Genetic analysis of a fetus with cryptophthalmos due to variants of FREM2 gene

Abstract

To explore the genetic etiology of a fetus with cryptophthalmos detected by prenatal ultrasonography. A fetus undergoing induced labor at 32nd gestational week due to absence of bilateral eye fissures detected by prenatal ultrasonography in January 2017 was selected as the study subject. Umbilical cord blood sample from the fetus and peripheral blood samples from its parents were collected for the extraction of genomic DNA. Pathogenic variants were screened through whole exome sequencing (WES) and verified by Sanger sequencing. Pathogenicity of candidate variants was verified by bioinformatic analysis and protein structure simulation. Based on the results of genetic testing, prenatal diagnosis was provided to the couple upon their subsequent pregnancy. The couple had four adverse pregnancies previously. The aborted fetus was the fifth, with fused bilateral upper and lower eyelids, poorly developed eyeballs, adhesion of the cornea with the upper eyelid, low-set ears, and abnormal plantar creases, and was diagnosed with cryptophthalmos. WES and Sanger sequencing revealed that the fetus has harbored compound heterozygous variants of the FREM2 gene, namely c.4537G>A (p.D1513N) and c.7292C>T (p.T2431M). Both variants were unreported associated with cryptophthalmos previously. Protein structure simulation showed that they may lead to loss of hydrogen bonds in the protein product. Based on the guidelines from the American College of Medical Genetics and Genomics (ACMG), both variants were predicted to be likely pathogenic (PM1_Supporting+PM2_Supporting+PM5+PP3+PP4; PM2_Supporting+PM3+PP3+PP4). The mother was performed prenatal diagnosis in her sixth pregnancy based on the variants detected in this family, and delivered a daughter with normal phenotype. The FREM2: c.4537G>A and c.7292C>T compound heterozygous variants probably underlay the pathogenesis of cryptophthalmos in this fetus. Above finding has enriched the mutational spectrum of the FREM2 gene.