Prenatal Diagnosis of Euploid Increased Nuchal Translucency on Fetal Ultrasound (II): RASopathy Disorders - Prenatal Ultrasound Findings and Genotype-phenotype Correlations.

Prenatal diagnosis of euploid increased nuchal translucency (NT) remains a challenge to obstetricians and genetic counselors, although increased euploid NT at prenatal diagnosis can be associated with a favorable outcome. Prenatal diagnosis of euploid increased NT should include a differential diagnosis of pathogenetic copy number variants and RASopathy disorders (RDs) including Noonan syndrome. Therefore, chromosomal microarray analysis, whole-exome sequencing, RASopathy-disorder testing, and protein-tyrosine phosphatase nonreceptor type 11 gene testing may be necessary under such a circumstance. In this report, a comprehensive review of RDs with its prenatal ultrasound findings and genotype-phenotype correlations is presented.