Their TTGE profiles of faecal microbiota were regressed against this second criterion by means of OPLS-DA algorithm: this criterion was chosen because F508del mutation was found in 24/36 (66.7%) of CF patients, thus allowing a common background to investigate the role of the other CFTR allele on faecal microbiota composition. The gene discussed is CFTR; the disease is cystic fibrosis.