Prenatal Sonographic Features of Rare Chromosome 13 Aberrations.

Objective: Trisomy 13 is one of the most common chromosome aberrations diagnosed in the prenatal period, and is associated with some specific dysmorphic features. Rare chromosome 13 aberrations other than trisomy 13 may cause other fetal abnormalities. The aim of the study was to analyze cases with those rare chromosome 13 aberrations.

Methods: We analyzed all prenatal tests performed in the Department of Clinical Genetics of the Medical University of Lodz from 2016 to 2021 to find all chromosome 13 aberrations.

Results: The most common aberration of chromosome 13 was a simple trisomy 13 (n = 16). We found five rare chromosome 13 aberrations other than simple chromosome 13 trisomy: mosaic trisomy 13 mos 47,XX,+13[11]/46,XX[10], mosaic monosomy 13 mos 46,XY,-13,+mar[9]/46,XY[31], duplication 13q21.1-q31, deletion 13q34 and deletion 13q31.1-q34. The deletion 13q31.1-q34 occurred in monochorionic diamniotic twin pregnancy.

Conclusion: Rare aberrations accounted for 24% of all chromosome 13 aberrations. Cases with mosaic monosomy of chromosome 13 and microdeletion 13q had similar abnormalities of the external genitalia and facial dysmorphia. The case with duplication 13q was very similar to the clinical features of chromosome 13 trisomy. Mosaic trisomy 13 can occur without any accompanying anatomical defects.