1/6. Origins of accessory small ring marker chromosomes derived from chromosome 1.Three patients with accessory small ring chromosomes derived from chromosome 1 are presented together with additional clinical details and cytogenetic analyses of a previously reported patient. cytogenetic analysis was undertaken by FISH using a reverse painting probe generated from one of the patients by microdissection of the r(1) chromosome and with a BAC923C6 which maps to 1p12. Results indicated that patients with r(1) chromosomes consisting of 1q12 heterochromatin and short arm pericentric euchromatin which extends to at least the BAC923C6 were associated with a normal or mild phenotype. patients with abnormal phenotypes possessed two types of rings. One patient had evidence for contiguous pericentric short arm euchromatin which extended from the centromere to beyond the BAC923C6. Two patients showed molecular cytogenetic results which were compatible with non-contiguous chromosome 1 euchromatin. The diversity of origin of r(1)s will hamper attempts to define phenotype/genotype relationships.- - - - - - - - - - ranking = 1keywords = accessory (Clic here for more details about this article) |
2/6. Multiple small accessory marker chromosomes from different centromeric origin in a moderately mentally retarded male.The occurrence of more than two small accessory chromosomes (SACs) in a single individual is extremely rare. Here, we characterize six SACs found in the cells of two different tissues of a moderately mentally retarded male. microdissection combined with regular FISH demonstrates that the SACs are ring chromosomes derived from the centromeres of different chromosomes. The SACs are often associated with the centromeres of other chromosomes. Immunofluorescence with an anti-CENP-C antibody demonstrates that the SACs contain an active centromere. A possible mechanism by which the SACs originated and their clinical relevance are discussed.- - - - - - - - - - ranking = 1keywords = accessory (Clic here for more details about this article) |
3/6. Multiple "marker" chromosomes: a novel cytogenetic finding in a patient with mental retardation and congenital anomalies.A patient with mental retardation and clinical manifestations suggestive of noonan syndrome was found to have in her peripheral lymphocytes multiple small accessory marker chromosomes, varying in number from one to five per cell and in size from about half the size of the q arm of a G group chromosome to less than a centromere. Occasionally, in the more elongated markers, a G-positive or a C-positive band could be identified, or the marker had the appearance of a ring. The origin and significance of these marker chromosomes are discussed.- - - - - - - - - - ranking = 0.2keywords = accessory (Clic here for more details about this article) |
4/6. Mechanisms of small ring formation suggested by the molecular characterization of two small accessory ring chromosomes derived from chromosome 4.Molecular cloning of a microdissected small accessary ring chromosome 4 from a moderately retarded and dysmorphic patient has been performed to identify the origin of the ring chromosome. FISH was performed with cosmids identified with the cloned, microdissected products and with other markers from chromosome 4. The present study clearly demonstrates that the small ring in this patient originates from three discontinuous regions of chromosome 4: 4p13 or 14, the centromere, and 4q31. It is suggested that the origin of the ring chromosome is a ring involving the entire chromosome 4, which has then been involved in breakage and fusion events, as a consequence of dna replication generating interlocked rings. A second severely retarded and dysmorphic patient also had a small accessary ring derived from chromosome 4. FISH studies of this ring are consistent with an origin from a contiguous region including the centromere to band 4q12. It is apparent that there are at least two mechanisms for the formation of small ring chromosomes. This adds a further complication in any attempt to ascertain common phenotypes between patients known to have morphologically similar markers derived from the same chromosome.- - - - - - - - - - ranking = 0.8keywords = accessory (Clic here for more details about this article) |
5/6. Molecular cytogenetic characterisation of a small ring x chromosome in a Turner patient and in a male patient with congenital abnormalities: role of X inactivation.The association of small accessory marker chromosomes in man with specific abnormalities has been difficult to define owing to variations in the chromosome origin and the size of the markers. In a patient with typical Turner phenotype and a 45,X/46,X, mar karyotype the marker was shown to be a small portion of the long arm of the x chromosome which included the centromere and XIST, a candidate gene for the X inactivation centre. Therefore the lack of any additional abnormalities was attributed to inactivation of the portion of the x chromosome in the marker. In a patient with a 47,XY, mar karyotype the mar was a small ring x chromosome which did not contain the XIST gene. For both markers the short arm breakpoints were localised between UBE1 and DXS423E. The congenital abnormalities of the male patient were attributed to the lack of X inactivation of the small ring and therefore disomic expression of normal genes possessed by the marker.- - - - - - - - - - ranking = 0.2keywords = accessory (Clic here for more details about this article) |
6/6. An accessory marker derived from chromosome 20 and its co-existence with a mosaic trisomy 20 cell line.We report a 16-month-old boy with delayed psychomotor development, dysmorphic features, and failure to thrive. He had a mosaic karyotype detected prenatally: mos 46,XY/47,XY, r(20)/47,XY, 20. After birth, the abnormal cell lines were confirmed in a number of tissues. The small ring chromosome was identified using fluorescence in situ hybridization as derived from chromosome 20. We compared our patient with previously reported cases of mosaic trisomy 20 detected prenatally and associated with an abnormal phenotype. In an attempt to characterize an r(20) syndrome, we also compared our case with two similar reports in the literature.- - - - - - - - - - ranking = 0.8keywords = accessory (Clic here for more details about this article) |