Prenatal diagnosis of a rare 1p36 heterochromatin variation with a ventricular septal defect in a twin pregnancy

Abstract Background The karyotype 46, Xn, add (1p36)? usually appears in patients with 1p36 deletion syndrome, also known as monosomy 1p36. Such a large segment of heterochromatin variation has not been reported previously. Case presentation One of the twins with ventricular septal defects underwent genetic amniocentesis for conventional karyotype analysis and array-based comparative genome hybridization (aCGH), which revealed the karyotype 46, XY, add (1p36)?. In G-band karyotyping of amnion fluid cells, the size of the additional segment was approximately 10–20 Mb; however, aCGH revealed no aberrations. The mechanism or reasons for this phenomenon are unclear; we speculate that poor growth cultures of amniotic fluid cells were the main reason. Conclusions By reporting such large segment of heterochromatin variation expands the understanding of chromosomal variations in clinical genetics. To avoid misdiagnosis, both chromosomal microarray analysis (CMA) and conventional karyotyping should be used for pregnant women who need to undergo invasive prenatal testing.