Method:

MIP scores were established using a Canadian CF population (n= 2,492) as estimates of the proportion of patients with MI among all patients carrying the same CFTR mutation, focusing on patients with p. F508del as the second allele. Comparisons were made to the registries from the US CF Foundation (n= 43,432), Italy (Veneto/Trentino/Alto Adige regions)(n= 1,788), and Germany (n= 3,596).

Results:

The prevalence of MI varied among the different registries (13–21%). MI was predominantly prevalent in patients with pancreatic insufficiency carrying “severe” CFTR mutations. In this severe spectrum MIP scores further distinguished between mutation types, for example, G542X (0.31) with a high, F508del (0.22) with a moderate, and G551D (0.08) with a low MIP score. Higher MIP scores were associated with more severe clinical phenotypes, such as a lower forced expiratory volume in 1 second (P= 0.01) and body mass index z score (P= 0.04).

Conclusions:

MIP scores can be used to rank CFTR mutations according to their clinical severity and provide a means to expand delineation of CF phenotypes.