Hypotrichosis simplex can affect all body hair (generalized; see 605389) or be limited to the scalp. Usually patients with the scalp-limited form of hypotrichosis present with normal hair at birth; they experience a progressive, gradual loss of scalp hair beginning at the middle of the first decade and leading to almost complete loss of scalp hair by the third decade. A few sparse, fine, short hairs remain in some individuals. Body hair, beard, eyebrows, axillary hair, teeth, and nails develop normally. Light and electron microscopy of hairs from patients with early hypotrichosis simplex revealed no structural changes, whereas hairs from patients with advanced hypotrichosis showed focal areas of defective cuticular structure. Men and women are equally affected (summary by Betz et al., 2000).
For a discussion of genetic heterogeneity of nonsyndromic hypotrichosis, see HYPT1 (605389). [from
OMIM]