Prenatal diagnosis of Coffin‐Siris syndrome: What are the fetal features?

Objective To present both our center's and previously reported experience of prenatal diagnosis of Coffin‐Siris syndrome (CSS) with regard to the laboratory testing and fetal features of this syndrome. Methods This was a retrospective study of eight pregnancies with fetal CSS identified by prenatal or postnatal genetic testing. Clinical and laboratory data were collected and reviewed for these cases, including maternal demographics, prenatal sonographic findings, chromosomal microarray and exome sequencing (ES) results, and pregnancy outcomes. Results A total of eight cases of fetal CSS based on molecular testing were detected. Two cases presented with an increased nuchal translucency (NT) in the first trimester. The remaining six were identified at the second trimester scan. Agenesis of the corpus callosum (ACC) was the most common sonographic finding, accounting for 5/7 (71.4%) cases in which a second trimester sonogram was performed: four had ACC as an isolated finding, and one had additional features of cerebellar hypoplasia and left congenital diaphragmatic hernia. Conclusion CSS should be included in the differential diagnosis when ACC is found by prenatal ultrasound. Both chromosomal microarray and ES should be options when counseling patients with a structurally anomalous fetus. Key points What is already known on this topic? Coffin‐Siris syndrome (CSS) is inherited in an autosomal dominant manner; most affected individuals have the disorder as the result of de novo CSS‐causing variants of genes in the BAF complex. In postnatal patients, the diagnosis is based on the presence of major and at least one minor clinical sign. What this study adds? CSS should be included in the differential diagnosis when a fetus presents with agenesis of the corpus callosum. In addition to chromosomal microarray, exome sequencing should be an option when counseling patients with a structurally anomalous fetus.