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Maternal uniparental disomy of chromosome 14 (upd(14)mat) is a rare chromosomal disease in which both chromosomes 14 are inherited from the mother, instead of one copy from each parent. The main clinical features of upd(14)mat, overlapping with those observed in Prader–Willi syndrome (PWS), are prenatal and postnatal growth retardation, hypotonia, feeding difficulties in the neonatal period with a catch‐up usually noted after 4 years and a progressive overweight after 6 years, joint hyperlaxity, motor delay, and early‐onset puberty. Learning difficulties are inconstant and mild dysmorphic features may be observed such as broad and tall forehead, short nose, small and large hands, and clinodactyly of the fifth fingers 1, 2, 3. Complete trisomy 14 (T14) mosaicism, on the other hand, is a very rare chromosomal condition associating failure to thrive, hypotonia, developmental delay, intellectual disability, congenital heart and genitourinary abnormalities, and abnormal skin pigmentation pattern. Patients with T14 mosaicism usually present with craniofacial dysmorphic features such as broad nose, hypertelorism, ear abnormalities, micrognatia, and cleft or highly arched palate 4. Although the phenotypic spectrum of upd(14)mat is thought to be mainly the consequence of fetal/placental T14 mosaicism and genomic imprinting, the coexistence of mosaic T14 and upd(14)mat in a living patient has, to our knowledge, not previously been described.

Feeder-free human embryonic stem cell (hESC) culture is associated with the presence of mesenchymal-like cells appearing at the periphery of the colonies. The aim of this study was to identify this early differentiation process. Long-term feeder-free hESC cultures using matrigel and conditioned medium from mouse and from human origin revealed that the appearance of mesenchymal-like cells was similar regardless of the conditioned medium used. Standard characterization confirmed the preservation of hESC properties, but the feeder-free cultures could not be maintained longer than 37 passages. The early differentiation process was characterized in the short term after switching hESCs cultured on feeders to feeder-free conditions. Transmission electron microscopy showed an epithelium-like structure inside the hESC colonies, whereas the peripheral cells revealed the acquisition of a rather mesenchymal-like phenotype. Immunochemistry analysis showed that cells at the periphery of the colonies had a negative E-cadherin expression and a positive Vimentin expression, suggesting an epithelial-mesenchymal transition (EMT). Nuclear staining of beta-catenin, positive N-cadherin and negative Connexin 43 expression were also found in the mesenchymal-like cell population. After RT-PCR analysis, Slug and Snail, both EMT-related transcription factors, were detected as up-regulated in the mesenchymal-like cell population. Taken together, our data suggest that culturing hESCs in feeder-free conditions enhances an early differentiation process identified as an EMT