Alopecia mice derived from albino ddY mice: breeding, histological and ultrastructural studies

Sparse-haired (SH) mice arose spontaneously in a stock of sib-mated albino ddY mice. Hair loss in the skin of SH mice begins at 3 weeks of age and progresses with age. On the basis of breeding studies between SH mice and albino ddY mice, the phenotype of SH mice is identified as autosomal recessive inheritance. Histological examination shows that numerous pilary canals begin to widen and the outer root sheath becomes thin at 1 week of age. The inner root sheath and the hair were separated. Ultrastructural examination reveals that electron dense materials which formed coalesced and irregularly coiled chains are seen at the level of firm attachment of the hair to its inner root sheath. At the level of hair and inner root sheath separation, linear materials with high electron density are observed in the exocuticle of the hair cuticle. These results suggest that the appearance of electron dense materials is closely related to the mechanism of hair loss in SH mice and SH mice may be useful as an animal model in human hypotrichosis.