Studies have shown that the binding of TFIIB to TBP is affected by the length of the polyglutamine tract in TBP. Extended polyglutamine tracts such as those found in neurodegenerative diseases cause increased interaction with TFIIB. This is thought to affect transcription in these diseases as it reduces the availability of TFIIB to other promoters in the brain as the TFIIB is instead interacting with the expanded polyglutamine tracts.