Amino-acid composition in trichorrhexis nodosa.

Trichorrhexis nodosa is a common shaft defect affecting scalp hair. Two-hundred scalp hairs exhibiting trichorrhexis nodosa were obtained from two normal females; samples were prepared from proximal shaft, pre-nodule, nodule and post-nodule sections and analysed for their respective amino-acid compositions. Significant reductions in cystine (P less than 0.001) of the pre-nodule, nodule and post-nodule sections, which decreased by 17.2%, 19.8% and 14.3%, respectively, and an increase in the acidic amino acids (P less than 0.03) were found, compared to values obtained from proximal shaft of the same hairs. The majority of nodules occurred within the last 10% of the shaft, and the similarity in amino-acid compositions between pre-nodule, nodule and post-nodule sections suggests that 'weathering' is the major factor influencing nodule occurrence. It is postulated that nodule formation requires a specific degree of exposure to 'weathering' together with a reduction in cuticle cell coverage. It is suggested that an initial structural defect, created by a change in the DNA coding for a cuticle polypeptide fraction, could be responsible for the selective and isolated presentation of the nodule within a 'weathered' section of hair shaft.