CFTR and cystic fibrosis: Most cases diagnosed as CFTR-RD have a severe mutation (usually present in the consanguineous affected by CF) and a residual function mutation, among which the most frequent are the [5T;12Tg] complex allele [10], the D1152H [17], or several complex alleles that are associated with some residual activity of the CFTR protein [18] or non CF-causing mutations that, however, can cause CFTR-RD, such as L997F associated with recurrent pancreatitis [19,20].