Low-Level Trisomy 14 Mosaicism: A Carrier of an Isochromosome 14 and a Supernumerary Marker Chromosome 14.

Trisomy 14 (T14) mosaicism is a rare chromosomal condition characterised by various clinical features, including developmental delay, growth impairment, and dysmorphism. Here, we report on a 12-year-old female referred for cytogenetic analysis due to short stature. Standard GTG-banding analysis on the patient's peripheral blood revealed mosaic Τ14 in the form of an i(14)(q10) in 3% of cells. Furthermore, a small supernumerary marker chromosome (sSMC) had been detected in the first trimester of pregnancy in chorionic villus sampling. A skin biopsy in the patient revealed the presence of a metacentric sSMC in 100% of cells. Cytogenetic and FISH studies showed that it was a de novo metacentric bisatellited sSMC derived from chromosomes 14 or 22. Oligonucleotide array-CGH using skin cells revealed no copy number variations. Studies for uniparental disomy 14 by microsatellite analysis confirmed biparental inheritance. To the best of our knowledge, this is the second report of a patient with 2 abnormal cell lines involving chromosome 14 in different tissues, one with mosaic T14 in the form of i(14)(q10) and one with an sSMC derived from chromosome 14, present in blood and skin, respectively. A rare mechanism of trisomy rescue events is proposed to explain the presence of the different cell lines in the tissues examined. This case highlights the importance of providing the cytogenetics laboratory with adequate clinical data to test for low mosaicism and analyse different tissues if necessary, thus contributing to the suitable clinical management of the patient.

Maternal uniparental isodisomy 20 in a foetus with trisomy 20 mosaicism: clinical, cytogenetic and molecular analysis.

The clinical significance of trisomy 20 mosaicism detected prenatally remains uncertain due to the rarity of liveborn cases with inconsistent clinical findings, and lack of long-term follow-up and outcome. We describe a case of true trisomy 20 mosaicism in a liveborn girl with maternal uniparental isodisomy of chromosome 20 in the diploid blood cells. Trisomy 20 mosaicism was originally detected in amniotic fluid (98%) and was confirmed in the term placenta (100%), as well as in the blood (10%) and urine sediment (100%) of the neonate. There was intrauterine and postnatal growth retardation, but otherwise the newborn manifested no gross abnormalities. At 9 months of age moderate psychomotor retardation, central hypotonia with peripheral hypertonia, numerous minor morphogenetic variants, marked kyphosis, and extensive Mongolian spot were observed. To our knowledge this represents the first case of trisomy 20 mosaicism detected prenatally and confirmed in different tissues of the newborn, where uniparental disomy was demonstrated in the diploid cell line. The clinical and laboratory findings in our patient are compared with those of five previously reported cases of UPD20, suggesting that maternal UPD20 might be associated with a characteristic phenotype.