Mosaic tetrasomy 14pter-q13 due to a supernumerary isodicentric derivate of proximal chromosome 14q.

Tetrasomy of proximal 14q is an extremely rare condition and has never been reported to be associated with survival. We here report on the first case of mosaic tetrasomy of 14pter-q13 due to a de-novo supernumerary pseudoisodicentric chromosome in a 2-year-old boy with multiple dysmorphisms and malformations. The marker was detectable in nearly 25% of lymphocytes as well as in cells from buccal mucosa. Detailed fluorescence in situ hybridization (FISH) analyses allowed the characterization of the marker to entirely consist of proximal 14q material and to be symmetric. The pattern of clinical features in our patient only slightly correspond to that of patients with trisomy of proximal 14q, but further cases are needed to define whether tetrasomy of proximal 14q is a separate entity.