Trismus following radiotherapy to the head and neck is likely to have distinct genotype dependent cause.

Trismus frequently occurs as a consequence of radiotherapy or chemo-radiotherapy to the head and neck, with a loss of function that can reduce the overall quality of life. Radiation can trigger an intense fibrosis within the masticatory muscles and transforming growth factor beta 1 (TGF β1) is involved in this process. As in other tissues the degree of fibrosis may be related to a single nucleotide polymorphism; C-T at position -509 in the TGF β1 gene.Trismus was measured in 62 patients before and after radiotherapy or chemoradiotherapy, blood was taken for DNA extraction, and genotype analysis of the TGF β1 gene. Trismus was analysed against, patient age, sex, tumour site and stage, radiotherapy, and chemotherapy.After radiotherapy or chemo-radiotherapy the reduction in mouth opening was shown to be significantly related to the presence of the T allele (p<0.001), with patients homozygous the most likely to be severely affected. No other patient, tumour or treatment factors were significant. Hence the TGF β1 genotype is likely to be an important predictor of the degree of post radiotherapy or chemo-radiotherapy trismus.