| RTH is caused by mutations in the beta thyroid hormone (TH) receptor. In RTH hearing impairment may occur. Brucker-Davis et al., Bethesda, MD, USA, studied hearing ability in 82 RTH patients (48 children and 34 adults) and compared the results with unaffected relatives (controls). Results in RTH and controls (c) were: inner ear infections 66% vs. 28%, speech problems 35% vs. 15%, abnormal speech reception threshold 21% vs. 0%, abnormal tympanometry 34% vs. 12%, abnormal acoustic reflexes 39% vs. 19%. The authors conclude that hearing loss is a more significant problem in RTH than previously recognized. Seventy-five percent are caused by middle ear problems, including ear infections, but 25% are caused by a seperate sensorineural mechanism. It has been previously reported that RTH patients have a 10fold higher risk of attention deficit hyperactivity disorder (ADHD) and that the mean IQ scores in RTH patients are 10 points lower than normal. The same group also studied the presence of dyslexia and slow learning in RTH families. No difference was found with regard to dyslexia between patients and unaffected family members, however 23/69 RTH subjects were slow learners as compared to 7/54 unaffected family members, being a significant difference. Also more ADHD was found in patients than in controls. (Comment: As RTH is caused by mutations in the gene of the 5-receptor of TH, these studies show the importance of the presence of the TH b-receptor for the development of the central nervous system in humans.) |
