Novel rearrangements between different chromosomes with direct impact on the diagnosis of 5p- syndrome

Insufficient gene expression and lost gene regulatory network may underlie the mechanism of Hirschsprung Disease in 5p-syndrome

Cri-du-chat syndrome (CDC, OMIM 123450) is a rare chromosomal syndrome that results from partial deletions on the short arm of chromosome 5, known as 5p minus. Substantial clinical and genetic heterogeneity were observed in CDC patients. Large efforts have been dedicated to correlating the deleted regions on 5p arm with observed symptoms in CDC patients. However, the genetic basis of many specific phenotypes, including the co-occurrence of Hirschsprung Disease (HSCR), have yet been clarified. Here, we conducted a study on two patients with CDC and HSCR using whole genome sequencing (WGS) analyses. Our WGS data confirmed the deletion regions on 5p associated with CDC and indicated potential unknown genetic mechanisms underlying HSCR. On the one hand, leveraging human single-cell atlas for developing enteric nervous system, we demonstrated that some affected genes in these two patients overlapped with those showing expression changes along the development pseudotime of enteric nervous cells (ENC) and overlapped with known HSCR genes including RET, NRG1, ERBB (ERBB2 and ERBB3), ITGB (ITGB1). On the other hand, integrating gene regulatory relationship estimated from single cell chromatin accessibility omics of enteric neurons, we found that the 5p deletion regions contained key cis-regulatory regions for HSCR-related gene GDNF. Taken together, our study reveals the genetic basis of HSCR or intestinal phenotypes in 5p minus patients, highlighting the importance of studying gene regulatory relationships to explain phenotypic heterogeneity.

Features of chromosomal abnormalities in relation to consanguinity: analysis of 10,556 blastocysts from IVF/ICSI cycles with PGT-A from consanguineous and non-consanguineous couples

Consanguineous marriage is defined as marriage between first or second-degree cousins, with high prevalence in many cultures and societies. Descendants from consanguineous unions have an increased risk for genetic diseases. Additionally, in consanguineous couples, chromosomal disjunction during embryogenesis could also be affected, increasing the risk of chromosomal errors. Nowadays, genomic testing allows to identify new genetic syndromes and variants related to copy-number variations (CNV), including whole chromosome, segmental and micro-segmental errors. This is the first study evaluating chromosomal ploidy status on blastocysts formed from consanguineous couples during IVF/ICSI treatments with Preimplantation Genetic Testing for Aneuploidies (PGT-A), compared to non-consanguineous couples. Although consanguine couples were significantly younger, no differences were observed between groups for fertilisation rate, blastulation rate and euploidy rate, once adjusted by age. Nevertheless, the number of blastocysts biopsied on day 5 was lower for consanguine couples. Segmental errors, and aneuploidies of chromosomes 13 and 14 were the most prominent abnormalities in relation to consanguinity, together with errors in chromosome 16 and sex chromosomes when the female partner was younger than 35. Once euploid blastocysts were considered for subsequent frozen embryo transfer, pregnancy outcomes were similar in both groups. The current findings point toward the fact that in consanguine unions, not only the risk of having a child with genetic disorders is increased, but also the risk of specific chromosomal abnormalities seems to be increased. Premarital counselling and tailored reproductive treatments should be offered to these couples.

5p deletion with congenital diaphragmatic hernia: a case report

Background

5p deletion syndrome is known as cri-du-chat syndrome, but there are no reports on congenital diaphragmatic hernia complications associated with it.

Case presentation

A 28-year-old primigravida Japanese woman was referred for 5 mm of nuchal translucency. Fetal growth restriction was found at 20 weeks, and a left-sided congenital diaphragmatic hernia was diagnosed at 24 weeks. The karyotype of the fetus was diagnosed as 46, XX, del(5)(p14) and referred to our hospital. At 36 ^+ 6 weeks, a 1524 g female infant was delivered after premature membrane rupture, with Apgar scores of 4 and 6 at 1 and 5 minutes, respectively. The baby was intubated immediately with sedation and muscle relaxation, after birth for initial treatment for congenital diaphragmatic hernia. The peripheral blood karyotype was consistent with the prenatal result. The infant was discharged alive, without any respiratory support, after the defect of the diaphragm was repaired.

Conclusion

The results of this study may be helpful for antenatal genetic counseling.