Monilethrix is characterized by beaded or moniliform hair, which results from the periodic thinning of the hair shaft. The beaded hair thus produced is subject to excess weathering and premature fracturing at the internodes. Clinically,
monilethrix presents with short, fragile, broken hair. The follicular abnormalities range from subtle perifollicular abnormalities range from subtle perifollicular
erythema and hyperkeratosis to horny follicular papule formation. At the ultrastructural level, cytolysis and
keratin tonofilament clumping (epidermolysis) are seen in the cortical cells of the bulb of the hair follicle. Microsatellite markers flanking the
keratin gene clusters at 17q12-q21 and 12q11-q13 were used to perform linkage analysis in a
monilethrix pedigree. This study demonstrates linkage of
monilethrix in a pedigree to microsatellite
DNA loci mapping to the region on chromosome 12 containing the
type II keratin cluster. A major group of structural hair
proteins, the basic type II trichocyte
keratins, map within this epithelial
cytokeratin gene cluster. This study implicates a mutation in a trichocyte
keratin gene in the pathogenesis of a structural hair disorder.