Intrachromosomal triplication of distal 7p.

Abstract

A female infant who died at 2 years of age with growth and psychomotor retardation, wide anterior fontanelle, downward slanting palpebral fissures, large, simple ears, joint dislocation/contractures, recurrent infections, and severe pulmonary hypertension was found to have a de novo 7p+ chromosome. The G banding pattern was suggestive of a triplication of 7p2l.3 and 7p22; results of fluorescence in situ hybridisation studies using a chromosome 7 specific library, a subtelomeric 7p repeat (109A6), and yeast artificial chromosome clones 786gl and 850al, which are respectively associated with the (CA)n repeat markers D7S517 and D7S513, supported the cytogenetic interpretation and showed that the middle repeat was inverted. The patient's phenotype was consistent with the 7p duplication syndrome, allowing for the effects of the extra burden introduced by the partial tetrasomy. The present rearrangement may have resulted from several meiotic events occurring at the four chromatid stage, namely an unequal crossover or interhomologue translocation with points of exchange at 7p22 and 7plS followed by the inverted insertion of 7p2l.3-p2l.2 at the former breakpoint junction; moreover, a further duplication including D7S517 within the terminal 7p22 band is also required.(7Med Genet 1998;35:78-80)

Tandem triplication of chromosome 13q14 with inverted interstitial segment in a 4 year old girl

“…20 21 It is interesting to note that in several cases an unequal distance between two FISH signals (the proximal and the middle versus the middle and the distal) indicated that either the middle segment was inverted or, less likely, the middle segment was in normal orientation, but the proximal and distal segments were inverted,1 4 6 probably, according to the illustrations, the cases of Rauch et al 2 and Harrison et al 3 and the present report. In the other patients, no special attention was paid to the issue of direct versus inverted triplication.…”

“…This type of triplication has so far been reported for the following chromosomal segments: 2q11.2-q21,7 2q37,25p14-p15.33,3 7p21.2-p21.3,49p13-p22,5 10q26,6 13q14 (present report), and 15q11-q13 120 21 It is interesting to note that in several cases an unequal distance between two FISH signals (the proximal and the middle versus the middle and the distal) indicated that either the middle segment was inverted or, less likely, the middle segment was in normal orientation, but the proximal and distal segments were inverted,1 4 6 probably, according to the illustrations, the cases of Rauch et al 2 and Harrison et al 3 and the present report.…”

“…More recent studies to determine more accurately the exact amount of duplication with cosmid FISH probes have, in a few instances, shown that some of the presumed duplications were in fact triplications of smaller segments 1-7. In some of these patients, unequal distances between the FISH signals showed that the middle segment of the tandemly arrayed three segments was in the opposite orientation to the two flanking segments,1 3 4 thus providing clues to the possible mechanism of formation.…”

Characterisation of interstitial duplications and triplications of chromosome 15q11–q13

“…In all patients tested, the triplication was maternal in origin. Proposed mechanisms include U-type exchanges among three chromatids (Wang et al 1999) or through several different meiotic events occurring sequentially (Rivera et al 1998). Alternatively, triplications may be formed via illegitimate recombination between a normal chromosome 15 and an unstable large SMC(15) intermediary (Schinzel et al 1994).…”

Tetrasomy 9p due to an intrachromosomal triplication of 9p13-p22

“…Only a few cases of intrachromosomal triplication have been described [Berry et al, 1990;Holowinsky et al, 1993;Schinzel et al, 1994;Cassidy et al, 1996;Rauch et al, 1996; Devriendt, 1998, personal communication;Harrison et al, 1998;Long et al, 1998;Rivera et al, 1998] These involved chromosomes 2, 5, 7, 10, 15, and 16. We describe the clinical manifestations of our patient, compare them with other cases of tetrasomy 9p, and discuss probable mechanisms causing this chromosomal aberration.…”