In CFTR and GATA4 genes (which mutations cause Cystic Fibrosis and a congenital heart disease, respectively), synonymous mutations may alter translational kinetics and protein folding by introducing non-optimal or rare codons [49, 50]; high ACT, AGG, ATT and AGC, or AGA CU values were seen in HPRT1 (which mutations occur in Lesch-Nyhan Syndrome) and GALC (which mutations cause Krabbe disease) genes, [51, 52]; finally BRCA1 and BRCA2 (major genes involved in Mendelian breast cancers) genes show an extremely low CUB compared to other oncogenes [53]. The gene discussed is HPRT1; the disease is cystic fibrosis.