"The majority of cases (80-90%) are due to mutations of the TCOF1 gene, located on chromosome 5, which encodes a nucleolar phosphoprotein “Treacle” 1. Two other genes also are known to cause Treacher Collins syndrome: POLR1C and POLR1D 3."
"zygomatic arch: malformed, underdeveloped or absent"
"History and etymology"