Dynamic mosaicism involving an unstable supernumerary der(22) chromosome in cat eye syndrome

Abstract

We have studied a girl, her sister and her mother who had a supernumerary marker chromosome in mosaicism. The marker was studied by cytogenetic methods and non-isotopic in situ hybridization with the single D22S9 DNA probe which maps to 22q11. The supernumerary chromosome was derived from a chromosome 22 and it did not present the same morphology in all the cells. At least 5 distinct types of the marker chromosome were detected and some of them were probably derived from each other (dynamic mosaicism). The proposita had an MCA pattern consistent with mild cat eye syndrome, while her sister and her mother had some of the manifestations described in this syndrome. A specific correlation could be established between phenotype and karyotype.

Small supernumerary marker chromosomes (sSMC) in humans

“…Starke et al, 2003b, case 13), (2) a minute chromosome of the same chromosomal region in a sub-population of the cells (e.g. Urioste et al, 1994, case III-2), or (3) the formation of different variants and a highly complex mosaic arising from minute or ring chromosomes being degraded in a subset of the studied cells (e.g. Starke et al, 2003b, case 33), (4) the disappearance of sSMC at least in the most frequently studied tissue, the peripheral blood (Fitzgerald and Mercer, 1980).…”

FISH characterisation of dynamic mosaicism involving an inv dup(15) in a patient with mental retardation

“…Unfortunately, we are unable to look at the tissue distribution of the SMCs instability in other cell lineages, as we were unable to obtain a skin biopsy from our patient and a second tissue was not tested in the family described by Urioste et al [1994]. It is also surprising why this form of mosaicism seems to be so rare and not more frequently observed, especially with chromosome 15, where hotspots for recombination anking the PWACR have been observed [Kuwano et al, 1992;Huang et al, 1997].…”

“…As far as we are aware, this has only been previously described in one case of a patient with``cateye'' syndrome where ®ve different and morphologically distinct SMCs, all derived from chromosome 22, were seen in a proposita and her less severely affected mother and sister [Urioste et al, 1994]. The severity of the phenotype correlated with the frequency with which the SMCs were observed in the patient's lymphocytes.…”

“…So far as we know, the only reported case to date was by Urioste et al [1994], who described a patient with a phenotype consistent with mild``cateye'' syndrome. On examination of lymphocyte cultures, 62 of 102 cells had an SMC which was found to be derived from chromosome 22 using FISH with the probe D22S9 which maps to 22q11.…”

FISH of supernumerary marker chromosomes (SMCs) identifies six diagnostically relevant intervals on chromosome 22q and a novel type of bisatellited SMC(22)

“…The mental outcome can be normal; 44% of patients showed normal or borderline normal mental development, 48% mild or moderate MR, and 7% severe MR. 13,14 Based on the variable appearance and genetic content of the CES SMCs, a relation between the different forms of the CES SMCs and the variations in the severity of the CES phenotype was considered, but no correlation was found. 14,15 The majority of SMCs (22) reported to date contain two copies of the CECR rendering the patients tetrasomic for this region; a few patients display one copy making them trisomic. 2,16,17 We performed FISH studies on nine unrelated patients with an SMC comprising one or two extra copies of the CECR.…”