Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Koolen-de Vries syndrome ?
    ### Response:
    Koolen-de Vries syndrome is a disorder characterized by developmental delay and mild to moderate intellectual disability. People with this disorder typically have a disposition that is described as cheerful, sociable, and cooperative. They usually have weak muscle tone (hypotonia) in childhood.
    