DEFINITION, CLASSIFICATION, AND CLINICAL FEATURES

Definition and diagnosis The term trichothiodystrophy (TTD) was coined by Price in 1979-19801-3 based on a series of cases, including the early report by Pollitt, Jenner, and Davies4 in 1968, of a family with mental and physical retardation and “trichorrhexis nodosa ” with abnor-mal amino acid composition of the hair. Brown et al5 in 1970 specifically described the congenital hair defect, consisting of trichoschisis, “alternating bire-fringence, ” and low-sulfur content. The designation for this unique hair shaft disorder is derived from Greek: tricho, hair; thio, sulfur; dys, faulty; and trophe, nourishment. Clinical features of patients with TTD are highly variable in expression and sever-ity, and phenotypes range from those with an isolat-ed hair defect to those with severe neuroectodermal findings and, rarely xeroderma pigmentosum (XP)– like changes (Fig 1). We reviewed the clinical features of TTD extensive-ly in this Journal in 1990 and proposed a dysmorphic CONTINUING MEDICAL EDUCATION Trichothiodystrophy: Update on the sulfur-deficient brittle hair syndrome