The Chinese teenager cannot even talk – but has to communicate with different types of GIGGLE.
Xu Pinghui, 13, has stumped doctors ever since she started laughing when she developed a fever as an eight-month-old baby.
Her parents are now desperate to find a cure.
Mom Yang Longying said: "Ever since then she has been laughing uncontrollably.
Her dad Xu Weiming added: "There is no happiness for us. Seeing her laughing we feel even sadder than if she were crying."
But Pinghui has been given new hope after doctors said her brain’s frontal lobe may have been damaged by the fever.
They now plan to carry out a CT scan on the teenager and hope this could provide answers to her mysterious condition.