Detection of a rare de novo 18p terminal deletion with inverted duplication in a Chinese pregnant woman

A case of prenatal diagnosis of 18p deletion syndrome following noninvasive prenatal testing

Background

Chromosome 18p deletion syndrome is a disease caused by the complete or partial deletion of the short arm of chromosome 18, there were few cases reported about the prenatal diagnosis of 18p deletion syndrome. Noninvasive prenatal testing (NIPT) is widely used in the screening of common fetal chromosome aneuploidy. However, the segmental deletions and duplications should also be concerned. Except that some cases had increased nuchal translucency or holoprosencephaly, most of the fetal phenotype of 18p deletion syndrome may not be evident during the pregnancy, 18p deletion syndrome was always accidentally discovered during the prenatal examination.

Case presentations

In our case, we found a pure partial monosomy 18p deletion during the confirmation of the result of NIPT by copy number variation sequencing (CNV-Seq). The result of NIPT suggested that there was a partial or complete deletion of X chromosome. The amniotic fluid karyotype was normal, but result of CNV-Seq indicated a 7.56 Mb deletion on the short arm of chromosome 18 but not in the couple, which means the deletion was de novo deletion. Finally, the parents chose to terminate the pregnancy.

Conclusions

To our knowledge, this is the first case of prenatal diagnosis of 18p deletion syndrome following NIPT.NIPT combined with ultrasound may be a relatively efficient method to screen chromosome microdeletions especially for the 18p deletion syndrome.

Detection of a rare de novo 18p terminal deletion with inverted duplication in a Chinese pregnant woman

Background

The 18p terminal deletion with inverted duplication is an extremely rare chromosome structure abnormality and the common clinical manifestations include intellectual disability and speech delay, etc. Up to now, only three confirmed cases were reported in Europe, and here, for the first time in the Asian population, we report a case of de novo 18p inv‐dup‐del in a Chinese pregnant woman. This structural variation was accidentally discovered by the noninvasive prenatal testing (NIPT) during her prenatal examination.

Methods

Next generation sequencing (NGS) based copy number variations (CNVs) screening and karyotype analysis were performed to verify the type and heredity of the rearrangement, and the fluorescent in situ hybridization (FISH) analysis was also used to confirm the terminal deletion and inverted duplication.

Results

The patient has a de novo 18p11.31‐18p11.1 inverted duplication with a 6.2 Mb 18p terminal deletion. This rare chromosome imbalance, most likely caused by the U‐type exchange mechanism, resulted in the aberrant phenotype of mental disability, speech delay, seizure, and strabismus. However, the rearrangement was not inherited by her unborn child.

Conclusion

This report added a new type of variation to the spectrum of 18p terminal deletion with inverted duplication, and demonstrated that the maternal chromosome rearrangement discovered in NIPT should not just be consider as an interference factor but also a potential indicator of previously undiscovered pathogenic chromosome structure variations in pregnant women.