A small supernumerary marker chromosome resulting in mosaic partial tetrasomy 4q26-q31.21 in a foetus with multiple congenital malformations

ABSTRACT

A parental diagnosis was performed for an unborn foetus of a healthy couple, who was due for ultrasound detection of multiple malformations and abnormal amniotic fluid karyotypes. For an accurate diagnosis, routine G-banding analysis and nextgeneration sequencing (NGS)were carried out. Finally, conventional cytogenetic analysis suggested that the foetus had a karyotype of47,XX,+mar[52]/46,XN,meanwhileNGSalso revealed a partial tetrasomy of 27.84Mbfrom4q26-q31.21 (117,385,735–145,225,759), and G-banding analysis excluded the couple to have carried the 4q26-q31.21 duplication. We have identified a de novo mosaic small supernumerary marker chromosomes (sSMC) derived from 4q26-q31.21 in a foetus with hemivertebra, polydactyly, abnormal ears, and heart and ventricular septal defect.