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Kristina Krasnov Miller

Class 2002
Education BA, Johns Hopkins University

Dr. Garry Cutting

Current Position Senior Consultant

Deloitte, Association for Women in Science

Research Interests

Importance of functional studies for diagnosing effects of rare disease-causing missense mutations

Cystic Fibrosis (CF) is an inevitably fatal autosomal recessive disease that is caused by a mutation in the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) chloride channel. Patients with CF suffer from chronic lung infections, bacterial colonization, pancreatic problems, and reproductive difficulties, typically succumbing to lung disease by their mid 20s-30s. My thesis project investigated the functional consequences of rare disease-associated mutations, which alter amino acids in cytoplasmic loop 4 (CL4) of CFTR that are completely conserved across 52 diverse species. Patients with missense mutations at the conserved R1070 residue have different disease consequences: patients who carry the R1070P or R1070Q mutation have severe CF, while those with R1070W have mild CF. To determine whether R1070 mutations cause disease by affecting CFTR localization, we used the FLP-In system to create stable polarized MDCK cell lines that express CFTR from the same genomic integration site. Confocal microscopy and biotinylation studies coincided with the disease level observed in R1070P and R1070W patients; however, patients with the R1070Q mutation had severe disease despite this mutant’s wildtype-like expression levels and retained function at the apical membrane. Re-analysis of patients bearing R1070Q revealed that 12 of 17 carried an in cis nonsense mutation, S466X; the five patients who did not had milder disease. Discovery of the in cis S466X mutation reconciles the apparent discrepancy between functional studies of R1070Q and the phenotype of patients bearing this mutation. Our results demonstrate that substitutions of evolutionarily conserved amino acids are not necessarily deleterious and emphasize that functional studies in relevant model systems are valuable for the interpretation of the disease-causing potential of rare missense mutations.