A supernumerary marker chromosome 15 tetrasomic for the Prader-Willi/Angelman syndrome critical region in a patient with a severe phenotype

• Published in: Journal of medical genetics 2003-07, Vol.40 (7), p.e84-84
• Main Authors: Maggouta, F, Roberts, S E, Dennis, N R, Veltman, M W M, Crolla, J A
• Format: Article
• Language: English
• Subjects: Age; Aneuploidy; Angelman syndrome; Angelman Syndrome - genetics; breakpoint; Cell division; Child; Chromosome Inversion; Chromosomes; Chromosomes, Human, Pair 15 - genetics; Electronic Letter; FISH; fluorescence in situ hybridisation; Genotype & phenotype; Humans; In Situ Hybridization, Fluorescence; Male; Microsatellite Repeats; Patients; Phenotype; Prader-Willi syndrome; Prader-Willi Syndrome - genetics; Prader-Willi/Angelman syndrome; Prader-Willi/Angelman syndrome critical region; PWACR; PWS; SMC; supernumerary chromosome; supernumerary marker chromosome; tetrasomy
• ISSN: 0022-2593; 1468-6244; 1468-6244
• DOI: 10.1136/jmg.40.7.e84

Small SMC(15)s do not contain the PWACR, can be either paternal or maternal in origin, and seem to have no phenotypic effect. 6, 9 Large SMC(15)s usually contain two extra copies of the q11-13 region, are exclusively derived from the maternal chromosome 15 homologues, and are associated with various abnormal phenotypes, including mental or growth retardation, seizures, behavioural problems, and dysmorphisms. 6, 10, 11 Mapping studies have shown that the small SMCs share the same two common proximal breakpoints, BP1 and BP2, 12 as standard PWS/AS deletions, whereas the large SMCs have at least three breakpoints, one similar to the distal breakpoint (BP3) of the PWS/AS deletions. 13, 14 Other rare variants of the inv dup(15) that do not follow the common pattern have also been described. The coexistence of SMC(15) with other chromosome 15 derived rearrangements has also been reported including an interstitial duplication 16 and an interstitial triplication. 17 The presence of two extra marker chromosomes 15 has been reported in all cells of a woman with repeated abortions 18 and in 47% of the cells of a severely retarded patient. 6 A further patient with mental retardation presented initially with three morphologically distinct markers. 19 The SMC(15) was subject to dynamic mosaicism with the marker, thought to be unstable during cell division, resulting in morphologically different forms of the SMC.