Issues arising from the prenatal diagnosis of some rare trisomy mosaics--the importance of cryptic fetal mosaicism.

Objectives: To add to the knowledge of fetal mosaicism, confined placental mosaicism (CPM), and uniparental disomy (UPD), in rare trisomies detected at prenatal diagnosis.

Methods: The origin of rare trisomy mosaics, mostly (8/11) seen in amniocytes, was examined in 11 cases by follow-up karyotyping and the study of microsatellite inheritance.

Results: Of the rare trisomies presented, three were mosaic trisomy 16 (two of which were CPM), and the remainder comprised single cases of mosaic trisomies of 8, 9, 10, 11, 12, 14, 5 and 15--the last two being CPM.

A series of supernumerary small ring marker autosomes identified by FISH with chromosome probe arrays and literature review excluding chromosome 15.

Seven supernumerary small ring marker autosomes were studied. The pantelomere probe (Oncor) in conjunction with scoring for dicentric rings was used to confirm ring morphology. The small rings were identified mainly by FISH with chromosome probe arrays (Cytocell) containing representations from all 24 chromosomes and the rings were derived from chromosomes 7, 8 (three cases), 11, 12, and 14.

Recombinants of intrachromosomal transposition of subtelomeres in chromosomes 1 and 2: a cause of minute terminal chromosomal imbalances.

Two cases of submicroscopic recombinants of intrachromosomal transposition of telomeres, one each from chromosome 1 and 2 are described. Meiotic crossing-over would generate the recombinants from these reciprocal rearrangements. In both cases, which were detected by FISH with subtelomeric probes, there is a minute deletion of the qter region and a second presence of the pter subtelomeric region on the respective qter, i.

Chromosome 13q neocentromeres: molecular cytogenetic characterization of three additional cases and clinical spectrum.

We report three new cases of chromosome 13 derived marker chromosomes, found in unrelated patients with dysmorphisms and/or developmental delay. Molecular cytogenetic analysis was performed using fluorescence in situ hybridization (FISH) with chromosome-specific painting probes, alpha satellite probes, and physically mapped probes from chromosome 13q, as well as comparative genomic hybridization (CGH). This analysis demonstrated that these markers consisted of inversion duplications of distal portions of chromosome 13q that have separated from the endogenous chromosome 13 centromere and contain no detectable alpha satellite DNA.