Inclusion Criteria:

          1. Signed written informed consent Prior to study participation, written informed consent
             from participants, or in the case of minors, written permission (informed consent)
             from parents, guardians, or legally acceptable representatives must be obtained
             according to local laws and regulations.

          2. Assent Assent from minor participants should be obtained per local laws and
             regulations and should be documented in accordance with local requirements.

          3. Study activities compliance. Participants must be willing and able to comply with
             scheduled visits, treatment schedule, laboratory testing, and other requirements of
             the study, including disease assessment by contrast-enhanced MRI.

          4. Age Patient must be aged ≥ 1 month (corrected age) to ≤ 25 years when starting
             trametinib.

          5. Study group Participants must belong to one of the following groups to be eligible.
             Group 1: NF1 with progressing/refractory LGG Group 2: NF1 with PN Group 3:
             Progressing/refractory LGG with KIAA 1549-BRAF fursion Group 4: Progressing/refractory
             glioma with activation of the MPAK/ERK pathway who do not meet criteria for other
             study groups

          6. Tumor Tissue Sample Tumor tissue will be required for all patients (minimally
             paraffin-embedded tissue block and additionally fresh frozen tissue [if available]).
             Patients with NF1 and LGG or PN can still be enrolled without tissue if no surgery or
             biopsy was conducted.

        7 Previous MRI At least two previous MRIS fro Group 1, 3, 4 and one previous MRI for Group
        2 must be available for central review.

        8. Prior therapy Participants must have failed at least one line of treatment including
        chemotherapy and/or radiation therapy except for plexiform neurofibroma (since there is no
        recognized standard treatment for his tumor).

        9. Prior therapy toxicity Patients must have recovered to grade ≤ 1 from acute toxic
        effects of all prior chemotherapy, immunotherapy or radiotherapy prior to enrollment except
        for alopecia and non-treatment related clinically insignificant laboratory abnormalities.
        prior to starting trametinib. Toxicities will be graded as per the National Cancer
        Institute Common Terminology Criteria for Adverse Events (CTCAE), version 5.0

        10. Prior therapy timeline Participants having previously received a chemotherapy agent(s)
        and/or radiation must conform to the timeline described below. There is no limitation on
        the number of previous treatments or cycles received.

          -  An interval of at least 28 days after the last dose of a myelosuppressive
             chemotherapy, and at least 42 days after the last dose of Nitrosoureas is required
             prior to starting trametinib.

          -  An interval of at least 28 days after the last dose of any biologic agents including
             monoclonal antibody treatment, immunotherapy, viral therapy and other investigational
             agent is required prior to starting trametinib.

          -  An interval of at least 84 days after the end of the radiation therapy is required
             prior to starting trametinib.

          -  An interval of at least 48 hours for short-acting colony stimulating factor agents and
             10 days interval for long-acting colony stimulating factor agents are required prior
             to starting trametinib.

             11. Life expectancy Patients must have a life expectancy of greater than 6 months.

             12. Performance level Patients must have a performance status corresponding to a
             Lansky/Karnofsky score ≥50.

             13. Organ Function Requirements

        Participants must have normal organ and marrow function as defined below:

          -  Total leukocytes ≥ 3,000/µL

          -  Absolute neutrophil count (ANC) ≥ 1, 000/µL

          -  Hemoglobin > 80 g/l (transfusion independent within last 2 weeks prior to starting
             trametinib)

          -  Platelet count ≥ 100,000/µL (transfusion independent within last 2 weeks prior to
             starting trametinib)

          -  Total bilirubin ≤ 1.5 times the ULN within normal institutional limits for age

          -  Alanine Aminotransferase (ALT) ≤ 2.5 × upper limit of normal (ULN)*

          -  Creatinine serum within normal institutional limits for age OR creatinine clearance
             ≥60 mL/min/1.73 m2 for participants with creatinine levels above institutional normal.

          -  Creatine phosphokinase ≤ 2x ULN

          -  A cardiac function defined as Corrected QT (QTcB) interval < 480 msec and LVEF ≥ lower
             limit of normal (LLN) by echocardiogram (ECHO).

          -  Blood pressure must be smaller or equal to the 95th percentile for patient's age,
             height and gender.

               -  For uniformity reasons, the ULN for ALT will be 45 U/L in this study

                  14. Reproductive status Children of childbearing and child-fathering potential
                  must agree to use adequate contraception (hormonal or barrier method of birth
                  control; abstinence) prior to starting trametinib and for the duration of study
                  participation. Should a female become pregnant or suspect she is pregnant while
                  she or her partner is participating in this study, she should inform her treating
                  physician immediately. Males and females treated or enrolled in this protocol
                  must also agree to use adequate contraception prior to the study, for the
                  duration of study participation, and 4 months after completion of trametinib
                  administration. Furthermore, females of childbearing potential (older than 10
                  years old for this study) must have a negative serum pregnancy test within 7 days
                  prior to starting trametinib. A urine pregnancy test will be done according to
                  evaluation calendar at at 30 days and at 6 months following the last does of
                  study medications.

                  15. Administration of oral medication Patients must be able to ingest and retain
                  enterally (per os, nasogastric tube or gastrostomy) administered medication and
                  be free of any clinically significant gastrointestinal abnormalities limiting the
                  absorption of the medication. Tablets cannot be crushed. If the patient cannot
                  swallow tablets, the liquid form should then be used.

        SPECIFIC INCLUSION CRITERIA

        Participants must belong to one of the following groups to be eligible.

          -  Group 1: NF1 with Progressing/Refractory LGG (42 patients).

          -  Group 2: NF1 with Progressing/Refractory PN (46 patients).

          -  Group 3: Progressing/Refractory LGG with KIAA1549-BRAF fusion (42 patients).

          -  Group 4: Progressing/Refractory CNS Glioma with activation of the MAPK/ERK pathway who
             do not meet criteria of other study groups (20 patients).

        Exclusion Criteria:

          1. Other investigational agents Patients who are receiving any other investigational
             agents.

          2. Cardiac exclusion criteria Patients who have an ejection fraction inferior to the
             institution LLN, a QTcB ≥ 480 msec or an absolute resting left ventricular ejection
             fraction (LVEF) of ≤ 39% are not eligible for enrollment.

          3. Presence of another malignancy Patient has any other malignancy except if the other
             primary malignancy is neither currently clinically significant nor requiring active
             intervention.

          4. Previous MEK inhibitor treatment Participants previously treated with a MEK inhibitor
             who showed less than stable disease during treatment.

          5. Tumor with BRAF V600E mutation Patients with a tumor presenting a positive BRAF V600E
             mutation.

          6. Other uncontrollable medical disease Patient has a severe and uncontrollable medical
             disease (i.e., uncontrolled diabetes, chronic renal disease or active uncontrolled
             infection), has a chronic liver disease (i.e., chronic active hepatitis and
             cirrhosis), uncontrolled intercurrent illness including, but not limited to, ongoing
             or active infection, symptomatic congestive heart failure, unstable angina pectoris,
             cardiac arrhythmia, or psychiatric illness/social situations that would limit
             compliance with study requirements.

          7. Known HIV infection Patient has a known diagnosis of human immunodeficiency virus
             (HIV) infection, hepatitis B or C.

          8. Previous surgery Patients who had major surgery within 2 weeks prior to starting
             trametinib.

          9. Allergy History of allergic reactions attributed to compounds of similar chemical or
             biologic composition to trametinib.

         10. Previous history of non-compliance Patients with a previous significant history of
             non-compliance to their treatment or medical regimen.

         11. Pregnant or breastfeeding patients Pregnant or breastfeeding female patients are not
             eligible for this study.