Study of TAK-935 as an Adjunctive Therapy in Participants With Developmental and/or Epileptic Encephalopathies

The drug being tested in this study is called TAK-935. TAK-935 is being tested to treat
people who have developmental and/or epileptic encephalopathies. This study will look at
safety, tolerability and pharmacokinetics of people who take TAK-935. Study drug will be
administered in a double-blind manner in Part 1 and in an open-label manner in Part 2.

The study will enroll approximately 20 participants. Participants will be randomly assigned
(by chance, like flipping a coin) to one of the two treatment groups in Part 1-which will
remain undisclosed to the participant and study doctor during the study (unless there is an
urgent medical need):

- TAK-935 low/ medium/ high dose

- Placebo (dummy inactive pill) - this is a tablet that looks like the study drug but has
no active ingredient

Participants will receive placebo or 100 milligram (mg) TAK-935 tablets, orally or through
stable G-tube/PEG tube, twice daily, in Part 1 (Day 1) and dose will be increased to 200 mg
(Day 11) and to 300 mg (Day 21). All participants who complete the double-blind treatment
period in Part 1 will have the option to continue directly into the Open-Label treatment
period in Part 2 where they will receive 200 mg TAK-935 tablets, orally or through G-tube/PEG
tube, twice daily and dose will be increased to 300 mg tablets, orally, twice daily (Day 41).
This dose level will be maintained until the final visit (Day 85) for the dose de-escalation
phase.

This multi-center trial will be conducted North America. The overall time to participate in
this study is 121 days excluding screening period of 30-41 days. Participants will make
multiple visits to the clinic, and a follow-up phone call will be conducted on Day 91 and at
the end of the 30-day follow-up period (Day 121), participants will return to the clinic for
a follow-up assessment.

Inclusion Criteria:

1. Has a documented clinical diagnosis of developmental and/or epileptic encephalopathies
with countable bilateral motor seizures, defined as an average of greater than or
equal to (>=) 2 per month during the past 3 months, based on the investigator's
assessment, and a monthly average of >=1 per month during the Baseline Period, based
on the seizure diary record.

2. Has been taking 1 to 4 antiepileptic drug (AEDs) at a stable dose for >=4 weeks before
Screening and the participant or participant's legally acceptable representative is
willing to keep the regimen(s) stable throughout the study.

3. Has an average of >=1 bilateral motor seizure per month during the 4-week Baseline
Period (that is., drop seizures, tonic-clonic, tonic, bilateral clonic, atonic,
myoclonic-atonic, myoclonic-tonic-clonic, focal seizures with bilateral hyperkinetic
motor features).

4. Must agree to not post any participant's personal medical data related to the study or
information related to the study on any web site or social media site (example,
Facebook, Twitter) until the study has been completed.

5. For participants with G-tube/PEG tube, G-tubes/PEG tubes should have been placed and
been functioning for at least 3 months prior to screening. Naso-gastric tubes are not
allowed.

Exclusion Criteria:

1. Has received TAK-935 in a previous clinical study or as a therapeutic agent.

2. Was admitted to a medical facility for treatment of status epilepticus requiring
mechanical respiration within 3 months before Screening.

3. Had a vagal nerve stimulator implanted within 6 months before Screening and settings
have been changed within 1 month of the Screening Visit and/or anticipated to change
during the study.

4. Is on ketogenic diet that has been started within 6 months of the Screening Visit, has
been changed within 1 month of the Screening Visit, or is anticipated to change during
the study.

5. Has degenerative eye disease.

6. Has a history of suicidal behavior or any suicidal ideation of type 4 or 5 on the
Columbia-Suicide Severity Rating Scale (C-SSRS) at Screening. If the participant is
unable to comply with the C-SSRS due to developmental status, a parent proxy may be
used for the completion of the C-SSRS. The Investigator may also use clinical
judgment, which must then be documented in the source document.

7. Positive for human immunodeficiency virus, hepatitis B, or hepatitis C infections.
(Note that participants who have been vaccinated against hepatitis B [hepatitis B
surface antibody (Ab)-positive] who are negative for other markers of prior hepatitis
B infection [example, negative for hepatitis B core Ab] are eligible. Also note that
participants who are positive for hepatitis C Ab are eligible as long as they have a
negative hepatitis C viral load by quantitative polymerase chain reaction [qPCR]).

8. Has an abnormal and clinically significant ECG at Screening in the opinion of the
investigator, for example, second or third degree heart block or a corrected QT
interval (QTc) greater than (>) 450 millisecond (msec). Entry of any participant with
an abnormal but not clinically significant ECG must be approved and documented by
signature by the principal investigator or appropriately qualified delegate.

9. Has abnormal clinical laboratory test results at Screening that suggest a clinically
significant underlying disease. If the participant has alanine aminotransferase (ALT)
and/or aspartate aminotransferase (AST) >2.5*the upper limit of normal (ULN), the
Medical Monitor should be consulted.

10. Has received any excluded medications, procedures, or treatments during the time
periods.

11. Has any a history of alcohol, opioid, or other drug use disorder, as per the
Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, within the
previous 2 years before Screening. Medical marijuana use is allowed.

12. Has unstable, clinically significant neurologic (other than the disease being
studied), psychiatric, cardiovascular, pulmonary, hepatic, renal, metabolic,
gastrointestinal, urologic, immunologic, hematopoietic, or endocrine disease or other
abnormality, which may impact the ability of the participant to participate or
potentially confound the study results.