Fig. 4.

FGF13 levels are reduced in X-linked hypertrichosis, and FGF13 is expressed in the human hair follicle. (A) qRT-PCR of candidate genes surrounding the insertion on control, carrier, and affected skin biopsies reveals that FGF13 levels are reduced by approximately fourfold in affected individuals relative to controls. (B) FGF13 qRT-PCR in control, carrier, and affected individuals reveals a dosage effect. (C) FGF13 expression normalized to K14 reveals that FGF13 levels are dramatically reduced by eighteen fold in affected cells relative to that of controls. qRT-PCR results are representative of the averaged values of three independent experiments on three controls, three carriers, and three affected individuals. Values are relative to the unaffected samples and standardized to the housekeeping gene GAPDH (in A and B). A Student t test was performed comparing each value to control 1 with a cutoff P value of 0.05 for statistical significance; **P < 0.01; ***P < 0.001. Error bars represent the SEM. (D) In situ hybridization of FGF13 in anagen hair follicles reveals expression in the outer root sheath (ORS) within the middle and upper portions of the hair follicle, where the sense probe produced no signal. (E) Immunofluorescence staining reveals that FGF13 localizes to the outer root sheath (magnified image) within the middle and upper portions of the human anagen hair follicle (n = 5). ORS, outer root sheath; IRS, inner root sheath; HS, hair shaft. (F) FGF13 expression is detected in the trichilemma (ORS) of telogen club-hair follicles by immunofluorescence staining. (Scale bar, 100 μm.)