An abnormality of the hair shaft in which the fine, brittle hairs show alternating light and dark zones when viewed under a polarizing microscope: Mike read about trichothiodystrophy in which the sulfur content of the hair is greatly reduced and mental retardation has frequently been a related feature.

Trichothiodystrophy is descriptive of the congenital fragile hair with multiple fractures resulting from low sulfur-containing amino acid, "cysteine", content of the hair, mental impairment, and short stature.