Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) congenital leptin deficiency ?
    ### Response:
    Congenital leptin deficiency is a condition that causes severe obesity beginning in the first few months of life. Affected individuals are of normal weight at birth, but they are constantly hungry and quickly gain weight. Without treatment, the extreme hunger continues and leads to chronic excessive eating (hyperphagia) and obesity.
    