Further dicentric X isochromosomes and deletions, and a new structure i(X)(pter to q2102 to pter).

Abstract

SUMMARY A new dicentric X isochromosome i(X)(pter-*q2102-*pter) of similar size to a normal X is described in a girl with gonadal dysgenesis. In this non-mosaic case with an X short arm duplication, most of the stigmata associated with Turner's syndrome were absent. This structure was compared with that of six i(Xq) and three del(X (1977), Niebuhr and Skovby (1977), and Verlinskaya and Mashkova (1977). Of considerable interest and significance as to their genesis is the proportion of isochromosomes that prove to be dicentric. Centromeric misdivision was proposed as the mechanism of origin of isochromosomes by Darlington (1939), who also predicted the existence of dicentric isochromosomes which he termed isodicentrics (Darlington and Wylie, 1953). This concept was developed in human material (de la Chapelle et al., 1966) and possible infracentromeric breakpoints and dicentric-producing long or short arm breaks were described. Therman et al. (1974) showed that dicentric X structures such as end-toend X fusions fitted the model of Gl chromatid break with G2 sister chromatid reunion, producing a dicentric chromatid at the following anaphase. A second alternative proposed by Therman et al. was a G2 chromatid exchange after homologous pairing of the adjacent type, analogous to the U type exchanges within a bivalent observed in plants (Jones, 1969). Though the existence of Xp isochromosomes has been doubted after the reinterpretation of one as an Xq deletion (de la , it has been suggested (Howell

De novo isodicentric X chromosome: 46,X,idic(X)(q24), and summary of literature

“…Our review indicated that mosaic cases, 45,X/46,X,idic(Xq), present with more Turner syndrome stigmata than do non‐mosaic cases, as expected. The patient reported by Daniel et al 1979 had widely spaced nipples, high narrow palate and cubitus valgus which may be attributed to one of three hypotheses: (1) the break point close to the XIST gene may have interfered with X inactivation, (2) two centromeres too close to each other may interfere with inactivation and replication of the X chromosome, and (3) more genetic material is deleted. The suggestion from Barnabei et al 1983 and Fryns et al [1983] that phenotypic findings and symptoms in isodicentric X patients are caused by loss of the chromosome fragment, that is, partial Xq deletion, supports the third hypothesis.…”

“…Therefore, most reported cases are ascertained at later ages due to amenorrhea and reproductive issues. [Daniel et al, 1979; Gaal et al, 1981; Barnabei et al, 1983; Fryns et al, 1983; Therman et al, 1986; Ponzio et al, 1987; Lebbar et al, 2002]. Patients with an isodicentric X chromosome with Xq deletion are deleted/monosomic for genetic material distal to the Xq breakpoint and duplicated/trisomic for the Xp arm [Barnabei et al, 1983].…”

X‐chromosomes attached by their long arm: case report and replication kinetics of the rearranged X‐chromosome

“…Dicentric X-chromosomes formed by long arm-to-long arm fusion are considered as one of the most informative structural abnormalities of the X-chromosome for testing this hypothesis, especially when the breakpoints are located near the juxtacentromeric region. Four cases showing breakpoints in the proximal region of Xq have been reported in female patients with gonadal dysgenesis and/or some of the Turner's stigmata (de la Chapelle et al 1978, Daniel et al 1979, Yu et al 1980, Matteiet al 1981. DNA replication sequence studies were performed in only two of these reports (de IaChapelleet al 1978,Yuetal.…”

“…Since the introduction of banding techniques, X-to-X-chromosome translocations formed by long arm-to-long arm fusion have been reported in only 15 patients. Recent reviews on this subject were presented by Daniel et al (1979), MatteietaL(1981)andYuetal. (1981.In these patients there are great differences in the location of breakage-reunion points in Xq, varying from proximally q21 to distally q28.…”

Replication and inactivation of and isodicentric X: presence of an inactive centromere influences the replication patterns

“…Since the introduction of banding techniques, idic(X) with long arm breakpoints of formation have been reported in only 18 patients (Daniel et al 1979, Mattei et al 1981, Yu et al 1980. These types of chromosome abnormalities are interesting for their phenotypic consequences, which may be minor, and for their relevance to the study of DNA replication of the X-chromosome.…”