Approximately 8% of patients diagnosed with chronic insomnia are actually suffering from a less common genetic problem called delayed sleep phase disorder, or DSPD.
Sekitar 80% pasien yang didiagnosis menderita insomnia kronis ternyata mempunyai masalah genetik yang jarang ditemui yaitu gangguan fase tidur tertunda atau DSPD (<i>delayed sleep phase disorder</i>)