The fetal phenotype of noonan syndrome caused by severe, cancer-related PTPN11 variants

Objective: Rare disease Background: The nuchal translucency measurement is the major focus of an early fetal ultrasound scan, with the goal to identify various inherited conditions, such as chromosomal aberrations and others. The diagnostic strategy for fetuses with increased nuchal translucency and normal karyotype is not clearly defined and may vary between countries. Case Reports: We describe 2 cases of Noonan syndrome diagnosed prenatally by ultrasound scanning and genetic testing. The prenatal ultrasound scans showed abnormal nuchal translucencies, cystic lymphangioma/cystic hygroma, and other findings. Both fetuses had normal karyotype; however, after additional analysis, pathogenic variants of the PTPN11 gene (encoding SH2 domain-containing protein tyrosine phosphatase) were found, previously frequently described as somatic variants in hematological malignancies in postnatal life, but not previously described with severe prenatal phenotype of Noonan syndrome. Conclusions: Our case reports confirm the hypothesis that severe, cancer related PTPN11 variants cause severe Noonan syndrome prenatal phenotype, when inherited in the germline. Analysis of pathogenic variants associated with Noonan syndrome should be included in the prenatal diagnostics for fetuses with increased nuchal translucency and normal karyotype.