Pili annulati, or 'ringed hair,' is a disorder in which scalp hairs show alternating light and dark bands. It is often an incidental finding, and the hair usually does not show increased fragility (Green et al., 2004).
See also pseudopili annulati (613241), a distinct entity.Clinical Features
Cady and Trotter (1920) reported 3 unrelated families with ringed hair. The condition was restricted to hairs on the scalp. Based on refractive patterns under transmitted and reflective light, Cady and Trotter (1920) concluded that the light areas were caused by the presence of gas in the interstices of the medulla and cortex of the hair shaft, and not by lack of pigmentation.
Ashley and Jacques (1950) reported a 4-generation pedigree with ringed hair inherited in an autosomal dominant pattern. Grossly, affected scalp hairs showed alternating light and dark bands with sharp demarcation. When observed en masse, hair appeared lusterless, graying, sandy-colored, or speckled. In some cases, affected hairs were shorter than unaffected hairs due to breakage at the light, gas-filled segment. Ashley and Jacques (1950) concluded that pili annulati was distinct from beaded hair, or monilethrix (158000). Pili annulati hairs are cylindrical throughout the shaft with no change in hair circumference, whereas those of monilethrix have constrictions in the hair at regular intervals. In addition, individuals with pili annulati usually have normal growth of hair, whereas those with monilethrix have alopecia as well as associated follicular keratosis.Inheritance
In 3 families with ringed hair reported by Cady and Trotter (1920), the transmission pattern was consistent with autosomal dominant inheritance.
Snell and Foley (1932) described 9 affected persons in 4 generations with an instance of male-to-male transmission, consistent with autosomal dominant inheritance.Mapping
By linkage analysis of 2 unrelated families with autosomal dominant inheritance of pili annulati, Green et al. (2004) found significant linkage to a 9.2-cM region on chromosome 12q between D12S367 and D12S1723 (maximum combined lod score of 4.78 at D12S1723). Molecular analysis excluded pathogenic mutations in the coding and 5-prime regions of the FZD10 gene (606147).Pathogenesis
Price et al. (1968) performed detailed studies using light and electron microscopy on pili annulati from a 17-year-old girl with no family history of the condition and no clinical problems. The light cavities were situated both centrally and peripherally in the cortex of the hair shaft. The authors postulated that pili annulati results from an inherent error of hair growth, resulting in air-filled cavities in the mature hair shaft.History
Cady and Trotter (1920) provided a review of cases of ringed hair reported in the 1800s and early 1900s. Affected individuals were described as having hair with alternating light and brown segments. Some of the patients had associated alopecia. The lighter segments were often attributed to air pockets or spaces within the hair shaft.