Genetic diagnosis for fetal Bardet-Biedl syndrome caused by BBS7 gene mutations: report of two cases / 中华围产医学杂志

ABSTRACT

Objective:To summarize the genetic diagnosis of two fetuses with clinically suspected Bardet-Biedl syndrome (BBS) and to provide information for genetic counseling and prenatal diagnosis of BBS.Methods:Case one had prenatal care on October 2018 in Shenzhen Maternity and Child Healthcare Hospital and was clinically suspected of fetal BBS as bilateral renal parenchyma echo enhancement as well as polydactyly (six toes on each foot) were shown on ultrasonic examination at 18 +1 gestational weeks. Case two was another suspected fetal BBS for enlarged kidneys with echo enhancement as well as polydactyly (six fingers and toes on each hand and foot) on ultrasonic examination at 26 +4 gestational weeks on August 2016 and the parent requested for termination. Parents of both cases requested for genetic analysis. Amniotic fluid sample was obtained in case one at 19 +6 weeks through amniocentesis, and umbilical cord specimen of case two and peripheral blood samples of the parents were collected. Genetic analysis of the fetuses and their parents was performed using exon capture and next-generation sequencing and the results were validated using Sanger sequencing. Results:Case one carried paternally inherited c.718G>A (p.Gly240Ser) (possible pathogenic) mutation and maternally inherited c.497C>A(p.Ala166Asp) (possible pathogenic) mutation in BBS7 gene. While one paternally inherited mutation c.1002delT(p.N335Ifs*47) (pathogenic) and one maternally inherited heterozygous mutation c.728G>A (p.Cys243Tyr) (possible pathogenic) were identified in BBS7 gene of case two. The three unreported missense mutations were predicted to be harmful by bioinformatics software and the mutation sites were conservative after comparing with multiple species-based protein sequences. Conclusions:Enlarged kidneys with echo enhancement and polydactyly may indicated a BBS fetus caused by BBS7 gene mutation. Whole exome sequencing could provide relevant information for prenatal diagnosis and genetic counseling in these cases.