22q11.2 deletion syndrome is caused by the deletion of a small section of chromosome 22. It results in a cleft palate, heart defects, autoimmune disorders, and more. The symptoms vary wildly and can be accompanied by learning disabilities and mental illness. Cystic fibrosis is caused by a point deletion.
The melody of Happy Birthday to You comes from the song  Good Morning to All , which has been attributed to American siblings Patty Hill and Mildred J. Hill in 1893, although the claim that the sisters composed the tune is disputed.
In 1967, a tribute song called Chet's Tune was produced for his birthday, with contributions by a long list of RCA/Victor artists including Eddy Arnold, Connie Smith, Jerry Reed, Willie Nelson, Hank Snow, and others. The song was written by Nashville songwriter Cy Coben, a friend of Atkins.