Molecular and Functional Basis of Cystic Fibrosis in Indian Patients: Genetic, Diagnostic and Therapeutic Implications

Abstract

Cystic fibrosis (CF, MIM#219700) is a common autosomal recessive disorder among Caucasians, which was considered as rare disease for Indian population. CF is caused due to presence of mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. In this study, we established a spectrum of mutations from both classical CF as well as from infertile male patients with congenital absence of vas deferens (CAVD). In Indian classical CF patients, we reported 14 previously known and eight novel mutations, viz. 3986-3987 delC, 876-6 del4, 1792 InsA, L69H, S158N, Q493L, 1530L and E1329Q. The frequency of delta 508 was found to be 27%. Absolute linkage between delta 508 and KM19-GATT TUB9-M470V-T854T haplotype predicts a relatively recent appearance of delta 508 mutations in Indian population. The CFTR gene analysis in CAVD infertile males documented 13 different CFTR gene mutations and 1 intronic variant that led to aberrant splicing. P.Phe 508 del (n= 16) and p.Arg 117 His (n=4) were among the common severe forms of CFTR mutations identified. The IVS-8-T5 allele (mild form of mutations) was formed with an allele frequency of 28.3%. Eight novel mutations were also found in the CFTR gene from our patient cohort. We also investigated whether genetic modifiers, viz. transforming growth factor (TGF-β) and endothelial receptor type A (EDNRA) of CF lung disease also predispose to CAVD in association with CFTR mutations, which were associated with the CAVD phenotype. Functional characterization of identified 11 novel CFTR gene mutations disclosed that a significant reduction in channel activity for L69H and S549N mutants in CFTR expressing cells was observed whereas impaired CFTR protein maturation was noticed only in L69H substitute CFTR. CFTR correctors (VX809) rescued the defect due to L69H mutation, which is evidenced from detection of C band in L69H mutant expressing cells pre-treated with VX809. The chloride channel activity in S549N and L69H mutant CFTR was also restored in presence of CFTR potentiators VX770. Above findings confirms heterogeneity of CFTR mutations in Indian classical and non-classical CF patients. They may help in developing a strategy to develop counseling and therapeutic approach for CF patients in India.