Congenital atrichias represent a large and heterogeneous group of inherited hair disorders. In this report, we describe a patient affected with alopecia universalis congenita (MIM 203655). Sequence analysis revealed a G to A transition at cDNA position 3034 of the hairless hr gene present in a homozygous state in the patient and in a heterozygous state in the patient's mother, and absent in the patient's sister. The mutation is predicted to result in the substitution of an asparagine residue for an aspartate amino acid (D1012N) at a position previously shown in the rat to affect hairless binding to thyroid hormone receptor. This study presents the first evidence in humans for the functional importance of the hairless thyroid receptor interacting domain 2.