A Patient with Noonan Syndrome with a KRAS Mutation Who Presented Severe Nerve Root Hypertrophy

We report a 45-year-old female with clinical features resembling Noonan syndrome (NS) who presented with significant nerve root hypertrophy. She was initially diagnosed with Charcot-Marie-Tooth disease because her gait disturbance gradually deteriorated and nerve conduction velocity was reduced. However, she did not carry a PMP22 gene mutation. RASopathies are a group of phenotypically overlapping developmental syndromes caused by germline mutations that encode components of the Ras/MAPK signaling pathway. These disorders include NS, cardiofaciocutaneous (CFC) syndrome, and Costello syndrome and are associated with molecular abnormalities in the Ras/MAPK pathway. The patient was suspected to have NS and related disorders because of pulmonary artery stenosis, lymphedema, distinctive facial appearance, and intellectual disability. Genetic analysis identified a heterozygous de novo mutation in KRAS (c.211T>G, p.Tyr71Asp), which is usually observed in patients with NS or CFC syndrome. Although our patient was diagnosed with NS, she revealed clinical manifestations that were typical to CFC syndrome, including intellectual disability. It has been reported that some patients diagnosed with RASopathies with mutations in PTPN11, SOS1, or KRAS developed nerve root hypertrophy. These results suggest that nerve root hypertrophy may be associated with RASopathy, although the onset mechanisms of nerve root hypertrophy are unknown.