SOS1 (son of sevenless homolog 1) encodes a RAS and RAC guanine nucleotide exchange factor (GEF) and is involved regulation of the RAS/ERK/MAPK pathway. Mutations in this gene are associated with Noonan syndrome (NS), an autosomal dominant disorder characterized by with congenital heart disease, short stature, facial abnormalities and myeloproliferative disease. 10-15% of NS patients have mutations in Sos1. The E846K allele is a missense mutation that causes a conformational change resulting in constitutive activation of the RAS/MAPK pathway. 

Most homozygous embryos die between E10.5 and the neonatal stage from multiple cardiac defects including atrial/ventricular septal defects, aortic valvular stenosis, ventricular hypertrophy and pericardial effusions. Surviving homozygous mice do not live beyond 10 months of age. 
Heterozygotes exhibit left ventricular cardiac hypertrophy, short stature, shortened skull length with triangular faces and blunt snouts, splenomegaly, and increased numbers of neutrophils and leukocytes.

These Sos1E846K mice exhibit phenotypes consistent with several features of Noonan syndrome including: cardiac hypertrophy, short stature, triangular faces and blunt snouts, splenomegaly, and hematologic disorders. 
Most homozygous embryos die due to cardiac defects.

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