Twin Infant with Lymphatic Dysplasia Diagnosed with Noonan Syndrome by Molecular Genetic Testing

Noonan Syndrome is an autosomal dominant disorder characterized by short stature, congenital heart defects, developmental delay, dysmorphic facial features and occasional lymphatic dysplasias. The features of Noonan Syndrome change with age and have variable expression. The diagnosis has historically been based on clinical grounds. We describe a child that was born with congenital refractory chylothorax and subcutaneous edema suspected to be secondary to pulmonary lymphangiectasis. The infant died of respiratory failure and anasarca at 80 days. The autopsy confirmed lymphatic dysplasia in lungs and mesentery. The baby had no dysmorphic facial features and was diagnosed postmortem with Noonan syndrome by genomic DNA sequence analysis as he had a heterozygous mutation for G503R in the PTPN11 gene.