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.


METHODS
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.


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.
Park
J P
JP
Department of Pathology, Dartmouth-Hitchcock Medical Center, Lebanon, NH 03756, USA.
Brothman
A R
AR
Butler
M G
MG
Cooley
L D
LD
Dewald
G W
GW
Lundquist
K F
KF
Palmer
C G
CG
Patil
S R
SR
Rao
K W
KW
Saikevych
I A
IA
Schneider
N R
NR
Vance
G H
GH
D000328:Adult; D005260:Female; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D007621:Karyotyping; D009030:Mosaicism / Q000235:genetics*; D014424:Turner Syndrome / Q000235:genetics* / Q000473:pathology*; D014960:X Chromosome