Many of the genes causing hair shaft defects have recently been elucidated. This continuing medical education article discusses the major types of hair shaft defects and associated syndromes and includes a review of histologic features, diagnostic modalities, and findings in the field of genetics, biochemistry, and molecular biology. Although genetic hair shaft abnormalities are uncommon in general dermatology practice, new information about genetic causes has allowed for a better understanding of the underlying pathophysiologies.

At the conclusion of this article, the reader should be familiar with the clinical presentation and histologic characteristics of hair shaft defects and associated genetic diseases. The reader should be able to recognize disorders with hair shaft abnormalities, conduct appropriate referrals and order appropriate tests in disease evaluation, and select the best treatment or supportive care for patients with hair shaft defects.