Post‐zygotic origin of isochromosome 12p

Abstract

The cytogenetic and DNA constitution of the foetus indicated the isochromosome 12p to be of paternal origin, and implied post-zygotic formation of the isochromosome 12p in the Pallister-Killian syndrome.

Pallister–Killian syndrome: tetrasomy of 12pter→12p11.22 in a boy with an analphoid, inverted duplicated marker chromosome

“…Previous molecular studies suggested either a mitotic or meiotic parental origin for this class of SMC or NMC (26). However, in our case, five DNA polymorphisms D12S352, D12S1725, D12S99, D12S358, D12S364 (located within 12pter/12p11.2) and one DNA polymorphism D12S367 (located within 12q) all showed the propositus had only obtained one paternal allele and one maternal allele, and showed equal dosage in both paternal and maternal alleles.…”

Interphase fluorescence in situ hybridization characterization of mosaicism using uncultured amniocytes and cultured stimulated cord blood lymphocytes in prenatally detected Pallister–Killian syndrome

“…Dutly et al [12] found that the origin of the supernumerary isochromosome 12p is predominantly maternal because of maternal meiosis II nondisjunction, followed by rearrangements leading to a duplication of the short arm and a loss of the long arm. However, in rare occasions, the supernumerary isochromosome 12p can be of paternal origin and may occur postzygotically [13].…”

Targeted prenatal diagnosis of Pallister-Killian syndrome

“…The isochromosome 12p is a small supernumerary marker chromosome consisting of two p arms of the chromosome 12. In the vast majority of cases, it is of prezygotic maternal origin, although paternal and postzygotic origin is also possible . Identification of the marker using classical cytogenetic banding techniques can be difficult.…”

“…In the vast majority of cases, it is of prezygotic maternal origin, although paternal and postzygotic origin is also possible. [8][9][10] Identification of the marker using classical cytogenetic banding techniques can be difficult. Resembling an isochromosome 21q, it may be mistaken with the tetrasomy of chromosome 21.…”