Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Familial esophageal achalasia ?
    ### Response:
    Familial esophageal achalasia refers to a cluster of achalasia within a family. Achalasia is a condition that affects the esophagus, the tube that carries food from the mouth to the stomach. In people with achalasia, the normal muscle activity of the esophagus is reduced and the muscular valve where the esophagus and the stomach meet doesn't fully relax.
    