Efficacy and Safety of Clemastine Fumarate in Children and Adults with Pitt‑Hopkins Syndrome: A Randomized Placebo‑Controlled Trial

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What is this study about?

The study focuses on Pitt-Hopkins syndrome, a rare genetic condition that leads to severe developmental delays, breathing difficulties and frequent seizures. The medication being tested is clemastine, an oral tablet normally used for allergy relief, but here it is being evaluated for possible benefits in this disorder. A matching tablet that contains only microcrystalline cellulose is used as a control, so participants receiving it will not get the active drug.

The primary purpose is to determine whether clemastine produces overall improvement in daily functioning as observed by caretakers. The trial is designed so that participants are assigned by chance (randomized) to either the active drug or the control tablet (placebo), and neither the participants nor the caretakers know which one they receive.

Participants will take the assigned tablet for a defined period while attending regular visits. During these visits, caretakers will complete questionnaires about behavior, fatigue, sleep, anxiety and quality of life, and simple physical tests such as a short walking assessment may be performed. Blood samples may also be collected to study how the drug is absorbed and cleared from the body (pharmacokinetics). After the treatment phase, the collected information will be analyzed to assess safety and any potential benefits.

1 randomization and receipt of study medication

after enrollment you are assigned to receive either the test medication (clemastine 6 mg tablet taken oral) or a placebo tablet that contains microcrystalline cellulose and has no active drug.

the assigned tablets are packaged and labeled for you to use at home.

2 daily medication administration

take one tablet each day at the same time, following the instructions provided in the study kit.

the dose is 6 mg of clemastine if you are in the test group; the placebo group takes a tablet with no active ingredient but the same appearance.

3 recording of symptoms and observations

keep a daily log of any changes in behavior, fatigue, sleep, or other symptoms as described in the study diary.

the log helps caretakers and researchers evaluate the effect of the medication over time.

4 baseline assessment visit

attend the first clinic visit after the start of medication to complete a set of questionnaires, including the caretaker global impression rating scale and other quality‑of‑life forms.

a short electroencephalography (EEG) recording is performed to capture brain activity at rest.

blood samples may be taken to measure pharmacokinetic parameters such as drug concentration.

5 regular follow‑up visits

return to the study site at predetermined intervals (for example, every month or as specified in the protocol) for safety checks and repeat assessments.

each visit includes repeat questionnaires, a brief physical examination, and another EEG recording if required.

additional blood samples may be collected to monitor drug levels and safety markers.

6 final assessment visit

at the end of the study period you attend a concluding visit where all final questionnaires are completed and the last EEG recording is done.

the overall treatment effect is evaluated using the caretaker global impression rating scale and other secondary measures.

all study medication is returned and any remaining tablets are disposed of according to study instructions.

Who Can Join the Study?

A diagnosis of Pitt-Hopkins syndrome that has been confirmed by a laboratory test that looks at the person’s genes.
The child must be at least 1 year old when the study starts.
The child must weigh at least 12 kilograms (about 26 pounds) at the start of the study.
The parents or a legally appointed representative must be able to understand the information about what the study involves.
The parents or legal representative must be willing to sign a written form that shows they agree to let the child take part in the study after they have been fully informed.

Who Cannot Join the Study?

Having another disease (called comorbidity) or a second brain development disorder besides Pitt‑Hopkins syndrome that would make it hard to see how the treatment works.
Being part of another research study at the same time unless you have approval first.
Taking the study medicine clemastine regularly in the six months before the trial starts.
Regularly using any medicines that are being tested in other “remyelination” studies (these are drugs that try to repair the coating of nerve cells) such as domperidone, liothyronine, quetiapine, testosterone, or bazedoxifene in the six months before the trial.
Changing the amount or starting/stopping any psychotropic medications (drugs that affect mood, thoughts, or behavior) in the four weeks before the trial.
Having any reason you cannot safely take clemastine (called a contraindication), such as a known condition called porphyria (a rare blood disorder) or an allergy (hypersensitivity) to clemastine or any of its inactive ingredients (excipients).
Regularly using, or planning to keep using, medicines that calm the brain (CNS depressants) such as sleeping pills, anti‑anxiety drugs, certain antidepressants, opioid pain medicines, other antihistamines that cause sleepiness (like promethazine), or drugs that block a chemical called acetylcholine (anticholinergic medication).

Where you can join this trial?

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Other Sites

Site Name	City	Country	Status
Avmhneuzy Uoc	Amsterdam	The Netherlands

Trial status

Country	Status	Recruitment Start
The Netherlands	Not yet recruiting	02.02.2026

Trial locations

Investigated drugs:

Clemastine Fumarate

Clemastine is an oral tablet that contains the active ingredient clemastine fumarate. In this study, it is being given to children and adults who have Pitt‑Hopkins syndrome to see if it can improve their symptoms. Clemastine is a medication that is usually used for allergies, but researchers think it might also help the brain function in this condition. The trial will look at how well it works, how safe it is, and how the body processes the drug.

Pitt-Hopkins syndrome – Pitt‑Hopkins syndrome is a rare genetic disorder that affects brain development and causes intellectual disability, speech delays, and characteristic facial features. Children often show early feeding difficulties and may have distinctive breathing patterns such as brief pauses in breathing. As they grow, motor skills develop more slowly, and many experience problems with coordination and balance. Sleep disturbances and episodes of heightened anxiety are common throughout childhood. Over time, individuals may develop repetitive movements and heightened sensitivity to sensory input.

Trial ID:

2025-524195-29-00

Protocol code:

PTHS-clemastine-01

Trial Phase:

Therapeutic exploratory (Phase II)

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Efficacy and Safety of Clemastine Fumarate in Children and Adults with Pitt‑Hopkins Syndrome: A Randomized Placebo‑Controlled Trial

What is this study about?

Who Can Join the Study?

Who Cannot Join the Study?