This study explores the neurobiological etiology of Williams syndrome and potential therapeutic targets for associated social, motor, and cognitive abnormalities. The main translational objective will be to test the effectiveness of Clemasntine on neurocognitive and other associated abnormalities in individuals with Williams syndrome.

The overarching aim of the research proposed is to examine the safty of Clemastine use for individuals with Williams syndrome. Further, we wish to examine the relationship between Clemastine treatment and cognitive, motor and behavioral deficits in individuals with Williams syndrome. This study is an open-label study with a blinded randomize withdrawal. Each participant will go through a baseline evaluation (see study outcomes) and will be treated with the FDA approved drug Clemastine, in an age dependent dose (dosage table below). After a substantial improvement will be noticed, the participants will be divided into 2 groups, in a randomized, double-blind, placebo-control study design.

Inclusion Criteria:

• Individuals with Williams syndrome, which has been confirmed by genetic testing.
• Ages 6-30.
• Normal values in safety variables (e.g. Normal ECG 120-129/80-84).
• No change in psychotropic medications and dosage during the last 4 weeks.
• During the study, no pharmacological change that may impact the study (e.g. ADHD
• medications).

Exclusion Criteria:

• Individuals with another genetic disorder besides Williams syndrome.
• Individuals with Williams syndrome, younger than 6 or older than 30 years old.
• Significant change in normal values in safety variables (e.g. high or low ECG).
• Change in medications and dosage during the last 4 weeks prior the beginning and
• during the study.
• Pregnancy.
• Using addictive substances such as alcohol.

This study is an open-label study with a blinded randomized withdrawal