Below is an instruction from Human. Write a response.
    ### Instruction:
    What are the genetic changes related to sick sinus syndrome ?
    ### Response:
    Sick sinus syndrome can result from genetic or environmental factors. In many cases, the cause of the condition is unknown.  Genetic changes are an uncommon cause of sick sinus syndrome. Mutations in two genes, SCN5A and HCN4, have been found to cause the condition in a small number of families.
    