Preferential derivation of abnormal human G-group-like chromosomes from chromosome 15

Abstract

The marked binding of antibodies specific for 5-methylcytidine to the short arm of chromosome 15 distinguishes this chromosome from the other human acrocentrics. This method has been used to study over 60 individuals including 12 who did not have Down's syndrome, but who did have an extra G-group sized acrocentric chromosome. In six cases the extra chromosome did not show intensive binding of anti-5-methylcytidine. In the other six cases, the extra chromosome contained a 5-methylcytidine rich band at each end indicating that both ends were derived from chromosome 15 and contained centromeric heterochromatin normally present on the short arm of chromosome 15. The duplication of short arm material in the abnormal chromosomes was confirmed in all cases by quinacrine staining, nucleolar organizer (Ag-AS) staining or C-banding. In three cases, the abnormal chromosome appeared to arise from two different chromosomes 15. Several possible mechanisms for the production of the abnormal chromosome are discussed. The individuals with this abnormal chromosome all showed some degree of mental retardation, but few common physical findings.

Supernumerary marker chromosomes in man: parental origin, mosaicism and maternal age revisited

“…33 Both groups of SMC(15)s were also shown to have asymmetrical breakpoints and, furthermore, the two main breakpoint regions occur at sites of duplicated genomic segments, 34 suggesting that these duplicons are responsible, at least in part, for the increased instability in this region, and the most popular theory for the formation of SMC (15)s is a U-type exchange between homologous chromosomes during meiosis I followed by illegitimate fusion of the chromatids and nondisjunction. 35,36 A combination of these events, with maternal age related nondisjunction as the primary mechanism, may go some way to explain the relatively high frequency with which SMC(15)s are ascertained in the human population.…”

Nucleolus-organiser regions in familial extra metacentric human chromosomes

“…Miller et al (1977) have shown a strong correlation between the amount of silver stain and frequency of participation in association. In the cases reported here, the marker chromosome carried an above-average number of l8S and 28S ribosomal genes and was involved more often than average in satellite associations.…”

“…Studies on rodent/man somatic cell hybrids have shown that only the NOR's of the species producing rRNA are stained by the Ag technique (Miller et al, 1977), and it has been assumed that this is a stain for active NOR's. Satellite association has also been considered as a measure of activity in production of rRNA as it is thought to involve those acrocentric chromosomes whose NOR's were involved in nucleolus formation in the previous interphase.…”

Inv dup(22), del(22)(q11) and r(22) in the father of a child with DiGeorge syndrome

“…9 To the best of our knowledge, a 22q11 duplication together with a deletion in the same patient has hitherto never been reported. Inverted duplications have been suggested to arise as a U-type exchange between homologous chromosomes 11,12 or inter-chromosomal recombination between inverted sequences. 6,13 Another alternative is repair of a broken chromosome through replication and end to end fusion.…”

“…6,13 Another alternative is repair of a broken chromosome through replication and end to end fusion. 11 We hypothesize that an inter-chromosomal recombination between inverted repeats combined with a recombination between sister chromatids during meiosis I gave rise to both a deleted 22q11 and an inv dup(22) containing the DGS region (Figure 2). The acentric fragments were lost.…”