Atrichia with papular lesions is a rare form of total alopecia, in which mutations in the hairless gene have been shown to underlie the phenotype. In the literature to date, atrichia with papular lesions has generally been reported to be inherited in an autosomal recessive manner. A few rare cases exist, however, in which parent-to-child transmission of atrichia with papular lesions has been documented. In this study, further investigations were carried out into the molecular basis of atrichia with papular lesions in a family with mother-to-son transmission by searching for mutations in the human hairless gene. Specific ally, we wanted to determine whether this case truly represented an example of dominantly inherited atrichia with papular lesions, or whether another mode of inheritance might be responsible for the disorder in this kindred. Pseudodominant inheritance, for example, occurs when an individual with a known recessive disorder has a clinically unaffected partner, but then unexpectedly gives birth to children who are affected with the same recessive disorder as the affected parent, and can easily be distinguished from classical dominant inheritance with molecular diagnosis and haplotype analysis. In the family reported here, we have determined that both the mother and son are, in fact, homozygous for a novel mutation in the hairless gene, R33X. We provide the first evidence for pseudodominant inheritance in atrichia with papular lesions, and at the same time extend our knowledge of pathogenetic mutations in the human hairless gene. Importantly, this information allows revisions in genetic counseling for risk of transmission for individuals in the family, previously impossible in the absence of knowing the genetic basis of atrichia with papular lesions in this unusual kindred.