Prenatal Diagnosis of Euploid Increased Nuchal Translucency on Fetal Ultrasound (I): Noonan Syndrome: Prenatal Diagnosis and Genetic Testing.

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 (NS). Therefore, chromosomal microarray analysis, whole-exome sequencing, RD testing, and protein-tyrosine phosphatase, nonreceptor type 11 () gene testing may be necessary under such a circumstance. In this report, a comprehensive review of NS with its prenatal diagnosis and genetic testing is presented.