A 5-YEAR-OLD girl has never had hair grow long enough to have it cut. Her foster mother reports that the hair has always been thin and that it breaks off easily with combing or rubbing. Her growth and development are normal, and she has had no health problems or associated complaints. Her natural mother and uncle have similar-appearing hair.
On examination, the scalp hair is dull, short, and thin (Figure 1). On close inspection, the hair has an uneven texture, but not all hair shafts seem to be affected (Figure 2). Hair breaks easily with gentle traction. The scalp is normal in color, with a fine scale. Prominent hair follicles are present on the occipital scalp and posterior neck. The eyelashes and eyebrows are normal; no pubic or axillary hair is present. Teeth, nails, and the remainder of the skin examined are normal. A potassium hydroxide preparation and culture