Monilethrix is a relatively common developmental hair defect that results in brittle, beaded hair (Fig. 8.9). The condition is autosomal dominant, and clinical manifestations usually appear after 2–3 months of age, when vellus hairs are replaced by abnormal, beaded hairs.

How is monilethrix caused?

Monilethrix is caused by mutations in one of several genes. Mutations in the KRT81 gene, the KRT83 gene, the KRT86 gene, or the DSG4 gene account for most cases of monilethrix. These genes provide instructions for making proteins that give structure and strength to strands of hair.

Is monilethrix inherited?

In most cases, monilethrix is inherited as an autosomal genetic trait. Genetic diseases are determined by two genes, one received from the father and one from the mother. Dominant genetic disorders occur when only a single copy of an abnormal gene is necessary for the appearance of the disease.