MRAS and left ventricular hypertrophy: Among 7 reported NS patients with MRAS mutations, 6 pediatric cases manifested severe early-onset HCM characterized by aggressive progression, including neonatal cardiac arrest and premature cardiac death in 2 individuals.[2,15–18] The inaugural adult case (p.Thr68Ile) was not documented until 2023, exhibiting only mild delayed left ventricular hypertrophy.