Small Supernumerary Marker Chromosomes (sSMC) in Patients with a 45,X/46,X,+mar Karyotype – 17 New Cases and a Review of the Literature

Abstract

Small supernumerary marker chromosomes (sSMC) can appear in a numerically normal ‘basic karyotype’, but also in a numerically abnormal one like a Turner syndrome karyotype (= sSMC^T). Here we present 17 new cases with such a mos 45,X/46,X,+mar karyotype. Moreover we reviewed all 512 cytogenetically similar cases available from the literature and supply for the first time data on occurrence, shapes and subgroups of this rare cytogenetic entity. sSMC^T are very rare in the common population (1:100,000) – however, they can be observed with a 45- and even 60-times higher frequency in infertile and (develop)mentally retarded patients, respectively. Even though sSMC^T derive from one of the gonosomes in >99% of the cases, there are also exceptional reports on sSMC^T derived from one of the autosomes. The majority of sSMC^T(X) form ring chromosomes, while most sSMC^T(Y) are inverted duplicated/isodicentric chromosomes. Although >500 sSMC^T are reported, a detailed characterization of the chromosomal breakpoints is only given for a minority. Thus, more cases with detailed (molecular) cytogenetic marker chromosome characterization are needed to provide information on formation and effects of an sSMC^T.

Dynamic mosaicism manifesting as loss, gain and rearrangement of an isodicentric Y chromosome in a male child with growth retardation and abnormal external genitalia

“…Since the idic(Y)(q11.23) cell line is more common and monocentric Y chromosomes are reported to be more stable than dicentric ones (Haaf and Schmid, 1990), 'initial' chromosome aberration is probably idic(Y)(q11.23), whereas i(Y)(p10) seems to be produced through the rearrangement of idic(Y)(q11.23). Taking into account previous reports (Haaf and Schmid, 1990;Stankiewicz et al, 2001;Codina-Pascual et al, 2004;DesGroseilliers et al, 2006;Liehr et al, 2007), one can suggest that instability of idic(Y)(q11.23) is the main reason for its loss and gain. Together this is evidence for post-zygotic origin of all cell lines apart from idic(Y)(q11.23) and suggests that the index case represents an example of dynamic mosaicism.…”

“…Recently, Liehr et al (2007) have shown that the majority of cases of marker chromosomes derived from the Y chromosome are 45,X/46,X,der(Y) mosaics. It has been long suggested that mosaicism is produced by post-zygotic instability of rearranged Y chromosomes, especially in cases of dicentric chromosomes.…”

Disorders of sex development: advances in genetic diagnosis and challenges in management

“…The majority of these sSMC are derived from sex chromosomes, generally either sSMC(X) ring or sSMC(Y), inverted duplication/isodicentric chromosomes. 29 However, their exact chromosome break points are rarely defined. Future more precise characterization of sSMC(X) or sSMC(Y) using molecular cytogenetic techniques may provide greater understanding of their cause and effect.…”

A unique mosaic Turner syndrome patient with androgen receptor gene derived marker chromosome

“…This concurs with the observations of the patient presented here with the absence of ovaries detected by the USG examination. Cole et al [1994] and Liehr et al [2007] reported MR for these Turner syndrome variant patients. Badeschi and colleagues [2008] described a male with severe MR with duplication on the X chromosome Xq12 to Xq12.1, which contains the OPHN1 gene.…”