A New Mutation in the Type II Hair Cortex Keratin hHb1 Involved in the Inherited Hair Disorder Monilethrix

The study investigated the genetic basis of monilethrix, a rare dominant hair disorder characterized by beaded hair due to periodic thinning and increased fragility. Previous research identified mutations in the type II keratin gene cluster on chromosome 12q13, specifically in the hHb6 keratin gene. This study examined two unrelated families and a single case, finding the prevalent hHb6 Glu 410 Lys mutation in one family and the single patient. In the second family, a new mutation, Glu 403 Lys, was identified in the hHb1 keratin gene, suggesting a mutational hotspot in these keratins. Both hHb1 and hHb6 are coexpressed in the hair shaft's cortical trichocytes, indicating that monilethrix affects the hair cortex.