Patient description: A 17 year old boy complains of vomiting, non-bloody diarrhea, abdominal pain, fever, chills and loss of appetite for the past 3 days. He ate a salad at a restaurant prior to his diarrhea onset. Physical exam was remarkable for pallor, jaundice, and diffuse abdominal tenderness. Lab results were as follows: Hemoglobin: 9.7 g/dL Platelet: 110,000 /cu.mm Creatinine: 3.6 mg/dL blood urea nitrogen (BUN): 73 mg/dL direct bilirubin: 2.4 mg/dL lactate dehydrogenase (LDH): 881 IU/L (normal: 110-265 IU/L) Peripheral blood smear showed a moderate number of schistocytes and helmet cells. Shiga-like toxin-producing E. coli (STEC) stx1/stx2 were found in stools. He has no other underlying disease and he is not on any medications.

Clinical trial eligibility criteria: eligible ages (years): 3.0-999.0,  Proteus Syndrome All participants in all Cohorts must meet the below Signed informed consent, and when applicable, signed assent Have a molecular diagnosis of Proteus syndrome with documented somatic AKT1 mutation from a CLIA-certified laboratory Have progressive and measurable disease (e.g., a measurable manifestation of Proteus syndrome with evidence or report of worsening of manifestation(s)/ in the last 12 months) Adequate organ function as indicated by the following laboratory values: Hematological Hemoglobin (Hgb) depending on age 5 years male and female: greater than or equal to 10.0 g/Dl 9 years male and female: greater than or equal to 11.5 g/dL 17 years female: greater than or equal to 11.0 g/dL 17 years male: greater than or equal to 11.5 g/dL  An individual who meets any of the following will be excluded from participation in this study History of Type 1 or Type 2 uncontrolled diabetes mellitus requiring regular medication (other than metformin or other oral hypoglycemic agents) or fasting glucose greater than or equal to 160 mg/dL ( if >12 years old) and greater than or equal to 180 mg/dL (if less than or equal to 12 years old) at the baseline/screening visit History of significant cardiac disorders Myocardial infarction (MI) or congestive heart failure defined as Class II-IV per the New York Heart Association (NYHA) classification within six months of the first dose of miransertib (MI occurring >6 months of the first dose of miransertib will be permitted) Grade 2 (per National Cancer Institute [NCI] Common Terminology for Adverse Events [CTCAE] current version) or worse conduction defect (e.g., right or left bundle branch block) Major surgery, radiotherapy, or immunotherapy within four weeks of the first dose of miransertib Any experimental systemic therapy for the purpose of treating Proteus syndrome (e.g., sirolimus, everolimus, high dose steroids, alpelisib) within two weeks of the first dose of miransertib, except for participants who were previously or are currently treated with miransertib under a Compassionate Use/Expanded Access program or existing protocol --Participants who were previously treated with or currently are receiving miransertib will be enrolled and treated according to the Schedule of Assessments/Study Visits defined in this protocol Intolerance of, or severe toxicity attributed to, AKT inhibitors (e.g., miransertib, uprosertib, afuresertib, ipatasertib) Concurrent severe uncontrolled illness not related to Proteus syndrome Ongoing or active infection