<unk>  appears to occur randomly and for unknown reasons. Prevalence is higher in females than males, with a ratio of roughly 3:2. The condition is observed on the left side of the face about as often as on the right side.
Parry–Romberg syndrome
Smith–Fineman–Myers syndrome
MORM syndrome
Sly syndrome
Imerslund–Gräsbeck syndrome
WHIM syndrome
Lujan–Fryns syndrome
Senior–Løken syndrome