Genetic Hair Disorders

The major types of hair shaft defects are associated with genodermatoses and syndromes. Clinically, hair shaft defects may cause an unusual appearance, or a fragile short and sparse hair. Light microscopy of hair shaft defects are classified by their morphology and it is an important tool for diagnosis. Hair shaft disorders are separated by hair fragility into those with or without increased fragility. Those with increased fragility include monilethrix, pili torti, trichorrhexis nodosa, trichorrhexis invaginata and trichoschisis. Hair shafts without increased fragility include pili annulati, loose anagen hair, wooly hair and uncombable hair. Advances in the genetic causes of the hair shaft defects are described in the different entities, which have allowed to understand the mechanisms of the defects and to elucidate normal and pathogenic pathways. In patients with hair shaft abnormalities as an isolated defect, the main problem is aesthetical. In contrast, when the hair shaft defects are associated with syndromes the prognosis will depend on the associations of each condition, especially when metabolic, neurologic or cardiac defects are present.