Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Solitary Kidney ?
    ### Response:
    When a person has only one kidney or one working kidney, this kidney is called a solitary kidney. The three main causes of a solitary kidney are
                
- birth defects. People with kidney agenesis are born with only one kidney. People born with kidney dysplasia have both kidneys; however, one kidney does not function.
    