A Novel Homozygous Loss-of-Function Variant in Causes Autosomal Recessive Noonan-like Syndrome.

Noonan syndrome is an autosomal dominant developmental disorder characterized by peculiar facial dysmorphisms, short stature, congenital heart defects, and hypertrophic cardiomyopathy. In 2001, was identified as the first Noonan syndrome gene and is responsible for the majority of Noonan syndrome cases. Over the years, several other genes involved in Noonan syndrome (, , , , , , , and ) have been identified, acting at different levels of the RAS-mitogen-activated protein kinase pathway. Recently, was recognized as a novel Noonan syndrome gene with autosomal recessive inheritance, and only four families have been described to date. Here, we report the first Italian case, a one-year-old child with left ventricular hypertrophy, moderate pulmonary valve stenosis, and atrial septal defect, with a clinical suspicion of RASopathy supported by the presence of typical Noonan-like facial features and short stature. Exome sequencing identified a novel homozygous loss-of-function variant in the exon 3 of (NM_181784.3:c.325del; p.Arg109Glufs*7), likely causing nonsense-mediated decay. Our results and the presented clinical data may help us to further understand and dissect the genetic heterogeneity of Noonan syndrome.