It would follow that TBI is a known risk factor for narcolepsy, known as post-traumatic narcolepsy.52–54 Six out of seven patients with craniocerebral trauma in the Ripley et al. 2001 study demonstrated low levels of orexin.51 In four of these patients, cerebral spinal fluid was collected 5 to 11 days after the trauma. This evidence concerns the gene HCRT and narcolepsy.