An integrated computational, clinical, and functional framework for assessing PTPN11 (SHP2) variant effects on ERK signaling and neural crest cell behavior in Noonan spectrum disorders

Germline mutations in PTPN11 cause Noonan syndrome (NS) and NS with multiple lentigines (NSML), yet how specific variants drive divergent clinical outcomes through distinct signaling and developmental mechanisms remains unclear. We find that germline and somatic mutations converge on N-SH2 and PTP domains but diverge at residue-level hotspots, reflecting distinct selective pressures. Clinical stratification of 18 pediatric patients reveals four distinct phenotypic classes including (i) the NSML-associated c.1403C>T (T468M) variant, characterized by lentigines, moderate growth impairment, and distinctive facial features; (ii) variants including the VUS c.1282G>A (V428M) and c.1432A>G (I478V), which were associated with cognitive deficits and variable growth impairment; (iii) c.1471C>A (P491T) and c.1472C>T (P491L), predominantly affecting cardiac and growth phenotypes with limited neurocognitive features; and (iv) a severe, multisystem class comprising c.172A>G (N58D), c.178G>A (G60S), c.844A>G (I282V), c.922A>G (N308D), and c.923A>G (N308S), spanning cardiac, growth, cognitive, and craniofacial abnormalities. Biochemical profiling in HEK293T cells revealed that PTPN11 variants stratify beyond simple gain/loss-of-function dichotomies into strong ERK-dependent hyperactivation, moderate ERK activation with variable protein stability and the paradoxical c.1282G>A variant, which did not increase ERK phosphorylation. In vivo, this variant drove excessive neural crest cell migration in chick embryos, suggesting that its effects on NCC migration may involve ERK-independent mechanisms or context-dependent signaling not captured by steady-state assays. ERK activation did not strictly correlate with clinical severity, yet these functional differences were associated with distinct growth, cardiac, pigmentation, and neurodevelopmental outcomes. Our data suggest lineage-specific sensitivity to SHP2 dosage, with dorsal root ganglia neurons appearing more vulnerable to reduced SHP2 stability than melanocyte precursors. Although direct correlations between specific signaling defects and individual clinical features remain complex, our findings provide a refined framework for PTPN11 variant classification, and reveal unexpected SHP2 functions in neural crest development.