Expanding the Noonan spectrum/RASopathy NGS panel: Benefits of adding NF1 and SPRED1

Background RASopathies are a group of disorders caused by disruptions to the RAS‒MAPK pathway. Despite being in the same pathway, Neurofibromatosis Type 1 (NF1) and Legius syndrome (LS) typically present with phenotypes distinct from Noonan spectrum disorders (NSDs). However, some NF1/LS individuals also exhibit NSD phenotypes, often referred to as Neurofibromatosis‐Noonan syndrome (NFNS), and may be mistakenly evaluated for NSDs, delaying diagnosis, and affecting patient management. Methods A derivation cohort of 28 patients with a prior negative NSD panel and either NFNS or a suspicion of NSD and café‐au‐lait spots underwent NF1 and SPRED1 sequencing. To further determine the utility and burden of adding these genes, a validation cohort of 505 patients with a suspected RASopathy were tested on a 14‐gene RASopathy‐associated panel. Results In the derivation cohort, six (21%) patients had disease‐causing NF1 or SPRED1 variants. In the validation cohort, 11 (2%) patients had disease‐causing variants and 15 (3%) had variants of uncertain significance in NF1 or SPRED1. Of those with disease‐causing variants, 5/17 only had an NSD diagnosis. Conclusions Adding NF1 and SPRED1 to RASopathy panels can speed diagnosis and improve patient management, without significantly increasing the burden of inconclusive results.
Adding the NF1 and SPRED1 genes to Noonan spectrum disorder/RASopathy NGS gene panels modestly increases clinical diagnoses without significantly increasing the VUS burden. Since a diagnosis of NF1 or LS would change patient management, the NF1 and SPRED1 genes should be included on all to Noonan spectrum disorder/RASopathy NGS gene panels, including those used prenatally.