<unk>  (pronounced ) is an X-linked recessive genetic disorder that may affect the blood, brain, peripheral nerves, muscle, and heart. It is caused by a variety of recessively inherited mutations in the XK gene on the X chromosome. The gene is responsible for producing the Kx protein, a secondary supportive protein for the Kell antigen on the red blood cell surface.
McLeod syndrome
McKittrick-Wheelock syndrome
Flynn–Aird syndrome
CAMFAK syndrome
Fryns-Aftimos syndrome
Danon disease
Rotor syndrome
Dennie–Marfan syndrome