It is likely that the elevated response in DRB1*15:01 homozygous individuals is due to increased expression of HLA-DQ6 in these patients, as studies in patients with narcolepsy have shown that allelic dosage of DQB1*06:02 is transmitted into significant changes in HLA-DQ6 heterodimer availability (35). Here, HLA-DRB1 is linked to narcolepsy.