. Degranulation, unlike respiratory burst activity, was not significantly different in neutrophils from GSD 1b patients as compared with controls. Both neutrophils and monocytes from GSD 1b patients showed decreased ability to elevate cytosolic calcium in response to the chemotactic peptide f-Met-Leu-Phe. In addition, calcium mobilization in response to ionomycin was also attenuated suggesting decreased calcium stores. Thus, reduced phagocytic cell function in GSD 1b is associated with diminished calcium mobilization and defective calcium stores. Defective calcium signaling is associated with a selective defect in respiratory burst activity but not degranulation.

Activation of the human neutrophil by calcium-mobilizing ligands. II. Correlation of calcium, diacyl glycerol, and phosphatidic acid generation with superoxide anion generation.

Calcium and protein kinase C (Ca2+/phospholipid-dependent enzyme) have been proposed to act as signals in triggering superoxide anion (O2-) generation by neutrophils. We have probed the adequacy and necessity of calcium and diacylglycerol (DG), activators of protein kinase C, in eliciting O2- generation and degranulation. Activation of neutrophils by the ligand 10(-7) M fMet-Leu-Phe triggered elevation of cytosolic calcium (fura-2) and a rapid, biphasic increase in labeled DG in [14C]glycerol and [3H]arachidonate prelabeled cells. Buffering of the fMet-Leu-Phe-induced elevation of cytosolic calcium with MAPTAM (a cell permeant EGTA analogue) inhibited O2- generation by 90% and degranulation by 50%, concordant with a role of calcium in signaling. However, buffering the increase in calcium also decreased DG. Since phosphatidylinositol 4,5-bisphosphate breakdown in response to fMet-Leu-Phe was not inhibited and phosphatidic acid levels were enhanced in MAPTAM pretreated cells, the removal of calcium may enhance further DG metabolism. Thus, a requirement for calcium could not be differentiated from a requirement for DG, and the profound inhibition of O2- generation in the presence of MAPTAM may reflect removal of DG. Four stimuli, fMet-Leu-Phe, 10(-7) M leukotriene B4, 100 micrograms/ml concanavalin A, and 200 nM ionomycin elevated cytosolic calcium and triggered release of specific granules, but only fMet-Leu-Phe and concanavalin A triggered substantial O2- generation. Nevertheless, all four stimuli significantly increased labeled DG. Therefore, elevated DG and elevated calcium may be necessary but do not appear adequate to elicit O2- generation. Only fMet-Leu-Phe and concanavalin A triggered generation of phosphatidic acid (PA) together with DG. Correlation of O2- generation with PA may reflect a requirement for PA per se or for a specific pool of DG that can be further metabolized to PA.