Atrichia with papular lesions (APL) is a rare autosomal recessive syndrome associated with irreversible hair loss and widespread papular lesions. A mutation in the zinc finger domain of the human hairless HR gene on chromosome region 8p12 produces a dysplasia of the pilosebaceous system.

In APL, the proximal and outer root sheath of hair follicles undergoes apoptosis and disintegration at the end of the anagen phase. Patients are born with scalp and body hair but develop irreversible hair loss beginning at a few months of age, with a frontal to posterior progression on the scalp. In some cases, patients are born hairless. Papular lesions erupt within the first year of life, most prominently under the midline of the eye, face, and extremities. Papular lesions are made of keratin cysts associated with malformation of the pilosebaceous system.